Impact of Mining and Agriculture on Metal Concentrations in Soil and Food Crops in Selected Local Government Areas of N asarawa State, Nigeria.
By
Okere John Uchechukwu
RegNo. 03552001
Being a Thesis Submitted to the Postgraduate School In Partial fulfillment of the Requiren1ents for the award of the Degree of Doctor of Philosophy (Ph.D)
In
Analytical Chemistry in the Department of Chemistry,
Faculty of Science, University of Ahuja, Ahuja, Nigeria
July, 2008 CERTIFICATION
We certify that this research work was carried out by
OKERE, JOHN ONYEMAUCHEKUKWU Reg. No. 03552001
for the award of Doctor of Philosophy (Ph.D) in Analytical
Chemistry in the Department of Chemistry, University of Abuja.
Prof. T.A. Arowolo Date External Examiner
...... 27 /...L·/l� '!. /...... ·· Date Prof. S.E. I(akulu·········· (Supervisor)�
6 :?)tit.� ...... ••••••••••• jog < ?---J1r Dr. C.D. Chup Date (Internal Examiner)
...... )�...... r.'9. .I.� .1. 7 ...... Dr. H.D. Aliyu Date Head of Department ��·············· Prof. N ...... ,..., ...... Dean, Postgraduate School
11 DEDICATION
This work is dedicated first, to God Almighty, who gives wisdom, knowledge and understanding liberally to them that ask from Him; and to my family (wife and children); Dorothy Okere, Ifeoma Okere, Chukuwdinma Okere,
Chukwuemeka Okere; to my late elder brother whose wish and encouragement was that I obtain a Doctoral degree in Chemistry.
Ill I l.l..;
ACKNOWLEDGEMENTS
Th is work was made possible during hectic and trying experimental times by
my Professor and Supervisor Samuel E. Kakulu, whose advice and guidance
helped produce a good research write- up with worthy experience.
Also, my gratitude goes to my fa mily; Dorothy Okere, Ifeoma Okere,
Chukwudinma Okere, Chukwuuemeka Okere whose encouragement and
assistance saw me through 3 years of intensive academic and research work.
My regards also goes to my nephew Kelechi Okere who assisted me in
computer processing of words, data and charts.
I will not forget the contribution of Mr. Richard Mmegwa, Mr. Monday Irene,
Mr. Chris Uwadiale, Ms Sarah Joseph and other members of Chemistry
Department, University of Abuja, whose conh·ibution in no small measure,
helped in the completion of all laboratory work.
Finally, my greatest thanks and appreciation goes to God who through
divine inspirations provided me with sound arguments in support of most of the
research findings, explanations and discussions.
John Uchechukwu Okere
July, 2008.
iv ABSTRACT
The total concentration of Cd, Co, Cu, Mn, Ni, Pb and Zn were detemlined in
the soil and plant materials from some selected local government areas of
Nassarawa state, Nigeria. The modified USEPA- 3050 me thod of HNOr
HCI04 - H202 was used in the preparation of soil sample fo r total deternlination
whilst the plant materials were digested with HN03 -H 202. The CaCh. DTPA
extraction method was used in the determination of the concentration of bio
available metals in soil samples. The flame atomic absorption spectrometry was
used in the de te rmination of metals in the soil and plant digests. A precision of
8.5, 6.1, 4.5, 3.1, 2.4, 1.2, and 2.5, percents were obtained fo r Zn, M,n, Cd, Cu,
Co, Pb and Ni respectively, for soil samples; whilst plant sample materials gave
precisions of 4.2, 3.2, 4.5, 3.3, 1.7, 2.9 and 3.2 percents respectively, for Zn,
Mn, Cd, Cu, Co, Pb and Ni. Quality assurance of the digestion me thod for trace
metal determination in soil was carried out by a recovery study and the analysis
of Certified Re ference Material (CRM); SD- M 2/TM ; Pacific Ocean soil sediment sample (1990). Percent re coveries of 89- 96% were obtain for most
metals. The range of metals (mgkg- 1) in the re ference soil materials were 71.8 -
76, 1165- 1200, 27.0 -37. 9, 0.09 -0. 15, 12.8- 14.1, 21.4 24.6 and 49.5 - 57.2
for Zn, Mn, Cu, Cd, Co, Pb and Ni respectively and these were in agreeme nt
with the Certified Values as show by the student t- te st.The soils were slightly
ac idic with the pH ranging from 5.9 - 6.7 in study are a and the percent organic carbon varied from 1.20 -1.53% The total metal levels in the soils (mkkg- 1)
v varied from 15.0 - 84.0, 160.0- 342.0, 41.0-76.0, 1.0-2.83, 0.1-0.4, 4.10-9.16 and 13.0 -39.0 for Zn, Mn, Cu, Cd, Co, Pb and Ni, respectively. The percent bio available metals in the soil ranged from 11-15, 10 -15, 15 -20, 7- 10, 5-10, 5-
10 and 2-4, fo r Zn, Mn, Cd, Co and Ni respectively, in (mgkg-1) The concentration of metals in plant material (mgkg-1) we re 1. 18 -9.3 (4. 13) fo r Zn;
6.4 -40. 0(18.25) for Mn; 0.1-0.7 (0.24) for Cd;l.8-6.8 (3 .78) fo r Cu; 0.10-0.98
(0.42) fo r Ni . Pb; 0.1-0.80 (0.36) and 0.01- 0.03 (0.02) fo r Co. Generally, mining and agticultural activities were suspected to be the major contributors of metals in the study area. The average concentrations of Zn, Mn, Cu, Cd, Co, Pb and Ni obtained in the study area fo r soil and food crops were compared with other regional studies, country standards and quality guidelines to evaluate their risk significance and quality assessments specified fo r the protection of human health. These levels compared favourably with results fi:om other regional studies, country standards, as well WHO/FAO benchmarks fo r soil and fo od quality standards . That the concentrations of metals in this study were lower than quality guidelines for agriculture, residential and commercial purposes indicate that there is currently no threat to human health in the use of the soil and consumption of fo od crops in these areas. r
VI TABLE OF CONTENTS
CHAPTER ONE Page
1.0 �ODUCTION 1
1.1 General Introduction 1-2
1.2 Heavy metals 2-3
1.3 Sources of Heavy Metals 3
1.3.1. Natural Sources 3-4
1.3.2 Anthropogenic Sources 7
1.3.2.1 Agricultural Chemicals 7
1.3.2.2 Mining 9
1.3.2.3 Industrial Emissions 10
1.3.2.4 Chemical Industry 11
1.4 Soil and plants as Indicators of heavy metal Pollution of the environment 12-1
1.4.1 Soils 12
1.4.2 Plants 15-16
1.5 Fate and Mobility of heavy metals in soil 19-20 1.6 Plant uptake of heavy metals in soil 20-21
1.7 Metal uptake and toxicity in animals 21-23
1.8 Significance of Some Heavy Metals to Plants and Animals 24
Zinc 24
Cadmium 24
Nickel 25
Manganese 26
Lead 26
Copper 26
Cobalt 27
1.9 Aim of study 27 -29
VII CHAPTER TWO 30 2.0 LITERATURE REVIEW ON HEAVY METAL
DETERMINATION SOIL AND PLANTS 30 IN 2.1 Sampling and Sample Preservation 30
2.1.1 Soils 31-33
2.1.2 Plants 33-35
2.2 Sample Preparation methods 35
2.2.1 Digestion of soil samples 36-39
2.2.2. Determination of total metals in soil 39-41
2.2.3 Sequential Extraction 41-44
2.3 Plant sample determination 45
2.3.1. Wet Ashing or wet-digestion 45-46
2.3.2 Dry Ashing 46- 48
2.4 Analytical techniques fo r metal determination in soils
and plant materials 48
2.4.1 Atomic Absorption Spectrophotometer (AAS ) 48
2.4.2 A typical published application of AAS 48
2.4.3 Atomic Fluorescence Spectrophotometer (AFS) 49
2.4.5 Neutron Activation Analysis (NAA) 49-50
2.4.6 X-ray Fluorescence (XRF) 50
CHAPTER THREE 51 3.0 EXPERIMENTAL 51
3.1 Study Area 51
3.2 Sample collection and preservation 51
3.2.1. Soil sample collection, preparation and preservation 56
3.2.2 Plant sample collection, preparation and preservation 56-57
3.3 Chemicals and reagents 58
3.4 Cleaning of glassware 58
3.5 Preparation of standard stock solutions of metals 59-60
3.6 Working Standard stock solutions of metals 60
3.7. Instrumentation 60
VIII 3.7.1 Atomic Absorption Spectrophotometer 60
3.7.2. pH meter 61
3.8 Digestion of soil samples for total metal determination 61
3.8.1 Recovery Studies 61
3.8 Extraction of soil sample for soluble metal determination 62
3.9 Digestion of plant (food crop) samples for metal determination 62-63
3.11. Reference sample material analysis 63
3.12. Determination of organic carbon of soil 63-64
3.13 Determination of soil pH 64
CHAPTER FOUR 65 4.0 RESULTS 65
4.1 Quality Assurance of Method 65
4.2 Total Metals in Soil 66
4.2.1 pH, Cd and Cu 67-68
4.2.2 Cobalt, Manganese and Nickel 68-69
4.2.3 Lead and Zinc 69-70
4.2.4 Percent Organic Carbon (O.C) in soil 74-75
4.2.5 Bio-Available Metal in Soil 75
4.3 Metals in Vegetation and Food Crops 76
4.3.1 Cadmium and Copper 76-77
4.3.2 Cobalt, Manganesse and Nickel 77
4.3.3 Lead and Zinc 78
CHAPTER FIVE 82 5.0 Discussion and Conclusion 82
5. 1 Variations of Metals in Soil, bio-Available Metal in Soil and Metals in Plants 82
5.1.1 Variation of Metal in Soil 82-84
5.1.2 Variation of Bio-Available Metal in Soils 84-86
5.1.3 Variation of Metals in Plants (Food Crops) and Its Implication
In Diet and and Human Consumption 86-88
IX 5.2 pH and % organic carbon 88-89
5.3 Health Implications of Some Metals (Cu, Cd and pH) found in
Study Area Above WHO FAO acceptable foods 89-91 I hrnits m 5.4 Relationship Bio-Available Metals inSoil with Levels in
Plants 91-93
5.5 Correlation Study 96
5.5.1 Conelations between metals in Soils (dry seasn) 101
5.5.2 Conelations Between Metals in Soil (Rainy Season) 102
5.5.3 Correlation Between Soil pH and Soil Metals in the Sh1dy
Area 102
5.5.4 Correlation Between Soil (O.C) and Soil Metal (Rainy Season)103
5.5.6 Correlation Between Soil pH and Soil Organic Carbon
for all Locations 104
5.6 Factors of Accumulations of Heavy Metals in Soils 104-106
5.7 Comparism of Metals in Soil of Study Area with Other Regional Study 108-109
5.8 Comparism ofMetals in Soil ofSh1dy Area With Soil Quality Criteria for Different Countries 109-110
5.9 Comparism of Heavy Metal in Food Crops/Plant in Study Area with Other Regional Studies and WHO Standards 111-114
5.10 Conclusion 115-117
5.11 Recommendations 118
5.12 References 119-139
X LIST OF TABLES
Table Pages
1.1 Average concentration of heavy metals m the earths crust their conm1on minerals 5 1 1.2 Concentration of heavy metals (mg Kg- ), dry weight in the lithosphere, soils and plants 5 1 1.3 Heavy metal contents (mgkg- ) of some fertilizers 8
1.4 World wide inputs of heavy metals into soils 8
1.5 Occmrence of metals or their compounds in effluents
from various chemical industries 12
1.6 Total background concentration of heavy metals in
Taiwan agricultural soils 14
1.7 Trace element contents of soils in Ulan -Ude, Russia 15
1.8 Heavy metal tolerance levels in some food crops 17
1.9 Concentration of heavy metals in some food crops in a regional study in Russia. 17
1.10 Phenotoxic symptoms induced in plants by heavy metals 18
1.11 Classification of elements according to toxicity and 24 availability 3.1 Description of sample locations and sites 57
3.2 List of manufacturers of reagent and chemicals used in
Sample Analysis 58
3.3 Instrument Conditions for AAS analysis 60
4.1 Precision of digestion method 66
4.2 Results of recovery studies 66
4.3 Concentration of metals in reference sample (SD -M-2/TM) 66
4.4 Mean concenh·ation of total metal, pH and O.C in soil for dry 1 season (mgkg- ) 71
4.5 Mean concentration of total 71
4.6 Summary of concentration of total metals and pH in soil from the LGA's in dry season. 72 4.7 Sununary of concentration of total metals and pH in soil from The LGA's in raining season 73
4.8 Sunu11ary of concentration of total metals and pH in soil from the study area, in dry and raining seasons 74
XI 4.9 Average concentration of bio avai !able metals in the
st-udy Area 76
4.10 ConcentratiOn of bioavailable metals in the LGA's 76
4. 11 Summary of metal concentrations in food crops in the
study area. 79
4.12 Sumrnary of metal concentrations in food crops from the LGA 80 4. 13 Percent organic carbon content of soil samples for dry
and rainy seasons 82
4.14 Soil pH levels 82
5. 1.1 Correlation between bioavailable metals and plant metals 96
5.1.2 Correlation between melals in soils (DSS ) 101
5.1.3 Correlation between metals in soils (RSS ) 102
5.1.4 Correlation between soil pH and soil metals in the study area 102
5.1.5 Correlation between soil (O.C) and soil metals (DSS ) 103
5.1.6 Correlation between soil (O.C) and soil metals (RSS ) 103
5.1.7 Correlation between soil pH and soil (O.C) for all locations. 104
5.1.8 Correlation between soil pH for both dry and rainySeasons 104
5.2 Comparison of concentrations of metals in soil of study 1 area with other regional studies (mgkg- ) 111
5.3 Comparison of heavy metals in food crops in the study
area with WHO standards and other regional studies. 114
xii LIST OF FIGURES Figure(s) Pages hi the 6 1.1 Trace metals movement Wit n environment 1.2 Essential trace elements in living tissues 23
1.3 Non-essential trace elements in living tissues 23
3.1 Map of Nigeria showing Nassarawa State 53
3.2 Map ofNassarawa State, showing LGA's samples 54
3.3 Small scale miners at work with their crude equipment 55
4.1 Levels of metals in soil from the LGA's 82
4.2 Mean concentrations of total metals in food crops from study area 83
4.3 Total concentrations of metals in food crops from the LGA's 84
5.1 Factors of accumulation of heavy metals in soils
(dry and rainy season) 107
xiii CHAPTER ONE
INTRODUCTION
1.1 General Introduction
Man's activities through agricultural, industrial and other teclmological ventures has led
to the evolution of environmental problems that are associated with pollution,
environmental degradation and ultimately the deshuction of his natural habitat. Large
areas of agricultural soils in Germany for example, are contaminated by heavy metals
which play significant role as pollutants. The history of civilization and modernization
has a strong link with the use of metals from the time of industrial revolution of the
nineteenth century. Since then, heavy metals have become very important for all aspects
of life. Many metal wastes originate from mining activities, indush·ial emissions,
industrial effluents, application of fertilizers, sewage sludges and pesticides etc. Elevated
metal concentrations in the soil can lead to enhanced crop uptake. Excessive metals in
human nutrition can be toxic and can cause acute chronic diseases. Cadmium and Zinc
for example can lead to acute gash·ointestinal and respiratory damage, acute heart, brain
and kidney damage at elevated concentrations1 .At higher concentrations, they interfere
with metabolic processes and inhibit growth sometimes leading to plant deatll.
Consequently quality standards were established, for threshold of heavy metal concentrations al lowed in soil and vegetation. For instance, in the European Union (E.U), maximum concentrations of lead and cadmium allowed in several agricult-ural crops were 3 recently enacted into law . The transfer ofheavy metals from soil to plant is dependent on three factors: viz; The total amount of potentially available metals in the soil (quantity fa ctor), the activity as well as the ionic ratios of elements (Z+Ir); charge to size or charge
to ionic diameter in soil solution (intensity fa ctor), and the rate of element transfer from 4 solid to liquid phases and to plant (Kinetics fa ctor) . Correlations were fo und between the soluble heavy metals concentrations in plants and their surrounding soil in several . stu dJes. 2
The total concentration of the trace metals in soils does not indicate the amount that is available for plant uptake5. For instance, Chukuma6, used a plant/soil ratio (p/s), as
an index of bio-accumulation of metals such as Zn, Pb and Cd in a Nigeria soil. It was observed that the metal concentrations in the leaves of Bilinga and congo grass did not reflect total concentration of three element s in the soil, suggesting a gap between bio available metals and total metal concentrations in the soil, Studies have shown that most
metal that accumulate in soils are transferred to plants through absorption. 5
1.2 Heavy Metals 3 Heavy metals are by definition elements having a density greater than five gm/cm . These elements may however exist in the biosphere in tr ace amounts or quantities (trace elements), and they include; antimony, bismuth, cadmium, copper, lead, nickel, mercury and zinc8. International scientific bodies in the European Commission directed and referred to heavy metals as those metals used and discharged industrially, of which Cd,
Cr , Cu, Hg, Ni, Pb, Zn and metalloid. As and are listed as representing the greatest hazards to plants and animals9. Toxicological studies have shown that some metals are deleterious to human and plant health in excessive levels and these include; Cs, Cu , Hg,
Ni Pb, Zn, Co, Cr, Mo, Sn, Fe, and Mn10. Heavy metals may also be trace metals when
2 their concentrations in the environment are in tr· ace levels
1.3 Sources of heavy metals in the environment
The sources of metal in the environment are fr om two major routes; viz: natural and
anthropogenic. Heavy metals are present in all uncontaminated soils as a result of
weathering from their parent rock materials. As a result of the increasing activities of
man, anthropogenic sour ces of metal pollution of soils have been more significant than
natural sources.
1.3.1 Natural Sources
Natural sources of heavy metal availability usually constitute the major background or baseline levels. These levels usually results from geological weathering of native rock fo rmation within the immediate environment. Rock phosphates 11, often contain high levels of trace metals especially cadmium, (Table 1.1). The concentr ations of metals in the earth's cmst and their common ore minerals are listed in Table 1.1 Most of the metals found as ore minerals derive fr om sulphide ores, except Cr. Arsenic is a by-product of
Cu-ores. Bi is also a by-product of Pb-ores while Hg and Cd are by-products of Zn-ores,
Trace metals are found in various kinds of soils, sediments, water bodies, organisms, and atmospheric dusts sometimes in normal background concentrations. Concem and wony arises when their levels either from weathering, laterization, mineralization or leaching processes 1ead to abnormal high concentrations relative to their normal background levels12. Though some trace metals are essential to life, they can be toxic at high concentrations, for example, Cd, Hg and Pb13; have been found to be toxic even at very low concentrations. Ore minerals are metallic aggregates in which the metalliferous
3 I l. L. I
metalliferous minerals are sufficiently abundant to make the aggregate worth mining. 4 Types and origins of ore deposits arc listed below1 . Volcanic Ores- (Na, B, N0 , AI, Fe, Mn-usually found in water table sedimentary 1. 3 manganese sublimates from hot springs).
2. Evaporation Salts- (K, Mg, NaCI CaS04 2H20, BaS04 (barites) CaC03 (limestone) 3. Sedimentary Ores-(P, Fe usually found in secondary enrichment veins) 4. Ore Soil-Ni, Cu, Pt, Cr, Ti, W, Fe. 5. Sink Hole Caves-Zn, Pb, Cu, Au, Sn, Mo, Fe found in sedimentary intermediate temperature veins. 6. Gems, rare earths, fe ldspar, quartz, mica from sedimentary ores. 7. Ni, Co, Ag, Pb, Zn, Cu, Au, As from cave ores. 8. Hg, Sb, Pb, Ag, Zn, Au from water table sedimentary ores.
Heavy metals also participate in geo-chemical cycles's. Soils which contain heavy metals will ultimately, through erosion and sedimentary processes end up as sediments, lmown to have high storage capacity for metals.15 Metals in solution, however, are the most bio
10 available for organisms . Table 1.1 shows the average concenh·ation of heavy metals in the earth's crust and their common minerals's, whilst Table lists the concenh·ations of 1.2, 7 heavy metals in the lithopshere16, soils1 and plants18, respectively. The high rainfall and commonly low pH of soils in many tTopical ecosystems provide optimum conditions for metal transpoti. On the other hand, intense weathering and leaching of metallic and leaching of parent materials results in residual accumulation of metallic oxides and hydroxide of Fe and AI in the soil, which can specifically sorb trace metals within a
's typical soil profile or strata . Figure 1.1 below illush·ates the fact that soil is a natural sink for pollutants from the environment.
4 Table 1.1 Average concentrations of heavy metals in the earth's crust and their 15 common minerals •
1 Metals Earth's Crust (mg kg- ) Ore minerals As 1.5 FeAsS, AsS,Cu Ores Bi - Pb Ores Cd 0. 1 Zns Ores Cr 100 FeCr204 Ores Cu 50 CuFeS2;CuFeS4;Cu3AsS40res Hg 0.05 HgS; native Hg;Zn Ores 3 4 Ni 80 (Ni, Fe)S8;NiAs; (Co, Ni) S Ores Pb 14 Pb2S3 Ores Sb 0.2 Sb2S3;Ag3SbS30res Zn 75 ZnS Ores
1 Table 1.2 Concentration of heavy metals (mg kg- ), dry weight, in the 16 17 18 lithrosphere , soils and plants •
Metal Lithosphere Soils Range (Soil) Plants Cd 0.2 0.06 0.01 -0.7 0.2 -0.8 Co 40 8 1-40 0.05 -0.5 Cr 200 100 5-3000 0.2 - 1.0 Cu 70 20 2-100 4-1 5 Fe 50000 38000 7000 - 550000 140 Hg 0.5 0.03 0.01 -0.3 0.015-0.30 Mn 1000 850 100-4000 15-100 Mo 2.3 2 0.2-5 1-10 Ni 100 40 10-1000 1.0 Pb 16 10 2-2000 0.1 - 10 Sn 40 10 2- 200 0.2 -0.3 10-300 8-100 Zn 80 5 As 0.15 2.5 0.4 -70 0.15- 1.5 Sb 0.05 0.75 0.05-3.0 0.05 -0.10
5 Anthr·opogenic Activity
Com ercial Agriculture
Glacial Ocean Activity Current �� Volcanic Winds Activity Climate
Hydrosphere
Precipitation from River·s Lakes Oceans Natural Rock
Erosion Weatherinl!
Aquatic Plants Animals
I Fertilizers Fossil Fuels Aquatic Habitat Power plant Automobles Waste product Atmosphere Sewage Sludge Habitat
Irrigation Sediment Mining Smelling Surface run off Metal Processing
Soil 20 Fig 1.1 Trace metal movements within the environment •
6 1.3.2 Anthropogenic Sources
Anthropogenic sources of heavy metals into the environment include a wide range of
human related endeavours lhrough which metals either in dissolved, suspended,
particulate, occluded, precipitated and/or associated ion find their way into the
environment. The anthropogenic sources of heavy metals into the soils include;
agriculture, mining, metal smelting and industrial emission etc. Pollutants released from v
17 bb anthropogenic sources exceed those from natural sources by more than two orders •
The highest concentration of heavy metals is in soil, but traces are also found in plants.
1.3.2.1 Agricultural Chemicals
Major agricultural sources of heavy metals include fertilizers, pesticides (insecticides,
fu ngicides, herbicides, rodenticides and nomatocides), sewage sludges, industrial
composts and manures etc.
Large quantities of fertilizers are added to soils by commercial and subsistent
farmers to improve soil fetiility and enhance crop yield. The compound that constitutes
fertilizers contains trace amounts of heavy metals as additives or impurities.21• Continued
fe rtilizer application may significantly increase heavy metal content in soil. Mortvedt and 22 Osbom , found that increasing the rates of usage of phosphate fetiilizers resulted in higher Cd content in the grains of winter wheat and soil. Generally, phosphate rocks are
1 1 known sources of cadmium in soils • Table 1.3 shows the heavy metal content of some . . 21 fiert1 11zers .
