k. 04 A SD9800005
INVESTIGATION OF THE ELEMENTAL CONTENTS OF SOME ENVIRONMENTAL SAMPLES FROM THE BLUE NfLE AND WHITE NILE AROUND KHARTOUM AREA
By Kama! Khalifa Taha
A thesis submitted in fulfillment of the degree of Masters of Science in the University of Khartoum
Department of Chemistry Faculty of Education October, 1997
29-37 TO
THE SOUL OF MY FATHER
TO MY MOTHER ACKNOWLEDGEMENT i
ABSTRACT ii
Chapter one Introduction 1 1.1. General introduction 1 1.2. Literature review 3 1.2.1. Trace and macro elements 3 1.2.2. Soil analysis 3 1.2.3. Sediment analysis 5 1.2.4. Plant analysis 7 1.2.5. Fish analysis 8 1.2.6. Water analysis 9 1.2.7. Environmental Analysis 11 1.3. Analytical methods 13 1.3.1. Atomic Absorption Spectrometry 13 1.3.2. Flame Photometry for determination of sodium and potassium 14 1.3.3. X-ray Fluorescence Spectroscopy 17 1.3.4. Colorimetry 19 1.3.5. Ultra Violet Spectrometry 21 Chapter two Experimental 23 2.1. Sample collection 23 2.1.1. Area of collection 23 2.1.2 Sampling 23 2.1.2.1. Water samples 23 2.1.2.2. Sediments 1 23 2.1.2.3. Plants 24 2.1.2.4. Soil 24 2.1.1.5. Fish 24 2.2.2. Soil pH determination 26 2.3. Analysis 26 2.3.1. X-ray Fluorescence Spectroscopy 26 2.3.1.1. Procedure 26 2.3.1.1.1. Solid samples 26 2.3.1.2. Water samples 28 2.3.1.2.1. Reagents 28 2.3..1.2..2. Procedure 28 2.3.2. Atomic Absorption Spectroscopy 29 2.3.2.1. Sapmle preparation for AAS 29 2.3.2.1.1. Soil and Sediments 29 2.3.2.1.2. Plants and fish 29 2.3.2.2. Standard preparation 30 2.3.2.3. Measurement 30 2.3.3. Colorimetry for total phosphorus determination 30 2.3.3.1. Reagents 30 2.3.3.2. Measurements 31 2.3.4. Flame Photometry for the determination of potassium and sodium.... 3 2 2.3.4.1. Reagents , 32 2.3.4.2. Measurements 32 2.3.5. Ultra Violet for the determination of iron 34 2.3.5.1 Reagents 34 2.3.5.2. Procedure 34 Chapter Three 38 3.1. Measurements 38 3.1.1. XRF measurement 38 3.1.2. AAS measurement 39 3.1.3. Flame Photometry 43 3.1.4. Colorimetry 43 3.1.5. Ultra Violet Spectromerry 43 3.2. Analysis 44 3.2.1. Soil analysis 44 3.2.2. Sediment analysis 53 3.2.3. Plant analysis , 63 3.2.4. Fish analysis 71 3.2.5. Water analysis 76 Conclusion 82 References 84 ACKNOWLEDGEMENT
Praise be to Allah, He by His Grace deeds of righteousness are completed. I would like to express my sincere thanks and gratitude to my Supervisor Dr. Ali Hamoud Ali for his fine and dedicated supervision of this thesis. My thanks are also conveyed to my Co-supervisor Dr. Mohammed Ahamed Hassan Eltayeb, for his utmost help and encouragement through out the course of this work. My thanks are also due to the Atomic Energy Commission (Sudan) for making their facilities available for me at all stages of this work. My thanks are conveyed to the Chemistry Department at the Faculty of Education U. of K. and also to the Physics Department, Faculty of Science, U. of K. My thanks, at last, to my friends Dafalla A. Hassan, Mohamed A. Elmalih and Yassir A. Abdu who stood behind me to finish this work ABSTRACT
This work was performed to evaluate the environmental pollution at the Blue Nile (BN) and White Nile (WN) around Khartoum state. Samples of soil, sediments, plants, fish and water were collected from the studied area and analyzed. The concentrations of some elements (K, Ca, Ti, Mn, Fe, Cr, Co, Cu, Ni, Sr, Rb, Na, P, Zn, Br, Y, Zr and Pb) were determined using the following analytical methods; atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), flame photometry, colorimetry and ultra violet spectrometry (UV). The data obtained was compared with the data from literature The data was statistically analyzed to compare the results obtained by the different methods. The results of most elements determined by more than one method were significantly similar. The statistical analysis together with the chemical analysis revealed that the soil and sediments of the BN and WN are significantly different. The extent of pollution was determined by calculating the enrichment factors. The enrichment factors in sediments were calculated using both Fe and Ti as reference elements where values were almost equal. Some elements were slightly enriched at some sites but not to a degree to indicate a serious pollution. The accumulation of elements in plants as a clue for pollution was also calculated. Some elements; P,Cu and Zn were accumulated. The elemental concentrations in fish and water were not that high but water was still higher than the WHO recommended concentrations.
11
Introduction 1.1. General introduction:
The place where we live and interact with the different living organisms and non- living things can be defined as the environment, the components of which are : i - The lithosphere (rocks and soil) is the reservoir of salts necessary for plants and animals in limited amounts. ii - The hydrosphere i.e. the water, fresh or saline has a vital role in dissolving these salts and transporting them. iii - The biosphere or plants and animals. The former consumes these salts in making food, so salts which are dissolved in water are uptaken by plants which are eaten by animals. iv - The atmosphere or the air we breath, holds all the volatile substances and gases that result from the combustion of fuel or reactions in the environment.
These environment components exist in a natural sort of balance but when human beings interfere this balanced system can be disturbed. Many interactions affect the environment to a great extent resulting in exposing the life of man to risk of pollution.
Anthropogenic activities as a result of industry and urbanization affect the environment. Hutton et cr/.(l) estimated the quantities of trace elements inputs to the land in the UK as a result of human activities that include use of articles containing the element, iron and steel production, fuel consumption, cement industry, phosphate, municipal waste disposal, sewage and sewage sludge disposal in tons per year, Cd (899), Pb (48361), Hg (113) and As( 1530).
In Khartoum state the main Nile and its two main branches the Blue and White Niles are the main sources of water used for drinking, cooking, industry, irrigation and many other usages. The silt carried by the water is either laid out at the banks or settled at the bottom as sediments. The salts poured into this water or at the shores can reach man through the different food chains i.e. via meat, milk, cereals, vegetables or water. Local people have the habbit of pouring wastes without pretreatment, these wastes in addition to those resulting from traffic, fertilizers and pesticide use, car wash and sewage all ad^ to the hazards of pollution in the environment.
In this study samples of water, plants, sediments, soil and fish were collected from stations at the Blue Nile (BN) and White Nile(WN) within the boundaries of Khartoum state in order to assess the impact of human activities that add to the hazards of pollution in the environment. These locations include a power station, industrial area, river transportation, brick burning place (clinks), traffic affected locations and waste dumping areas. The objectives of this study are:
1 - Establishment of background baseline data for pollution levels. 2 - Assessment of the anthropogenic activities that affect the environment components under study. 3-The impact of such activities as waste dumping, sewage discharge, traffic, car wash and fertilizers on the biota living on the aquatic ecosystem. 1.2. Literature review 1.2.1. Trace and macro Elements Trace analysis may be quantitatively defined as determination of constituents making less than 0.01 % of a sample. Some of these trace elements are essential for living organisms which need them in very small amounts. When they exceed the need of the organism they become toxic and hence hazardious. The lower limit of a trace concentration is zero, but practically the lower limit is set by the sensitivity of the available analytical methods and in general is pushed downwards with the progress of ana1ysis(2) while macro elements constitute more than 90 % of the dry weight of the sample. These trace elements are essential for the growth of plants so they can reach man directly through eating plants or indirectly by meat or milk. They can also reach him through water or air. The samples under study include soil, plants, sediments, fish and water. Some of the previous data and literature are given below.
1.2.2. Soil Analysis
Soil is the sink of salts and therefore one of the sources of nutrients to plants. In so being it is related to food chains and highly affects the health of man. Yousif et alQ) investigated soils from central Sudan using XRF. He determined the concentration of K, Ca, Mn, Cr, Fe, Ti, Ni, Cu, Zn, Rb, Sr, Y and Zr. Irene et al.w also used XRF for the determination of V, Cr, Ni, Cu, Zn and As in soil using Ga as an internal standard. They corrected for the overlap between V and Ti, where the Ka lines of V superimpose on KP lines of Ti. To correct for that Kp / Ka for Ti was calculated from V free standards, then the (Ka of V) x Kp / Ka was subtracted from the V value. Shapiro et al.(5) determined K and Na in soil by flame photometry. Kane(6) analyzed soil for Cu, Zn, Ni, Co, V, Cr, Cd, Ba and Sr utilizing both flame and electrothermal atomic absorption. Othman(7) used A AS for the determination of Fe, Ca, Mg, Na and K in clays collected from Khartoum area. He separated the free iron oxides by weak acid extraction and showed that most of the Fe was part of the structure of the clays i.e. not free oxides. He also determined Fe by Mosbaeur spectroscopy. Again Fe was determined colorimetrically by chelation with cyanide. He also used XRF for the determination of Ti, Fe and Ca in the clays. Vogel(8) stated that Fe can be determined by its reaction with the thiocynate. The concentration of P2O5 as avaiable P was determined in soil by Hegemann et al. (9) by the reaction with molybdovandate. Bates et al°0) determined P in some Nigerian soils colorimetrically using molybdate for total P and molybdovandate reaction for available P. They found that the concentration in the surface is higher than the deeper soil. Abdurahman(11) analyzed soil from Bagair in Khartoum outskirts using flame photometry for the determination of Na and K. She used AAS for determination of Fe, Zn, Ca, Mg and Cr. P was determined colorimetrically using the molybdenum blue method. She correlated the elemental concentration in the soils to the pH values where she concluded that the pH had a negative correlation with Mn, Ca, Na and K in plants. Proctor et al°2) had already recorded high levels of Cr in soils from tannery sites. Eltayeb et al.(13> determined Sr in soil from the Nuba mountains in Sudan by XRF where they found the concentration to range between 85.7-1485.6 ppm. Fleming et #/.(14) found that Zn signal in a solution with high Fe concentration is increased when determined by AAS. The concentration of Pb is also high in soil samples. Juan et al{15) concluded that Fe and V increase the Pb signal by 17 to 106 % respectively. Goldschmidt(16) found an average of 1 % Ti with ordinary soil. He also stated that Ti is resistant to weathering processes and is usually associated with clay fractions. Kubota(l7) stated that the normal Co content of surface soil ranges between 1-40 ppm with the highest frequency in the 3-15 ppm interval. He also added that soil throughoutthe world contains Ni within the broad range from 10-100 ppm while the range at the USA was <5-200 ppm. Beckett el (?/.(l8) stated that the application of sludge and certain phosphate fertilizers may be an important source of Ni. Hassona (19) analyzed soil from Elguneid scheme (Sudan) using XRF and AAS and determined the concentrations of some elements Br, Co, Cr, Mn, Ni, Cu, Zn, K, Ca and Ti. He measured Na by flame photometry. Elidirisi (20! analyzed soil from the BN around Khartoum state for Mn, Fe, Co, Ni, Cu, Zn and Pb by AAS.