7 1 21 Table 1.3 Heavymetal contents (mgkg- ) of some fertilizers
Fertilizer
Co Cr Ni Pb Zn Cd
Nitrochalk (N.P.K) 0 0 2 - 15 -
Calcium Nitrate 0.1 Trace (Tr) - - 1 Tr
Ammonium Sulphate <5 <5 <5 Tr-200 0-800 0-15
Super Phospahate 0.02-13 0-1000 Tr-32 Tr-92 70-3000 0-25
Potassium Chloride 0.1 - <1 <1 0.3 Tr
Urea 0.01-10 5.25 Tr <1 0.4-40 Tr
Fannyard Manure 0.03-6 - Tr - 4-360 Tr
Table 1.4 shows the worldwide inputs of heavy metals into soils 19• These sources are typical representation of anthropogenic inputs to soil metal load. 19 Table 1.4 Worldwide inputs of heavy metals into soils (x 103 ton per annum)
Source As Cd Cr Cu Hg Ni Pb Zn Agriculture and Animals Wastes 5.8 2.2 82 67 0.85 45 26 316 x Atmosphere Fallouts 13 5.3 22 25 2.5 24 233 92 Coal Ashes 22 7.2 298 214 2.6 168 144 298
Discarded Manufactured Products x x 38 1.2 458 592 0.68 19 292 465 Fertilizer and Peat 0.28 0.2 0.32 1.4 0.01 2.2 2.9 2.5 Logging and Wood Wastes 1.7 1.1 10 28 1.1 13 7.4 39 Municipal Sewage and Organic Waste 0.25 0.18 6.5 13 0.44 15 7.1 39 Solid Wastes from metal Fabrication 0.11 0.04 1.5 4.3 0.04 1. 7 7.6 11 Urban Refuse 0.4 4.2 20 26 0.13 6.1 40 60 Total x x x 82 22 898 971 8.3 294 759 1322.5 * These inputs do not include mine tailings and slag at smelter site ** Metals used for industrial installations and durable goods are assured to have definite life span and to be released into the environment at a constant rate. *** Totals are rounded up
Pesticides are commonly classified according to the target group of pest organisms; insectides, fu ngicides, herbicides, rodenticides and nomatocides. Some of these pesticides contain trace metals such as Cu, Mg, Mn, Pb, Zn and Cr either as an active ingredient, impurity or contaminant. For example, in a study of the effect of the
8 application of copper fu ngicides to cocoa plantations in Ondo State, Nigeria, it was found that copper concentrations were higher in soils in the areas of application of 23 plants . Arsenic has accumulated in orchard soil fo llowing years of application of 24 arsenic containing pesticides . Being present in an atomic form (e.g H2As04), this element is absorbed as acid phosphates by hydrous Fe and Al oxides. Inspite of the capacity of most soil to tie up arsenates, long term additions of arsenical sprays can lead to toxicity for sensitive plants.
The practice of adding sewage sludge to agricultural land is well established. Not only is this a convenient way of disposal, sewage sludge is also a useful and cheap source of nitrogen and phosphorus that may improve the physical and micronutrient condition of soil. As sewage output has increased and conversions to orgamc fertilizer (in some places), and farmland manure, have been and likely to become more widely used on agricultural land. Heavy metals such as Cd, Zn, Cr, Cu, Pb, Co, 2 Ni and Hg accumulate by absorption in the soil to which sludge is applied 5. The heavy metal content of sewage sludges depends to a large extent, on the nature of the proportions of industrial and domestic wastes, from where they are derived.
1.3.2.2 Mining
Heavy metals are generated through smelting processes, foundries, steel production processes, alloy metalising processes, hydrometallurgy, pyrometallurgy, corrosion processes and recycling of metal waste scraps. The ultimate sink for these pollutants, is the immediate environment. For instance, in Pb, Cd and Zn mining districts of
Bergischeland, Germany, acute heavy metal pollution occurred in the soil of
9 2 meadows (lowlands), lying downstream from nearby mines 6.
As a result of this, studies on heavy metal accumulation in vegetations showed that root vegetables exceeded the tolerable levels of Pb and Cd concentrations, thereby suggesting a direct impact of mining activities on bioaccumulation of heavy
2 metals 6. Widespread Cd contamination in soils occurs through mining, smelting, 3 em1sswn from coal fire plants and heavy use of phosphate fertilizers 1 . The main sources of Cd pollution in the environment are through metals smelters 24.
1.3.2.3. Industrial emissions
All solid particles in smoke from fires, coals gas thermal plants, gas flaring and factorr chimneys are eventually deposited on land or sea. Most forms of fo ssil fu el contain some heavy metals. Similarly, industrial processes involving metal smelting soil/or refining often results in large aerial inputs of heavy metals to neighboring soils and vegetation. Another major source of aerial contamination is the lead that emanates from petrol combustion. According to Lagerweff and Speclite27 this accounts for about 80%of the total Pb in the atmosphere. Lead is added to petrol as organic Pb compound (lead-tetraethyl). About 50% of this falls somewhere within
7 the region of 100 metres from the road or highwa/ • The remainder is distributed widely in the biosphere. It was found that there is correlation between atmospheric
Pb emissions from traffi c exhausts in high density traffi c areas of Abuja- Nigeria, and the levels of Pb deposited on tree barks and soil within road vicinities28. Selenium and Sulphur are components of coal. Coal based thermal plants release Se, as selenium oxides into the atmosphere as (fly ash) or degradation of seleniferous rocks
10 containing Smgkg-1 Se, could be toxic. Selenium levels of soil can produce
vegetation containing toxic seleiunm levels as reported by Rao et al29 .
Chemicals industry 1.2.4
Zdeneck and Mecislav30 reported that heavy metals like Ag, As,Cd, Cr, Cu, Hg,
Pb and Zn are released into the environment through various use-related sources that
include;
(I) Battery liquids, carbide sludges -pollution of immediate environment results
fr om disposal practices. Most garden soils where carbide wastes (from
welders) are dumped, lose their population of soil nematodes and earthworms
which are important economic organisms. The vegetation around such waste
sites may also undergo discoloration (chlorosis) of its leaves and greenery.
(2) Chemical additives like detergents, fu els and lubricants, photographic fi lm
liquid wastes, x-ray fi lm developer liquid wastes, rubber waste products,
vulcanizing wastes, plasticizers, pigement and paint waste effluents (contain
driers like Cu, Zn, Mn, Pb and Co naphthenates) which are added into
landfills, waste dumpsites or incinerators.
:3) Pharmaceutical and medicinal preparation such as drugs detergent related wash
wastes, germicides, disinfectants and fumigants contain trace amounts of
organometallic substances which are discarded as industrial effluents into
drains and nearby sewage ways.
11 Table 1.5 Occurrence of metals or their compounds in effluents fr om various Chemical Industries 31• 32 Industry Metals
Al As Cd Cr Cu Fe Hg Mn Pb Ni Sn Zn v
Mining Operation and Ore * * * * * * * * *
Processing
Mettallurgy and Electroplating * * * * * * * *
Chemical Industries * * * * * * * * * *
Dyes and Pigments * * * * * *
Ink Manufacturing * * * *
Pottery and Porcelain * *
Paint * * *
Photography * * *
Glass * * *
Paper Mills * * * * * * *
Leather Training * * * * * * *
Phrumaceuticals * * * *
Textile * * * * * * * * *
Nuclear Technology *
Feliilizers * * * * * * * * * * * * *
Chloro-alkali Production * * * * * * * * * * * * *
Petrolew11 Refining and * * * * * * * *
Production
1.4 Soils and Plants as Indicators of heavy metal pollution of the environment 1.4.1 Soils
Studies have show that soils and plants remain the major natural receptacles, sinks or drain pits afor heavy metals in the environment. As man acquires new technology, so are vast amounts of wastes that are discarded into the environment.
Table shows worldwide inputs of metals into soil. For example, in an attempt to 1.4,
12 determine the impact of h·affic density on metal distribution in Abuj a, Nigeria, soil and
8 tree bark samples were used to determine the levels of metals in the cit/ . The Pb and Zn concentrations in the soils and tree bark in Abuja were generally higher than those of Cd, Cu and Ni suggesting that automobiles are major source of these metals in the roadside environment.
Zdeneck and Mecislav30, have used soil to show the impact of chemical wastes from metturgica 1 plants, sludges and chemical industries, on heavy metal contamination of the environment used as landfills and dumpsites in the Czech Republic. The study revealed that hazardous chemical waste landfillswere rich with high concentrations of
Pb, Cd, Hg, As and Cr; whilst landfills around metallurgical plants have their soils enriched with high concentration of Pb, Cd, As, Fe and Cr, respectively.
Lagerweff7, also conducted a study on roadside soils highways and discovered that roadside soils are polluted with Cd from tyres and lubricant oils from automobiles.
Some peculiar characteristics of soils as indicators fo r soils as indicators for metal pollution are that they contain colloidal organic matter which has strong affinity for heavy metal cations and the retention of added metals is often well correlated with the amount of organic matter in soil31(a)_ Also, organic matter in soil may provide sites fo r cation exchange reactions and its strong affinity for heavy metal cations is due to ligands ( chelates) that form complexes with metals32(a).
Chen and Lee33, in a study to establish the total background concentrations of heavy metal in Taiwan agricultural soils (Tablel.6), found the lower limits, upper limits and mean concentrations of topsoil heavy metals, indicating that most regional soils
13 remain the common environmental sinks fo r heavy metals , and as such, can be used to monitor metal pollution of soils in agricultural fa rmlands.
Table 1.6 Total background concentration of heavy metals in Taiwan agricultural soils33•
Elements Total Concentration (n=l 00) Upper Limit
Range Mean Lower Limit mg/kg
mg/kg (8) Arsenic ND - 10.8 4.54 3.28 10 Cadmium 1.02 - 3.41 1.74 0.62 3 Chromium 22.9 -98.9 43.2 1 5.1 100 Copper 7.15 -35.1 20.3 7.63 35 Mercury 0.47 0.13 0.10 0.49 ND- Nickel 18.6- 66.7 43.2 12.6 60 Lead 7.50 -138 32.6 28.2 120 Zinc 30.1 -392 180 80.5 120 * Chen, M and Lee T (1995) Not only this, soils are characterized with presence of organic matter, which have been regarded as the binding material for metal deposition because, metals are fairly 34 3 immobile in soils ' 5. Soil and its use as an indicator to monitor environmental metal levels, has received considerable attention in both local and regional studies.
The trace metal levels in urban soils are known to have dramatically increased as a result of human influence. Nationwide surveys of natural Norwegian soils have shown geographical disuibution patterns in the upper 5-l Ocm of the soil for elements such as Pb, 4 Zn, and Cd, conesponding of to environmental deposition pattem (Steinners et al) 1 . In most of these studies, it was possible to discem regional gradients in metal levels accumulated in soils and these were found to correlate with data on their sources of distribution. (Table 1.5).
In an attempt to evaluate the impact of soil retention of u·ace metal prior to irrigation
14 with (i) sewage water (ii) river water and (iii) no-irrigation, it was fo und that parent top
soils contained varying amounts of trace heavy metals that ranged from moderate to low;
thereby suggesting that native fa rmland soils remain natural index for soil metal pollution
monitoring in agliculture (Table 1.9)34.
1 Table 1.7 Trace elements content of soi134 (mgkg- ) in Ulan-Ude Russia
Metals Pb Mo Cu Zn Mn
Surface (01 - 20cm) 10 1.8 13 40 410
Subsurface (34 - 44) 6 1.10 5.2 170 13
Subsoil (60 - 70 em) 10 2.4 26 68 750
Deep soil (110-1 20cm) 6 1.8 8.0 28 40
The study of soil heavy metal levels fr om regional and local investigations have provided information as to while soil acts as critical environmental sinks for heavy metals resulting from various sources. Such studies have also provided local, regional and country bench marks that informs action levels for soil metal pollution mitigation and remediation programmes, because most of the background levels are usually higher than control guide levels in these studies.
1.4.2 Plants
Several studies have been carried out in Nigeria on the use of plants as environmental pollution indicators of metal deposition. For example, tree 42 43 barks, mosses and fru its have been used by Osibanjo and Aj ayi, . Onianwa and Aj ayi . 44 4 Ademoroti and Kakulu 5, to determine atmospheric metal deposition in soils and plants, respectively. Here, plants (e.g tree bark), have been used as bioindicators m
15 48 Table 1.8 Heavy metal tolerance levels in some food crops . Element Brown Fruit type Leaf type Root type Rice Vegetables (n =90) vegetables vegetables (n 144) (n 112 1 = = Mgkg- vegetable (dry matter basis Arsenic 0.17 0.05 0.12 0.05 Cadmium 0.07 0.11 0.24 0.21 Chromium 0.16 0.26 0.02 0.03 Copper 2.48 3.52 4.64 3.00 Mercury 0.00 1 0.02 0.04 0.03 Nickel 0.54 0.95 2. 1 4 1.63 Lead 0.43 2.1 3.69 2.58 1 Zinc 39.2 27.7 38.1 27.4 Table 1.9 Concentration of heavy metals in some fo od crops in a regional study in Russia (mgkg-1 dry mass)34•
Plant Specie Variation of the Metals (mean concentrations 111 100 plant experiment samples
Mn Zn Co Cu Pb Time Medicago Without 14.2 16.1 1.14 9.5 0.9 Initial Sativa L Irrigation 74.4 25.5 3.2 14.8 9.1 after With irrigation 14.4 19.1 0.69 9. 1 0.6 Initial From river water 104.4 25.8 5.2 17.5 11.4 after Sewage 14.3 21.9 0.76 9.5 1.0 Initial liTigation 157.5 37.3 4.2 22.8 13.8 after Elymus Without 10.0 31.0 0.70 10.0 0.6 Initial Sibiricus Inigation 186.5 29.6 4.3 13.8 2.5 after With Irrigation 9.7 19.4 0.68 10.3 0.6 Initial From river water 166.6 28.1 5.7 21.5 2.7 after Sewage 9.6 29.7 0.57 9.6 0.6 Initial Irrigation 140.9 26.7 5.9 18.1 0.8 after Bromoposis Without 14.4 19.3 0.39 4.8 1.0 I:nitial Pumpeliana Irrigation 225.2 33.0 5.7 22.5 15.0 after (Scriber Holub) With Irrigation 10.7 21.7 0.43 Traces 1.1 li1itial From river water 18.6 21.7 0.43 26.6 13.1 after Sewage 15.4 15.4 0.41 Traces 0.7 Initial Irri gation 134.7 28.0 3.8 19.6 1.2 after Without 11.7 17.5 0.47 Traces 0.6 Initial Avena Sativa Irrigation 125.0 34.0 5.8 19.6 1.2 after With Irrigation 9.8 16.6 0.40 4.9 0.6 Initial From river water 417.8 35.1 6.0 16.4 3.1 after Sewage 14.9 26.7 0.40 5.0 0.6 Initial liTigation 307.3 31.0 4.6 14.0 2.1 after
17 1.5 Fate and Mobility of Heavy Metals in Soil
The fa te of heavy metals added to soil will be controlled by a combination set of chemical reactions and by a number of physical and biological processes acting within the soil. The mobility of heavy metals in soils depend on their form and source; for instance, in sludges, a large proportion of metals are associated with 4 organic matter, and a small amount are present in sulphides, phosphate and oxides 5 .
Lead is emitted from combusted petrol as bromchloride, but it is readily converted to
5 PbS04 and oxysulpahte in the atmosphere or soil (Olsen and Skogerboei . Metal ions will enter soil solution from these various forms at greatly different rates. These ions may then;
(a) Remain in solution as they may be leached off,
(b) Taken up by plants,
(c) Be retained by soil in sparingly soluble or insoluble form
Colloidal organic matter has strong affinity for heavy 3 metal cation 1 , for they may provide sites for cation exchange reactions because of the presence of groups that form chelates and/or complexes with metal ions, and these groups include carboxylic, phenolic, alcoholic and carbonyl fu nctional 2 species3 . In general, the stabilities of these complexes increase with increasing pH.
Heavy metals also participate in geochemical cycles31• Soils which contain heavy metals will ultimately, through erosion and sedimentation processes end up as sediments; for sediments and soil are known to have a high storage capacity for heavy metals7. It is known that metals in solution however, are the most bioavailable
19 I l. I. '
3 for organism 0. The relative role of various sources of metals and their fate within the soil, relative to the background levels in various areas need careful assessment and monitoring. To evaluate or ascertain the extent of the impact of metallic pollution in soils, it is worth while establishing their natural background levels first. The natural concentration of some heavy metals in surface soils and plants are listed in Table
16,17,18 1.2 0
The majority of metals that enter the soil are transported in dissolved or suspended form. Although heavy metals are found in varying concentrations in the soil, they are nevertheless able to complete for adsorbing surfaces with the much more abundant cations of alkali and alkaline earth metals.
1.6 Plant Uptake of heavy metals in soil
The uptake of heavy metals via plant roots is generally the most important pathway of absorption. The extent of heavy metal absorption by plant depends upon t eh ionic potential of the metal concerned56. The ionic potential of a metal is defined as the ratio of its charge of the ionic radius at a given state in the soil. For example, 24 Be , with an intermediate ionic potential of 5.9 (i.e 2+/0.34A0), has a tendency to get 2 precipitated56, while Cd +, with a lower ionic potential of2.0, (2/0.97A), has a greater tendency to migrate. The competitive interactions among heavy metals during absorption are complex and have little been studied.
Some heavy metals are concentrated in the roots of Plants57• The concentration of heavy metals in the shoots is affected not only by uptake and transport
(translocation) fr om the roots, but also by the rate and stage of plant growth58.
20 Concentration also differs in the various parts of the shoots. Cereals, in particular
concentrate metals greater in the leaves and stems than in the seeds58. ln the latter
respect, Ni seems to differ from other heavy metals; it is often more concentrated in
the seeds than in the leaves and stems.
1.7 Metal uptake and toxicity in Animals
A broad but concise overview of heavy metals uptake and
toxicity in animals is from the stand point of environment pollution, heavy metals
(for toxicity assesements), may be classified into three major criteria59, viz:
(a) Non-Toxic
(b) Toxic
(c) Very toxic
In the classification presented in Table 1.11, Venugopal and Luck/0, have shown that a metal is toxic to animals when concentration levels exceed those required for nutrition by factors ranging fr om 40-220. The living matter of organisms consist of elements which have very low atomic weights: viz H2, C, 02, Na, Mg, P, S, CI, K and Ca60. These elements have been known to be essential fo r life. Others occur in very small amounts in the living tissue that for a long time, there were precise concentration measured and were often mentioned as occurring in 'traces' or in mirco
6 amounts. Trace heavy metals can be divided into three groups 1 ; v1 z:
1. Dietary essential e.g;Cu, Zn, Fe etc.
2. Possible essential e.g; Se, Co etc.
3. Non-essential e.g; As, Pb, Hg, Cr, Cd, V etc.
21 explain what happens in a living tissue during deficiency and over supply of essential
and non essential trace elements
r Optimal
Deficiency Growth of living tissue
Metal Concentration �
59 Fig 1.2 Essential Trace elements in living tissues (toxicity profile)
r Tolerable Toxic
Growth of living tissue
Very Toxic (Lethal)
Metal Concentration
Fig 1.3 Non-Essential trace elements in living tissues (toxicity profile)59
Table 1.11, lists the classification of essential and non-essential trace elements
found in living tissues according to their toxicity and availability
23 Table 1.11 Classification of elements according to toxicity and availability59
Non-Toxic Toxic Very Toxic (Lethal)
Na c F Ti Ga Be As Au K p Bi Hf La Co Se Hg Mg Fe Rb Zr Os Ni Te Ti Ca s Sr w Rh Cu Pd Pd H Ci Ai Nb Tr Zn Ag Sb 0 Br Si Ta Ru Sn Cd Bi N Re Pt
1.8 Significance of some heavy metals to plants and animals
The significance of some heavy metals to plants and animals have both positive and negative impact depending on the type and nature of the metal under consideration
Zinc: Zinc is considered by the National Academy of Science (NAS) USA, as an essential trace element in human and animal nutrition and recommended daily dietary allowances of 15mg/day for adults, 1 Omg/day fo r children and additional supplement fo r pregnancy and lactation periods are also recommended. The W.H.0.63 (World
Health Organization), recommends 4-lOmg/day depending on age or sex. However,
Zn plays an important role in several plant metabolic processes, it activates enzymes as it is incorporated in meta1lo enzymes. It is involved in electron transport systems and in protein, carbohydrate, nucleic acid and lipid metabolism. It forms complexes with DNA and RNA and affects the stability of these compounds63 . The normal concentration of Zinc in plants growing on unpolluted soils varies fr om 8-1 OOmgkg-1 ,
Visible toxic symptoms of Zn in plants includes; growth retardation, stunted growth
1 and chlorosis at concentrations above 200mgkg- 65. Zinc deficiency may exacerbate
24 the effects of known teratogens, especially in diabetic animals66. A zinc defiencny
syndrome occurring during human pregnancy results in increased maternal morbidity,
abnormal taste sensations, prolonged gestation, inefficient labour, atonic bleeding,
and increased risk to the fetous67.
Cadmium: Cd is toxic to both plants and animals when present in the environment in
excessive bioavailable concentration. Elevated levels ofCd in plants and fo od creates a otential hazard to human health68. Generally, the background concentration of Cd in terrestrial plants varies between O.l-2.4mgkg-l, dry weight 69-70. Cadmium inhibits photosynthesis and transpiration in plants 71. Excessive Cd in so causes stunted plant a growth, small curled and chlorotic leaves and leaf margins; veins show a red-brown coloration.
To animals, Cd is a cumulative poison for it is stored mainly in the kidneys and kidney tubules, rhinitis (inflammation of the mucous membrane of the nose) emphysemia (a chronic disease of the lungs in which the alveoll become excessively distended), and other chronic disorder results72. A condition of chronic Cd poisoning known as "itai-itai" was observed in Nigrata Village in Toyoma City region of
Japanin the 60s. Excess Cd in the diet was found to impair kidney fu nctioning and hence to disturb the metabolism of calcium and phosporus, leading to bone disease.
The disease causes excessive demineralization and embittlement of tl1e skeleton. Tl1e origin of this disease was traced back to a diet of rice grown on paddy soils polluted with Cd fr om a mine source72.
Nickel: has low toxicity compared to zmc, manganese and chromium. It does not
25 accumulate in tissues (body tissues), but extrapolating animal studies to humans,
toxic symptoms could manifest with a daily intake dose of 250mg/day of soluble
nicke172. Higher dose may result in skin disorders (dermatitis), respiratory disorders
and carcinogenesis (of nose and lungs) in humans73 . However, 30-73 mgkg-1
ingestion of Ni (as NiS0 -6H 0) may be toxic to humans 74. The symptoms in plants 4 2 of Ni toxicity include chlorosis, stunted growth. Brown interveinal necrosis and other
symptoms7 3. The development of chlorosis is usually attributed to iron deficiency
induced by antagonism for nickel75. However, lower levels of Ni (25mgkg-1) had a
beneficial effect on cornyield, whereas at higher levels, yield was sharply reduced76.
Manganese: High concentration of manganese, however, in the body causes to cause
chronic Mn poisoning effect similar to Parkinson's syndrome disease77. Also, manganese inbalanced amino acid content of potatoes and reduced leaf cell number
and shoot dry weight of sugarcane78' 79. Manganese high presence in soil caused both height and weight of soyabeans plants to reduced70.
Lead: health effects of a toxicagical nature (in man), is measured by the blood lead levels. The effects are neurotoxic which includes irreversible brain damage. Such toxic level is reached when the blood Pb levels exceeds 1 00-120mg/dL (daily level).80 Severe gastro intestinal symptoms start to be observed in adult lead mine workers at blood Pd level of 80-1 OOmg/dL (blood)80. In non fa tal cases, permanent severe mental retardation with other neurologic symptoms are observed are levels as low as 40-60/dL80. The International Agency for Research on Cancer (IARC), classified Pb in group 3 (Inadequate evidence for carcinogenicity in humans).
26 Phenotoxic symptoms induced in plants by Pb include, stunted growth, small curled and chlortic leaves and leaf margins, veins show a red-brown coloration8 1 .
Copper is not a cumulative systematic poison77 ; it is considered an essential micronutrient for human nutrition since it is required in many enzymic reactions.
Phenotoxic symptoms observed include; early leaf fall; stunted growth; abnormal development of root cap; reduced number of root hairs 72 Copper is an essential element for plants that plays an important role in carbohydrate, nitrogen and cell wall metabolism72, It acts as a co-enzyme and in involved in seed production and disease
72 resistance . Cobalt is considered an essential nutrient molecule (part of vit.B12 molecule)77. Concentrations higher than lmg/kg body weight may be considered a health hazards to humans 77. Since the concentration of Co as related to the potential toxicity in water is negligible, health authorities have not issued maximum concentration levels, with the exception of USSR with a maximum Co level of lmg/Jitre of water77 .
1.9 Aim of Study
Mining operations and the release of metals into the environment especially; soils, vegetation and aquatic environments, have generated interest in heavy metal pollution of soil used for agricultural purposes, Uncontrolled human activity in mining and agricultural areas still remain maj or sources of environmental pollution.
For example, mineral build-up into soils fr om acid mine drains have caused severe pollution problems affecting fo od crops in South Africa82.
The need to enhance agricultural prodt1ction has led to the use of agricultural
27 chemicals, i.e. fe rtilizers and pesticides, which are known to contain some levels of
heavy metals. Tn an attempt for plants to absorb nutrients from the soil, these metals
are absorbed along with other nutrients via their roots. For instance, the Japanese
case of 'Itai-Itai disease was caused by Cd in rice grown in polluted soils. The need
to mine economically beneficial minerals sustainably, without polluting surrounding
soil used for agricultural purposes cannot be over emphasised. Nasarawa State is a
State in Nigeria known for mining and agriculture as the main occupation of the inhabitants. In an attempt to carry out these processes, the environment 1s
contaminated with metals released fr om mining or from agricultural chemicals 111 order to improve agricultural yield of crops.
The aim of this study therefore, is to determine the levels of Zn, Mn, Cd. Cu, Co, Pb and Ni in soils and selected fo od crops in some Local Government Areas of
Nasarawa State - Nigeria, in order to;
(i) assess the possible enrichment of soils and food crops with these metals as a
result of the human activities in the area, via mining and agriculture
particularly,
(ii) ascertain possible potential risks of these metals to life and
environment by comparing results with acceptable levels of metals in foods,
(iii) compare the levels in this study with those of world soils and other
country standards/guidel ines.
(iv) provide baseline data of the heavy metal contents in the study area in order to
28 monitor the effect of human activities to environmental pollution.
(v) determine the levels of bio available metals in the soil which are likely to
affect human health through food-chain.
(vi) establish link between seasonal variations of soil metal levels.
(vii) provide necessary data for legislation for better fo od quality and health.
29 CHAPTERTWO
LITERATURE REVIE\V ON HEAVY METAL DETERMINATION
IN SOIL AND PLANTS
2 .I Sampling and Sample Preservation
The validity of the conclusions drawn from chemical analysis of samples depends, among other things, on the methods used in obtaining and preserving the sample. Sampling and any subsequent separations are the greatest sources of enor in chemical analysis. An ideal sample should be identical in a 11 of its intrinsic properties with the bulk of the material from which it is taken. In practice, a sample is satisfactory if the properties under investigation correspond to those of the bulk material within limits set by the nature of the test. According to Kratochvil and Taylor83, the major steps in sampling are;
1. identification of the site(s) from which the sample is to be taken
2. selection and obtaining of gross samples of the analyte
3. reduction of each gross sample to a laboratory-size sample suitable for
analysis.
4. determination of appropriate sampling time/period before analysis.
Kratochvil and Taylor83, developed a comprehensive list of recommendations for sampling field soils and vegetable crops including fmits, leaves and nuts and the preparatory steps to be fo llowed before these materials are subjected to actual chemical analyses. The recommendations comprises ofthe following;
30 1. cleaning to remove tissue surface contamination (plant materials)
drying to stop enzymic reactions (food materials) 2.
3. grinding to reduce particle size for analysis (soil materials)
4. drying to a constant weight (soil and vegetable materials)
Soil and plant tissue sampling and preparation procedures were also reviewed by
Lockman85. Here, it was recommended that soil samples be stored in pre-cleaned
cellophane bags. Cleaning is usually done using dilute mineral acids (HCl or HN03),
and dried before samples are stored in them,
t n workplace involve Further pretrea me t of soil samples, usually at the laboratory
grinding to fine particle sizes (2mm) in a mortar after drying to remove moisture
completely, in an oven at moderate temperature (70-80°C), or air drying in a dust-free
atmosphere.
2.1.1 Soils
Soil sample collection, preparation and preservation techniques vary depending on the type, nature and aim of the investigation. For example, Remon et al 85, used a
systematic sampling system to evaluate heavy metals at a former metallurgical land fill
site, because the metals under investigation were not leacheable and very immobile in the soil. The metals analysed include; Cu. Cr, Mn, Ni, Pb and Zn. The polluted sites were believed to have a highly heterogeneous soil composition, hence the choice of
systematic sampling technique.
In most sampling techniques according to Quackenbush, et al87, it 1s important to
31 mention that efforts are aimed at reducing enors, ensuring representativeness of sample,
achieving uniformity or homogeneity of samples and ultimately the reduction of
sampling enors. Field soil sampling technique may involve a combination of factors
which include;
1. deleanation of field into pendons or grids, line acreages, transects of equidistant
sizes, quadrants, areas or sections, for actual sample collection.
2. collection of replicate samples (minimum 3 Nos) of soil materials inordcr to
obtain an acceptable average concentration (e.g. of metals) in soil at (�20cm)
soil depth.
3. collection of guide/control samples which arc not affected by the conditions of
the test area usually at (20cm soil depth).
4. complete homogenization grinding and swvmg of fragment samples into
unifonn composites before other sample work-up procedures, are fo llowed
5. drying of soil samples before analysis.
According to Kramer and Twigg88 , factors that determine selection of a sampling
procedure include;
1. purpose of inspection
2. nature oflot size
3. nature of test material
4. nature of test procedures
Samples for analysis should be large enough, (usually 2kg bulk) or more, for all
32 intended determinations. Cochran89', recommended 250g fo r soil samples (must be homogeneous, pretreated and dry), lOOg fo r spices and IOOOg for fruits and vegetables.
Manual methods of sampling soil materials (powdered or granulated) are subject to numerous errors. Quackenbush et al87, studied the factors that may cause bias in soil sampling. According to their investigation, they listed factors that may lead to sample bias of soil materials as; particle shape and size, particle adhesiveness and the distribution of particles ·within soil strata. For most topsoil sampling, they suggested that layers between (0-30cm), of topsoil, gave the ttue representation of soil conditions, where plants arc grown. Most of these difficulties are overcome by fine grinding (200
250mm), mixing, drying 60-70°C for 24hrs of large soil sample (bulk or composite), before analysis.
87• Rs. Soil sample preservation method as suggested and reported by some workt;rs
89 ° involved the rinsing of sample with dilute (I :3) nitric acid followed by drying al 60 c
(' in an oven for 24 hours. This process will eliminate microbial and fu ngal alterations of soil. Most soils of loam and alluvial origins contain reasonable amount of organic 4 matter, which encourages microbial and fungal growths,8 . pH measurements of soil samples are however done with fresh untreated dry soils, to avoid unreliable pH readings from acid rinses.
2.1.2 Plants
In sampling of plant tissues (food crops), fo r trace metal analysis, it is important to select several types of plants which may include; root vegetables (RV), leaf vegetables
(LV) and fru it vegetables (FV), in order to have representative sample of all the crops
33 in a given farmland. In some exceptional cases, presampling procedures may involve the cultivation of certain plant species in a given polluted field before they are harvested (at maturity), for trace metal determinations. In a survey of heavy metal pollution of vegetables in a fo rmer ore-mining region of Bergischeland, Germany,
Zumbroich26, established test gardens containing different types of vegetables, to ascertain the levels of trace metal accumulation in them. The metals investigated include; Pb, Cd, Hg and Zn. The analysis revealed that 40% of the test vegetables
(dwarf beans, lettuce, spinach, carrots and celery) and particularly, root vegetables, exceeded the tolerated levels of Pb and Cd concentrations, after harvesting. This is because the enrichment behaviour of various cultivated plants differs according to their 2 physiological and physiognomic characteristics 6.
In a related sh1dy involving the accumulation of heavy metals in soils and plants in industrially polluted fields, Barman, et al 90; can·ied out sampling of vegetable species directly at farmlands where industrial effluents flow through. Control/guide vegetable samples were collected from farmlands within the vicinity of Kalipur Village, India, where no industrial effluents were identified.
Different researchers adopt different sampling options to carry out investigation on plant tissues. It is worthwhile mentioning that laboratory pot experiments with plant samples may not give a true representation of field fann conditions and situations. Soil types and soil characteristics (in field farms), may differ from laboratory pot experiment investigations. It is therefore proper to posit that for proper random sampling of vegetation materials, consideration must be given to natural
34 I .. l :
farmland conditions where pollutants are suspected to be present. This procedure will
prevent sampling enors resulting from lack of randomness in sample selection or
deficiency fr om human bias or judgment.
For some plant and food samples, changes in composition may occur during or after
sampling. According to Baker 91 et al, typical changes include
gain or loss of water, loss of volatiles, physical inclusion of gases, reaction with
container material, temperature regimes inside container or foreign matter inside
container. Baker et al, suggested that plant materials be analysed in the laboratory for parameters sought within 48hours after sample pre-treatment. Preservation of plant materials (including fo od crops), as reported by Benton Jones et al84, for metal analysis, required pre-treatment which involves washing of plant materials with clean distilled water followed by rinsing with dilute HCl or HN03
In summary, the aim of sampling is to secure a portion of the material that satisfactorily represents the whole. The more homogeneous a sample is, the greater chances of obtaining a true and reliable result of finding after analysis. The more heterogeneous the material the greater difficulties required in efforts and time to obtain a truly representative sample, with true and reliable result of finding after analysis.
2.2 Sample Preparation Methods
The purpose of sample preparation 1s to m1x thoroughly a large sample in the laboratory. This apparently homogeneous sample must then be reduced in size and amount for subsequent analysis. Grier92, reported results of a survey based on
35 I I
questionnaires submitted to 20 plant scientists. The problems encountered by the
analysts in the preparation of samples for analyses included difficulties in obtaining representative small samples from large samples; loss of plant material; removal of extraneous materials fr om plants without removal of plant constituents; enzymic changes before and during analyses; compositional changes during grinding; changes in unstable components and special preparation problems in analysis of oil seed 2 materials9 . According to Etenmann93, if a sample is not prepared properly fo r analysis, or if the component become altered during preparation, the results will be inaccurate regardless of the effort, precision of the apparatus and the teclmiques used in the analysis.
2.2.1 Digestion of soil samples
The detennination of metals in soils is generally affected by the ·method of sample preparation and the analytical technique employed. Most analytical techniques require that the sample be in a solution before analysis which therefore makes the method .of sample preparation very critical in metal determinations in soil. Utilisation of single mineral acid and a combination of acids have been used in the digestion of soil samples prior to analysis of metals.
94 For instance. Anderson , used 2M HN03 in a ratio of 1:10 (sample to acid) mixture in a water bath for 2 hours fo r the preparation of soil sample in the analysis of Pb, Cu, Zn,
Cd, Cr, Co and Ni with a flame atomic absorption spectrophotometer. Recoveries of over 90% (total metals in soil) were achieved.
36 I . I
Miller and McFee95, detennined total Zn, Pb, Cu, Ni and AI in soil by digesting with 16M HN03 and HC104 usmg an aluminium digesting block followed by 1 CP-AES. A recovery of 95% average (total analyte metals), were obtained.
96 Gupta and Chen used HN03 - H202 system for the extTaction of Cr, Cu, Fe, Ni, Pb and Zn in soils and sediments. Here, H202 (a strong oxidant), dissolved all organic bound metals while HN03 removed all inorganic bound metals, hence achieving total metal recoveries up to 99% of analyte samples.
97 Sinex et al , used boiling HN03 - HCl (9:1) ratio to remove trace Cr, Mn, Fe, Co, Cu,
Zn, Cd and Pb from soil sediments. Recoveries up to 91% of metals and coefficientof variation of less than 8% were achieved.
Bakhlar et al 98, developed a lwo-step digestion process for soil samples, using H202 to oxidise organic matter, fo llowed by an HC1 digestion as first step. In the second step, dilute HF (0.1M) was used to digest soil samples with metal concentrations below
FAAS detection limits solution concentrations higher than the FAAS detection limit of
1 1 0.02 mgkg- Cu, 0.07 mgkg- Ni, 0.19 mgkg -I Pb and 0.01 mgkg -I Zn, were required by employing fairly larger soil samples or employing more sensitive analytical techniques e.g. ICP-AES etc. Here recovery studies with soils spiked with trace metals yielded between 92% and 104% of added metals.
86 Remon et al , employed hot HN03 with ICP-OES analytical finish to determine metals present in soil and vegetation in a former metallurgical landfill in order to monitor the impbcations in risk assessment of the soil and vegetation and site
37 I .. , I
restoration. The metals investigated included Cr, Ni, Cu, and According to the Zn Pb.
two International Proficiency Tests, Geo PT -1 and Geo PT -2, laboratory errors were
below the analytical errors expected for XRF analysis, that is, less than 1%, 1.4%, and
2% for major elements above 75% recovery with coefficients of variation between 1 -
10% and less than 5%, 8% and 10% for trace elements near 1000, 100 and 10 ppm,
respectively. Analytical precision were checked by choosing random samples in
triplicates. The relative coefficient variation was routinely between 1% and 8% and
never higher than 10%.
The effects of heavy metal pollution on declining populations of redwood ant
colonies in forests of Finland, have been studied by Eeva et ae9. Redwood ants which
are important economic insects active in food-chain, were considered to be good
indicators of pollution, because the declining populations of colonies of these ants were
correlated with high level forest ecology pollution from heavy metals in southwest
Finland. Here HN03 -H202 acid system was used to digest the insects, fo llowed by an
1 CP-MS determination. Levels of Al, Cu, Cd, Ni, Zn, As, Pb and Hg determined, were significant and caused morphological mutations in the bodies of redwood ant workers.
Detection limits were up to ppt level and below. Metal recoveries averaged 90% using this digestion scheme.
00 Amacher1 , suggested a digestion with HN03. HCl and H202 mixture in a conical flask on a hot plate (USEPA, 1986100a)), to be suitable fo r routine assessment of soil contamination with trace metals. Here, recoveries with spiked soil samples of analysed metals were in agreement and coefficients of variation were also within acceptable
38 , I I
limits (<10%), compared with other digestion schemes.
It has been suggested however, that USEPA reflux method does not give complete
dissolution of metals fr om anthropogenic sources in soils 100, hence the concentrations
0 determined, could not represent total metals in soil Flegal1 1 used H2S04 - HN03
combination to obtain near total concentrations of trace elements in sediments after
quantifying these elements with ICP-AES and ICP-MS. The elements evaluated
included Al, Ag, Cd, Cr, Cu, FE, Mn. Ni, Pb and Zn. Detection limits for trace metals
in the soil matrix ranged from 0.01 mgkg-1 for Cr and 0.1 mgkg-1 for Cd. Results
obtained gave acceptable coefficients of variation less than 10%.
2.2.2 Determination of total metals in soil
Determining the total trace element concentration of a soil is the first step in evaluating
its potential health or ecological hazard 100. A standard, relatively safe, method that
allows for the recovery of at least approximately 90% of soil bound metals may be . considered reliable in most laboratories working with trace metal contaminated soils 101
2 Nicola, et al10 developed a modified procedure for the analysis of total trace metals that can be used in all kinds of soils, including those with oil and grease contamination using HN03 - HC1 04 digestion combination. Recoveries obtained were 99, 94, 114, 92 and 83% for Cd, Cu, Ni, Pb and Zn, respectively, for standard reference material (SRM)
NIST 2710 (Montana Soil), Canada.
The dissolution of the silicate matter would enable the detennination of the total metal content of soils and sediment samples for the determination of the total metal content.
39 I I •
3 Forstner et al1 0 , recommended the HF - HN03 mixture in the digestion of soils and
sediments fo r total metal content evaluation. Sensitivity of this method was high (in the
ppb range), while metal recoveries were well above 90% fo r most of the metals
investigated.
104 Agemain and Chau proposed a triple acid system (HN03 - HC104 - HF), in a ratio of
4:1 :6, for the dissolution of all kinds of sediments and soils fo r heavy metal analysis.
Recoveries ranged from 91% fo r Sr to 103% for V occurring as trace elements, and
from an average of 96% for Na to 102% for Fe occurring as major elements.
Baker and Amacher 105, used USEPA SW-846 (reflux method) involving digestion with
HN03 - HCl -H202 acid combinations. This method though, gave good percentage
recoveries ranging from 80% - 90% of total metals determined, it excluded most trace
metals trapped within crystal lattice of silicate minerals. Results for total metals content
of soils as non - silicates using USEPA method 3050 (i.e. HNOs - H202), systems, gave
recoveries between 90% - 95% of total metals in soils and sediment samples thereby ·
offering a better and improved digestion scheme than the USEPA SW - 846 (Reflux method).
If total elemental analysis is desired, a rapid and precise method will he an aqua-regia,
° (UNO, HCl), HF digestion for 1 hr at 1 00 C or digestion with HN03 - HCI04 - HCI -
HF - H202, system in Teflon beakers in a hot plate, proposed by Bakhtar et al106,
In an attempt to recover all metals in organic and silicate structures of oil samples, . 4 . 10 . 107 . Agemam and Chau , Tessier et a 1 1 , used act'd comb' mat10ns mvo1 vmg. HNO 3 -
HC104 HF and HN03 - HF acid regimes, respectively. Boiling was done in specialized
40 I ''
Teflon digest equipment in fume cupboard to avoid accidents in the use of HF - HN03
- HCl 04 combination. This procedure yielded comparable recovery results between 92
- 140% with soils spiked with known weights of trace metals
95 Miller and MCFee , however, used HN03 - H202 for reliable and combined determination of total metals in both soil and vegetation, respectively, with gentle heating for I hr at 100°C until digestion reaction stops. This method gave metal recovery values of between 90 - 95% in soil and sediment samples and 92% - 95% of metals in vegetation samples.
2.2.3 Sequential Extraction
Sequential extraction of metals, allows for better assessment of metal bioavailability, speciation of metals in soil and the possibility of mobilization of metals from soil matrix 108. Various extractants and extraction methods have been developed to assess metal bioavailability, specialization or mobilization in soils.
The problems that may arise when using different extractants in soil analis as posited by
Ahnstrom and Parker109, include;
(a) limited selectivity of particular extractant fo r metals m a particular
soil phase.
(b) limited knowledge of metal distribution among soil phases.
(c) use of many chemical systems in highly contaminated soils.
(d) possible introduction of other artefacts during extraction process,
(e) Indiscriminate application of procedures without any standard guidelines.
41 I,I
2.3 Plant Sample Metal Determination
Detem1ination of trace metals in plant samples could be achieved by employing two
major analytical procedures; viz: wet - ashing or wet - digestion and dry ashing or dry
oxidation. The choice of method depends on the analyst and the precision of the
process adopted. Whatever process is adopted will be informed by the need to achieve
maximum recovery of all metals in the plant material. It is also important to conduct
sampling of plant species over a period of time; say at the peak of their growth or at a period where maximum pollution of soil occurred.
2.3.1 Wet Ashing or Wet Oxidation
The determination of trace metals in biological samples requires the destruction of the organic matter during sample preparation stage131-133. The choice of method depends to some extent on the metals to be determined. The organic-matter in biological systems is usually destroyed by oxidation, either by the use of oxidising acids or in the
. 134 · 135 143 139 dry state wtt' h au - . et as 1111g' can gtve' h'tg h bl ank va 1 ues c.1rom t1 1e act'd s use d ; w 1 4 whereas dry ashing is prone to losses of metals either by volatilization or by adsorption 1 0 onto the contai11er. The wet oxidation reagents commonly employed include HN03,
H2S04, HCl, and H202. Most of the methods require the use of one or a combination of the reagents for effective digestion of the organic matter136. Although good recoveries were obtained for most metals studied, yet there were losses in Pb using a combination of
HN03 - HC104 - H2S04 on the one hand, and HN03 - H2S04, on the other hand. The use of perchloric acid with nitric acid or with nitric - sulphuric acid mixtures has been 137 suggested by Smith , for the rapid decomposition of many organic compounds that are difficult to oxidise. The use of HN03 -H202 (30%), for the digestion of biological materials, for trace metal determination, has also been well documented 138
45 I ,
Wet oxidation procedures usmg two acid mixtures, HN03 - H2S04 and H202,
1 36 were recommended by Gorsuch ,for the digestion of various fo od samples; while
Tolg , recommended HN03 - H202 for the digestion of biological metals of
vegetables origin. Tolg141, also posited that the digestion of vegetable samples with
HN03 -H302 systems, may lead to volatilization of As, Se, Hg and some other metals. Since the results of Miller and McFee's, (USEPA method 3050)95, involved the use of HN03 - H202 systems to digest and extract metals from silicate lattices of soils, the addition of H202 (a strong oxidizer) to this pair will further ensure total destruction and extraction of metals in biological systems and silicate bound metals.
2.3.2 Dry ashing
Dry ashing involves the heating of a weighed sample material at high temperature in a crucible until constant weight is achieved without flaming. Ashing in porcelain 2 crucible at temperatures ranging from 400 - 550°C, is satisfactory14 . The chief advantage of the dry ashing technique is that larger amount of samples can be mineralized. The process though long, does not require the constant attention of the analyst and avoids the use of large volumes of reagent, thereby minimising blank values. Losses depend on the temperature and time used for ashing and in some instances on the form of chemical compound in which the element is present in the 44 sample1 .
The Association of Official Analytical Chemist Method145, for the determination of pb in biological samples e.g. evaporated milk, involves the following dry ashing steps;
(a) dry at 120°C overnight in an oven.
(b) transfer into a muffl e fumace at 250°C and slowly increase the temperature to
46 I 1
350°C in steps of 50°C.
maintain at 350°C till smoking ceases and increase to SOO"C steps of 75°C. (c) in
(d) maintain at 500°C for 16 hrs. Dry ashing method often requires ashing aid to fa cilitate decomposition of the organic
matter. HN03, H2S0 equimolar mixture ofNaN03, and KN03146 etc., have been used as 4 ashing aids. According to Lynch1 47, dry ashing is the most satisfactory method if no loss of metal occurs at temperatures up to about 500°C fo r the determination of total organic carbon (O.C) in soils, and values are obtained by gravimetric weight differences.
Theirs 148, summarized reported losses during dry ashing, and recommended a dry ashing procedure for biological materials that involves, drying and pre-ashing the sample in a specific apparatus with the aid of a hot plate and an infra-red lamp.
Gorsuch1 44, found that dry ashing of cocoa at 550°C, gave satisfactory recoveries for Sb,
Cr, Co, Fe, Mo, Sr and Zn. A modified dry ashing technique which does not allow for metallic loss, have been proposed by Elvidge and Garratt' 147(a\ involving complete combustion of sample in a commercial bomb calorimeter, in an atmosphere of oxygen144. With light and bulky fo ods, preliminary compression improves combustion.
Using this process, wet materials must be dried before combustion147(a). About 3-4g of material can be burned in one step under an initial pressure of 30 atmospheres of oxygen.
According to Theirs 1 48, asenium loosely bound in blood serum, may volatize as unknown compound at 560°C, while boron, volatizes with steam from acid solution.
Cadmium volatizes as the chloride or metal at temperatures between 400°C and 500°C148.
Chromium, volatizes as cliromylchloride at the low temperatures (200°C) under oxidising conditions according to reports by Schulek et al1 49' For Cu, volatilization have been
47 I I ..
reported by Zonneveld et a 1 150 , as prophylin compounds when petroleum samples are
burned; as copper acetate in vinegar; and are reduced to metal which is not dissolved by
HCI.
Fe, volatizes as ferric chloride at 450°C in most fo od samples 150 Pb, in blood
samples and petroleum stocks except in the presence of sulphates151; while Hg, volatizes
as metal below 450°C151-155, during ashing of samples. Nickel and Vanadium150,
volatizes as porphylin compounds, when petroleum samples are burned, while zinc
volatizes as chlorides below 450°C150.
2.4 Analytical Techniques fo r Metal Determination in Soils and Plant
Materials
2.4.1 A AS (Atomic Absorption Spectrophotometer)
Atomic absorption spectrophotometry is used for determining the concentrations
of metallic elements in solution. It relies on the analyte solution being aspirated into a
flame, which enables the atoms of the clement to be determined, to absorb radiation
from a hollow cathode lamp source which is unique to each element to be measured.
The teclmique therefore, provides high specificity and sensitivity for the analyst. It also
features fu ll gas control (acetylene or nitrous oxide), and background correction. The
optical systems are made of silica coated mirrows for long life and stable performance. All fixed gas piping is made fr om stainless steel and gas lines are
fitted with flame arrestors and blow back valves.