1.2.3. Sediment
Trace elements in sediments are of two origins*21}: i - geochemical or lethiogenic origin which result from weathering processes and include elements such as Rb, Sr and Zr. ii - antliropogenic origin which includes elements that are enriched by human activities such as Cr, Cu, Zn, Cd, Hg and Pb. Mn and Fe belong to the second group and by their own accumulation can cause other elements to accumulate i.e. scavengers. Their distribution in sediments is mainly controlled by redox conditions. Lu and Chen(22) carried out experiments to quantify the effect of environmental conditions and sediment types on the long term migration of soluble species. They concluded three trends: i - an increase of the released amount of Fe and Mn for progressively reducing conditions. it - an increase of the released amount of Cd, Cu, Ni, Pb and Zn as the environment became more oxidant. iii - no significant change in the concentration of Cr or Hg.
The reason of the release of Fe and Mn in reducing environment while other elements concentration increase might be due to the formation of sulfide solids. Under aerobic conditions the metallic sulfides might yield higher solubility solids (Cd, Cu, Ni, Pb and Zn) while the solubility of Mn may be decreased by the oxidation states or lower solubility oxides and hydroxides. The formation of H2S in sediments makes it reducing and so the mobility of metals is controlled by the metal sulfide solubility. Metals forming less soluble sulfides e.g. Cu2S with Ksp — 2.0E- 47, C11S with Ksp = 8.5E-45, PbS with Ksp - 3.4E-28 and ZnS with Ksp = 1.6E-24 remain fixed in sediments whereas metals which have more soluble sulfides such as FeS with Ksp = 6.3E-18 and MnS with Ksp =7.0E-I6 should be relatively mobile. Forstner(23) concluded that these processes are controlled by bacterial activity and subsequent complex formation than by ion migration since the calculated stability constant for the sulfide compounds are usually exceeded by concentration of these heavy metals in the pore water(24) . Holmes(25) had found that summer creates an oxygen poor environment which causes challophillic elements to precipitate meanwhile during winter the turbulence created by the strong winds causes the water to be aeriated and oxidizing resulting in a remobilization of some metals. During summer the microbiological activities increase causing an increase in sulfide and decrease in oxygen resulting in the deposition of sulfides of some elements e.g. Zn, Cd, Cu and Ni. On the contrary during winter the sulfides are oxidized and the soluble oxides are released and removed by the current. The study of the sediment's fraction < 63 |Lim has been widely used for some intercomparisons by Fostner and Salmons(26) for the following reasons : i - natural or anthropogenic trace metals are mostly associated with clay and silt size particles as these fine particles are richer in oxide / hydroxide of Fe and Mn coating scavengers of trace elements. ii - this fraction is equivalent to the suspended and deposited material from suspension partially incorporated in the bottom sediment i.e. the average metal content in the fraction < 63 (j.m of the sediment is comparable with that of the suspended matter. iii - the amount of performed studies made in sedimentary material < 63|nm from different areas allow valuable comparison. Dillon et al. (27) found that acidification affects the Pb accumulation in fresh water sediment by altering the sedimentation + mechanism which reduces Pb 2 t]ll1s stable Pb retention in the acidified lake.
1.2.4. Plant Analysis Hasso et al(2i) used XRF for the analysis of contaminated and uncontaminated tropical plants, where they found that concentration of K or Ca below 0.3 % wt does not affect noticeably the intensity of Mn lines while the intensity of Zn, Cu and Fe lines are not influenced by K or Ca concentration below 0.75 % wt. At higher concentrations absorption by the two elements occurs. Hutton(29) also used XRF for plant analysis and compared the results with the chemical analysis results where a good agreement was found. Eledrisi(z0) analyzed plants from the Blue Nile area at Khartoum using AAS for determination of Fe, Mn, Co, Ni, Cu, Zn and Pb concentrations. Abdurahman(11) analyzed plants from Bagair at a tannery site, a textile site and a natural site to study the effect of industry on the concentration of elements. She analyzed P colorimetrically, Na and K by flame photometry while she used AAS for Cr, Mn, Fe, Ca and Mg. She found high elements concentration at the industrial sites with a pronounced high Cr at the tannery site. Adam(30)analyzed sorghum grown in Gezira (Sudan) and found it to contain concentrations of Cu, Fe, Zn and Mn within the range commonly reported for plants. He also found that Fe concentration in sorghum does not reflect the availability of Fe in Gezira soil but the greater affinity of Fe to chelate. Blias(31) found four levels of P in different species of plants. He also found the roots to contain more P than the stem. Hayati et a(.^2)m England and Yahia(33) in Sudan found that the relationship between the uptake of an element by plant and its concentration in soil is limited. Greville et al. (34) compared two species of plant sludge Deroceras reticulatium and Arisonsui subfuscus for their tolerance to Zn, Cd and Pb where the average for the control group was Pb (2.8 - 3.3 ppm), Cd (7.3 - 7.4 ppm) and Zn (229 -373ppm) respectively. The average for the contaminated group was Pb (139 - 375 ppm), Cd (59.4 - 46.4 ppm) and Zn (651 - 733 ppm). Hassona (l9) determined some elements in sugarcane at Elguneid scheme then calculated the accumulation factors where the values were P (219), Cu (14.5), Mn (9.8), Cr (52.7) and Zn (32.7), where he attributed the accumulation of these elements to the use of fertilizers and pesticides.
1.2.5. Fish Analysis
Benemarya et al.(35) analyzed Tilapia in lake Tanganyika using HNO3 / HCIO4 for digestion and AAS for analysis where Cu range was 0.9-5.5 ppm , Zn was 15.5-147 ppm and Se was 1.3-2.1 ppm. Lowe et al.(16) in two successive seasons analyzed fresh water fish for Zn and Cu and gave the ranges 7.7-168.1 and 0.29-38.6 ppm respectively. The concentrations of Zn and Cu were determined in Tilapia Niloticus in lake Maryut (Egypt) by Elnabawi et al{37) found it to be 39.0 and 15.4 ppm
8 respectively. Khan el al.{n) determined trace elements in marine fish at the bay of Bengal and found the following ranges of concentrations in ppm, K (2720-11693), Ca (249-7961), Mn (1.89-7.4), Fe (37.9-388.0), Ni (2.7-15.2), Cu (0.65-58. l),Zn (26.0-93.8), Rb (2.00-21.6) and Sr (9.06-16.0). Sharif et al (3g) also determined elements in the flesh of marine fish from the Bay of Bengal by AAS after digestion with HNO3 / HCIO4 where they found the following concentrations in ppm Ca (4431-31046), K (7035-12347), Fe (60.55-454), Zn (18.86-33.89), Cu (3.333- 4.688), Ni (6.439-7.575), Pb (1.672-2.561), Sr (15.75-80.75), Rb (3.38-27.85) and Mn (5.005-11.144). The discrepancy in their results was due to the different locations they worked at.
1.2.6. Water Analysis
Water analysis is very challenging due to the low concentrations of elements so they are susceptible to interelement interferences and matrix effect. Alkali and alkaline earth elements and counter ions associated with do greatly interfere. Therefore the XRF analysis of water requires the preconcetration of elements in water samples. Selective precipitation is not necessary, thus nonspecific multielement reagents are appropriate. Therefore coprecipitation and broad spectrum precipitation have been combined with XRF. Carbamates are used for the determination of trace elements in water due to the low solubility of their metal che1ates(40) . Luke(4l) used sodium diethyl dithiocarbamates (NaDDTC) to preconcentrate trace elements in water at pH 4 in presence of a suitable metal spike serving as a carrier and an internal standard. He had determined Ni, Co, Cu, Hg,Pb, Fe, Zn and Cd at pH 4 but not Mn. He concluded that when working with an amphoteric elements like Zn the excess of ammonia should not be added otherwise incomplete recovery will result. He also added that Cr (VI) precipitates at pH 4 as carbamates while Cr (TFT) as hydroxide. Under et of. (42) stated that dibenzyl ditbiocarbamates (DBDTC) was the best coprecipitating agent of all dithiocarbamates due to the low solubility of its complexes that it needed no metal carrier. Quantitative recoveries were found by Ulrich and Hopke(43) for Mn, Fe, Co, Ni, Cu, Zn, Se, Sb, Hg, Cd and Pb with detection limit around 1 ug/g for 100 ml sample using ammonium pyrrolidine dithiocarbamates (APDC). They added that (APDC) is a convenient coprecipitant, at concentrations below 10 u,g/L, more than (NaDDTC) especially for Zn and Pb. They also found adequate recoveries for Fe, Ni, Cu, Se, Pb, Zn, Hg, Cd, Ti, Cr and Th independent of the alkaline ion concentration level . Elder et al.(44) had earlier precipitated at pH 2 with fresh (APDC) solution and obtained good recoveries for Cu, Hg and Pb though not for (45) + Mn or Zn. Pradznski and coworkers used (APDC) and Fe 3 as a carrier and reported a detection limit of 1 ^ig/L for V, Cr, Mn, Cu, As, Se, Hg and Pb. Pik et_al. (46) used (APDC) as a coprecipitant together with Mo as a carrier. They used Mo which is a 4d element for two reasons, the carrier element present in gross amount can not be determined after coprecipitation so Mo is suitable when 3d elements are analyzed. Moreover the characteristic x-ray emission of Mo does not interfere with the most sensitive lines of the specified anaiyte elements. Elkhatim (47) used (APDC) together with methylisobutylketone for the extraction and quantitative determination of Pb, Cd and As in water from the Nile and other parts of Sudan using AAS. She also determined Na and K by flame photometry. Other elements, Cu, Zn, Fe, Ni, Cr, Mn, Ca and Mg were determined directly using AAS. Leyden et al.(18) studied the interferences in coprecipitation with (APDC) where they found Fe to have a positive interference to Cr, but Cu and Cd had negative interferences to it. Fe, Mn and Cd had negative interferences while Pb had a positive interference to Co.
10 Calcium, Cr, Fe, Co, Zn, Cd and Pb had negative interferences to Cu. Zn was found to have a positive interference by Fe and a negative interference by Cu. Some researchers had analyzed water directly using A AS. For instance Chamarro et al.(49) found the concentration of Ca to range from 0.76 jig/g to 108.4 jug/g using AAS, but with flame emission the range was found to be 0.59-109.9 ng/g. Motomizaef
1.2.7. Environmental Analysis
The environmental awareness became a great issue nowadays that concerns all the inhabitants of this planet and many studies had been carried out to see how the n concentrations of elements increase due to human activities and whether it may reach levels to affect human life through food chains. Some of these studies can be mentioned. Scoullos(55) determined lead in sediments from the gulf of Elefesis near Athens where he found a concentration range of 500-600 ppm in industrial areas but the concentration dropped to about 40 ppm in non-industrial areas. He used AAS after HF/ HNO3 digestion of < 61jxm size sediment. The Pb / Zn ratio proved that they were from the same origin. The correlation coefficient between these elements showed that they came from the same origin. Hoffman et af56) analyzed water and plants to monitor pollution. Roland et a/.(57) had studied pollution in seals detecting Cd, Hg, Se, Pb and Cu using AAS. Mcneilly et a/.(58) investigated Pb and Zn in soils and vegetation from North Wales. Richard et 1) studied the variation in Texas marine sediment with seasons. Elhassan(C2) had analyzed chemical effluents from tanning activity for biological oxygen demand, chemical oxygen demand, sulfide, chromium and ammonium salts. His results indicated that Cr and S~2 were found to be the most hazardous pollutants. Alsenoy(63) analysed sediments for heavy elements in the Scheldt Estuary using XRF and AAS, then she measured the extent of pollution by calculating the enrichment factors taking Fe as a reference element. She concluded that Zn, Cd, and Pb were enriched in the industrial area, a fact she attributed to anthropogenic
12 factors. Lyngby e 1 al (64) studied the background and contaminated area sediments in Denmark, the following concentrations were obtained Cd(6.2,18.7), Cu( 153,369), Hg(0 6,1.9), Pb(16l,370), Zn(1013,2100) in ppm for background and contaminated sediments, respectively. Atchison et of. (65} found that the blue gills with the highest concentration of heavy metals were from the environment with high concentrations of heavy metals in water in two Indiana lakes. Brown et al(W)) found a high relation between the distribution of elements in sediments and the concentrations of these elements in non-migratory fishes from lake Ontario. Saleh et of.^7) found that Pb unlike other trace elements had a bioaccumulation tendency in fish flesh.
T.3. Analytical methods:-
The techniques that are most extensively used for the determination of inorganic pollutants in the environment are :
1.3.1. Atomic Absorption Spectrometry:-
It is an elemental analytical method based upon the absorption of electromagnetic radiation by the atomic vapour of elements. The characteristic radiation of a certain element emitted by an appropriate source is absorbed by the vapour containing the atoms being analyzed.
A reduction in the intensity of the radiation when it passes through an absorbing medium i.e. a sample appears. The degree of absorption is determined by comparing the intensity of the transmitted beam when no absorbing species is present i.e. a blank with that transmitted when the sample is present.
13 For a monochromatic collimated radiation passing through an atomic vapour, the reduction in the intensity of the incident radiation can be related to the concentration of the absorbing species and the thickness of the absorbing medium, both relations being combined in the Beer-Lambert law which has the mathematical formula :
L o g ~~ = sC I (U) ^ t where : I = incident radiation intensity. L = transmitted radiation intensity. e = molar absorbtivity or molar absorbance. C = concentration of the analyte. L = path length of the absorbing medium or celHength (cm ).
Log IQ/1 js known as the absorbance A. Hence equation (1.1) can be written as
A ~ sCl (i.2) In this method a calibration curve is made by measuring the absorbance of samples with known concentrations i.e. standards. The unknown concentrations of the samples can then be calculated after measuring its absorbance.
1.3.2. Flame Photometry for Determination of Sodium and Potassium :(68,69)
The basic principle is that when a solution containing a metallic salt (other metallic compounds) is aspirated into a flame e.g. propane burning in air, a vapour which contains atoms of the element may be formed. Some of these gaseous atoms may be
14 raised to an energy level which is sufficiently high to permit the emission of radiation characteristic of that element. The following processes occur in a rapid succession : 1- Evaporation of the solvent leaving a solid residue. 2- Vaporization of the solid will dissociate into its constituent atoms which will be initially in the ground state. 3- Thermal excitation of some atoms by the flame to higher energy levels and attain a condition in which they can radiate energy when they drop back to the ground level.
So the resulting emission spectrum consists of lines originating from excited atoms or ions. The transition from the excited to the ground state will result in the emission of a radiation of frequency ( v ) according to the equation :
A£ - Ei - Eo - hv = ~L (i.3)
where : Ej = energy of the excited state. Eo = energy of the ground state. h = Planks constant. v = frequency of the emitted radiation. c = velocity of light. X = wavelength of the emitted radiation.
Since the atoms of every element give definite characteristic line spectrum, so there are different excitation states associated with different elements. There are possible transitions between excited states resulting in a complex spectra.
15 The relation between the ground state and excited state population is given by the Boltzmann equation :
-A E I k T N. = N (1.4) where : Nj = number of atoms in the excited state.
No ~ number of atoms in the ground state
gj/g0 - ratio of statistical weights for ground and excited states. E ~ excitation energy. k = Boltzmann constant. T — temperature in Kelvin. Calculations showed that only small fractions of atoms are excited even under high temperature and low excitation energy. Table (1.1) shows the fractions of activated atoms at different temperatures (68, 69)
Table (1.1) Fractions of activated atoms of Na, Ca & Zn at different temperatures Element Line 2000O K 3000° K 4000Q K Na 589.0 ran lx 10-5 6 x 10-4 4x10-3 Ca 422.7 nm 1 x 10-7 4x10-5 6x10-4 Zn 213.9 ran 7.31 x 10-15 1.48x10-7
Emission spectra are complicated compared with absorption spectra. Thus atomic absorption is less prone to intereJement interference than flame emission spectroscopy (68), [n view of high proportion of ground state to excited state atoms,
16 it is clear that atomic absorption spectroscopy is more sensitive than the flame emission spectroscopy. The elements whose resonance line is concerned with low energy values are sensitive to flame emission spectroscopy than those associated with high energy e.g. Na with an emission line of wavelength 589.0 nm shows great sensitivity to flame emission spectroscopy than Zn ( 213.9 nm ) which is relatively insensitive.
1.3.3. X-ray Fluorescence Spectroscopy :(70)
This is a non-destructive multielemental method of analysis that depends on the production of different x-rays by different elements when they are excited by a source such as particles ( electrons, protons or ions ), some radioactive sources e.g. Cd-IO9> Fe-55 or a tube. When the target atom being excited absorbs an incident photon of energy an electron from ai-> i^^r shell is ejected (photoelectron ) and a vacancy results. An electron from ,<,*; outer shells will drop to fill this vacancy releasing an amount of energy equals to the difference in the binding energy of the two orbitals concerned with the electron transition. This energy is known as the x- ray characteristic of a particular element, thus XRF is a qualitative method of analysis in addition to its quantitative use. The absorption of x-rays in matter follows an experimental law which is :
1 — lot (1.5) where : I = transmitted intensity through thickness x cm. lo = incident x-ray intensity (photon / sec ).
mass attenuation coefficient ( cm2 / g ).
17 px - density ( g / cm2).
A simplified equation that relates concentration of intensity of radiation is: /,. = ((,' ,.K ,).T,.C ,.(/> d), (1.6) introducing the absorption factor 1 T * / ( P d)s where: aj = absorption coefficient for the element i.
(pd)s = density of the sample ( Gi.Ki) = sensitivity ( Si).
Equation (1.6) will become:
r - S , C , a , Thus the concentration can be related to the intensity of the x-rays by the following relation,
C, = j^-.o, (,.9)
It is clear from the above equation that the concentration is proportional to the intensity of the characteristic x-rays and therefore the intensity (counts/sec) is used for quantitative analysis. There are two approaches for the determination of the concentration of elements in the samples,
18 a) by determining the values of a," and Sj for the element then applying equation (1.9) b) by using standards of the same matrix with known concentrations of elements then matching that with the sample using the following equation, c c /, " /, (UO) where :
Cs, Cj = are the concentrations of standard and sample respectively.
Is» ]\ = intensities of standard and sample respectively.
This method of analysis suffers from some interelement problems like, i~ absorption problems. ii- secondary fluorescence where the x-rays of an element can excite some atoms of another with lower energy. iii- scattered radiation which results from the grain size effect.