2,4_2 A Typical Published Application of AAS 156 Sanders , published a typical application of AAS m the determination of wear
metals 111 used lubricating oils. From the anal ysis of wear metals in lubricating
48 oils, employing ASTM methods D810 and D811 (American Society for Testing
Methods), typical levels of wear metals in used diesel crank case oil are listed. In this study also, sensitivities, detection limits and average percentage recoveries were listed.
Richard, 157, have also published some applications of AAS in the determination of metals in soils, plants and other media. For instance Cu, have been quantified in fertilizers, alloys ore concentrates, plants and soil, while Zn have also been quantified in plant tissues, soil extracts and vegetation 158-159•. Cd have been fo und in fe rtilizers vehicle tyres, roadside soils on highways, human urine samples and table wines. Pb and Mn in fertilizers, stainless steel metal scraps, fertilizers and roadside soils. Others include, Ni in petroleum products and synthetic detergents and uranium in fish and marine planktons.
2.4.3 AFS (Atomic Fluorescence Spectrophotometer)
In atomic fluorescence spectrophotometer, atoms are generated the same way as in atomic absorption spectroscopy, except that a cylindrical fl ame is used. The fl ame is irradiated by resonance radiation from powerful spectra sources, and the fl uorescence that is generated in the flame is measured at right angles to the incident beam of radiation. This 1s done to minimize the contamination of fluorescence signal by limiting the light source. While atomic absorption spectroscopy can be used in the ppm (1o- 9 M solution), atomic fluorescence spectroscopy can detect contaminants in the ppb (1o-6 M solution) range.
2.4.4 Neutron Activation Analysis (NAA)
In neutron activation analysis, a weighted sample together with a standard that contains a known weight of the clement sought is exposed to nuclear bombardment, The
49 I, I
radioactivity of the clement in the sample is then compared with the radioactivity
111 the standard; generally, a chemical separation is required to purify the isotopes of the elements sought and to remove the entire induced radioactivity. The quantity of the element in the sample is then calculated fr om the ratio of the separated activities. Results obtained by neutron activation generally are within 5% of the true value, and replicate analysis under favourable conditions are within 2 -3% of the mean. The attractive feature of the neutron activation analysis are its wide applicability, high sensitivity (0.001 Ippm), and satisfactory accuracy and prec1s1on. Numerous applications are in pollution studies, agriculture and soil analysis.
2.4.5 X-Ray Fluorescence
The use of X - Ray for the identification of chemical components is based on emission methods, involving secondary or fluorescent emission. Measurement of the intensity and wavelength of fluorescence radiation is a well established method of analysis, which has been applied to the determination of elements from 11Na to
92U in powder, liquid or metal samples. The method is rapid (1 - 4mins), independent of the chemical combination of the element and non destructive in the sense that the specimen examined is not destroyed. X-Ray spectroscopic instruments are quite expensive. Coefficient of variation in the range 0. I - 1.0% can be obtained. In some instances, determinations in ppm (10-6) range can be measured.
50 I I.
CHAPTER THREE
EXPERIMENTAL
3.1 Study Area
Nasarawa State is located in the Guinea Savannah belt of North Central Nigeria,
° between latitudes of go and 1 0°E and longitudes 7° and 9 N. It is bounded in the
North by Kaduna State, North-East by Plateau State, South East by Taraba State,
South by Benue State and North-West by the Federal Capital Territory (FCT),
Nigeria. (Fig 3.1). The primary occupation of the population is agriculture. Over
90% of its citizens are involved in the production of food crops (Maize, Yam,
Rice, Cassava, Millet, Guinea corn, Potato, Sorghum), tree crops (Cashew,
Orange, Mangoes, Sheanut), Cash crops (Groundnuts, Beniseed, Soyabean) and
Vegetables (Lettuce, Carbbage. Carrot, Onions etc.). Other agricultural related activities include animal production e.g. cattle, goats, pigs, sheep and poultry. Many inhabitants of the state are also engaged in open - cast pit mining of ore minerals, precious stones and solid minerals (gems), granite cutting and quarrying. Four local government areas were selected for the study and these include; Karu, Keffi ,
Akwanga and Nasarawa Eggon respectively. (Fig. 3.2). These are areas where mining activities and agricultural production go on hand-in-hand. The choice of these areas was based on logistic reasons during sample collections.
3.2 Sample Collection and Preservation
Soil and vegetation samples were collected from four different LGA's as shown in
Fig. 3 .2. A description of the sites or locations where samplings were carried out are
51 listed in Table 3 .1. Sampling was carried out between March 2004 and September,
2004, which covered both rainy and dry seasons. This was also within a cropping year.
52 {
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3.2.1 Soil Sample Collection, Preparation and Preservation
Soil samples were randomly collected fr om 0 - 20cm depth of topsoil in farmland locations (Table 3.1), with scooping stainless steel knives, at equidistant quadrants along line acreages of the farmlands, (500)meters apart). Three sampling points were randomly selected to make up a composite sample from a designated site/location, giving a total of nine (9) sampled spots within 3 different farmlands per LGA.
Soil control samples were obtained from soils around homes within the area of sampling where mining activities, fertilizer and pesticide applications were absent.
Interactions with members of the community showed that these areas had not experienced agricultural and mining activities in the last fi ve years.
Soil sample preservation prior to analysis included, drying of sample for 48hours at room temperature, grinding the samples in a mortar to reduce particle sizes and
sieving of the grounded soil sample with a 2.0mm stainless steel sieve. Soil fractions less than 2.0mm were collected and stored in clean polythene bags fo r laboratory analysis.
3.2.2 Plant Samples Collection, Preparation and Preservation
Plant samples namely; potato, yam and carrots, lettuce and carbage, millet and maize, were bought from local markets around village farmlands where soil samples were carried out. This was because of restriction by farm owners to sampling of crops in their farms. Plant samples were collected at the period ofharvest.
The peels of root vegetables (potato and yams), were chopped together with their
56 tubers into pieces and dried in the sun for 7 days. The dried fragments were then
crushed into powder in a mortar and sieved through stainless steel sieves and the
fractions passing through the 2.0 mm sieve were stored in polythene bags ready for
analysis.
Leaf vegetables (lettuce and carbage) were chopped into fi ne shreds with kitchen
knives and dried in the sun fo r 7 days. The dried leaves were pulverized in mortar
with piston, and stored in clean polythene bags ready for ana lysis.
Cereals (millet and maize) were further dried under sun for days, pulverised in a 4
mortar and sieved through stainless steel sieves to obtain powdered sample that was
stored in polythene bags ready fo r acid digestion and AAS analysis.
Table 3.1 Description of the sample location and sites.
L.G.A Villages(s)/Community_ Area/Sites Karshi l ag fatm land interior ofKarshi road about Karu Vi l e 1 kms off Abuj a-Keffi ex ress road O p Masaka Masaka Community fam1 land 4kms off express
road on Abuja- Keffi road . Gunduma Gunduma village farmland north of Gunduma village . Keffi Keffi Village Fannland around Nasarawa Polytechlmic site about 2kms offKefi Town Angwan Maisari Village Farmland offMaisari Village (2kms away). from Keffi Akwanga road . attara l age Farmland between boundry of Karu and Keffi T Vi l LGA. Akwanga Andaha Community Community farmland 21Gns north of Andaha Community. Nunku Community Community farm land 4kms notih ofNunku village. Akwanga Angwan Zaria Fannland 20kms to Mm·araba - fo rest junction, Village along Keffi - os road. J N/Eggon N/Eggon Community Community farmland 20kms to Lafia. Mada Station Community Village farm settlement 5kms fi:om Akwanga. Igga Village Village fann settlement 1 Okms from N.Eggon Local Govt. H/Q.
57 I .. I .
3.3 Chemicals and Reagents
With the exception of H202 (30%) and DTPA all reagents used were of analytical grade (A.R). Table 3.2 lists the manufacturers of the chemicals/reagents used and most of them were manufactured by BDH Chemicals, Poole, England.
Table 3.2 List of Manufacturers of Reagent and Chemicals used in Sample Analysis
Chemical/Reagent Manufacturers
ZnS04 BDH, Poole, England
MnCh2H20 BDH, Poole, England
CuClz2H20 BDH, Poole, England
3CdS048H20 BDH, Poole, England
CoS047H20 BDH, Poole, England
Pb(N03)z6H20 BDI-I, Poole, England
Ni(N03)26H20 BDH, Poole, England
NaOH, HN03, HCl 04 (60%), CaCl2 BDH, Poole, England
K2Cr2 07, FeS04, NaF Merck, Germany
H2S04 Indicator (diphenylamine) M&B
H202 (30%), H3P04, DPTA KT Flukka, Biochemical, Germany
3.4 Cleaning of Glassware
All glass wares used were washed with detergent, rinsed with distilled water and followed with dilute nitric acid (5%). They were all finally washed and rinsed with distilled water.
58 I . i.
3.5 Preparation of Standard Stock Solutions of Metals
1 1000 mgL- Zn
4.4 g of ZnS04. 7H20was dissolved in 1 Oml deionised water, followed by 20 ml of
3 5M HC 1. This was diluted to 100 cm in a volumetric flask with deionised water to
1 give lOOO mgL- Zn.
1 1000 mgL- Mn
3.60 g of MnCh4H20, was dissolved in 25 ml deionised water, fo llowed by 50 ml of
3 2M HN03. This was fu rther diluted to 100 cm in a volumetric flask with deionised
1 water to give 1000mgL- Mn.
1000 mgL -J Cu
2.68g of CuC022H20 was dissolved in 25mls deionised water, followed by 50 ml of
3 5M HCI diluted to 100cm in a volumetric flask with deionised water to give 1000
1 mgL Cu
1000 mgL -I Cd
2.4g of 3CdS04.8H20, was dissolved in 10 ml of deionised water, fo llowed by the
3 addition of 50 mls of 5MHC 1. This was diluted to 1 000cm in a volumetric flaskwith
1 de-ionized water to give 1 OOOmgL- Cd.
1 1000 mgL- Co
4.7 g of CoS04,7H2HO, was dissolved in lOmls of SM HC1, fo llowed by dilution with
3 deionised water to 1000cm in a volumetric flask. The resulting stock solution
1 contained 1000mgL- Co.
59 I •. I
1000 mgL-1 Pb
1.6 g of analytical grade Pb(N03)2, was dissolved in deionised waster and made up to
1 1 IOOOcm- in a volumetric flask to give 1000 mgL- solution of Pb .
1000 mgL-1 Ni
4.95 g of Ni(N03)2 6H20, was dissolved first with 100 mls deionised water and
3 1 diluted to 1 00cm in a volumetric flask to give 1000 mgC Ni.
3.6 Working Standard Solutions for Instrument Calibration
The working standard solutions were prepared by serial dilutions of standard stock
solution of metals with de-ionized water in a volumetric fl ask.
3.7 Instrumentation
3.7.1 Atomic Absorption Spectrophotomer
A Pye-Unicam SPS Atomic Absorption Spectrophotometer (AAS) in the fl ame
mode was used. The air - acetylene fl ame was also used in the determination
of metals in samples. The instruments operational conditions as listed in the operations manual (Table 3.3), were used in analysis.
T able 3.3 Instrument conditions fo r AAS analysis (mode) Elements Wavelength (nm) Bandwidth (nm) Lamp current j (rnA) Cd 228.8 0.4-0.5 4 Co 240.7 0.2 8 Cu 324.8 0.4-0.5 4 Pb 217.0 0.4-0.5 4 Mn 279.5 0.2 7 Ni 232.0 0.2 8 Zn 213 .9 0.4 - 5.5 6
60 I., I
3.7.2 pH meter
A pH meter Phillips A66 model was used in the pH determinations of so11 samples.
3.8 Digestion of Soil Samples for Total Metal Determination
95 modified USEPA 3050 method (Miller and McFcc) , ustng A a combination of HN03 - HC 104 - H202 was employed in the digestion of the soil 3 samples for total metal analysis. 10cm HN03 was added to lOg of soil in conical flask and this was heated on a hot plate at about 1 00°C for I5mins. On cooling, 3 another 5cm HN03 acid was added and heating was continued for 30mins, at same 3 temperature until the volume was reduced to about 5cm and allowed to cool. This 3 was followed by the addition of 5cm I-1202. When the peroxide reaction had 3 subsided, 1 Ocm of HCI04 was added and boiling continued until digestion was 3 completed. The digest was allowed to cool, filtered and diluted to 1 00cm in a volumetric fl ask with deionised water. The digests were stored in plastic bottles for analysis.
Five replicates of each sample were prepared and analysed for total metal determination, in order to evaluate or test for the precision of the method.
Reagent blanks were analysed to assess the contribution of reagents to metal levels.
3.8.1 Recovery studies
A dry season soil sample fr om Karu LGA was used for recovery studies. Here, samples of soil were spiked with known metal concentrations. The resulting soil
61 I .. I ..
sample was subjected to same digestion procedure as in (3.8) above.
3.9 Extraction of Soil Sample fo r Soluble Metal Determination
( D PTAExtraction)
22 A two-step sequential extraction procedure by Maize et a1 1 , was adopted in the determination of bioavailable metals in soils of the study area. This involved 3 mixing of 5 g of soil sample with 20 cm of 0.01 M CaCh solution with vigorous shaking for 1 hour. The resulting solution was collected and stored in a conical flask.
The residue (filtrate), was then rinsed twice with deionised water and resuspended 3 3 into 20 cm of 0.005M DTPA solution, 5cm of O.IM CaC12 and/or O.IM NaOH
solution was added for adjustment of pH = 7.3, under continuous agitation. After shaking for another 1 hour, the supernatantsolution was removed by filteration.
The combined filtcrates of 'mobile fractions' and 'mobilizable metal fractions' were 3 3 used for AAS analysis, 1 cm of total combined digest was diluted to 10 cm , with de-ionised water for AAS analysis of Zn, Mn, and Cu. While the remaining digests were aspirated directly in AAS for the determination of Co, Cd, Pb and Ni, without further dilutions.
3.10 Digestion of Plant (Food Crop) Samples fo r Metal Determination
5 g of prepared food crop samples were weighed into 125 ml conical flaskusing the 3 3 USEPA 3050 method by Miller and Mcfee95. 10cm of HN0 was added and the mixture was heated fo r 15 rnins on a hot plate at 100°C. The digest was allowed to cool 3 and another 5 cm of HN03 was added and heating continued fo r 30 mins at 1 oooc.
The volume of the digest was reduced by boiling to about 5cnv and this was
62 I , I
3 allowed to cool. 5cm of de-ionized water was added. When effervescence subsjded,
0 cm3 of H202 (60%) was added and heating continued fo r another 15 mins. The fi nal I digest was allowed to cool and fi ltered. The fi nal volume of digest was made up to
50cm3 1ml of digestate was then pipetted and made up to 100 mls for AAS analysis of Zn, Mn and Cu, while the remaining digestion extract was directly aspirated into
AAS for analysis of Cd, Pb, Co and Ni, respectively.
3.11 Reference Sample Mate•·ialAna lysis
Reference soil sample material (SD - M - 2/TM), from International Atomic
Energy Agency (IAEA), was used to assess the suitability of the digestion method for metal determination in soils, fo llowing the digestion procedure in 3.8 above.
3.12 Determination of Organic Carbon Content of Soil
Reagents and apparatuses;
(a) Potassium Dichromate Solution (IM).
(b) Sulphuric Acid (H2S04)-Silver Sulphate Solution
(c) Fenous Sulphate (FeS04)-Sulphuric Acid Solution
(d) Diphenylamine Indicator.
(e) Erlenmeyer Flask, Pipettes, Burrettes, Thermometer, Hot plate.
3 0.5 g of soil sample was added into a 500 ml Erlenmeyer flask and 10cm ofK2Cr201 was a added fo llowed by 20 cm H2S04. The flask was heated gently to I50°C and allowed to cool. The digest was diluted to 200 mls with distilled water. Excess K2Cr201 solution was then back titrated with standard FeS04 solution, after the addition of 10 cm3 85%
63 I-hP04 acid solution, 0.2 g of NaF and drops of indicator (diphenylamine 30 hydrochloride). The end-point is blue to purple. Blank determinations were also carried out. The difference in litre values for blank and soil samples were used to calculate the 159 percentage organic carbon % O.C), as proposed by Jackson et al . The percent organic carbon is deduced as fo llows;
%0.C = (ml) FeS04 (blank)-mlCF eS04) sample wt of sample (g)
3.13 Determination of Soil pH130
Soil pH was determined using a soil - water ratio of 1:2.5. About 20 g of dried soil 3 sample was weighed into a 1 00cm3 beaker fo llowed by the addition of 50cm of distilled
- deionised water and this was shaken vigorously with a glass rod fo r 15 minutes.
Homogeneous stirring was achieved when the beaker was later transferred to a magnetic stirer and allowed for another 15 minutes. The suspension was filtered and the pH of the filtrate was determined with pH instrument (Phillips A66 model), twice and the mean value calculated.
64 I. I . .
CHAPFFR FOUR
RESULTS
4.1 Quality Assurance of Method
The precision of the digestion method of soil and plant materials for metal
analysis are listed in table 4.1. The precision for most metals were less than 10%
for both soil and food crops, which is an indication of good digestion processes.
The good precision for soil digestion was further corroborated with good
recoveries obtained fo r the study (Table 4.2). For most of the metals studied, the
recoveries varied from 84-96%, which shows that the method adopted for soil
sample preparation for total metal determination good. is
The results of the analysis of the reference soil sample by the test method further
indicated that the method is good for soil analysis (Table 4.3). For most metals
studied, the concentrations obtained for the reference standard were within
certified values and these were verified with the t-test at 99% confidence limit as
t-calculated were less than t-tabulated.
For plant materials, the precisions obtained were Zn(4.2), Mn(3 .2), Cd(4.5),
Cu(3 . 3 ), Co( 1.7), Pb(2.9) and Ni(3 .2) (Table 4.1 ). This suggests that the HN03
H202 method for plant material preparation for metal analysis is good.
65 I. I
Table 4.1 Precision of Digestion Method (0/o ) (n = 5)
Metals Soils Plants
Zn 8.5 4.2 Mn 6.1 3.2 Cd 4.5 4.5 Cu 3.1 3.3 Co 2.4 1.7 Pb 1.2 2.9 Ni 2.5 3.2
Table 4.2 Result of recovery studies (n = 5)
Metal Metal added (mg) Amount of metal Recovery 0/o Recovered (mg)
Zn 73.20 65.15 89±6 Mn 52.00 46.80 90±4% Cu 102.00 94.86 93±2% Cd 3.70 3.11 84±5% Co 0.70 0.67 95±2% Pb 12.20 11.22 92±1% Ni 24.00 23.04 96±2%
1 Table 4.3 Concentration of metals in reference sample (SD - M-2/TM) (�-tgg- ) Metal This study Certified value
Mean± sd(n =5 Range Mean (n =5) Range
Zn 73.7±2.0 (7 1.8- 76.4) 74.8 (72.0 - 78.3) Mn 1186.8±24.2 (1165 - 1200) 1170 (1100 - 1190) Cu 32.3±2.3 (27.02 - 37.9) 32.7 (31.7-34.2) Cd 0.125±0.0 (0.09 - 0.15) 0.113 (0. 108 - 0.149) Co 13.8±0.4 (12.80 - 14.10) 13.6 (13.1 - 14.2) Pb 22.9±2.2 (21 .40 - 24.60) 22.8 (20.1 - 25.6) Ni 54.8±2.5 (49.52 - 57.20) 56.1 (53.3 - 58.5)
4.2 Total Metals in Soil
The summary of pH results and total metal levels in the soils of the study area are listed in Tables 4.4 - 4.8.
66 I, I
4.2.1 pH, Cd and Cu
Generally, the soil pH were between slightly acidic to neutral with Ak:wanga recording the
least acidic pH of 5.9 (Table 4.4). For instance, the pH for Karu LGA was 6.5+ 0.1 and the
pH for Akwanga LGA was 5.9 + 0.1 during the dry season. The pH of the soil samples in dry
season varied from 5.9 - 6.6 with an average of 6.4 + 0.1 (Table 4.4) whilst the pH in the
rainy season varied fr om 6.1 -6.7 with a mean of 6.5 + 0.1 (Table 4.5). The soil pH for
Keffi (pH= 6.6 and 6.7) was the highest while the soil pH for Akwanga LGA (pH = 5.9
and 6.1) were the lowest for dry and rainy seasons. Generally, the soil pH in the rainy
season was slightly higher than those of dry season. The pH of control sites for dry
season was 4.7 + 0.1 while that of the rainy season soil sample was 5.0 + 0.1.
Cadmium concentrations in the soil samples were generally low both in dry and rainy
seasons (Tables 4.4 and 4.5). The highest cadmium concentration was recorded in
Angwan Maisari Village in Keffi LGA during the dry season while the lowest Cd concentration was recorded in Mada Station in Nasarawa Eggon LGA. Cadmium concentration was lower in the dry season than rainy season, for instance during the study period, the mean Cd levels in Keffi LGA in dry and rainy seasons were 2.0 and
2.43 mgkg-1 , respectively (tables 4.4 and 4.5). For most soils sampled in the study area, Cd levels were low. The mean total Cd level in soils of the study area was 1.55 +
1 1 0.32 mgkg- with a range from 1 .1 - 2.0 mgkg- for dry season and 1.9+0. 3 2 0.3 2mgkg-
1 with a range fr om 1.51-2.43mgkg-1 for rainy season (Table 4. 8).
Copper concentrations in the soil samples were high comparing only with zinc (Table
4.4 and 4.5). Generally, Cu levels in soil during the rainy season were higher than the
67 I I
levels in dry season. The highest Cu concentration was recorded in farmlands at Igga
Village in Nasarawa Eggon LGA, while the lowest Cu concentration was found in
farmlands at Tattara Village in Keffi LGA. For instance, the copper concentration fo r dry
and rainy seasons in N/Eggon LGA were 70.0 and 86.2 mgkg·' respectively, with mean
values of 70.0 ± 2.3 mgkg-1 and 86.5 ± 2.4 mgkg-1 (Tables 4.1 and 4.7). The mean total Cu 1 level in the soils of the study area was 56.5 ± 1.77 mgkg- , with a range from 44 - 70.0
mgkg-1 (dry season), and 65.5 1.75 mgkg-1, with a range from 51 .7 - 86.2mgkg-1 (rainy
season), (Table 4.8).
4.2.2. Cobalt, Manganese and Nickel
Cobalt concentrations in the soil samples were also generally low both in the rainy and dry
seasons (Tables 4.4 and 4.5). The highest soil cobalt concenh·ation in the dry and rainy
seasons was recorded fo r fannlands in Keffi town (near Nasarawa Polytechnic), Keffi
LGA, while the lowest Co concentration was recorded in Karshi in Karu LGA. Mean 1 cobalt concentrations for both dry and rainy seasons were 0.25 + 0.20 mgkg· , with a range 1 1 1 from 0.20 -0.35 mgkg- and 0.28 ± 0.20 mgkg- , with a range from 0.2-0.4 mgkg- respectively. For most soils, the cobalt levels were ve1y low, but within expected values when compared with similar studies elsewhere (Table 5.3). The mean total Co levels in 1 the soil of the study area (mgkg- ) were 0.25 + 0.20 with a range from 0. - 0.20-0.35 (dry season), and 0.28 ± 0.20 with a range from 0.2 - 0.4 (rainy season), respectively (Table 4.8).
Manganese levels were generally high in soils of the study area as expected (see Table
1.2). The highest level of Mn was found in the soils of farmlands in Karshi Village in
Karu LGA, whilst the lowest level was recorded in Keffi Village (Near Nasarawa
Polytechnic), in Keffi LGA. The mean concentrations of Mn fo r dry and rainy seasons
68 I .I
1 1 1 were 231.2 + 5.4mgkg- , with a range from 180.0 - 320.0 mglcg- and 242.2 ± 5.2 mgkg-
with a range from 190.0 - 322.3 mgkg-1 , respectively (Table 4,8). The levels of Mn obtained
in this study fall within expected values for most world soils (Table 1.2 and 5.2 respectively).
Nickel levels were generally low, compared with the range expected for most world soils
(Table 1.2). The highest level of nickel was fo und in the soils of community farmland in
Nasarawa Eggon in N\Eggon LGA (30.0mgkg-1)whilst the lowest level (14.0 mgkg-1),
was recorded in Gunduma village in Karu LGA. (Table 4.5 and 4.6).