Instrumentation
The main parts of the XRF spectrometer are : i- the primary beam source (in this work it is a radioisotope Cd 109, 25 mCi activity and half life 1.3 years ). ii- the detection system which is 30mm active area Si (Li) detector. iii- a multichannel analyzer to record the spectra. • ix - a computer for spectral analysis. 1.3.4. Colorimetry
Some elements complex with organic and inorganic ligands giving colored complexes that absorb in the visible region ( 400 nm-700 nm ).
19 When a monochromatic light passes through these colored complexes in a homogeneous medium part of it is absorbed. The colorimetric measurement consists of comparing under well-defined conditions the absorbance by a sample of unknown concentration with that by another with known concentration.This method is concerned only with the visible region. The absorption obeys Beer-Lambert law equation (1.1).
So the concentration of the unknown can be calculated using the formula,
A c C ' ~ si
20 1.3.5. Ultra Violet Spectrometry
It is the absorption of radiation in the UV or VIS regions of the electromagnetic spectrum that results in electronic transitions between molecular orbitals. The energy is relatively high corresponding to about 105 J mol"1. This is equivalent to a wavelength range of 200-800 nm or a wave number range of 12000-50000 cm" • All molecules can undergo electronic transitions but m some cases absorption occurs below 200 nm where atmospheric absorption necessiates the use of expensive vacuum instrumentation. The absorption in the UV and VIS obeys Beer-Lambert law equation (1.1). Iron is determined by its reaction with 1,10-phenanthroline to form an orange-red complex. This complex (C]2H8N2)Fe+^nas a stable color at pH range of 2-9. Below pH 2 the color is weak and develops slowly. The complex obeys Beer-Lambert law (1.1) in its absorption and remains unchanged for many months. The 1,10-phenanthroline is a weak base, in acidic solutions the essential species is the phenanthoium ion PhH+ so the complex formation reaction can be represented by the equation.
Fe+2 + 3 phH+ -> Fe(Ph)+2 + 3H+ The ferric ions in the sample can be reduced by hydroxlamine hydrochloride, sulfur dioxide or hydroquinone. The pH range is 2-9 but 3.5(73) is recommended to prevent precipitation of various ion salts like phosphate. The complex formed absorbs at wavelength 510 nm. Some elements are to be avoided e.g. Ag and Ba. Divalent ions that give stable complexes are to be avoided also or diluted to less than the concentration at which they do not affect. Some elements interfere (74) when they are higher than a certain limit, Cd (50ppm), Hg (Ippm), Zn (lOppm), Be (5()ppm),
21 W (5ppm), tungestafe decrease the color intensity, Cu (lOppm), Ni (2ppm), Sn+2(20ppm), Sn+4(50ppm), F" (SOOppm) if the pH > 4 and P (20ppm).
The instrument consists of a light source ( a deuterium lamp ), a wavelength selector, a sample container or cuvette, a radiation detector, a signal processor and a readout device.
22
CHAPTERJWQ
Experimental
2.1 Sample collection 2.1.1 Area of collection
Samples of water, sediments, plants, soil and fish were collected from nine stations at the Blue Nile and White Nile around Khartoum state between latitudes 14° 45'N and 16° 30'N, and longitudes 30° O'E and 33° 30'E, Fig (2.1). The area of the state is about 12416.25 km^ . The samples were collected in duplicate within a month interval between each sampling time in the period between May and June 1995. These locations were thought to be affected by different human activities such as farming, power stations, industry and traffic. These stations are numbered down stream at the map.
2.1.2 Sampling 2.1.2.1 Water samples
Water samples were collected in duplicate using plastic garicans of two liters capacity to which a stainless steel weight was tied to make it sink to a 0.3 -1.0 m depth. At the laboratory the water was filtered by a Whatmann filter paper 42 and its pH was measured using a calomel electrode and a pH meter Table(3.27). Two to three drops of HNO3 were added to maintain the pH at 1 to 2 so as to minimize sorption at the walls in addition to prevent the organisms activities, then kept in the dark.
2.1.2.2 Sediments Sediment samples were collected in duplicate using a stainless steel cup with holes at the bottom from about 1 m depth and kept in plastic containers. The samples were frozen then freeze-dried at - 40°c and at a pressure 40-60 mbar. The dry samples were sieved and the <63um size was refereeze-dried at the same conditions and kept in plastic containers.
2.1.2.3 Plants Plant samples were uprooted from the banks of the two rivers in duplicate. All samples were animal fodder Sorghum bicolor ( Abu Sabeen ) which is a Sudanese variety commonly used in central Sudan. At the laboratory the samples were washed with tap water then with distilled water and cut into small pieces with stainless steel knife. The plant was oven dried at 85°c for 72 hours to a constant weight. The dry pieces were minced using stainless steel mixer. The powder was kept in plastic bags.
2.1.2.4 Soil Soil samples from the root zones ( depth 0-20 cm ) of the plants were taken in duplicate with stainless steel knife in plastic containers. The soil was oven dried at 105° for 48 hours. The dry soil was ground in an agate mortar then kept in plastic containers
2. J.2.5 Fish Tilapia Niloticus fish samples were purchased from the fishermen at the collection stations (when possible). The fishes were bisected using stainless steel knife and the viscera were separated from the flesh. The flesh was freeze-dried at -40°c under a pressure of 40-60 mbar. The dried flesh was ground with an agate mortar and kept in plastic containers
24 Fig. (2|lSites of sample collection
1. Soba 2. Algerief 3. Green Village A- Burr! Power Station 5. River Transportation 6. Tutl 7- Gabal Awlia 8. Lamab 9- Khartoum Industrial
25 2.2.2 Soil pH determination About 10 g of the dry, sieved soil was placed in a beaker. 50 ml of distilled water was added and stirred for two minutes. The solution was left to stand for 15 min, then the pH of the supernatant solution was measured.
2.3 Analysis 2.3.1 X-ray Fluorescence Spectroscopy An energy dispersive X-ray fluorescence (XRF) spectrometer with a Cd-109 source with energy 22. IKev , a Si(Li) detector (ORTEC) with a resolution of 180 ev at Ka line of iron (Fe) with 6.4 Kev, MCA Camberra 35 plus, a preamplifier and an amplifier. A computer was used for the collection of the spectra and their analysis. Fig. (2.2) shows the XRF instrument setup.
2,3.1.1. Procedure 2.3.1.1.1. Solid samples About 1 g of the dry sieved solid sample of fish, plant, soil, or sediment was weighed accurately then pressed into a pellet of 4.9 cm^ area using a 10 tons pressing machine. The standards were prepared in a similar way. Each pellet was irradiated with CdlO9rayS. The time of collection for soil and sediment samples was 500 seconds while for plant and fish was 1000 seconds. The spectra were transferred to the computer. The software " Axil " package developed by the IAEA was used for the spectral analysis. The simple quantitative method of analysis that depends on equation (2.10) was employed to obtain the elemental concentrations. The standards, Lake sediment STM5 and Hay powder (V-10) were analyzed for the accuracy of the measurements comparing the certified
26 BiAS SUPPLY
Si-(Li) Detector PREAMP AMP
Liquid Nitrogen
Copper Rod
r-i
109 Fig. 2.2 X-ray spectrometer with Cd excitation isotopic source. values with our experimental values Tables (3.1 & 3.2). The results of the analysis of the different types of samples were obtained.
2.3.1.2 Water samples Analysis of water samples by XRF suffers from high scattering due to the low matrix elements. Thus usually analysis of water samples by this technique requires a preconcentration step prior to the analysis. In this study APDC was used.
2.3.1.2.1 Reagents 1- Ammonium pyrrolidine dithiocarbamates (APDC ) a 1% solution was prepared by dissolving lg of the solid in 100 ml of distilled water and the solution was filtered. 2- Ammonium molybdate, 0.322 g of the salt was dissolved in 500 ml of distilled water. 3- 10% nitric acid for the pH adjustment. 4- 10% ammonium hydroxide for the pH adjustment.
2.3.1.2.2 Procedure
Five portions each of 100 ml of the distilled water was transferred to a beaker then 2, 4, 6, 8ppm and lOppm from Zn, Cu, Co, Cr, Ni, Se, Fe, Pb and Mn were added to each beaker. The pH was adjusted to 4.4 (± 0.1). One ml of the molybdate carrier was added followed by 5 ml of APDC, then the solution was stirred for 30 seconds and allowed to stand for 30 min. The precipitate was filtered under suction through a Millipore polycarbonate filter paper with a pore size 0.45 \xm and 47 mm diameter. A blank was prepared similarly. The thin films were air dried. The filters were analyzed by the XRF spectrometer with the loaded
28 side towards the x-ray beam. The software " Axil" was used for the analysis of the spectra. The recoveries were obtained in percentages as in Table (3.27). The water samples were coprecipitafed in a similar way and the concentrations were determined.
2.3.2 Atomic Absorption Spectroscopy A Perkin Elmer model 1130 spectrometer was used for the analysis. It consists of a light source ( hollow-cathode lamp ), a burner, a monochromator, a detector which is a photomultiplier tube. The system was interfaced to a computer for the concentration calculations.
2.3.2.1 Sample preparation for A AS
The samples for AAS were in a liquid form to attain the homogeneity of the sample, therefore the solid samples should be brought into solution either by wet digestion using acids or dry ashing at high temperature then the ash is dissolved in acids. The wet digestion method was employed for sample preparation as follows:
2.3.2.1.1 Soil and sediments About 0.1 g of the dry sieved sample Avas weighed accurately and put into a Teflon beaker then 4 ml of HF was added. The beaker was heated on a sand bath for 10 min then opened and left to near dryness, then 3 ml of aquaregia was added and heated to near dryness. The beaker was washed with distilled water and filtered in a 50 ml volumetric flask then completed to the mark. About 0.1 g of the standard STM5 was similarly digested and prepared.
2.3.2.1.2 Plant and fish About 1 g of the sieved sample was weighed accurately in a beaker then 10 ml of A.R. nitric acid was added, covered with a watch glass and left overnight. The
29 beaker was henied gently on a rand brfh til? t'^e brown fumes ceased. About 3 ml of perchloric noid were added and the beaker vas reheated half covered to drive the white fumes of the ?cid. The beaker was washed with distilled water, filtered in. 50 ral volumetric flask and filled to the mark. About Ig from each of Hay Powder (V-10) and Freeze-dried animal Blood (A-13) were digested simiinrly.