There were high levels of nickel in the soils of Nasarawa Eggon LGA compared with
other areas studied, both in dry and rainy seasons, suggesting that there must be a
local source. Like other metals, the Ni levels were slightly higher in the rainy
season, (Table 4.4 and 4.5). For instance, the mean Ni concentration in the soil of
Nasarawa Eggon community farmland in N/Eggon LGA was 38.0 mgkg-1in the rainy
season compared with 30.0 mgki1 of the same community in dry season (Table 4.4 and
1 4.5). The mean total Ni levels in the soil of sampled sites were 19.0 + 0.49 mgkg- 1 1 with a range from 14.0 - 30.0 mgkg- for dry season and 21.50 + 0.5 mgkg- with a range
from 16.0 - 38.0 mgkg-1 for rainy season, (Table 4.8).
4.2.3 Lead and Zinc
Lead concentrations in the soil samples were low both in the dry and rainy seasons
(Table 4.4 and 4.5). The highest soil Pb concentration in the dry and rainy seasons
was recorded in Tattara Village Kefli LGA, 7.90 and 9.16 mgki1 and mean
1 1 values of 7.9 + 0.4 mgkg- and 9.16 + 0.0 mgkg- respectively (Table 4.6 and 4.7). The 1 mean total Pb levels in the soils of the study area were 6.35 + 1.67 mgkg- with a range
69 I •:,
1 1 of 4.2 - 7.96 mgkg- (dry season), and 7.57 + 1.65 mgkg- with a range of 5.3 - 9.16 mgkg-1 (rainy season) , respectively (Table 4.8). Like other metals Pb levels were higher for soil samples in the rainy season than dry season (Tables 4.4 and 4.5).
Generally, Zinc concentrations m the study area were slightly higher in the rainy season (Table 4.4 and 4.5). The highest mean Zn levels in the dry season was
recorded in Mada Station in N/Eggon LGA, with a concentration of 74.0 + 4.6 1 1 mgkg- whilst the lowest (19.0 + 4.6 mgkg- ), was recorded in Angwan Masari
Village in Keffi LGA (Table 4.6). Generally, the mean concentrations and range of Zn in the soils of the study area both in the dry and rainy season were 42.50 ± 1 3.4 mgkg-1 , with a range of 19.0 - 74.0 mgkg-1 and 45.92 ± 3.4 mgkg- with a range of 19.8 - 78.0 mgkg-1 , respectively (Table 4.8).
70 I'· ..
1 Table 4.4 Mean concentration of total metal (mgkg- ) pH and organic Carbon (0/o ) in soil fo r dry season
Metal Karu Keffi Akwanga N/Eggon Control
Zn 23.20 19.00 52.00 74.00 18.70 Mn 320.0 180.0 200.0 225.00 135.0 Cu 52.00 44.00 60.00 70.00 32.00 Cd 1.70 2.00 1.10 1.40 0.80 Co 0.20 0.35 0.20 0.25 0.10 Pb 7.20 7.90 4.20 6.10 2.00 Ni 14.00 16.00 16.00 30.00 6.00 pH 6.5±0.1 6.6±0.1 5.9±0. 1 6.4±0.1 4.70±0.1 o.c 1.44 1.50 1.32 1.20 1.36
1 Table 4.5 Mean concentration of total metal (mgkg- ) pH and O.C in soil fo r rainy season Metal Karu Keffi Akwanga N/Eggon Control
Zn 30.50 19.79 55.40 78.00 18.70 Mn 322.0 198.0 204.2 244.6 189.0 Cu 58.60 51.70 65.50 86.20 37.90 Cd 2.00 2.43 1.53 1.70 1.00 Co 0.20 0.40 0.235 0.30 0.20 Pb 8.33 9.16 5.30 7.50 4.16 Ni 16.00 16.00 16.00 38.00 8.00 pH 6.6±0.1 6.7±0. 1 6.1±0. 1 6.6±0.1 5.0±0.1 o.c 1.47 1.53 1.35 1.26 1.39
71 I �
1 Table 4.6 Summary of concentration of total metal (mgkg- ) and pH in soil from the LGA's in dry season; Concentration
Metal Karu Keffi Akwanga N/Eggon Zn Mean±s.d 23.20±5.8 19.00±4.6 52.00±4.6 74.00±4.6 range 18.20-28.20 15.00-23.20 48.00-56.00 70.00-78.00 Mn Mean±s.d 320.0±4.6 180.0±2.3 200.0±4.0 225.0±2.9 range 280.0-360 160-200.0 165.0-235.0 200.0-250.0 Cu Mean±s.d 52.00±2.3 44.0±3.4 60.00±3.4 70.00±2.3 range 50.00-54.00 41.00-47.00 55.00-65.00 68.00-72.00 Cd Mean±s.d 1.70±0.2 2.0±1.2 1.10±1.2 1.4±0.2 range 0.18-0.22 0.34-0.36 0.1-0.23 0.24-0.26 Pb Mean±s.d 7.20±0.2 7.90±0.4 4.20±0.1 6.10±0.2 range 7.00 - 7.40 7.50 - 8.30 4. 10-4.30 6.08 -6.12 Ni Mean+s.d l4.00 + 1. 1 16.00+ 2.3 16.00+3.4 30.00 + 4.6 range 13.00-15.00 14.00 -18.00 13.00-19.00 26.00 - 34.00 pH 6.5 + 0.1 6.6 + 0.1 5.9 + 0.1 6.4 +0.1 range 6.4 - 6.6 6.5 - 6.7 5.8 - 6.0 6.3 - 6.5
72 I .. '.
1 Table 4.7 Summary of concentration of total metal (mgkg- ) and pH in soil from the LGA's in rainy season.
Metal Karu Keffi Akwanga N/Eggon Zn 30.50±0.6 19.79±1.1 52.40±6.2 78±6.9 Mean±s.d Range 30.00 - 31.00 18.79 - 20.79 40.00 - 60.00 72.00 -84. Mn Mean±s.d 322.0±2.3 198.0±1.1 204.2±0.0 244.6±4.6 Range Cu 302.0 - 342.0 188.0 - 208.0 204.0 - 204.4 204.6 - 284.6
Mean±s.d 58.60±3.4 51.70±0.6 65.50±8.9 86.50±2.4 Range Cd 55.90 -61.90 50.70 -51.70 60.50 - 76.00 84.00 - 88.20
Mean±s.d 2.00±0.6 2.43±0.4 1.53±0.3 1.70±0.2 Range Co 1.50 - 2.50 2.03 -2.83 1.23 - 2.83 1.50 - 1.90
Mean±s.d 0.20±0.00 0.40±0 .0 0.25±0.0 0.30±0.0 Range Pb 0.15- 0.25 0.38 - 0.42 0.20 -0.35 0.27 -0.33
Mean±s.d 8.33±0.0 9.16±0.0 5.25±0.1 7.50±0.1 Range Ni 8.23 - 8.43 9.10 -9.14 5.20 - 5.40 7.40 -7.60
Mean±s.d 16.00±1.1 16.00±2 .3 14.00±1.1 38.00±1.1 Range pH 15.00 - 17.00 14.00 - 18.00 12.00 - 16.00 37.00 - 39.00
6.6±0. 1 6.7±0.1 6.1±0.1 6.6±0. 1
Range 6.5 -6.7 6.6 - 6.8 6.0 - 6.2 6.5 -6.7
73 Table 4.8 Summary of concentration of total metals and pH in soil of the study area, in dry and rainy seasons
Metal Concentration Concentration Mean concentration 1 1 1 mgkg- (DSS) mgkg- (RSS) (All seasons)(mgkg- )
Zn IVIean±s.d 42.5±3.4 45.92±3.4 43.98 range 19.00 - 74.00 19.79 - 78.0 Mn Mean±s.d 231 .2±5.4 242.2±5.2 236.7 range 180.0 - 320.0 190.0 - 322.3 Cd Mean±s.d 1.55±0.37 1.9 1±0.32 1.73 range 1.1 -2.00 1.51 - 2.43 Cu Mean±s.d 56.5±1.77 65.5:::: 1.75 61.00 range 44.0-70.0 51.7-86.2 Co Mean±s.d 0.25±0.20 0.28±0.20 0.26 range 0.2-0.35 0.2-0.4 Pb Mean±s.d 6.35±1.67 7.57±1.65 6.96 range 14.00-30.0 16.00-38.00 Ni Mean±s.d 19.00± 0.49 21.50 ±0.5 20.25 range 14.00 - 30.00 16.00 - 38.00 pH Mean±s.d 6.35±0.21 6.50±0.23 range 5.9-6.6 6. 1-6.7
4.2.4 Percentage Organic Carbon in soil
Organic matter in soils provide adsorption sites for metals160. High soil organic matter content (expressed as percent organic ca!bon) entails high metals content in soils and vice- versa, due to the fo rmation of covalent bonds with heavy metals160. The highest organic
74 carbon content in soil was fo und in Keffi LGA with dry and rainy season values of 1.50 %
and 1.53%, respectively (Table 4.13) and (Tables 4.4 and 4.5). The total mean organic
carbon content of soil in study area was 1.36 ± 0.01 (dry season) and 1.39 ± 0.01 (rainy
season), (Table 4.13) and (Tables 4.4 and 4.5) with a range from 1.20 - 1.53% for the
sampling period. The lowest soil organic carbon content was recorded in Nasarawa
Eggon sampling seasons. LGA with a mean vahte of 1 .20 ± 0.0 tl1rougl1out the
4.2.5 Bioavalable Metals in Soils
Bioavailable metals in soil are those available fo r plant root absorption as other plant
nutrients. The highest bioavailable metal in the study area was Mn, having concentration
1 1 of 29.81 ± 1.37 mgkg- , with a range of 18.0 - 48.0 mgkg- (Table 4.9). The trend
followed the order Mn > Zn > Cu > Ni > Pb > Cd > Co (Table 4.9), for all bioavailable
metals under consideration in the shtdy area. The lowest bioavailable metal was Co, with
1 1 mean concentration of 0.02 ± 0.06mgkg- with a range ofO.Ol - 0.06 mgkg- • The highest
concentration of bioavailable metals in the LGA's of study area were observed fo r Mn in
Karu LGA, with a value of 48.0 mgkg-1 (Table 4.10) whilst the lowest concentration of bioavailable metal was observed for Co in Karu and Akwanga LGA's, each with a value
of 0.01 mgkg-1 , respectively (Table 4.10)
75 Table 4.9 Average concentration of bioavailable metals in the study Area (DTPA-extr·actablemetals) Concentration in (mgkg-1)
Metal Concentraton ± s.d Range Range (%) Bioavailable metel Zn 5.81±0.75 2.09-11.10 11-15 % Mn 29.81±1.37 18.00-48.00 10-15 % Cd 0.28±0.12 0.17-0.40 15-20 % Cu 4.91±0.75 3.08-7.00 7-10 % Co 0.02±0.06 0.01-0.06 5-10 % Pb 0.49±0. 19 0.21-0.79 5-10% Ni 0.61±0.11 0.28-1.20 2-4 %
Table 4.10 Concentration ofbioavilable metal in the LGA's (mgkg-1)
Metal Karu Keffi Akwanga N/Eggon Zn 2.7'8 2.09 7.28 11.10 Mn 48.00 18.00 24.00 29.25 Cu 4.16 3.08 5.40 7.00 Cd 0.3 1 0.40 0.17 0.22 Co 0.01 0.06 0.01 0.02 Pb 0.58 0.79 0.21 0.37 Ni 0.28 0.48 0.48 1.20
4.3 Metals in Vegetation and Food Crops
4.3.1 Cadmium and Copper
The summary of the concentration of metals in the fo od/vegetable crops from all the
LGA's and the study area are listed in Tables 4.11 and 4.12. Generally, the
Cadmium concentration varied fr om 0.09 - 0.70 mgkg-1 dry weight. The highest concentration of cadmium in the study area of 0.39 mgki1 was found in yams, whilst the LGA's with the lowest concentration of cadmium were Akwanga (0.08 mgkg-1 ) and N/Eggon (0.09 mgkg-1) see Table 4.12.
76 I,I
1 Copper concentration in vegetables and food crops varied from 1.8 to 6.9 mgkg-
(Table 4.1 1). The highest mean concentration of copper in the study area was 4.70
mgkg-1 , fo und in potato (Table 4.1 1). The LGA with the highest concentration of
copper was N/Eggon with a value of 6.90 mgkg-1 (Table 4.12), recorded for carrots, whilst the LGA with the lowest concentration of copper was Keffi with values of 1.8 mgkg-1 for (yam) (Table 4.12) , and 1.90 mgkg-1 for (carbage),
4.32 Cobalt, Manganese and Nickel
Cobalt concentration in fo od crops were generally low but varied fr om 0.01 - 0.05 mgkg-1 (Table 4.1 1). The highest Co concentration in the study area was 0.05 mgkg-1 , recoreded for yam in Keffi LGA (Table 4.12), whilst the lowest Co concentration in the study area was 0.01 mgkg-1 , recorded for many crops (Table 4.12). The LGA with the lowest concentration of cobalt were Karu (potato, carrot, lettuce, millet and maize); Akwanga (carrot, carbage, millet and maize and N/Eggon for (lettuce), with values of 0.01 mgkg-1 respectively (Table 4.12)
Manganese concentrations in food crops and plants were the highest for all the metals studied and varied from 6.4 - 40 mgkg-1 (Tables 4.11 and 4.12). The highest
Mn concentration in the study area was 40.0 mgkg-1 found in potato in Karu LGA
(Table 4.12), whilst the lowest manganese concentration in the study area was 6.4 mgkg-1, found in maize in Keffi LGA (Table 4.12)
Nickel concentration in fo od crops varied fr om 0.10- 0.98 mgkg-1 (Table 4.11 and
4. 12). The highest Ni concentration in the study area was 0.98 mgkg-1 , fo und in
77 I •..I
potato in N/Eggon LGA (Table 4.12), whilst the lowest Ni concentration in the study
area was 0.10 mgkg-1 for carbage in Karu LGA, potato in Akwanga LGA and maize
in Keffi LGA (Tabl 4.12
4.3.3 Lead and Zinc 1 Lead concentration in fo od crops in the study area varied fo rm 0.10 - 0.80 mgkg-
(Table 4.11 and 4.12). The highest Pb concentration in the study area was 0.80mgkg-1
observed in Keffi LGA for yam tubers. (Table 4.12), whilst the lowest lead
concentration was 0.10 mgkg-1 , found in Akwanga LGA in lettuce and maize (Table
4.12)
Zinc concentrations in fo od crops and in vegetation in the study areas varied fr om
1.18 - 9.3 mgkg-1 (Table 4.12). The highest Zn concentration in the study area was
9.30 mgkg-1 fo und in N/Eggon LGA in yams (Table 4. 12), whilst the lowest concentration of Zn was 1.18 mgkg-1 recorded for Keffi LGA in lettuce (Table 4.12).
The average concentration of Zn in allvegetation (food crops) were as follows; Karu
1.86 mgkg-1 , Keffi 1.33 mgkg-1 , Akwanga 5.20 mgkg-1 and N/Eggon 8.14 mgkg-1
(Table 4.12). The total mean concentration of Zn in all the LGAs for food crops was
4.13 mgkg-1 (Table 4.12)
78 4.11 Summary of metal concentration in fo od crops from the study area 1 (mgkg- )
Metals Potato Yam Carrot Carbage Lettuce Millet Maize Zn Mean ± 4.61±0.70 4.58±o.70 4.49±1.04 3.97±0.65 3.89±0.64 3 .78±0.60 3.67±0.58 s.d Range 1.4-9.2 1.45-9.3 1.25-9.0 1.25-8.0 1.18-7.8 1.24-7.08 1.24-6.68
Mn Mean ± s.d 25.3 ± 1.27 20.65±1.20 18.83±1.32 15.28±0.2 18.58± 1.39 17.63±1.19 12.0±0.97 Range 14.0 -40.0 12.0-35.0 8.2-36.0 86-24.2 7.2-38.0 7.6-30.4 6.4-21.4
Cd Mean ± s.d 0.31 ±0.13 0.39±0.14 0.29±0. 17 0. 19±0. 12 0.16±0.08 0.19±0.1 0.18±0.11 0.10-0.28 Range 0. 16-0.41 0.4-0.7 0.15-0.60 0.09-0.32 0.09-0.18 0.11-0.24
Cu 2.89±0.43 Mean ± 4.7±0.52 4.5±0.54 4.5±0.48 3.23±0.36 3.0±0.04 3.65±0.49 s.d 2.0-5.0 Range 2.4-6.8 1.8-6.4 3.2-6.9 1.9-4.0 2.0-4.2 2.1-5.9
Co Mean ± 0.03±0.04 0.03±0.04 0.02±0.0 0.02±0.04 0.02±0.04 0.02±0.03 0.02±0.03 s.d Range 0.01-0.04 0.02-0.05 0.01-0.03 0.01-0.02 0.01-0.04 0.01-0.02 0.01-0.02
Pb Mean ± 0.50±0.19 0.45±0.20 0.40±0.20 0.29±0. 18 0.23±0.14 0.32±0.15 0.27±0.13 s.d Range 0.18-0.78 0.15-0.80 0.13-0.78 0.12-0.61 0.10-0.40 0.13-0.50 0.10-0.35
Ni Mean ± 0.44±0.23 0.45±0.22 0.41±0.22 0.41±0.23 0.43±0.20 0.42±0.21 0.39±0.22 s.d 0.10-0.90 Range 0.10-0.98 0.16-0.96 0.08-0.88 0.01-0.94 0.13-0.80 0.15-0.84
79 I '
Table 4.12 Summary of metal concentration in food crops from the 1 LGA's (mgkg- )
Metal LGA's Potato Yam Carrot Carbage Lettuce Millet Maize LGA mean (x) Zn Kam 2.05 1.96 1.92 1.84 1.79 1.90 1.76 1.86 Keffi 1.40 1.45 1.55 1.25 1.18 1.24 1.24 1.33 Akwanga 5.80 5.60 5.50 4.80 4.80 4.90 5.00 5.20 N/Eggon 9.20 9.30 9.00 8.00 7.80 7.08 6.68 8.14
Mean (x)= 4.61 4.58 4.49 3.97 3.89 3.78 3.67 4.13 Mn Kam 40.0 35.0 36.0 24.2 38.0 30.4 21.4 32.0 14.0 12.0 8.2 8.6 7.2 7.6 6.4 9.0 KeCll Akwanga 20.0 17.0 14.9 12.5 12.1 11.5 10.0 14.0 N/Eggon 27.2 18.6 16.2 15.8 17.0 21.0 10.2 18.0
Mean(x)= 25.3 20.65 18.83 15.28 18.58 17.63 12.0 18.25 Cd Karu 0.41 0.40 0.15 0.26 0. 18 0.2 1 0.28 0.27 0.40 0.70 0.60 0.32 0.18 0.20 0.12 0.36 Kaffi AKWANGA 0.16 0.21 0.20 0.08 0.09 0.11 0. 10 0.14 N/Eggon 0.25 0.23 0.21 0.09 0.18 0.24 0.20 0.20
0.24 Mean (x)= 0.31 0.39 0.29 0.19 0.16 0.19 0.18 Cu Karu 3.20 3.80 3.70 3.00 3.00 3.10 2.04 3.12 Keffi 2.40 1.80 3.20 1.90 2.00 2.10 2.00 2.20 Akwange 6.40 6.00 4.20 4.00 2.80 3.5 2.50 4.20 N/Eggon 6.80 6.40 6.90 4.00 4.20 5.9 5.00 5.60
Mean (x)= 4.70 4.50 4.50 3.23 3.00 3.65 2.89 3.78 Co Kam 0.01 0.02 0.01 0.02 0.01 0.01 0.01 O.Dl Keffi 0.04 0.05 0.03 0.02 0.04 0.02 0.02 0.03 Akwanga 0.02 0.02 0.01 0.01 0.02 0.01 0.01 O.Dl N/Eggon 0.03 0.02 0.03 0.02 0.01 0.02 0.02 0.02
Mean 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 (x)= Kam 0.64 0.5 1 0.52 0.32 0.27 0.40 0.35 0.43 Pb 0.78 0.80 0.78 0.61 0.40 0.50 0.33 0.63 Keffi Akwanga 0.18 0.15 0. 13 0. 12 0.10 0. 13 0.10 0.13 N/Eggon 0.38 0.34 0.15 0.12 0.14 0.25 0.30 0.24
0.36 Mean (x)= 0.50 0.45 0.40 0.29 0.23 0.32 0.27 0.14 Ni Karu 0.22 0.16 0.08 0.10 0.13 0.15 0.14 Keffi 0.47 0.30 0.38 0.28 0.3 1 0.40 0.10 0.32 0.32 Akwanga 0.10 0.38 0.31 0.30 0.47 0.28 0.40 0.90 N/Eggon 0.98 0.96 0.88 0.94 0.80 0.84 0.90
0.42 Mean(x)= 0.44 0.45 0.4 1 0.4 1 0.43 0.42 0.39
80 I .
Table 4.13 Percent organic carbon content of soil sample fo r dry and ra·ny season. Location %organic carbon %organic carbon mean±s.d (O.C - DSS) (O.C - RSS) Karu 1.44 1.47 1.44±0.02 Keffi 1.50 1.53 1.52±0.02 Akwange 1.32 1.35 1.34±0.02 N/Eggon 1.20 1.20 1.20±0.01 Mean(x) ±s.d 1.36±0.01 1.39±0.01 1.38±0.0 1
Table 4.14 Soil pH levels
Location pH(DSS) pH(RSS) Mean±s.d Karu 6.5 6.6 6.6±0.1 Keffi 6.6 6.7 6.7±0.1 Akwanga 5.9 6.1 6.0±0.1 N/Eggon 6.4 6.6 6.5±0.1 Mean(x) ±s.d 6.35±0.1 6.5±0. 1 6.4±0.1
81 • 350 1� Karu 1 [lil] I 325 Keffi .;::-' 300 1
8 275 �Akwanga l 0 ,. ..._E 250 �. NiEggon I §i 225 6 � -ro'- ...... 2oo c r-:- != . Q) 175 t= .f= g 150 0 . § -E� . u 125 · I=. . . ' ...... E 100 g f= ·' >::::: 75 �� · F !:::: i; 50 - F=� N .. g� - � 00 25 �D�� § �� � �· "• . I �I= � §g �� � I 1 �� I I ' . . ·;F" � 0 �:. �� �� �� �!II� DSS RSS ��DSS§ RSS DSS R$S DSS RSS DSS RSS DSS RSS DSS RSS Zn Mn Cd Cu Co Pb Ni � Metals in soils from LGA's . Levels of metals in soils fr om LGA's and concentrations :from dry to rainy seasons Figure 4.1 variation in
·co :· I.·•-;I t 0 p. D v� m rrot De: rbage 1 I De� Lt:ttuce tim illet '� : --·: -� M r.-\ \ � 5 . aize eJ) W M s \\ .._,
= o- ,\ '""'0 mn I ' ... , .' � . , II� r - � i � ... ! = �I1;l. f•i \:'" ili. li: ' 5 I . � � '- I I-iT 00 u li = ._. r- q 0 , I)�;I- Itt u \ II ' ' � u \ ': I r- I' .
I }. 11\ i j \ YJ Il m. ;I \.,·, I! rttT 1\ tij 5 i )l III . 11 - � . ' i'l I � ·: , �;� n .. . i � • I- . . I ./ I= �I . . ·A:: ·•· I \ ! id , . . �r· - , �.� : ' I .1 h � '.t= ']' _, 0 n . Mn ed Nt Metals in food crops (all season)
Figure Mean concentrations of total metals food crops from study area 4.2 in D Karu
354------LJ Keffi !IT] Akwanga ,...,-- � N/Eggon \
\ ·.
'.