2.3c2.2 Stomtorffs preparation The ?*mford stock solutions of Zn, Mn, Cr, Co, Cu, Ni, Fe and Pb were prepared by dissolving the appropriate amount of the respective metal salt, 4.3987 g of Z11SO4.7H2O, 2.8744 g of KM11O4, 2.8289 g of K^C^Oy, 4.9389 g of
Co(NO3)2.6H2O, 3.9295 g of C.USO4.5H2O, 4.9533 g of Ni(NO3)2.6H2O, 7.02 i 3 g of (NH4)2FeSO4 and 1.5983 g of Pb(NO3)2 in the minimum amount of mfric dcid in a 500 ml voiiwietric flask and filled to the mark with distilled water to prepare a 1000 ppm stock solution of respectively.
2.3.2.3 Measurement The spectrometer was set for each element. A series of dilutions of each element were prepared ?»nd the absorption for each was measured . In this computerized spectrometer f.'>e calibration curves were plotted automatically and the concenfraHons were calculated. The results for each type of samples and standard concentrations in the were determined
2.3.3 Colorim^try for total phosphor!*?! Th.e analysis for total phosphorus was carried for samples in solution which were already wet digested. 2.3.3.11 Regents 1- Phosphorus 1000 ppm stock solution was prepared by dissolving 0.4393 g of KH2PO4 in 1 L of distilled water. 2- Molybdate solution was prepared by dissolving an accurately weighed 6.25 g of (NH4)6Mo7O24.4H2O in 50 ml of warm distilled water. 70 ml of cone. su'furic acid was added to 100 ml of distilled water. The molybdate was filtered into the suJfuric acid then stored in the dark.
3- I g of metol was dissolved in 100 m! of distilled water and filtered to remove the insoluble part.
2.3.3.2 Measurements A colorimeter model Corning 40 was used for the measurement of phosphorus concentration. A series of 2.5, 5.0, 7.5 and 10 ppm were prepared from the stock solution in a 50 ml volumetric flask , 2 ml from molybdate and a similar portion of metol were added then made to the ro?rk with distilled water. The bottles were shaken vigorously and frequently for 10 min to develop the blue color. The absorbance was measured at 630 n.m after 30 min. Table (2.1) shows the absorbance of the standards from which the calibration curve figure (2.3) was plotted. The accuracy of the method was checked by analyzing the Hay Powder (V-10). A portion of 5 ml from each sample already digested (2.3.2.1 ) was transferred to a 50 ml volumetric flask then treated similar to the standards. The absorbance was measured for the different types of samples and the concentrations were calculated using the slope of the calibration curve. The percentage was obtained using the equation :
0/ _ C(mg) x solution volume(ml) ••'0 = 10 x aliquot (nil) x sample u eight(g) The concentration of P in.Hay powder (V-10) was measured. The concentration of P in the different group of samples were similarly determined.
Table (2.1) Concentration & Absorbance of phosphorus of the standards
F conc.( ppm ) Absorbance
0.00 0.00
2.50 0.045
5.00 0.087
7.50 0.127
10.00 0.172 The interference by Fe was checked by taking two samples in duplicate, to one of each sample excess of ammonium hydroxide was added to precipitate Fe(OH)3 while the other was not treated similarly. The solution was filtered then its absorbance was measured. The absorbance was found to be the same for the both samples. 2.3.4 Flame Photometry for the determination of potassium and sodium This method was used to detennine the concentrations of Na and K in all samples of soil, sediments, plants, fish and water. All of the samples were in solution.
2.3.4.1 Reagents 1- Potassium 1000 ppm stock solution was prepared by dissolving 1.9069 g of KC1 in I L of distilled water.
2- Sodium 1000 ppm stock solution was prepared by dissolving 2.5420 g of NaCI HI 1 L of distilled wafer.
3- Distilled water was used for all dilutions. 2.3.4.2 Measurements Flame photometer model Coming 410 which consists of a burner, filter and a propane fuel was used for analysis. A series of dilutions were made from the
3:1 stock solutions of Na and K and the corresponding emission intensities were measured. Tables (2.2) and (2.3) show the intensities the standards from which the calibration curves Fig (2.4) and (2.5 ) were made. The already digested samples were diluted, their intensities were measured and the concentrations were calculated.
Table (2.2) Concentration of potassium vs intensity Cone, of K ( ppm ) Intensity (arbitrary units ) 00.00 0.000 10.00 0.070 20.00 0.140 30.00 0.200 40.00 0.270 50.00 0.330 60.00 0.400
Table (2.3) Concentration of sodium versus intensity
Cone, of Na ( ppm ) Intensities (arbitrary units ) 00.00 0.000 05.00 0.040 10.00 0.080 15.00 0.110 20.00 0.150
The accuracy of the method was verified by the analysis of reference standard Freeze-dried blood (A-13). 2.3.5 Vltra VioJet Spectrometry measurements for the determination of Iron Iron was measured by this method in all samples under study which were in a liquid form.
2.3.5.1 Reagents 1- Hydroquinone : A 1 % solution was prepared by shaking one & of the compound with 100 ml iron free deionized water.
2- Sodium citrate : 250 g of the dihydrate salt were dissolved in 1 L of deionized water.
3- 1,10-phenanthroline : 0.5 % of the monohyrate salt was prepared in warm deionized water.
4- Concentrated sulfuric acid.
5- Hydrochloric acid for the pH adjustment.
6- Ferrous ammonium sulfate hexahydrate FeSO4(NH4)2.6H2O was used for the preparation of the iron standards by dissolving 0.0712 g in the minimum amount of nitric acid in a 500 mJ volumetric flask then completed to the mark to make 1000 ppm solution
7- Deionized water was used for all preparations.
2.3.5.2 Procedure
Standards of 0.5, 1.0, 1.5 and 2.0 ppm of Fe+2 were transferred to 100 ml volumetric flasks with 2 ml of H2SO4. The pH was adjusted to 3.5 by citrate or Hcl. About one ml from each of hydroquinone and 1,10-phenanthroline was added. The solution was left to stand for at least an hour time then the flask was filled to the mark with deionized water. The absorbance was scanned and the
34 maximum absorbance was found at X 507.2 nm. The absorbance of the standards was measured and a calibration curve was mnde Fig.(2.6). About five ml from the samples offish, soil, sediments and plants digest were treated similarly. Five ml of the acidified BN and WN water were analyzed in the same way. Then the absorbnnce wns measured Table (2 4).
Table (2.4) Absorbance of iron standards
Cone, (ppm) Absorbance 0.0 0.000 0.5 0.137 1.0 0.211 1.5 0.321 2.0 0.418
35 rij». ( 2.X ) Phosphorous consentration vp absorbanrc "v determined by colorimHr
4 6 8 10 Phosphorous concentration ( ppni )
Kig. ( 2A ) Potassium conr:pni.ration vs intensity as determined by flame photome
10 0 30 40 50 60 70 Potassium concentration ( ppm ) he. ( 2.5) Sodium concentration vs intensity as determined by flame photometry
4 fl 12 16 Sodium concentration (
Pig. ( 2.fi ) Iron Concentration vs Absorbance as determined by UV
0.
o
0.2 0.4 0.6 0.8 1 1.2 1,1 2.2 Concentration ( ppm )
37
ResultsLand Discussion
3.1 Measurements
The analysis was carried for all samples of soil, sediments, plants, fish and water using XRF, AAS, flame photometry, colorimetry and UV spectrophotometry.
3.1.1 XRF measurement
This technique was used to measure all of the elements under study except Na, P and Ni. Na and P are low atomic number elements which are difficult to measure using Cd-109 as a radioactive source but it Fe-55 was used P could have been measured. The Ni value appears to be near the detection limit of the system therefore valves determined for this element by XRF are not reliable.
The accuracy of the method was determined by analyzing a standard material lake sediment STM5 supplied by the IAEA. The comparison of the certified and experimental values (Table 3.1) show an accuracy of about 10 % for all elements except Ca, Fe and Rb with an accuracy of about 13 %.
Some elements when determined by this technique had fitting problems due to statistical reasons (software). The parameter that determines the extent of agreement between the expected value and the experimental one is the Chi- square (x) which is defined as :
X = J~ J— (3.1) where :
O = observed frequency and E =•• expected frequency. a value of X2= 0 - 1 signifies an exact agreement between the experimental and certified value but a large value indicates a poor agreement. For Cu, Zn and Pb the Chi-square value was greater than 2.1 indicating some fitting problems.
To check the accuracy of the technique for biological samples the analysis of the standard material Hay powder (V-10) which was also supplied by the AIEA was carried. The comparison of the certified and experimental values (Table 3.2) show about 10 % accuracy which is acceptable for this technique.
3.1.2 AAS measurement
The elements Fe, Mn, Cu, Cr, Co, Zn and Pb were measured by this technique. All solid samples were wet-digested, thus both the accuracy of the digestion and measurement were to be checked.
For soil and sediments a similar standard ( STM5), which was wet-digested, was analyzed. Table (3.3) shows both experimental and certified values. The accuracy was less than 10 % for all elements indicating that both digestion and measurments were reliable.
39 Table (3.1) Certified value as compared to measured concentrations in lake sediment STM5 By XRF Element Certified value Experimental value Accuracy (%) K % 1.04 1.00 ±0.24 4.0 Ca% 4.47 5.07 ±1.40 13.0 Ti% 1.11 1.07 ±0.29 3.6 Cr ppm 6.9 6.5 ± 0.3 5.8 Mnppm 1129 1213.3 ±341 7.5 Fe % 9.29 8.09 ± 2.22 13.0 Cu ppm 206 188.8 ±36.07 8.0 Zn ppm 63 69.1 ±10.5 9.7 Rb ppm 56 48.6 ±12.03 13.2 Srppm 660 641±176 2.9 Y ppm 29 30.5 ±8.4 5.2 Zrppm 104 112 ±27 7.7 Nbppm 40 36 ±7.2 10.0 Pb ppm 18 16.4 ±2 8.9
The biological standard Hay powder (V-10) was analyzed to check the accuracy of themethod A good agreement between the certified and experimental values was obtained (Table 3.4). The accuracy was within a 10 % range making it an acceptable.