.-... \ 1'.',J '' ' \\ -� � \ Oil \\\ \ s \ . ._, '\ \ L 20" ---;: \1 ·�0 �\ ' � \I .--- \ \ "<:!" � \I I- 00 �\ \ 15 � � ��--! \ \ C.) \ l 1 = \ \ V\\1 yl i � '1''\ il-- r0 ' \ v HT v l\tmt/\�
� 5 � N\11/�
0 Metals in food crops from the LGAs
Figure 4.3 Total concentration of metals food crops from the LGAs in
' • �:-;·.r
•!.;,. I. I
CHAPTER FIVE
DISCUSSION AND CONCLUSION
5.1 Variation of metals in soil, bioavailable metals in soil and metals in
plants
5.1.1 Variation Metals in Soil of
Generally, the concentration of metals m the soil samples m the study area were higher than metal concentrations from the control sites, inchcating that human activities in the study area are contributing to metal levels. For instance, the range of
1 Zn concentration in all the sites varied fr om 19-74 mgkg- (Table 4.4) dry season result. whilst the concentration of zinc in the control site was 18.7 mgkg-1 , showing that man-made activities have affected the levels of metals in the area. Similarly, the range of other metals in the study sites were in the same trend (Table 4.4 & 4.5). This could be due to the application of fertilizers by fa rmers in an attempt to increase agricultural production and yield of crops. For instance, the common fertilizers used in the area which include super-phosphate, N.P.K and Urea, are known to contain trace amounts of metals21 such as Cd, Co Cr, Ni, Pb and Zn. The yearning for increased fo od production for the growing population have justified the intensive application of mineral fertilizers to fa rmlands in recent times. Fertilizer consumption in Africa 19 amounts to about 19 kg ha-1 for arable and permanent croplands
(UNEP)177. From this deduction by Nriagu19, it means that sulphate and super
1 phosphate fertilizers (Table 1.3) will add to soil Cd content, about 285-475 mgkg- 1 yr- and over a period of ten years of consistent application, about 2850-4750 mgkg-1
85 Mining acbvities in the area would lead to the production of mine spoils and tailings
which are known to contain minerals that would be hydrolysed and hence release their metal contents into the environment. Minerals such as galena (PbS), spharelitc
(ZnS) etc. that are common in the area may contribute to the metal levels of the study sites with Zn and Pb enrichment.
Pesticides are seldomly used by farmers in the study areas except for emergency situations, hence contributions fr om pesticides to soil metals and bioavailable metals will be insignificant.
It is also important to discuss observed results vis-a-vis the soil geology of the study area. The geology of the study area is also important in the contribution of metals to soil and their variation in soil. For example, mining activities by the inhabitants of the study area are centred on the following mineral ores. The elements of interest of this work are underlined. a. In Karu LGA, minerals like Tantalitc [(Fe, Mn)(Ta, Nb)206]. Galena (PbS) and
Spharelite, (ZnS) are common in the soil geology and may contribute to background concentrations of metals like Mn, Pb and Zn in the soil. b. In Keffi LGA, the chief mineral mined include molybdenites (MoSi. PbMo04), also refened to as wulferites, will account for observed background concentration of
Pb in the soil. c. In Akwanga LGA, columbite (Fe, Mn, Mb, Ta) will add to background soil enrichment by manganese, while in
86 d. Nasarawa Eggon LGA, calcopyrites containing (CuS, FcS2, As, Ni, Co, Cu,
Au) mined in the area will contribute to soil metals and soil bioavailable metal concentrations in the area.
Since mining activity are optimum in the dry season but are usually not carried out during the peak of rainy season, mine spoils and tailings are washed away into adjoining land by erosion hence the concentrations of most metals determined are higher during rainy season.
Background sources of metals are usually susceptible to physico-chemical 176 processes such as occlusion and flocculation, including secondary alterations like laterization, precipitation and mineralization resulting from natural weathering and leaching of metals into other environmental receptacles such as (meadows -lowlands, drains and nearby water bodies like streams); and these phenomena explain metal variations in soil.
5.1.2. Variation of bioavailable metals in soil
Most African soils generally contain very little clay or organic matter19 and tend to be light and sandy. The concentrations of bioavailable metals in the soil were higher than the concentration of metals in the plants (Table 4.9 & 4.1 0). For instance, the range of bioavalable zinc in the soil 2.09 -11.10 mgkg-1 compared with the range
(1.3-8.1 mgkg-1) found in fo od crops (plants). This observation may be explained by 3 the fa ct that bioavailability of metals in soil is influenced by three major factors8 which include soil pH, soil organic carbon content and cation exchange capacity
(CEC), of the various metals. In this study, a soil pH range of between 5.9-6.7
87 ' 'I
obtained, indicated a slightly acidic to neutral soil composition. For example, it has been proved that low pH content of soil (pH =1 .0-4.0 acidic soil) encourages precipitation of certain metal ions unto soil surface with corresponding reduction of 33 metal solubility in soil solution and hence less bioavailability of such metals in soil .
Conversely, high pH content of soil (pH= 5.0 -7.0), slightly acidic to neutral soils, enhances adhesion of certain metals unto soil surface thereby leading to increased 33 solubility and bioavailabilily of the metals in soil solution . This phenomenon account for and explains the higher levels of Mn, Zn and Cu found in the study area
(Fig 4.2 & 4.3) in comparison to Co, Cd, Pb and Ni, respectively.
Also, the organic carbon content of soils in the study area ranged from 1.20 - 1.53%, indicating very low soil organic matter. The interplay of these soil characteristics may have accounted fo r observed levels of bioavailahle metals with different variabilities as fo llows; Zn (11-15%) and 5.81mgkg-1 ; Mn (10-15%) and 29.81 mgkg-1
; Cd (15 -20%) and 0.28 mgkg-1 Cu (7 - 10%) and 4.9 mgkg-1 Co (5 -10%) and 0.02
1 1 mgkg 1 Pb (5 -10%) and 0.49 mgkg- ; Ni (2-4%) and 0.61 mgkg- (Table 4.9). ;
This scenario also justifies the assertion that not all soil metals are bioavailable fo r
5 plant root uptake ' 6. The cation exchange capacity of soil (CEC) (though not determined in this work), is the ability of soil surfaces to exchange metal ions through surface adsorption unto its surface in preference for other metals ions present in the soil matrix. CEC is therefore, the soil retention ability of metals unto its surface under certain physical and chemical conditions as temperature, pH and metallic interactions within the soil in:f1uencedby the presence of soil organic matter.
88 The processes of chemical absorption (occlusion), physical adsorption (adhesion) and
precipitation may also h bioavailable metal concentrations account for t e variations of
found in the study area.
5.1.3 Variations of Metals in Plants (Crops) in the study area and its implication
in diet and Human-Animal Consumption.
The study of metal concentrations in soils and plants are used not only to determine
pollution levels, but also for risk assessment and implication on human and animal 62• 164 health 1 163• • Studies have proved that different plants have varying abilities and
preferences for metals present in soil47. Plant physiology (structure of cell walls) and physiognomy (nature and specie of plant type or taxon) contribute to their metal 47 enrichment and absorption capacities from the atmosphere, soils and water bodies .
This postulation may have informed higher levels of Mn (18.25 rngkg-1); Zn (4. 13 mgkg-1) and Cu (3.78 mgkg- 1); compared to the values for Cd (0:24 mgkg-1); Co
(0.02 mgkg-1 ); Pb (0.36 mgkg-1) and Ni (0.42 mgkg-1 ) for plants (food crops) in the study area. (Fig 4.2 and Table 5.3), respectively.
Generally, the concentration of metals in the soils were higher than the concentration
in plants (food crops) 168' 169' 170' 171. For instance, in the dry season, concentration of
Zn in the soils of the study area varied from 19.0 - 74.0 mgkg-1 , whilst their levels in 1 plants varied from 1.3-8.14 mgkg-1 , Mn 180.0-320.0 mgkg-1 and 9.0 -32.0 mgkg- , Cu
44 -70 mgkg-1 and 2.2 - 5.6 mgki1 ; Cd 1.10 -2.0 mgkg"1 ; and 0.14 -0.36 mgkg-1 ; Co
0.20 - 0.35 mgkg-1 ; and 0.01-0.03 mgkg-1 ; Pb 4.2-7.9 mgkg-1 ; and 0.13-0.63 mgki1 ;
Ni 14-30 mgkg-1 and 0.14 -0.90 mgkg-1, for soils and plants, respectively, ( Table 5.1)
89 I l ./
and this is largely because not all the soil metals are available plant root uptake.
Dietary implications of all the metals (Zn, Mn, Co, Cd, Co, Pb and Ni) under
consideration suggest that the consumption of food crops from the study area will not
pose any danger to man and grazing animals in the area. For example, the level of Cu
metal concentration fo r most worl d plants is between 4-15 mgkg-1 18, and the results
obtained in the present study is below the limits found fo r most world plants (2.2 -
5.6 mgkg-1 ). Also, Cu levels in present study for fo od crops (2.2 - 5.6 mgkg-1 ) were 63 within acceptable limits (Table 5.2), compared with WHO, FAO Standards of 30 mgkg-1 but fell short of the level set for paddy rice in Taiwan, ROC, which is 2.8 mgk g -1 .
18 Cd levels m food crops was lower than the values reported for world pants but within for Canada (Agriculture) 1.4 and (Agriculture) limits 174 mgkg-1 Denmark 5.0 mgkg-1 (Table 5.3). The Cd levels found in fo od crops in present study (0.2mgkg-1) did not exceed WHO/ FAO Standards of 2.0 mgkg-1 (Table 5.3). However, Cd levels in soil in the study area (1.10-2 .0 mgkg-1) exceeded limits found for world sandy soils (Table 5.2) and may have derived from a local source i.e. fertilizers.
Pb levels in present study (0.36 mgkg-1), however, was below values obtained for world plants and crops18. (0.1 - 10.0 mgkg-1), and lower than limits set
48 for paddy rice in Taiwan, ROC (0.43 mgkg-1) and WHO/ FAO Standards fo r fo ods
(2.0 mgkg"1)63. Other metals i.e. Zn, Mn. Co and Ni were within acceptable limits found in soils and plants elsewhere and conform with WHO/ FAO Standards for
90 • l L I
food.
5.2 pH and % Organic Carbon
The overall soil pH in the study area was characterized by acidic to neutral soil with
total organic carbon relatively low. Even though some trace elements in soils and 3 crops showed reduced availability with increasing pH1 8, the only common trend
noticed was reduced availability with reduced organic carbon content. There was a
correlation between soil pH and soil organic carbon fo r dry and ramy seasons
(r=0.54, p>O.O 1) and (r=0.60, p>O.Ol) (Table 5.5.7) , respectively. According to
Agemain and Chau 175, the type of metals and type of organic matter present in soil,
will influence the ability of acids to extract metals. Organic matter fo rms complexes
with metals in soil. High soil organic matter content provides ligands fo r metals
. . 1 60 . a d sorption w h ile t h e reverse is the case with 1 ow organtc matter content . Tl11s
explains why there is generally low metal content of soil and plants in the study area below most soil quality criteria, compared with studies in other regional studies where high soil organic matter were found. For instance, in a study of soil characteristics, heavy metal availability and vegetation recovery in a heavily polluted soil at a former metallurgical landfill, and its implications on risk assessment and site restoration by Remon et al86, it was found that most of the soils sampled were characterised by high organic matter content (5.7 - 10.0%) and an alkaline pH of 7.7 -
9.6 which were closely correlated (r = 0.94). In the present study, there was also significant correlation between soil metals (Cd, Co and Pb), with soil pH with values of r=0.914, 0.979 and 0, 977, (at p > 0.01) respectively for dry season soil samples.
91 l: I
(Table 5.5.4), while r = 0.761, 0.504, 0.960 (at p>O.Ol) also showed significant
relationship between Cd, Co and Pb and soil pH for rainy season. Soil pH IS a
crucial factor m the extractability of exchangeable (bioavailable) metals in
soils. In studies conducted in Taiwan on rice fields, soil pH around 7 had the lowest rate of metal extraction (particularly Cd), compared to
33 amended soils . This means that bioavailable Cd at soil pH=7 will not be available for plant root uptake. In the present study, where soil pH generally ranged from slightly acid to neutral, pH=(5.9-6.7) cadmium and lead concentrations in soils and plants remained low and probably explains the results obtained for these metals.
5.3 Health implications of some metals (Cu, Cd and Pb) found in study area above WHO/FA 0 acceptable limits in foods
Copper is not a cumulative systemic poison, but doses up to OOmg in food per day 1 will cause symptoms of gastroenteritis with nausea. Values of 30 mg even for many days, has not caused poisoning. Limited data are available on chronic toxicity of copper, but individuals with Wilson•s disease (disorder of copper metabolism) are at additional risk from the toxic effects of copper174•175'176. Copper is considered an essential element for human nutrition since it is required in many enzymic reactions.
79 Daily requirements has been estimated at 2.0 mgkg-1 (NAS)178 . The (USEPA)1 of fo od, considered a provisional body requirement of 5.3 mgkg-1 in human fo od.
According to USEP A report, toxicological studies did not show increase of tumour incidence on rabbits based on orally administered copper compounds, and by
92 � I ! i
extension in human dietary needs in food at 5.3 mgkg-1 level.
Even though Cu is an essential clement, it can cause anaemia, liver and kidney
. 23 . d amage at 1 . g h 1 1 concentratiOns . In the present study average Cu levels m plants
ranged from 2.20 - 5.60 mgkg-1 (Table 5.1 ) comparing this result with WHO
Standards, fo r Cu in fo od crops of 30 mgkg-1 ) (Table 5.3), it was fo und that the levels
of Cu metal in the study area were below acceptable limit for fo od. In the present
study, the average levels of Cd found in food crops or plants ranged fr om 0.1 4rngkg-1
for all food crop samples. (Table 5.1). Comparing this result with the WHO/FAO
Standards for Cd in food at 2.0 mgkg-1, (Table 5.3), the toxicity that may result from
Cd pollution of plants in the area will not be expected. Generally, the background
concentration of Cd in terrestrial plants varies between 0.2-0.8 mgkg-1 , dry weight and results obtained in this study fall within expected levels for plants and food crops. However, if the present levels are not maintained in the near fu ture, the possibility of Cd poisoning of fo od crops may not be ruled out, since the levels in soil
(1.55 mgkg-1) far exceed the levels fo und in most world soils (0.06 mgkg-1), some of the possible health consequences include; renal tubular dysfunction and pulmonary emphysema, acute demineralization and cmbrittlcmenl of the skeleton (Ita-Ita disease), gastroentrilis, hypertension, cancers and osteoporosis.
Lead health effe cts of toxicological nature, is measured by the blood Pb levels. Toxic levels may lead to irreversible brain damage or acute neurological dysfunction particularly in children. In the present study, average Pb levels in plants ranged from
0.13 - 0.63 mgkg-1 (Table 5.1). Comparing this result with values for WHO/FAO
93 • l .. ..
Standard of 2.0 mgkg-1 (Table 5.3), there may not be any possibility of Ph-related health hazard arising from fo od consumption from areas. Toxic blood Pb levels of
100- 120 mg/dL-1 have been reported to cause death in enfants between the ages of 1-
1-15yrs180. Gastrointestinal symptoms among mine workers at blood Pb levels of 40-
60 mg/dL and encephalopathy in adolescents and aggressive behavioural tendencies 18 have also been reported 0. Lead toxicity interferes with Fe metabolism and inhibits the fo rmation of heme in animal blood cells180. Bryce-Smith and Waldron181, have also implicated Pb as a casual factor for increased delinquent behaviours among juveniles in large industrial ci6es with large scale Pb emissions into the atmosphere.
Studies, have shown thai levels of Pb in grains, tubers and roots show little deviation from the background levels in soils, resulting from nearness to highways, traffi c density, direction of wind flow and distance of farmlands to source of Pb pollution and hence accumulate as much bioavailable Pb as possible within the environmene83.
The possible sources of high Pb inputs to soil and vegetation in the study area are mining and agriculture.
5.4 Relationship between bioavailable metals in soil with levels in plants
The soil layer (0-30cm) depth is the area where most bioavailable metals are present for uptake by plant roots. Table 5.1 lists the levels of bioavaiiable metals in soil alongside those in plants in the study area.
Generally, the concentration of bioavailable metals in the soil were higher than the concentration of metals in plants. For example, the concentration of bioavailable Zn in the soil is 5.8 mgkg-1 while the concentration of Zn in plants (within same area) is
94 1 ••
4.13 mgkg-1 • This represents 13% of total metals in soil as bioavailable metals and
9% of total metals in soil as absorbed by plants. This shows that plants (or fo od crops) were only able to absorb about 9% of total zinc found in soil in the study area, suggesting that not all bioavailable metals are available for plant absorption. This picture has implications in assessing the true levels of metallic pollution of food crops. Hence, concentration of metals in soil and the concentration of bioavailable metals in soil cannot be used as best index for the measurement of food crop pollution but rather the actual metal concentration in plant materials. This is because man and plants co-exist in a contagous food-chain.
Lindsay and Cox 118 had reported that below soil pH 7. 7, the predominant soluble species of metals like Zn, Mn, Cd, Cu and Pb exist in their M2+ state and that their exchangeable fractions occur in the exchange sites of soil clays and organic matter
(i.e. mobile and mobilisable forms) within the soil solution and soil matrix. This phenomenon may have informed the higher percentage of bioavailable metals and plant metals recorded fo r Mn, Zn and Cu in the present study. Other metals like Cd,
Co, Pb and Ni maybe considered exchangeable or weakly bound to soil organic matter and hence be readily absorbed by plants or leached out. According to Lindsay and Norvell, ttB(a) high soil pH (i.e acidic to neutral soil) and low percentage organic carbon (OC) content of soil, enhances the amount of extractable metals with chelating agents like EDTA or DTP A and therefore provides a means of assessing soil bioavailable metals. Correlation studies showed that there was strong relationship between concentration of bioavailable metals in soil and plant metals.
95 Table 5.1.1 shows the correlation between bioavailable metals m soil and plant metals within a cropping season.
Table 5.1.1 Correlation between bioavailable metals and plant metals
Bioavailable metal (r) Metals 0.75* Zn** *** 0.94* Mn*** Strong CotTelation ** good Correlation 0.88* Cu*** * fa irly good correlation 0.76* Cd** 0.85* Co*** 0.47 Pb 0.69* Ni**
Correlation was significant at (p) = 0.01 confidence limits.