40 Table (3.2): Certified value as compared to measured concentration for the Hay Powder (V-10) by XRF
Element Certified value Experimen. value Accuracy ( %) Ca % 2.16 2.10 ±0.3 2.8 Crppm 6.5 n.d. Feppm 185 195.7* 28 5.8 Cuppm 9.4 10.6 ± 2.0 17.0 Znppm 24 22.1 ± 2.8 7.9 Brppm 8 6.7 ± 0.7 16.3 Rbppm 7.6 6.9 ± 0.7 9.2 Srppm 40 37.1 ± 4.3 7.3 Pbppm 1.6 1.4 ± 0.3 12.5 Nippm 4 <5.4
When the XRF and AAS results were compared for elements determined by both methods, it was clear that the AAS results were more accurate. This is obvious since the AAS measurements are relatively free from interference, samples were homogeneous because they were in solution. For these reasons AAS results were given the preference.
41 Table ( 3.3 ) Certified value as compared to measured concentrations in lake sediment STM5 by AAS
Element Certified value Experimen. value Accuracy(%) K % 1.04 1.02±0.20 1.9 Crppm 6.9 7.0 ± 0.4 1.4 Mnppm 1129 1133.5 ±230 0.4 Fe % 9.29 9.15 ±1.30 % 1.5 Cuppm 206 208 ±31 0.1 Zn ppm 63 62.1 ±10.5 1.4 Coppm 44 48 ±2.3 9.1 Pbppm 18 19.6 ±1.5 8.9
Table (3.4) Certified value as compared to measured concentration for the Hay Powder (V-10) by AAS
Element Certified value Experimen.value Accuracy (%) Ca % 2.16 2.14 ±0.3 0.9 Crppm 6.5 6.8 4.6 Feppm 185 189.7 ± 22' 2.3 Cuppm 9.4 10.0 ± 1.2 6.3 Zn ppm 24 22.6 ± 2.3 5.8 Pbppm 1.6 1.49 ± 0.2 6.9 Nippm 4 4.2 ± 0.6 5.0
42 3.1.3 Flame photometry This technique was used to measure Na and K in all digested samples and water. The accuracy of the method was checked by the analysis of a standard material which was a Freeze-dried animal blood (A-13) where a good agreement between the experimental and certified values was reached (Table 3.5). The accuracy was less than 10%.
Table(3.5) Concentrations of K & Na in the Freeze-dried animal Blood (A-13)
Element Certified value Experimental value K (ppm) 25000 22500 Na (ppm) 15000 15385
3.1.4 Colorimetry The total P was measured by this technique. The accuracy of the method was determined by the analysis of the standard material Hay powder (V-10) where a high accuracy was achieved (Table 3.6). No Fe interference was found. Table(3.6) Certified value as compared to measured concentration of P in Hay powder (V-10)
Element Certified value Experimental value P (ppm) 2100 1965
3.1.5 Ultra Violet spectrophotometry This technique was used for the determination of Fe in all samples under study. The maximum absorbance was found to be at 507.2 nm while the literature value
43 was 510 nm which may be due to an instrumental setting. The accuracy of the method was checked by the analysis of both STM5 and the Hay powder (v-10) standards. An accuracy of about 5.7 % for the standard STM5 and 3.8 % results were obtained thus the certified and experimental values were in a good agreement (Table 3.7). Table (3.7) Certified values as compared to measured concentration of Fe byUV
Element certified value experimental value Fe (in STM5) 9.29 % 8.76 % Fe (in Hay powder) 185 ppm 178 ' ppm
3.2 Analysis 3.2.1 Soil Analysis The soils at all stations of the BN and WN were found to be alkaline (Table 3.8) The pH ranges were found to be 8.20 - 8.80 and 8.00 - 8.10 for the BN and WN stations at Khartoum state, respectively. The concentrations of the alkali elements Na and K were high and the slight difference of pH values between the two groups of stations may be due to the slight difference in the average concentrations of Na and K which were found to be Na (0.69 %) and K (0.86 %) at the BN station and Na (0.67%) and K (0.70 %) at the WN stations (Table 3.11). Hassona (19) reached to similar results for pH values, Na and K contents at Elguneid soil which is so close to the BN soil at Khartoum state since they both belong to the same valley of the BN.
44 Table (3.8) The BN & WN Soil pH
Station 1 2 3 4 5 6 7 8 9 PH 8.80 8.75 8.40 8.50 8.60 8.20 8.10 8.00 8.10
The XRF results for the soil of the BN and WN at Khartoum (Table 3.9) show that the concentrations of almost all the elements were high at the BN stations, a fact may be attributed to the origin of this clay soil which was derived from the Ethiopian blataeu, and coarse particles of the Nubian sandstone formation and basement complex as stated by Yassin(75). The concentration of Ti was constant at all stations of each group. This result is similar to what Goldshmidt(16) concluded about Ti as weathering resistant, so its concentration was always constant. The AAS results (Table 3.10) of soil analysis generally show a higher elemental concentrations at the BN than the WN stations, a trend similar to what was found by XRF technique, a fact may be attributed to the origin of the soil.
45 Table (3.9) Mean & range of elemental concentrations in soil by XRF
Element BN WN Mean Range Mean Range K % 1.03 0.94-1.26 0.73 0.85 - 0.64 Ca % 3.94 3.22-4.50 1.45 1.13-2.05 Ti % 1.82 2.1 -1.39 0.88 0.78 - 0.95 Fe % 10.39 9.10-11.2 5.30 3.90-6.10 Mn ppm 1514 1206-1742 654 609 - 706 Cr ppm 50.82 32.6-95.7 38.04 28.00 -48.07 Co ppm 55.08 44.30-92.10 23.37 18.50-26.50 Cu ppm 70.02 56.00 - 84.00 67.93 57.60 -80.70 Zn ppm 107.18 89.50-124.80 120.67 80.70-199.30 Br ppm 07.51 04.70 -9.13 06.10 05.00 - 06.80 Rb ppm 37.05 29.40 -46.70 44.20 38.40 - 48.00 Sr ppm 271.48 226.00-302.00 193.17 176.90 - 206.00 Y ppm 32.58 28.90 - 35.90 28.63 28.10 -29.10 Zr ppm 103.68 100.40-109.50 146.67 111.00- 191.00 Pb ppm 32.07 24.60 - 39.50 52.33 40.00 - 60.40
46 Table (3.10) Mean & range of elemental concentration in soil by AAS Element BN WN Mean Range Mean Range Fe % 8.38 3.43-11.34 3.92 3.02-4.54 Mn ppm 1523 920 - 2500 507 420 - 590 Cr ppm 89.67 5.8 - 158.1 71.67 52.6-105.8 Ni ppm 61.95 75.2-47.9 46.73 40.2-51.5 Co ppm 92.77 33.7-128.4 36.7 32.9-41.3 Cu ppm 52.9 23.3-90.7 45.0 36.4-51.6 Zn ppm 198.82 295.6-151.0 142.9 104.3-206.6 Pb ppm 77.12 42.8-114.9 49.67 25.3 - 65.7
When the XRF and AAS results are compared for the elements measured by both analytical methods, the concentrations of all elements were comparable by both techniques except Zn and Pb. A T-test was performed to compare the AAS and XRF results for elements determined by both techniques and a significant difference was found between Co, Zn and Pb while the values for Fe, Mn and Cu were significantly similar. The high concentrations of Zn and Pb especially at the BN stations may be related to the high Fe concentration there as was already reached by Felming et al(14) and Juan etal(15) but at the WN stations Cu, Fe, Mn, Pb and Zn were found to be equal while Co was again different. The T-test was also carried to compare the elemental concentrations at the BN and WN stations. The test revealed that the elements of lethiogenic origin; Ca, Co, Fe, Mn, Sr, Ti and Y were significantly different in the two areas while those of anthropogenic origin; Pb, Zn, Cr and Cu were not significantly different. The results of AAS were taken for comparison with data from literature for those elements measured by both methods.
47 Table (3.11) Mean & range of K , Na and P concentrations in soil ( in % ) Element BN WN • Mean Range Mean Range Na 0.6888 0.3906-0.9918 0.6685 0.6276-0.7182 K 0.8644 0.4622-1.7245 0.7015 0.4685 - 0.8772 P 0.6833 0.3799-1.2663 0.4332 0.2587-0.7684
The XRF and flame photometry results for K (Fig. 3.1) were almost identical for both groups of soil samples indicating a reliable measurement When comparing of Fe concentrations by XRF, AAS and UV (Fig. 3.2) a reasonable agreement at both areas of study was obtained. The slight difference between the AAS and UV results may be due to the time interval between the two measurements as was reached by Willis et al(76) who found a discrepancy between the AAS and colorimetric results which he reasoned for a month interval between the two measurements while in this study there was a three months time gap between the AAS and UV measurements. Phosphorous was measured colorimetrically. The average elemental concentrations for the BN and WN stations can be seen in Fig. (3.3). The results of this study when compared with those reached by Hassona(19 J who worked in Enguneid scheme, a similarity is observed between his results and the results of this study from the BN stations at Khartoum, except for Co, Cu,Zn and Ni concentrations which are high at BN, because both soils under study belong to the same origin. The results from the WN stations in this study show an agreement in Co, Cu and Ni concentrations. The difference in P concentration is due to the fact that in Hassona's study available P was measured while in this study the total P was determined.
48 The results reached by Yousif et ai (3) showed a slight difference from this study.This may be because he made his analysis using only XRF technique and his samples were from different parts of central Sudan while this study was confined to a small area. Table (3.12) Comparison of results of soil analysis with data from literature
Element BN WN Hassouy) Yousif*J) Elidrisi1*" Bon(77) Vin1"" K ppm 10300 7300 11110 14000 13600 Cappm 39000 14000 25290 10000 13700 13700
Mn ppm 1523 506 896 781 816-1516 850 850
Cr ppm 89.7 71.7 259 43 70 200 Fe ppm 84000 39000 53770 65000 33000-94000 38000 38000 Ti ppm 18000 8800 11187 10000 4600
Co ppm 92.8 36.7 88 40.8-104 8 8
Ni ppm 62 46.7 41 75 41.3-72 40 40 Cuppm 53 45 45 23 25-78.3 20 20
Zn ppm 199 143 72 34 40.8-106 50 50 Br ppm 7.5 6.1 11 5 5.0
Rb ppm 37 44 65 100 100
Sr ppm 271 193 140 300 300 Y ppm 32.5 28.6
Pb ppm 77.1 49.7 19.8-149 10 10
Zr ppm 343 490 337 >• 300 P(ll) ppm 7100 4200 801
Na(1)ppm 8300 6600 8060
K(1) ppm 10400 7300
(ll) = determined by coiorimetry. (l) = determined by flame photometry.
49 Fig (3 1a) Potassium concentration as determined by XRF & Flame Photometry in the soil from the BN
46%
54%
C3 K (XRF) HK(fl.phot)
Fig (3.1b) Potassium concentration as determined by XRF & Flame Photometry in soil from the WN
49%
51%
EH K (XRF) • K(fl.phot) Fig. (3.2 a ) Fe concentrations in soil from the BN as determined by AAS, XRF & UV
31% 35%
34% • AASi • UV !
Fig. (3.2 b ) Fe concentrations in soil from the WN as determined by AAS, XRF & UV
24%
43%
/
0XRF HAAS • UV ! 9 Fig.(3.3) Average elemental concentrations in soil from BN &WN JT7 8 7 6
;Ss 5 TO =i 4 ID O c o O
D Blue Nile K Ca Ti Mn Fe E White Nile Element
300
250
& 200 o "I 150 0) o 100 c o O 50- •Blue Nile 0- •White Nile stations because she worked in the same area of the BN around Khartoum state. All results of this study were within the ranges of her results. The Data from Bowen(77) and Vinogradov(78) have a good agreement with the results of this study except for Zn, Co and Cu which were high in the Nile around Khartoum a fact that may be due to the nature of the Nile soil being rich with elements.
3.2.2. Sediment Analysis
All sediments samples (< 63 jum size) were analyzed by the techniques employed in this study. A T-test was again done to compare the results of XRF and AAS results for sediments (Table 3.13 and 3.14) respectively where Cu, Co, Cr, Fe and Mn were significantly similar, but Zn and Pb were significantly different. The high Fe concentrations may had affected Zn and Pb signals(I4>15) . The elemental concentrations in the two areas were compared by the T-test that showed no significant difference in the concentrations for the elements which are of lethiogenic origin; Fe, Mn, Ca, Rb and Sr were significantly different while those of anthropogenic origin; Cr, Cu, Co, K, Pb and Zn were not different. The averages of K concentration determined by flame photometry were in a good agreement with the results obtained by XRF for both types of sediment samples Fig.(3.4). The P was measured colorimetrically (Table 3.15).
53 Table (3.13) Mean & range of elemental concentrations in sediments by XRF Element BN WN Mean Range Mean Range K % 0.91 0.5-1.12 0.79 0.51-1.11 Ca % 3.97 2.89-4.50 1.53 0.72 - 2.05 Ti % 1.85 1.62-2.03 0.92 0.41-1.33 Fe % 10.45 9.97-11.27 5.25 1.24 - 8.43 Mn ppm 1495 1316-1933 815 273 -1437 Cr ppm 57.15 31.8-119.2 44.45 29.8-52.1 Co ppm 47.72 40.2 - 57.4 38.8 29.0-45.3 Cu ppm 74.1 51.5-96.6 62.3 44.1-77.1 Zn ppm 101.4 89.70-114.0 116.4 66.0-187.7 Br ppm 8.85 5.5 -15.2 8.15 2.8-11.95 Rb ppm 33.35 31.3 -37.3 46.5 33.5-57.52 Sr ppm 287.1 234.6 - 320.0 221.8 209.6-231.2 Y ppm 31.5 30.0 - 34.2 29.8 17.4 -41.7 Zr ppm 134.1 93.7-240.4 139.8 124.4-156.0 Pb ppm 29.65 16.4 - 46.1 41.1 19.1 - 64.7
The Fe was determined by UV in the sediment samples and when compared with the XRF and AAS results they were identical Fig. (3.5).
The comparison between the elemental concentrations for the BN and WN stations (Fig. 3.6) shows higher elemental concentrations at the BN a fact may be attributed to the origin ofthe silt ofthe BN which is derived from the origin ofthe BN i.e. the Ethiopian blataeu.
54 Table (3.14) Mean & range of elemental concentrations in sediments by AAS Element BN WN Mean Range Mean Range Fe % 9.17 8.03-11.75 3.01 1.64-4.22 Mnppm 1627 1210-2620 667 270 -1330 Cr ppm 113.5 62.3 - 164.7 182.6 55 - 344.8 Ni ppm 78.75 59.1-115.7 56.7 51.3-67.4 Co ppm 83.0 36.3-177.5 40.95 21.5-60.4 Cu ppm 45.9 16.7 - 92.7 30.2 9.8-66.0 Zn ppm 217.5 154.3-270.2 216.8 358.5-83.4 Pb ppm 77.43 54.7-119.6 42.7 10.9 - 70.0
Table (3.15) Mean & range of K , Na and P in sediments Element BN WN Mean Range Mean Range Na % 1.02 0.14-1.38 0.85 0.64-1.21
V 0/ IV /0 0.82 0.33-1.01 0.75 0.50 - 0.95
O 0/ r^ / 0 0.40 0.11-0.64 0.52 0.44-0.52
When the results of this study are compared with the results from the Schledt * river(62) at the North Sea (Table 3.16), the concentrations of K, Cr, Zn and Pb were higher at Scheldt than their concentration in this study, this may be a result of the pollution at the Schledt river since it i° an industrial area. On the other 55 hand the concentrations of Ca, Ti, Mn, Ni and Cu were higher at the BN stations, a fact may be related to the origin of the silt of the BN. The results reached by Othman(7) who analyzed clay soil (<63 jim size) from the BN and WN around Khartoum state are quite similar to the results reached for K, Ca, Ti, Na and Fe by this study (Table 3.16). The international mean of elemental concentrations in sediments(79) around the world is less than the concentrations at the BN and WN around Khartoum state. The difference may be due to the fact that the international mean is for a number of different places all over the world while this study was confined to an area suspected of being polluted as a result of some human activities. The time factor should be considered as the international standard was determined along time ago. The contribution of sources other than the soil crust to the measured element concentration in sediments is measured by a factor known as the enrichment factor (E.F) which was defined by Zollar et al(80) for element X by :
(X f Fe) E.F(X)= sediment {XIFe),oll ™ When the value of the E. F. is > 1 there is an enrichment of that element compared to the average earth crust concentrations. Depending on the source, contribution to the measured elemental concentration can be said to be enriched from anthropogenic source i.e. pollution or a natural source. The element to be taken as a reference element should be : 1 - of high concentration in soil and rock. 2 - a very small pollution source. 3 - easily determined by a number of analytical techniques. 4 - free from contamination during sampling.
56 Fig. (3.4 a ) Potassium concentration as determined by XRF & Flame Photometry in sediments from the BN
47%
53%
• K(xrf) • K(fl.phot)
Fig. (3.4 b ) Potassium concentration as determined by XRF & Flame Photometry in sediments from the WN
49%
-' j 51%
BK(xrf) • K(fl.phot.)