The analysis revealed that there was strong correlation (***) between bioavailable Mn and plant Mn at (r = 0.94 and 0.98, p > 0.01). Similarly, there was also strong conelation (***)
between bioavailability Cu and plant Cu (r = 0.88 and 0.92, p > 0.01), Co; r = 0.85 and
0.83, p > 0.01 Zn; r = 0.75 and 0.73, p > 0.01; Cd; r = 0.76 and 0.74, > 0.01 ; Ni; r = 0.69 p and 0.67, p > 0.01 (Table 5.1.1), respectively fo r corresponding bioavailable metal and plant metals. However, there was no significant relationship between bioavailable Pb
and Pb found in plant tissues in the study area (r = 0.47 and 0.45, p > 0.01 ). This can be 4 164 explained by the fact that Pb is the most immobile metal in soil solution16 . Xian corroborated this assertion that the uptake of bioavailable metals by plants is relative to their solubility sequence in soil solution, which corresponds to the chemical forms the metals assume to stimulate their mobility arid uptake by plants. 4 Also, Anderson 18 , posited that there is a close relationship between the ionic radii of metals and their individual correlation coefficients as bioavailable species in soil. Cd
96 . ' ·--
and Pb are too large to occupy the positions that other heavy metals would, rather, they arc retained by soi organic matter. I
97 1 Table Variations of metal concentration in soil, bioavailable metals in soil and metals in plants (mgkg- ) dry 5.1 and rainy seasons Metals Season Samole (DSS) Rainy (RSS) Drv : Season Sample Locations Total metals Total bioavailabie metals Total bioavailabie metals in plants in soil metals in plants i 'Yo : % soil metals in 1 �- in (food crops-) I soil -2 3�io 2. 18 -1.86. -- Zn 12 8 11 19.00 2.09 '. j KeffiKaru · ,�·- 'I i.33 7 52.00 7.28 I 5.20 l-+ 10 A�' -0.03 10 )i 5- lI 0.-1-3 i 8 ?b I I 0.63 10 i I 0.13 5 3 0.21 Ii 0.37 I 0.24 6 .:1 0.-+9 .! 0 i9 II 0.36 ± 0.18 I 7.25 . i! 5.25 '4.20 - 7.90 0.21 - 0.79 0.13 - 0.63 I 10 - r::mge i ! 5- 3 8 0.28 i 0.14 I 2 Ni I 0.32 I I 3 * Cd levels in soil are high and may have derived from a local source. Anthropogenic source via fertilizers and mining activities may not be ruled out. 0\ 0\ . I • 5.5 Correlation Studies 5.5.1 Correlations between metals in soil, bioavailabe metals and metals in plants. Correlation studies are important in the analysis of similarities (relationships) between paired data; and several researchers have fo und usefulness of such studies in comparing data in heavy metal analysis. Lee et al176, have used statistical comparisons to fi nd common grounds of metal linear regressions of paired data to deduce similarities (positive correlations) and dissimilarities (negative correlations) of metals in soils and plants. A statistical software, SP lOSS used for various data analysis was found useful in these comparisons and have been employed in this study for data analysis. Some of the most widely employed statistical formulae used to evaluate variants of the empirical figures obtained in laboratory analysis include; Kruskal-Wallis analysis of variants, Spearsman's correlation coefficient, Pearson's correlation coefficient, etc. In these analyses, the variants are usually significant at 99% confidence limits (p=O.O 1) or at 95% confidence limits (p = 0.05). The correlation analysis revealed the fo llowing in the study. 1. There were inter- element correlations between metals in the study area for Cu/Zn.Co/Zn, Co/Cu, Pb/Ni, Pb/Cd, Pb/Co, respectively. 2. Soil pH correlated with certain metals significantly and these include Cd, Co and Pb. There were no correlations of soil pH with Zn, Mn, Cu and Ni. 100 . l •. ! 3. Soil pH had slight but reasonable correlation with soil organic carbon with (r) values of r=0 .54 and = 0.60 = 0.01 for the dry and rainy seasons, r at p respectively. 4. There were no significant correlations between most metals under study and percent organic carbon (OC) in the study area. However, there were slight but significant correlations between metals trapped in organic matter for the pairs which include Cd/Zn, Cd/Mn. Pb/Zn, Pb/Mn, Pb/Mn, Pb/Cu, Pb/Cd and Pb/Co respectively. Table 5.1.2 Correlation between metals in soils (DSS) Zn Mn Cu Cd Co Pb Ni Mn -0.208* Cu 0.973** 0.023 Cd -0.748 -0.073 -0.766 Co -0.339 -0.609 0.509* -0.730 Pb -0.648 0.216 0.633* 0.976 0.643* Ni 0.845* -0.193 0.803* -0.279 0.064 -0.145 There was strong correlation (r) between Cu/Zn (r =0.97, p > 0.01); Cd/Pb (r=0.97. p>O.O 1); Zn/Ni (r=0.84, p>0.01); Cu/Ni (r=0.80, p>O.O 1); Pb/Cu, (r=0.63 p>O . 01): Pb/Cd (r =0.97, p>0.01); Pb/Co (r =0.64, p>0.01); respectively in soils sampled during the dry season. 101 Table 5.1.3 Correlation between metals in soils (RSS) Zn Mn Cu Cd Co Pb Ni Mn -0.099 Cu 0.970** 0.022 Cd -0.820 -0.190 -0.686 Co 0.983 ** -0.222. 0.967** -0.719 Pb -0.595 0.275 0.387 0.902" -0.509 Ni " 0.772* 0.043 0.895* -0.294 0.827* 0.050 There was a strong correlation (r) between Cu/Zn, (r=0.97, p>0.01); Co/Zn(r =0.98, p>0.01); Co/Cu (r =0.96, p> 0.01); Pb/Cd, (r =0.90, p>_0 .01); Ni'/Zn (r =0.77, p>_0 .01); Ni/Cu (r =0.89, p>_0 .01); Ni/Co (r =0.82, p>O.OI); respectively in soils sampled in the rainy season. Table 5.1.4 Correlation between soil pH and soil metals, in the study area Mn Cu Pb Ni Zn Oi Co Soil pH and soil metal (DSS)(r) -0.473 -0.476 -0.453 0.914* 0.979** 0:977** 0.058 Soil pH and soil metal (RSS)(r) -0.485 -0.485 -0.114 0.761 * 0.504* 0.960** 0.246 Correlation between soil pH/Cd was significant at (r=0.91, p>0.01); pH/Co (r=0.97, p>_0 .01); pH/Pb (r =0.97, p>_0 .01); in the dry season soil samples. Also there was strong correlation between pH/Cd (r =0.76, p>_0 .01); pH/Co (r =0.50, p>0.01); pH/Pb (r =0.96, p> 0.01); respectively for soils sampled in the rainy season. 102 � l Table 5.1.5 Correlation between soil (OC) and soil metals (DSS) Zn Mn Cu Cd Co Pb Ni Mn 0,121 Cu 0.757* 0.757* Cd -0.994 -0.994 -0.994 Co 0.425 0.425 0.425 0.425 Pb 0.638* 0.638* 0.638* 0.638* 0.638* Ni -0.834 -0.834 0.834 -0.834 -0.834 -0.834 There was significant correlation between (O.C) in parent soil for Cu/Zn (r =0.75, p> 0.01); Cu/Mn (r =0.75, p>_O .Ol);Pb/Zn (r =0.63, p> 0.01); Pb/Mn (r =0.63, p>_0 .01); Pb/Co (r =0.63, p>_0 .01); Pb/Cd (r =0.63, p>_0.0 1); Pb/Cu (r = 0.63) p> 0. 0 1 respectively for all soils sampled in the dry season. Table 5.1.6 Correlation between soil (OC) and soil metal (RSS) Zn Mn Cu Cd Co Pb Ni 0.068 Mn 0.854* Cu 0.804* -0.957 Cd -0.957 -0.957 0.295 0.295 Co 0.295 0.295 0.636* 0.636* Pb 0.636* 0.636* 0.636* -0.786 -0.786 Ni -0.786 -0.786 -0.786 -0.786 There was significant correlations between (O.C) in parent soil samples for the fo llowing combinations Cu/Zn (r = 0.85, p>0.01) Cu/Mn (r=0.80 p > 0.01); Pb/Mn (r = 0.63, p > 0.01) Pb/Co (r=0.63, Pz o.01), Pb/Zn (r=0.63, p > 0.01), Pb/Cd (r=0.63, p> 0.01), respectively for soils sampled in the rainy season. 103 Table 5.1.7 Correlation between soil pH and soil organic carbon (O.C) for all locations Soil pH (DSS) Soil pH (RSS) vs VS soil (OC) soil (OC) r=0.541* r = 0.603 There was significant conelation between soil pH and soil (O.C) for dry and rainy seasons as fo llows; (r = 0.54, p > 0.01) and (r = 0.60, p > 0.01), respectively. Table 5.1.8 Correlation between soil pH for both dry andrainy seasons DSS pH RSS pH DSS pH 1.000* 0.995** RSS pH 0.995* 1.000* Conelation is significant at p = 0.05 level Conelation is significant at p= 0.01 level There was strong correlation between soil pH's in the dry and rainy seasons. There was gradual marginal proportionate increase in soil pH from all locations of the study area. 5.6 Factors of accumulation of heavy metals in soils The average fa ctors of accumulation of metals in soils for Karu, Keffi, Akwanga and Nasarawa Eggon are represented graphically in Figure 5.1. The degree of contamination of soils by heavy metals in each location is evaluated using the fa ctors of accumulation of the metals, which is a ratio of metal concentration in a given location to average concenh·ation in conh·ol soil in that location within the period of sampling. Figure 5.1 showed that there was no significant difference in the pattern of 104 accumulation among the metals during the study. Lead appeared to show prominence in soil accumulation in the study area with an overall mean fa ctor of accumulation of 3.17 and a range from 2.10 - 3.95. Nickel was next with an overall mean fa ctor of accumulation of 3.16 and a range from 2.33 - 5.00., for dry season soil samples. The natural source of Pb in Kant and Keffi LGA's may have been from mining activities of galena (PbS) and molebdenites (MoS2 Pb, Mo04), respectively, during the dry seasons. Nickel is found in chalcopyrite's (CuS FeSo, As, Ni, Co, Cu, Au) mined in Nasarawa Eggon, which gave the highest accumulation factor for nickel (5.0 in dry season and 4.75 in rainy season), (figure 5.1). The factors of accumulation for Zn are 1.24, 1.01, 2.78 and 3.95 fo r Karu, Keffi . Akwanga and Nasarawa Eggon, respectively. Mining of spharelites (ZnS) are predominant in all the locations sampled during the dry season. The degree of contamination of soil with Mn, Cd and Cu were lower than those fo r Pb, Ni, Co and Zn. The-dry season values of heavy metal factors of accumulation are listed below. Zn (1.01 - 3.95) range, with an overal mean value of2.24 Mn (1.33 - 2.37) range, with an overal mean value of 1.71 Cd (1.37 - 2.50) range, with an overal mean value of 1.93 Cu (1.37 - 2.18) range, with an overal mean value of 1.76 Co (2.03 - 3.57) range, with an overal mean value of 2.50 Pb (2.10 - 3.95) range, with an overal mean value of3.17 Ni (2.33 - 5.00) range, with an overal mean value of 3.16 105 The factors of accumulation of metal in soil in the study area fo r rainy season are as fo llows: Zn (0.51 - 2.01) range, with an overal mean of 1.18 Mn (1.04 - 1.70) range, with an overal mean of 1.27 Cd (1.53 - 2.43) range, with an overal mean of 1.91 Cu (1.36 - 2.27) range, with an overal mean of 1.72 Co (1.00 - 2.00) range, with an overal mean of 1.43 Pb (1.27 - 2.20) range, with an overal mean of 1.81 Ni (2.00 - 4.75) range, with an overal mean of2.68 The factors of accumulation of metals in soil, in the study area for rainy season followed similar patte111 as the dry season values fo r all metals, but were slightly lower. This can be explained by enhanced leaching of metal ions in soil solution and increased uptake of metals by plants from the soil during rainy season. Also, levels of metal in control soils generally increased in the rainy season thereby providing a higher denominator of metal concentration of soil leading to lower values of factors of accumulation as observed. The flow of the highest value of metals accumulated in soil to the lowest accumulated metal in the study area followed the sequence: N P b Z n Co > C u > i > > M C d. (fig 5. 1) n > 106 1 l : J ,· , . Accumulation Factor ., r· ' . �):>- (tl "1 II:> (1(l I'll (')t;)' "* 0 ,...... (/). (/)"1 c Q_ 0 '·< ....., 0 II:> '0) (') 4 c (') (1) t:: 0) (f) , .. 3 __ , ! ' -� Oc II:> ::. -< 0 0) ::l :3 0 Cl...... , t:r' 03 ('[) :J II:> '< ·5. (f) (D 8 0) ...... (tl (f) 0 0 -t.) Vl :J 0 ... . U> :::1 n> VJ 3 0 -o - If>· (1) ,--.., ({) 0.. .�· �- ::l 0.. "1 .. . t.) · ·...-:a Vl rt> z t.) Vl ' C> illlll!tllW ::::J . lll lllll -··V> 111� r�J �· )> rtl ?2- c.o . < tll CD . 0 c?3 Q.l -. :J - ····-·· ··-··-·······- ·-··-·-·· 107 • � I I 5. 7 Comparison of metals in soil of study area with other regions Table 5.2 lists the levels of heavy metals in soil from the study area in comparison with soil heavy metal levels fr om other regions. The concentration of metals in the study area were compared with other regional studies and guideline criteria fo r other countries (Table 5.2). Generally, the levels of metals in the study area were lower than the levels for agricultural soils of industTially developed countr·ies. For instance, the Zn levels in the study area ( 42.5 mgkg-1) were much lower than most studies reported. (Table 5.2) Zinc concentr-ationin soil from the study area is 42.50 mgkg-1 and was lower than the levels found in world sandy soils (Table 5.2). Zinc concentration also compares with the value 4 for world soils (40.0 mgkg-1) and the levels fo und in Ulan-Ude, Russia3 (mgkg-1) Manganese found in-the study of (23 1 .2mgkg-1) was far lower than typical area concentrations in soils (100- 400mgkg-1) with a value of 850 mgki1 117 (Table 1.2).Also, 1 134 the values obtained from an unpolluted fi eld in Russia was 410 mgkg- • Cadmium concentration from typical garden soils in Denmark were fo und to be 1 around 0.5 mgkg-1 , much lower than those obtained from farm land soil (1.55 mgkg- ), in this study. Cadmium levels in typical farm soils used to cultivate paddy rice in Taiwan, 1 61 ROC were found to be around 10 mgkg- 1 (Table 5.2), and (1.27 mgkg-1) in farmlands 4 near Annaka, Japan 16 . Copper level in soil (56.6 mgkg-1) was higher than those for world soils (12.0 mgkg-1) and 1 world sandy soils ( 13.0 mgkg- ) 173. The value obtained in this study fell below values 108 . I . 73 in Norway (100.0 rngkg-1) 1 , Netherlands (190.0 rngkg-1)168, France, Taiwan (urban 2 soils)16 , 150.0 mgkg-1 and South Africa (cultivated soils), 100 mgki1)165• Cobalt in typical soils has values ranging from 1-40 mgkg-1 17(Table 1.2). With 1 median values of 8.0 mgkg- • The cobalt concentration in soils fr om study area was lower than values obtained for most unpolluted soils in Europe1 68 and Asia 161'. (Table 5.2). Lead average concentration in soil, in the study area was 6.35 mgkg-1 • Values of 34 Pb concentration in Russia (10.0 mgki1) , Japan (27.0 mgkg-1), Taiwan (120.0 mgkg-1 polluted soil), World sandy soils (22 mgkg-1), World soils (15.0 mgkg-1); were much higher than the figure obtained in the study area. This value 6.5 mgkg-1) in the study area was lower comparatively with the higher values obtained for Norway (50.0 mgkg-1); France (100.0 mgkg-1), Denmark (20.0 mgkg-1), etc. (Table 5.2). Nickel concentration in this study (19.0 mgkg-1) compares with values fo r world soils, (25 mgkg-1), but higher than values for world sandy soils (13.0 mgkg-1). This value was also lower than Ni values for Norway (30.0 mgkg-1), Denmark (30.0 mgkg-1) and France (50.0 mgkg-1) 5.8 Comparison of metals in soil of study area with soil quality criteria for diffe rent countries. Table 5.2 hsts the heavy metal quality criteria in soil for different countries. Heavy metal concentration from the study area compare favourably with values obtained in most developed countries like Switzerland, Norway, France, Taiwan and 109 I l.i. Canada. For example, Zn level in soil from study area ( 42.50 mgkg-1 ) though compares favourably with values for world sandy soils and world soils, was below standards set by most developed countries (Table 5 .2) Mn values also fa ll within acceptable limits for world soils and soil quality criteria fo r Canada and Russia. Cd level in study area (1.55 mgkg-1) was within acceptable limits for Canadian urban and agricultural soils, Taiwanian agricultural soils. It was however above the criteria set in Annaka, Japan, and those for agricultural soils in Denmark. (Table 5.2). Cobalt level found in study area (0.25 mgkg-1) compared favourably with standards set for typical world soils (Table 1.2) 1 7, and below Canadian urban soil criteria of 300 - 72 mgkg 1 1 • Lead level in study area (6.35 mgkg-1) fell below most soil criteria set in different countries for agricultural, urban and commercial soils, while Ni level exceeds values found in world sandy soils but within acceptable limit for other soil quality criteria in most countries. Since diffe rent soil conditions and characteristics determine the speciation and/or bioavailability of heavy metals in them, it is important and necessary to evaluate soil heavy metal pollution implications, not only by the amounts found in native soils, but also the actual amounts fo und in local plants available for human consumption. 110 Table 5.2 Comparison of concentration of metals in soils of the study area with other regional studies (mgl Region Zn Mn Cd Cu Co Pb Ni Refere nces This study 19-74 180- 1.1- 44-70 0.2- 4.2- 14-30 320 2.0 0.35 7.9 Lusaka, Zambia 35.0 0.16 16.0 163 (Unpolluted field) Kalipur village India 309.7 6.11 41.5 180.0 90 4 Ulan-Ude, Russia 40.0 410.0 13.0 10.0 34 Amaka, Japan 148.0 1.27 27.0 164 Canada (Urban soils) 200 200 2.0 91 300 260 210.0 172 (Commetical 250 250 2.0 100 150 200 200 172 Taiwan R.O.C(Rmal 80.0 10.0 100.0 120.0 100.0 161 polluted soils) World sandy soils 45.0 13.0 22.0 13.0 173 World soils 40.0 12.0 15.0 25.0 165 Switzerland (guide value 200.0 50.0 50.0 166 N01way 150 100 50.0 30.0 173 Netherlands (action levels) 720.0 190.0 530.0 210.0 168 France 200.0 100.0 100.0 50.0 173 Taiwan R.O.C (urban 200 150.0 100.0 120.0 162 soils) South Africa 185.0 100.0 5.5 15.0 165 Dem11ark (Agriculture) 500 0.5 500 20 30 167 Denmark (Commercial) 1000 5.0 500 400 30 167 5.9 Comparison of heavy metals in food crops/plants in study area with other regional studies and WHO Standards. Table 5.3 lists the concentrations of heavy metals in food crops in study area, with 111 I L l. values obtained from other regional studies and WHO Standards for fo ods. Majority of the concentrati ons of heavy metals under consideration viz·' ' 'Cd ' ' Co Ni Cu Mn and Zn are within acceptable limits for fo od by WHO/F AO regulations. However, the level of Pb (0.36 mgkg-1 ) (Table 4.12) obtained for fo od crops in study area is about one-fifth of WH0 benchmark, of (2. 0 mgkg -I ). Even though the sources of Pb into soil and vegetation within the study area may have derived from mining activities and agricultural application of phosphate fertilizers, it was not enough to cause adverse effects in soil and vegetation. The major mineral sources of Pb in the area include galena ores (PbS) and molybdenites (MoS2, Pb, Mo04), which contribute to background concentrations of Pb in the soil. Application of phosphatic fertilizers, though not regulated may have built up soil enrichment of metaWc Pb over the years of 164 its application, since lead has the least tendency to be leached out of the soil matrix . The plant- levels of Zn in the study area, falls within the limits set for forage plants in Russia (Zharnikov)170, and below the limits for agriculture (Kovalsky) 171 Zinc levels in present study also falls below levels set in Taiwan, R.O.C for paddy rice, (Table 5 . 3) and other regional standards for Canada (agriculture), Taiwan (agriculture), Denmark (agriculture) and WHO Standards for food. Manganese levels in present study (18.25 mgkg-1) was within acceptable values for world plants and crops (Alloway)18 (15-100 mgkg-1), and Russian standards for agriculture (Table 5.3). Cadmium metal level for fo od crops (0.14-0.36 mgkg-1in present study 1 was below values for world plants/crops (0.2 - 0.8 mgkg' ) (Table 5.3), but above Taiwan 1 standards for rice (0.07 mgkg-1) and below WHO standards for fo od crops (2.0 mgkg- ). 112 Values of Cd in other regional studies were above levels found in present study. (Table 5. 3) For copper, the value obtained 3.7 mgkg-1 is below WHO, Russia (Agric); Canada (Agric) and other-country standards except fo r limits set for paddy rice in Taiwan, Republic of China. (Table 5.3). There is no available infonuation on quality criteria for Co in fo od by WHO. probably because cobalt has been identified as an essential micronutrient in fo od. However, the level of Co in this study (0.02 mgkg-1) was below values obtained in most world plants1 8 and other regional studies (Table 5.3). Values for Co in Russia (agriculture and forage plants) are above those obtained fo r world plants in this study for fo od crops (Table 5.3) Nickel levels in fo od crops fe ll within limits obtained for most world plants and below standards set in Canada, Taiwan (agriculture) and Denmark. Nickel levels in fo od crops in study area, were found to be above the lower limit set for paddy rice in Taiwan, Republic of China. 113 Table 5.3 Comparison of heavy metals in fo od crops in study area with WHO Standards and other regional studies. Region Zn Mn Cd Cu Co Pb Ni Reference Russia (agtic) 45.00 30.00 - 8.5 0.625 - - 163 Russia 16.1 14.2 - 9.5 1.14 0.9 - 170 (forage plants) Taiwan (R.O.C) 39.2 - 0.07 2.8 - 0.43 0.54 48 Paddy Rice World plants 8-100 15-100 0.2-0.8 4-15 0.05-0.5 0.1-10 1.0-2.0 18 and crops Canada 200 - 1.4 63 40 70 50 172 (agriculture) Taiwan (R.O.C) 80 - 10 100 - 120 100 169 Agriculture Denmark 500 - 5 500 - 40 30 167 (AgricultlU'e) WHO/FAO 1000 - 2.0 30 - 2.0 - 63 Standards This �tudy 4.13 18.25 0.24 3.78 0.02 0.36 0.42 Range 1.33-8.14 9.0-32.0 0.14-0.36 2.2-5.6 0.01-0.03 0.13-0.63 0.14-0.90 114 5.10 CONCLUSION Levels of metals in the soil and plants from the study area were higher than control sites indicating that man made activities had affected the concentration of metals in the area. Mining and agricultural activities have also played major roles in the area because of the use of improper mining procedures (open-cast mining) and the use of fertilizers and other agricultural chemicals on farmlands. As a result of mining, mine spoils and tailings which are known to be affected by erosion lead to the release of metals into the environment. Percentage bioavailable metals were lower than soil background metal levels. Also, plant metal levels were lower than soil bioavailable metal levels in all the locations of the study. Plant metal levels were found to be lower than critical levels permitted for plants and compares with other regional studies and standards by WHO/FAO respectively. This study also afforded the establishment of baseline levels for metals which include Zn, Mn, Cd, Cu, Co, Pb and Ni in the study area. The environmental hazards produced by heavy metals are strictly linked to their bioavailability and mobility in soil solution. The distribution of heavy metals between the soil' solid phase and soil solution is of paramount importance in evaluating the environmental impacts and consequences generated by the presence of these heavy metals in soil. Increase in heavy metal concentration in soil solution results in increase in plant uptake of such metals. This assertion is justified by higher metal concentration values for rainy season than their dry season values. 115 This study revealed the impact of mmmg and agriculture on soil heavy metal bioavailability and absorption by fo od crops grown on farmlands within areas of mining activity and linked anthropogenic sources as major fa ctor fo r soil heavy metal enrichment. The study also revealed marked seasonal variations in metal levels with strong inter - element correlations within the periods of sampling. Rainy season soil and plant sample results showed higher values for heavy metal levels in the enviromnent. Results in this study also revealed that the total concentration of metals in soil, do not indicate the amount that are available fo r plant uptake because, all heavy metals fo und in soil may be absorbed by plants, leached out of soil through solubilization or insolubilized in the soil by humic substances and organic matter in soil. It was also found that bioavailable metals have correlation with plant metals, with varying percentages of absorbable metals by different food crops. The general trend observed in metal concentration levels in fo od crops was as fo llows; root vegetables (RV's) > leaf vegetables (LV's) > fruit vegetables (FV's). DTPA sequential extraction was used to identify and quantify bioavailable metals in soil with observed strong conelation with amount of total metals in soil and plant metals, it was also fo und that soil pH ranged from slightly acidic to neutral during the periods of sampling (rainy and dry seasons), and is proportional to the organic matter content of soil. Whereas the pH of soil solution has direct relationship with soil organic matter, the latter has some relationship with soil metal content under cetiain soil pH conditions. It was also observed that higher organic matter content of soil results in higher soil metal content 116 while lower organic matter content also results in lower soil metal content. The results of the digestion methods adopted in this work gave acceptable and good coefficients of variation, recovery percentages of soil metal contents, and compared favourably with results for cetiified soil reference materials (CRM's). This shows that the digestion and sample preparation method adopted in this work was reliable and can be recommended fo r use in similar studies elsewhere. There was good correlation between metals in soils, pH, metals in plants and organic matter (i.e. organic carbon) for most metals under investigation in this study. Their levels were within acceptable limits compared with levels in world soils and plants and also WHO quality criteria fo r metals in food. It will however be worthy to mention that levels obtained lor Cd and Pb in soil require attention and possible mitigation plans in the study area. Cadmium and Lead levels in soil for all locations exceeded values obtained fo r world soils. Possible health risks (none for now), that may arise from heavy metal pollution of fo od crops in the study area have been identified and the database fo r heavy metal concentrations of Zn, Mn, Cu, Cd, Co, Pb and Ni in soil and selected fo od crops in the study area have been established to serve as guide for further investigations. 117 5.11 Recommendations There would he need for; • Soil management targeted at reducing the concentrations of heavy metals in soil, particularly for those metals that are likely to exceed acceptable levels fo r international soil quality criteria, ie Cu, Cd and Pb introduced into the soil through fe rtilizers and mining activities. • Constant monitoring of levels of metals in soils and fo od crops in the study area, other parts ofNasarawa State and Nigeria in general. Expanded survey to cover other heavy metals with health risk potentials, in the state and other parts of Nigeria. Regulations on appropriate mining procedures and proper use of chemical fertilizers in soil for agricultural production of food crops. • Shift from heavy dependence on phosphatic fertilizers and pest icides on farmlands and developing environmentally sustainable programs for plant nutrient enhancement and enrichment. 118 5.12 REFERENCES 1. Geldmacher (1984): "Physiological effects of heavy metals on Human Health". Bulletin of Environmental contamination toxicology Vol. 66-67. 53, pp. 2. Baker, K.L (1989): "Terrestrial; higher plants which hypoaccumu]ate metallic elements - A review of their distribution, ecology and phytochemistry. Biorecovery Vol l,pp. 81 - 126. 3. Commission of the European Union, 2002 ... Guide values for metal concentrations in agricult-ural soils. 4. Brumer, (1986): "Transport of heavy metals from soil matrix to plants" - Technical review of transport phenomenon of elements on soil to plant J. Soil. Sci, Vol 176, pp. 232 - 245. 5. Srikanth, R and S.R.P Reddy, (1991): Lead, Cadmium and Chromium levels in vegetables grown in urban sewage sludge in India. Food Chem. 40, 229 - 234. 6. Chukwuma, C. (1993): Cadmium, Lead, Zinc from terrestrial plants in Enyigba - Abakaliki lead and zinc mine; Search for a monitoring plant species in trace element distribution. Bulleting Environ Contamination Toxicology. Vol. 51. pp 665-671 . 7. Sharma, A.M. and Sharma, Y.M. (1994) : Metallic pollution of soil, sources, impact and management, Seminar Paper, dept. of soil Science and Agricultural Chemistry, J.N. Kristi Vishwavidyakakya Jabulpur, M.P India 482004. of Indian Pollution, Vol. 1 "In Control of metallic pollution of soil of India Poll. Vol. 1. 8. Tiller, K.G. (1989): "Heavy metals m soils and their environmental 119 significance" In: B.A. Steward, (Editor), Advances in Soil Sci Vol.9, pp.l13- 176. 9. Wild, A. (1994): "Soil and the Environment", An Introduction. Cambridge Universities Press, New York, U.S.A. Pg. 145 Bowen, H.J.M (1996): "Trace elements is Biochemistry" Academic Press, 10. London. Pg 126 11. Baechele, H.T and Wolstein, F. (1984): "Cadmium compounds in mineral fe rtilizers". The Pert. Soc. Proceedings No 226, London. Pg. 34-42. 12. Salomons, W. (1993): "Non linear and delayed response to toxic chemicals in the environment" - In contaminated soils (Ed) pp. 225, Kluwer Academic Publishers, London. 13. Cook, J. (1979): "Environmental Pollution by Heavy metals". Inter.J. of Environmental Studies Vol. 9 pp. 253 - 266. 14. Field Outline of Geology: Princeton University Press (1979): "Illustrations of the origin of ore deposits". New Jersey, U.S.A. Pg. 224 15. Palsma, A.J., Diependal, M .J. "Sustainable Soil Use Ibid pp. 1609. 16. Goldschmidt, V.M. (1958): Geochemistry, Oxford Univ. press, London pp. 120- 128. 17. Bowen, H.J.M. (1967): Trace elements in Biochemistry, Academic Press, London. 18. Alloway, W.H. (1968): Element recycling, Adv. Agrons Vol. 20 pp. 235 - 274, pp! 224 - 238. 120 19. Nriagu, J.O (1990): "Global metal pollution poisoning of the biosphere" .1. Environ Sci., Vol. 32, pp. 7-32. 20. Ward, N.A. (1995): "Trace elements" pp. 321 - 351. Co-ordinated by Field. F.N and Blackie, HRJ. Environmental Analytical Chemistry, Academic Press; Glasgow, Scotland. 21. Swaine, D.J. (1962): "The trace clement contents of Fertilizers commonwealth Bureau of Soils, Tech. Paper No. 52, Comm. Agric Bureau, Fann Ham Royal, Bucks. 22. Mortvedt, J.J. and Osborn, G (1982): "Studies on the Chemical forms of Cadmium contamination in phosphate fertilizers". Soil. Sci. Vol. 134. pp. 1 8 5- 1 9 2 . 23. Asubiojo, M. (2005): "Determination of anthropogenic effects of copper fungicide application to cocoa crops in Ondo State - Nigeria". In Adventures in the world of trace elements Inaugural lecture, OAU University Ile-Ife, Nigeria Publ. By Guardian Newspapers, Monday, March 2i11, 2006 pp. 58." 24. Foy, C.D (1978): "The physiology of metal toxicity in plants". The Pert. Soc. Proceedings No, 226, London. 25. Sommers, G. (1979): "Pot experiments to establish the danger levels of Cu, Pb and Zn, in relation to the application of sewage sludge and refuse materials 1n agriculture". Land Forsclung. San derhaft Vol. 35, pp. 350- 364. 26. 26. Zu mbroich, T. (1991): "Heavy metal pollution from mme pits" paper 121 published in Germ. Assoc. of Soil Scientists. Vol. 3 pp.51-53. 27. Larganveff, J.V. and Speclite A.\V. (1970): "Contamination of roadside Soils and vegetabon with Cd, Pb and Zn" Environ. Sci. Techno!. Vol.7pp. 583 - 586. 28. Kaku lu, S.E. (2002): "Trace metal concentration in roadside surface soil and tree bark; A measure of local atmospheric pollution in Abuja-Nigeria. Environ Morn. Assess. Vol. 2, pp. 50 - 52. 29. Rao, S.B. (1995): "Selenium; Friend or Foe" Science Reporter, Vol. 2, pp. 50- 52. 30. Zdeneck, K and Mecislav, K. (1997): "Heavy metals in soils contaminated fr om different sources", A survey, Dept. of Environmental Chemistry, Inst. of Chemical Technology, Prague, Czech Republic. 31. Dean, J.G. (1972): "Removing heavy metals form waste water" Environ. Sci. Techno!., Vol. 6, pp 518 - 522. 31�a) Hogson, J.F. (1963): "Chemistry of the Micronutrient elements in soil". Adv Agron. Vol. 15. pp. 119-159. 32 U.S. Environ Protection Agency (1971): "Water Quality Criteria Data Vol. 2, Washington, D.C. US Government Printing Office. 32.(a) Stevenson, F.J. and Ardakari, M.S. (1972): "Organic matter reactions involving micronutrients in soils. "In Micronutrients in Agriculture, pp. 79 - 114, Soil Science Soc. of America. 33. Chen, Z.S. Lee T. (1995) : "Establishment of background total concentrations of heavy metalsjn Taiwan (ROC)". A Review 122 34. Abasheyeva, J. (1992): "Ideological principles fo r possible application of purified sewage to soil irrigation" Siberian Branch of the Russian Academy of Sciences, Ulan Ude, Russia. 35. Nriagu, J.O. (1990): "(global metal pollution poisoning of (he biosphere" .1. Environ Sci., Vol. 32, pp. 7-32. 36. Ho, V.B. and Tal, K.M. (1988): "Effe ct of rain on lead levels in roadside vegetation in Hong Kong" Bull. Environ. Contain Toxicol 23, pp. 658-660. 37. Brinkmann, K. (1994): "Lead pollution in soils in Milwaukee County, Wisconsin" Environ. Sci. Health A29, pp. 909-919. 38. Kretzehmar, S., Bundt, M., Sabario, G., Wilke, W., and Zech, W. (1988): "Heavy metals in soils of Costa Rican Coffee Plantations" Adv. Geoecol. 32, pp. 721-726. 39. Jaradat, Q.M., and Mornani, K.A. (1 999): "Contamination of roadside soils, plants and air with heavy metals in Jordan. A comparative study; Turkish J. Chern 23. pp. 209-220. 10 40. Kim, K.W., Myung, J.H., Agu, J.S. and Chou, H.Z. (1988): Heavy melal contamination in dust and stream sediments in the Taejon area, Korea: J. Geochem. E l r. 64. 409-419. 41 xp o pp. 41. Steinnes, K., Solbergcr, W., Petersen, M.N. and Wren, C .I (1989): "Heavy metal pollution by long range atmospheric transport in natural soils of Southern Norway Water, Air, Soil, pollution 45, pp. 207-2.18. 42. Osibanjo, 0. and Ajayi, S.O. (1980): "Trace metals levels in tree bark 123 as indicators of atmospheric pollution" Environ. Int. 4, 239-244. 43. Onianwa, P.C. and Ajayi, S.O. (1987): "Heavy metal contents of epiphytic acrocarpous mosses within inhabited sites in South West, Nigeria". Environ. Int. 13, 191 - 196. 44. Ademoroti, C.M.A. (1986): "Levels of heavy metals on bark and fr uits of trees in Benin City, Nigeria" Environ. Poll. (Ser B) II, 241 - 253. 45. Kakulu, S.E. (2002): "Trace metal concentration in surface soil of Jos Tin Mining areas" A measure of soil metal pollution in Jos. Nigeria. Environ Morn. Assess. Vol. I. pp.48-52. 46. Laaksorvirta, K. Olkkonen, H. and Alakuijala, P. (1976): "Observations on the lead content of lichen and bark adjacent to a highway in Southern Finland". Environ. Poll. II, 247-255. 47. W.H.O. Working Croup. (1989): "Lead environmental aspects". Environ. Health Criteria, No.85, 1989. 48. Lin, M. (1991): "A study on the establishment of heavy metal tolerance through the heavy metal concentration in fo od crops" Res. Inst. of soil Sci. National Chung Hsing University, Taichung, Taiwan, Republic of China. 49. Collins, J.C. (1981): "Zinc in effects of heavy metal pollution on plants Vol. I, Chapt.5, N.W. Lepp Ed) London. Applied Science Publishers. 145- 169. 50. Pahlsen A.M.B. (1990): "Toxicity of heavy metals (Zn, Cu, Cd, Pb) to vascular plants" Lit. Rev. Water, Air and Soil Pollution, Vol. 48,280-281. 124 51. Kaplan, D.l. (1990): "Phytoavailability and toxieity of Be and V'' Water, Air and Soil Pollution, Vol. 50. 43-5 1 . 52. Mishra, D. and Kar, M.I. (1974): "Nickel in plant growth and metabolism" Bot. review. Vol. 40, 395-452. 53. D'ltri, M.F. (1972): "Epidemology and toxicity of mercury" In the environmental mercury problem, CRC Press, 73-86. 54. Leeper, G.W. (1978): "Managing the heavy metals on land" Marcel Decker (Ed), New York, USA. 55. Olsen, K.W. and Skogerboe, R.K. (1975): "Identification of soil lead compounds from automotive sources. "Environ. Sci Techno!. Vol. 9, pp. 227-230. 56. Bhadoria, A.K.S. (1994): "Heavy metals in soil, their problems and remedies" In water and nutrient management in soils" V.S. Tomar (Ed) Proceedings held at Summer Inst. Dept. of Soil Sci. and Agric. Chem. Jabalpur, India, May 30th - June 18th. 57. Loneragan, J.F. (1975): "The availability and adsorption of trace elements in soil - plant systems and their relations to movement and concentrations of trace elements in plants". Academic Press, New York, USA. Pp. l 09 134. 58. Jarvis, S. and Jones W. (1 978): "Uptake and transport of Cd by perennial ryegrass from flowing solution culture with a constant concentration of Cd and Pb" Plant soil Sci. Vol. 49, pp. 332-342. 125 59. Wood, J.M. (1974): "Biological cycles for toxic element"- m the environment. Env. Sci. Vol. 183, pp. l049-l052. 60. Ven ugopal, B and T .D). Lucky (1975): "Toxicology of non-radioactive heavy metal and their salts". heavy metal toxicity safety and hormology In (eds) Euckey, Venegopal and Hutcheson Thieme publishers, Stuggart W. Germany. 61. Underwood, K.J. (1971): "Trace elements in human and animal nutrition" 3 rd Ed. London, Academi Press. 62. American National Academy of Science (NAS) (1977): Baltimore Uni. Press pp. 1 4 7 1 6 3 . W HO/FAO (1974); Wood, J.M. (Ed): "Biological cycles fo r toxic elements in the environment" Environ. Sci. Vol.183, pp.1 049 1052. 64. Bowen, H.J.M. (1979): Environmental chemistry of the elements; Academic Press, New York pp. 125 - 135. 65. Gupta, V.K. and Potalia, B.S. (1990): "Zinc-Cadmium Interaction 111 Wheat". J. Indian Soc. Soil Sci., Vol. 3893, pp 452 457. 66. Jameson, S. (1980): "Zinc and pregnancy". In Zn in the environment Part II" Health effects" J.O. Nriagu (Ed), New York; John Wiley and Sons Publ. pp. 183-197. 67. Pahlsen, A.M.B (1989): "Toxicity of heavy metals to vascular plants" Lit. Review, In Water, Air and Soil Poll. Vol.47, pp.287-319. 68. Frank, T (1986): "Metal toxicity to agricultural crops". In metal 10ns m 126 98. Bakhtar, D. (1989): "Dissolution of soils and geologic materials for simultaneous clement analysis by AILS and AAS" Analyst Vol. 114 pp. JCP 901-909. 99. Eeva, T., Sovari, J. and Koivunen, V. (2003): "Effect of heavy metal pollution on redwood ant populations". Dept. of Bioi. Univ. of Turku, Finland. 100. Amacher, M.C. (1996): "Ni, Cd and Pb pp.739-768 In. J.M. Bigham (ed) Methods of soil analysis, part 3, Chemical methods. Soil Sci. Soc. of America Inc. Madison, W.I. USA. 3rd edition. 100(a) USEPA (1986): "Test methods for evaluating solid wastes USEPA S.W 846, U.S. GovernmentPrint Office, Washington D.C 101. Flegal, A.R (1991): "Dissolved trace element cycles m San Francisco Bay Estuary". Marine Chemistry. Vol. 39, pp. 329-363. 102. Nicola, C., Marie Claud. T. and William, H.U. (2000): "A digestion method for trace recovery from oil and grease contaminated soils" Soil Sci. Soc. of America .J., Vol. 64, pp. 609-612. 103. Forstner, U. (1979): "Metal pollution in the aquatic environment". Berling, Springer verlag, pp. 486. 104. Agemain, H. and Chan A.S.Y. (1975): "Atomic absorption method for the determination of twenty elements in lake sediments after digestion". Analytica Chimica Acta. Vol. 80, pp. 61-66. 105. Baker, D.E. and Amaeher, M.C. (1982): "Ni, Cu, Zn and Cd, 326. In page A.L. (eds) Methods of Soil analysis". Part 2, 2nd ed. Agron monograph. ASA 130 and SSSA, Madison W.I. USA. Pp 323-326. 106. Bakhtar, D. (1991): "Comparison of fi ve soil digestion methods in determining element levels in contaminated soil", pp. 238, in Agron. Abstracts, ASA, Madison W.I. 107. Tessier, T. (1979): "Sequential extraction procedure for the speciation of particulate traces metals". Analysis Chern. Vol. 51, pp. 844- 850 108. Becket, P.H.T. (1989): "The use of extractants in studies on trace metals in soils, sewage sludges and sludge treated soils", pp.143-176, Adv. In soil Sci. Springier verkg, New York. 109. Ahnstrom, Z.S. and D.R. Parker (1977): "Development and assessment of a segmental extraction procedure for the fr actionation of soil Cd" Soil Sci. Soc. Am. 1; Vol. 163, pp. 1650-1658. 110. Sposito, C. (1982): "Trace metal Chemistry in arid zone soils amended with sewage sludge". In Fractionation of Ni, Cu, Zn, Cd and Pb in solid phases Soil Sci. Soc. Amer. J. Vol. 46, pp. 260-264. 111. Chester, R. and Hughes M.J. (1969): "Trace clement geochemistry of North pacific pelagic clay core". Deep Sea Research, Vol.16, pp. 23-33. 112. Shuman, L.M. (1985): "Fractionation method for soil micro elements". Soil Sci. J. Vo1.140, pp. 11-22. 113. Zeien, H. (1995): "Chemische extraction Zur bcstimmung der bindings farmen von schivcr metallen in baden". Bonnar baden Kundi Abhanol. Bonn, Germany. 131 114. Iyengar, S.S. (1981): "Distribution and plant availability of soil Zn. Cd, Pb and Cu fractions" Soil Sci. Soc. Am. J. Vol. 45, pp. 737-739. 115. Li, Z. and L.M. Shuman (1996): "Heavy metal movement m metal contaminated soil profiles" Soil Sci. Vol.1619( 10), pp. 493-503 . 116. Chao, T.T. (1984): "Use of partial dissolution techniques m geochemical exploration" ..J. Geochem. Explore. Vol. 20, pp. 101-135. 117. Shuman, L.M. (1982): "Separating Soil Fe and Mn oxide fractions for micro element analysis". Soil Sci. Soc. Am J. Vol. 46, pp. 1099-1102. 118. Lindsay, W.L. and Cox, F.R. (1985): "Micro nutrient soil testing fo r the tropics". Pert. Res., Vol. 7, pp. 169-199. 118(a) Lindsay and Norvel (1978): Development of a DTPA soil test for Zn, Fe, Mn and Cu" Soil Sci. Soc. Am J. 42: 421-428. 119. Kelling, K.A. (1977): "A fi eld study of the agricultural use of sewage sludge", (iii) Effect on uptake and extractabilify of sludge - borne metals. J. Environ, Qual. Vol., 6 pp. 352-358. 120. Caviatta, C. (1993): "Evaluation of heavy metal during stabilization of organic matter in compost produced from municipal soil waste". Biores Technol, Vol. 43, pp. 147-153. 121. Chen Z.S. ( 1992): "Clean up on Cd and Pb polluted soil usmg chelating agents". Geotcch, Netherlands A.A. Balkems (Publ.), pp. 365-368. 122. Maize, I.A. (2000): "Evaluation of heavy metal availability in polluted soils by two sequential extraction procedures using factor analysis" Environ Poll. 132 Vol.l lO, pp. 3-9. 123. Grant Gross, M. (1971): "In Procedures in Sedimentary Petrolology" Carver R.E. ( ed) New York, Wiley Interscience. 124. Strickland, F. (1960): "In Procedures in Sedimentary Petrology" Carver R.E. (ed) New York. Wiley. 125. Degens, R. (1960): "In procedures in Sedimentary Petrology" pp. 214 126. Trask, K. (1939): In procedures in Sedimentary Petrology" In sampling the destruction of organic matter in sediments and soils pp. 12-15. 127. Schopt, T. and Manheim R. (1967): "American Public Health Association" pp. 1203-1 204. (In determination of organic matter in soils and tissues). 128. Black C.R. (1965): "In procedures in Sedimentary Petrology" (in the determination of total carbon). pp. 1-81. Carver R.E. (ed) New York, Wiley Interscience. 129 Jackson, M and Van Syke, R (1958) In the Procedures in Sed. Petrology. Pp. 214-242 129( a) Lynch, G.R. (1954) "The destruction of total organic matter" August, vol. 79, pp.137 130. Agronomics Catalogue (1992): Instruments for monitoring the agricultural environment. ELE Publication, pp.26. 131. Boyer, K.\V., Horwitz, W. and Albert, R. (1985): "Intel-laboratory variability in trace element analysis". Anal. Chern. 57, pp. 454-459. 132. Horwitz, W., Kamps, L.R. and Boyer, K.W. (1980): "Quality. Assurance in 133 I • the analysis of fo ods for trace elements" .J. Assoc. Of Anal. Chern. 63, pp. 1344- 1354. 133. Horvvizt, W. (1982): "Evaluation of analytical methods for regulation of fo ods and drugs". Anal. Chem. 54, 67A, 68A, 70A, 72A, 74A, 76A. 134. Garfield, M. (1980): "Optimizing Chemical Laboratory-Performance through the Application of Quality Assurrancc Principles". AOA Chemists. Washington, D.C., USA. 135. Lise-Samse Peterson K. and Edl< Larson, (2002): "Uptake of trace elements and PAI-l's by fru its and vegetables from contaminated soils" Environ. Sci. Tech., Vol. 36, pp. 170. 136. Gorsuch, T.T. (1959): "Radiochemical investigations on the recovery for analysis of trace elements in inorganic and biological materials" Analyst (London), Vol. 84, pp. 135 - 173. 137. Smith, G.F. (1953): "The wet washing of organic material mploying hot concentrated perchloric acid. The liquid fire reaction. Anal. Chin. Acta, Vol. 5 pp. 397-42 1. 138. Buhler H. (1983): "Heavy metals in estuarine shellfish from Oregon" Archives of Environ. Contamination and Toxicology, Vol. 12, pp. 15 20. 139. FAO/SIDA (1983): "Manual of methods in aquatic environment research part 9. Analysis of metals and organo-chlorines in fish. FAO /Fish Technical Paper pp. 33. 140. Middleton, G. and Stuckey, R.E. (1953): "The preparation of biological 134 I ·· • materials for the determination of trace elements critical review of existing procedures. Analyst Vol. 78, pp.532-542. 141. Tolg, G. (1974): "Wet Oxidation procedures - In method in Clinical Analysis. Vol. 1 - Analytical methods (1 ;. Karte ed) part B, pp. 698 - 710 Academic press. New York. 142. "LTA - 600 Low temperature dry asher" Trace - Jab, Richmond, C.A. 143. Bowen H.J.M. (1967): "Comparative elemental analysis on standard plant material" Analyst, Vol. 92, pp. 124 - 131. 144. Gorsuch T.T. (1976): "Accuracy m trace analysis: Sampling. Simple Handling and Analysis" Pub 422. National Bureau of standards Washington DC. 145. Horwitz, W. (ed) (1975): "Official Methods of analysis of the Association of Official Analytical Chemists Ii11 ed, Washington DC. 146. Bowen H.J.M. (1968): "Use of sodium and potassium nitrates for decomposing organic samples for elemental analysis" Analytical Chemistry. Vol. 40, pp. 969 - 970. 147. Lynch, G.R. (1954): "The destruction of organic matter" Analyst, Vol. 79. pp. 137. 147(a) Elvidge, D.A. and Garratt, D.C. (1954): "A note on a bomb technique for preparing samples for the determination of Pb in fo odstuffs". Analyst, 79, pp. 146 - 147. 148 Thiers, R.E. (1957): "Contamination in trace element analysis and its control" 135 . I L ._ Methods Biochem Anal, Vol. 5 pp. 273-335. 149. Schulek, K. and Laszlovsky, .J. (1960): "Problem of destruction and enrichment in microanalysis". Microchim, Acta 6, pp.485-50 1. 150. Zonneveld, H. and Gersons, L. (1966): "A rapid dry ashing method" Lebensm Unters Forsch. 131, pp.205-207. 151. Steele, R.J. (1984): "Trace metal analysis of foods by Australian Laboratories" Food Technol. Anst. 36 (3), pp.l35-130, pp.138-139. 152. '\tVolf, W.R. and Hamly, J.M. (1984): Trace element analysis": In analysis in fo od contaminants (J. Gilbert ed) pp.l57-206, Elsvier Applied Science Publishers, London. 153. Hocquelett, P. (1984): "Use of atomic absorption speetroscopy with electro thermal atomization for the direct determination of trace elements in fish oil and vegetables, Cd, Pb. As and Sn" Review for Corps Grab, Vol. 31, pp. 154. Noller, K. and Bloom R. (1978): "Methods of analysis of major and minor elements in foods". Food Techno] Australia Vol. 30(1), pp.I 1-19 and pp. 22 - 23. 155. Ames, R. (1966): "New Instrumental procedures for determination of trace elements Wallerstein Lab. Comm. Vol. 29 (100), pp.107-1 13. 156. Sanders, J.B. (1971): "In the applications of AAS to the analysis of Petroleum Products" Varian Techtron Pty. Ltd. Springvale, Australia. 157. Richard, C. (1963): "Atomic Absorption Spectrometry" Pittsburg Inference on Analytical Chemistry, Pittsbufe P.A.USA. 136 157(a)Van Nostrand Scientific Encyclopedia 51" edition Mineralogy" (1977) 158. Fassel, V.A. and R.N. Kniselcy (1974): "AAS and ICP-OES" Anal Chern., Vol.45, pp. 11OA-I l20A. 159. Jackson M. (1958): "In the procedures in sedimentary petrology: Carver, R.E. (ed). New York, Wiley Interscience, pp.222-225. 160. McBridge, M.B. (1989): "Reactions controlling Heavy metal solubility" In.B.A. Stewart (ed) Advances in Soil Sci. Vol. 10, pp.l - 47. 161. Zueng - Sam Chen(2000) "Relationship between heavy metal concentration in rural soils of Taiwan, and uptake by plants" Dept. of Agricultural Chemistry, National Taiwan Univ., Tapei 106, Taiwan, R.O.C. (A review). 162. Chen, Z.S. (1999): "Proposal regulation of soil pollutants in Taiwan, an soils" Proceeds of 6111 workshop on soil pollution and prevention, "Taiwan. R.O.pp 169-207 In Chinese with English Abstract and tables). 163. Nwankwo and D. Klinder R. (1979): "Cadmium, lead and zmc concentrations in soils and fo od grown near a zinc and lead smeller in Zambia'' Hull. Environ. Contam. Toxicol. 22, pp. 625 - 63 1. 164. Xian, X. (1989); "'Response of kidney bean to concentration and chemica] forms of Cd, Zn and Pb in polluted soils Environ. Pollut. Vol. 57. pp. 127-137 165. Berow, M.L, and G.A. Reaves (1984): "Background levels of trace elements in soils", pp. 333 - 340 In proceed. Inst. Int. Conf. on environmental contamination CEP Consultants, Edinburgh, Scotland. 166. Federal Office of Environment, Forests and Landscapes (FOEFF) (1987): 137 I. • "Comments on Ordinance relating to pollutants in soils Hem. Switzerland. 167. Danish EPA (2000): Toxicological soil quality criteria and cut oil criteria fo r soil (Danish EPA, 2000). 168. Netherlands (Dutch EPA) (1999): "As in Environ. Pollution". Vol. 95, pp. 45-56. 169. EPA/ROC (1998) 170. Zharnikov, Baldayer, S.N. and Sobenikova, K.F. (1973): "Protein 1.1. Vitamin fo od and mineral nutrition of agricultural animals". Ulan-Ude: Burya Book Publishing Mouse, 181 pages (In Russian). 171. Kovalsky, V.V. (1974): "Biochemical Ecology" Moscow: Nauka 190 pages (In Russian). 172. CCME(1999): "Canadian Soil quality guidelines for the protection of environment and, human health: Canadian Council of Ministers of the Environment, Winninpeg. 173. Kabata Pendias, W. A.S. Dubka, Chlopecka, M. (1992): "Background levels and environmental influences on trace metals in soils of temperate humid zone of Europe", pp.61-84. In Adriano, (ed) Biogeoehemistry of trace metals CRS Press. Boca Raton, Florida. 174. Mbila, M.O. (2001): "Distribution and movement of sludge derived trace metals in selected Nigeria soils" Journal of Environ. Quality 30. pp. 1607-1 674. 175. Agemain K. and Chau A.S.Y. (1976): "Evaluation of extraction techniques for 138 determination of metals in aquatic sediments" The Analyst, 101, pp. 761- the 767. 176. Lee, B.D., Carter� B.J., Blister, N.I. and Weaver. B. (1977): "Factors influencing heavy metal distribution in six Oklahoma benchmark soils Soil Sci. Am.J. Vol. 61, pp. 218-233. 177. UNEP, 1987: "Environmental data report, United Nations Environmental Programme Blackwell, Oxford. 178. NAS, (1977): National Academy of Sciences Drinking Water and Health Vol. 1 - 8 prepared for USEPA by the National Research Council. Washington D.C., National Academy Press. 179. USEPA (1985): Guidance manual for Compliance for Public Water Systems. Washington D.C. USEPA publications of NTIS, Springfield. V.A. 1RO. Gairola M. J. (1992): "Tobacco, Cd and Health" Smoking related diseases Vo1. 3pp. 1-6. 181. Bryce Smith J. and Waldron H.A. (1974): Lead Behaviour and criminality" The ecologist 4, pp.367-377. 182. Page A.L. (1971) "Lead quantities in Plants, soil and air near some major plants, soils and highways in Southern Carlifonia. Hilgardia Vol. 41. pp. 1-31. 183. Sakal, R. (1992) Depthwise distribution of heavy metals in soils rece1vmg sewage sludge" J. Indian Soc. Soil Sci. Vol. 40, pp. 732-737. 184. Anderson, A. (1977c): "The distribution of heavy metals in soils and soil materials as influenced by the ionic radius". Swed. Agric. Res. Vol. 7 pp. 139 I I i