57 Fig. (3.5a) Fe concentration in sediments from the BN as determined by AAS, XRF & UV
31% 36%
V
33%
Fig (3.5b)Fe concentration in sediments from the WN as determined by AAS, XRF & UV
18%
54%
28%
58 Fig.(3.6) Average elemental concentrations in sediment from BN & WN 10 9 8 7 c o 6 5 rat l 4 41 U 3 o o 2 1- r\ '. Na BBlue Nile E White Nile
300
250 I 200 •S 150
100 o O
D Blue Nie E White We Co Cu Ni Br Rb Pb Zn Zr Table (3.16) Comparison of results of sediments analysis with literature data Element BN WN Schledt(W) Othman(/) Mean sed.(79) K ppm 9000 8000 15000 8000(10000) Cappm 40000 15000 2000 - 7000 29000(20000 ) 66000 Ti ppm 19000 9000 2800 11000(11000) Fe ppm 92000 30000 64000 83000(72000) 41000 Nappm 10000 9000 9000(15000) Mnppm 1627 666 940 770 Cr ppm 114 183 220 70 Co ppm 83 41 14 Ni ppm 79 58 31 52 Cu ppm 50 30 24 33 Zn ppm 218 217 260 95 Pb ppm 77 43 100 19
Table (3.17) shows the enrichment factors for sediments taken from the different locations. It can be seen that Na is enriched at station 7 where vehicles are washed with different types of soap, at station 4 which is Buri power station, and at station 2 that has no seen source of Na enrichment a condition may be a natural process. P is enriched at station 7 , at station 8 where the White Nile tannery wastes were used to be discharged and at station 9 where the industrial wastes are dumped. Mn is slightly enriched at station 2 where brick clinks are there. Cr is slightly enriched at station 2. Co is enriched at station 4 and at station 7. Zn is enriched at all the WN stations, a fact may be explained as a natural phenomena. Generally elements are not enriched to indicate a serious
60 pollution condition. Goldschmidt(16) argued that Ti is among the most abundant elements in the rock(4400 ppm) which is the parent of soil (4600 ppm). It and a number of its common compounds are insoluble so it would make an acceptable reference element if data for Si, Al and Fe were not available though it is difficult to determine by many techniques. Alsoney found a constant Ti concentrations in the sediments of the Schldet (63) (0.25 %). The enrichment factor using Ti as a reference element was calculated (Table 3.17). When E.F. values using Fe and Ti as reference elements are compared it is seen that they are almost similar. An explanation for that may be the strong relation between Fe and Ti in soil. The correlation factor between Ti and Fe was found to be (p= 0.00) in both sediments and soils of the BN and WN.. Table (3.17) The enrichment factors for sediments
St. K Ca Ti Fe Na P Mn 1 1.2(0.8) 1.4(0.9) 1.6 (0.6) 2.0(1.3) 1.3(0.8) 1.0(0.6) 2 0.8(0.7) 1.0(0.9) 1.1 (0.9) 1.4(1.3) 0.1(0.2) 1.8(1.6) 3 1.2(1.1) 1.1(1.1) 1.0 (1.0) 1.5(1.5) 1.0(1.0) 1.2(1.0) 4 0.8(1.0) 1.2(1.3) 1.0 (1.1) 2.2(1.3) 1.2(4.3) 0.3(0.3) 5 0.7(0.6) 0.8(0.8) 1.0 (1.0) 0.2(0.2) n.d. 0.2(0.2) 6 0.3(1.0) 0.3(0.7) 0.3 (3.7) 1.0(0.6) 0.7(0.8) 0.1(0.3) 7 2.0(1.4) 1.7(1.2) 1.5 (0.7) 5.7(3.8) 20(3.0) 0.3(0.2) 8 1.6(0.8) 1.3(0.9) 1.4 (0.7) 1.3(0.9) 13(9.1) 0.1(0.1) 9 1.0(0.9) 1.2(1.1) 1.0 (1.0) 0.7(0.7) 7.7(8.3) 0.4(0.4)
61 St. Ni Cu Zn Br Rb Sr 1 1.4(0.9) 2.0(0.3) 1.0(0.7) 1.7(1.0) 1.3(0.8) 1.4(0.9) 2 0.8(0.7) 2.0(1.8) 1.0(0.4) 1.2(1.2) 0.5(0.5) 1.0(0.8) 3 2.4(2.4) 0.8(0.7) 1.2(1.2) n.d. 1.2(1.2) 1.2(1.2) 4 1.0(1.0) 0.6(0.7) 1.0(1.1) n.d. 0.7(0.8) 1.2(1.4) 5 1.0(1.0) 0.7(0.7) 1.1(1.0) n.d. 1.4(1.3) 1.0(1.0) 6 1.0(1.3) 0.4(1.5) 0.5(1.7) n.d. 0.3(1.1) 0.3(1.0) 7 1.0(0.9) 0.7(0.5) 2.2(1.6) 1.0(0.9) 2.4(1.7) 1.6(1.7) 8 1.0(1.3) 0.4(0.3) 2.5(1.7) 2.0(1.4) 1.2(1.0) 1.7(1.0) 9 1.2(1.2) 1.0(1.0) 1.2(0.7) 1.4(1.4) 0.9(1.0) 0.8(0.8)
St. Co Cr Y Zr Pb 1 1.1(0.7) 1.3(0.8) 1.5(1.0) 1.6(1.0) 1.2(0.7) 2 0.4(0.7) 7.8(7.5) 0.7(1.7) 1.8(1.7) 0.8(0.8) 3 0.6(0.6) n.d. 1.0(1.5) 2.7(1.5) 0.5(0.7) 4 4.0(0.4) 1.7(1.9) 0.8(0.9) 1.0(0.9) 1.2(1.4) 5 0.5(0.5) 0.6(0.7) 1.0(1.1) 1.0(1.1) 1.5(1.5) 6 0.2(0.8) 0.6(2.0) 0.3(1.1) 0.3(1.1) 0.5(1.6) 7 2.8(1.9) 2.0(1.8) 1.6(1.7) 2.0(2.7) 0.5(0.4) 8 0.9(1.0) 0.9(1.0) 1.4(1.0) 1.5(1.0) 0.2(1.1) 9 1.2(1.2) 1.2(1.2) 1.0(0.7) 0.7(0.7) 0.5(0.5)
( ) = E. F. using Ti as a reference element n.d. = not detected
62 3.2.3 Plant Analysis: The XRF results of the elemental concentrations for Sorghum bicolor (Abu Sabeen) samples (Table 3.18) and the AAS results (Table 3.19) were compared using a T-test; Fe, Mn, Pb and Zn were significantly equal in the BN and Fe and Pb were significantly different in the WN. The T-test for the elemental concentrations for the samples from the two areas were significantly similar. The concentration of Zn was high by AAS which may be as a result of interference fromFe(14-l5). The mean values for the concentration of K determined by XRF and flame photometry were identical for both groups of samples (Fig. 3.7). The concentrations of Fe measured by XRF, AAS and UV spectrometry were almost similar (Fig. 3.8). Table (3.18) Mean & range of elemental concentrations in plants by XRF Element BN WN Mean Range Mean Range K % 2.62 3.50-1.90 1.80 1.50-2.30 Ca % 0.92 0.40- 1.90 0.73 0.50-1.20 Fe ppm 518.88 255.6-823.0 1533.3 1167 - 2039 Mnpm 57.22 39.2 - 76.2 57.93 47.2 - 64.3 Cuppm 30.42 18.2-48.7 25.57 19.8-28.5 Zn ppm 44.78 35.0-55.6 84.1 48.4-122.5 Br ppm 20.93 6.6 - 39.6 5.77 5.0-7.2 Rbppm 9.93 5.8-14.8 3.87 3.0-5.6 * Sr ppm 50.05 32.7-79.3 25.1 19.8-32.7 Pbppm 1.5 1.0-2.4 1.27 1.2-1.4
63 Table (3.19) Mean & range of elemental concentrations in plants byAAS
Element BN WN Mean Range Mean Range
Cr ppm 10.22 3.6-21.4 13.6 10.4-18.3 Mn ppm 80.0 40.3-117.0 41.4 22.1-54.3 Fe ppm 561.1 289 -1003 840.7 680,-978 Co ppm 2.12 1.3-2.8 2.43 2.1 - 2.8 Ni ppm 3.6 1.6-6.2 5.2 1.6-10.2 Cn ppm 17.6 10.0-23.2 21.8 17.6-26.3 Zn ppm 51.0 10.6-68.2 37.2 10.3-76.5 Pb ppm 4.2 1.7-9.0 3.5 2.6-4.4
Table (3.20) Mean & range of K , Na and P in plants
Element BN WN Mean Range Mean Range Na % 0.29 0.18--0.46 0.27 0.19-•0.33
K % 2.05 1.44--2.79 1.85 1.20--2.51 P % 0.37 0.19-•0.52 0.27 0.15-•0.44
Table (3.21) and Fig.(3.9) show the comparison of the elemental concentrations in the plants of the BN and WN stations. The Fe concentration in the plants from the WN was higher than that of the BN plants though its concentration in the soil of the BN was higher. This could be attribiu-d to the soil mineralogy composition at the two sites, in the clay soil of the BN Fe maybe chelated as was reached by Othman (7) thus being not available for the uptake by plants. Burstorn (tU) reported that Mg and Ca had negative effect upon Fe physiological processes in plants, similarly Ca was found to be higher in the BN than the WN and the concentrations of Fe was higher in the WN than the BN. Hayati et al(12) in England and Yahia (33) in Sudan found that the relationship between the uptake of an element and its concentrations was limited. Similarly elements that have the capability of forming complexes Co, Ni, Cu and Cr were also higher at the WN plants than those of the BN though their concentrations in the WN soil samples were low. The reason may also be in the clay soil where chelation limits the bioavailability of the elements. The results reached by Elidrisi(20) who worked in the BN around Khartoum state were compared with the results from the BN in this work (Table 3.21) where a good agreement was noticed. A difference in the concentration of Co can be seen. The concentrations of elements in the plants of the WN were compared with the results from Omdurman(20) where the agreement was moderate a fact which may be attributed to the different geographical locations.
The accumulation factor which has the same definition as the enrichment factor was calculated for the plants (Table 3.22) where P was highly accumulated in both the BN and WN plants, Cu and Zn were moderately accumulated and the remaining elements were not.
65 Table (3.21) Comparison of results of pl?»nt analysis with literature data Element BN WN ElidrisP^ Omdur12^ K ppm 26200 18000 Ca % 9200 7300 Fe ppm 561.1 841 47-2455 ' 134-3345 Mnppm 80 41.4 7.6-162 13.9-91.0 Cr ppm 10.2 13.6 Co ppm 2.1 2.43 0.003-0.63 .007-0.6 Ni ppm 3.6 5.2 0.07-4.8 0.4-4.4 Cu ppm 17.6 21.8 2.4-15.0 2.9-18.8 Zn ppm 51 37.2 6.6-48.9 11.2-36.5 Br ppm 20.93 5.8 Rb ppm 9.93 3.9 Sr ppm 50.05 25.1 Pb ppm 4.2 3.5 4.5-19.0
66 Table (3.22) accumulation factors for plants
Station P Mn Cr Co Ni Cu Zn Pb
1 182 23 12 10 11 76 100 33
2 30 4 144 5 6 40 193 3
3 253 23 20 4 13 95 106 9
4 233 2 21 0.05 8 156 47 6
5 572 3 14 4 21 74 61 30
6 87 1 9 1 2 9 2 1 average 226 9.3 37 4 10 75 84 14
7 172 1 13 3 4 49 43 9
8 209 0.04 10 4 2 17 6 4
9 345 1 11 2 8 14 3 1 average 242 1 11 3 5 27 17 5
67 Fig. (3.7 a ) Potassium concentration as determined by XRF & Flame Photometry in plants from theBN
44%
V.'J 56%
• K (xrf) HK (fl.phot.)
Fig. (3.7 b ) Potassium concentration as determined by XRF & Flame photometry in plants from theWN
49%
51%
HK(xrf) UK (fl.phot.)
68 Fig (3 S a ) Fe concentrations in plants from the BN as determined by AAS, XRF & UV
32% 33%
35%
Fig. (3 8 b ) Fe concentrations in plants from the WN as determined by AAS, XRF & UV
23%
49%
28%
69 Fig (3.9) Average elemental concentrations in plants from BN & WN
o
at u c oo
Fe • Blue Nile m White Nile
Q. a o 2 +* a> u oc o
Co Cu Ni Br Rb Pb • Blue Nie Element ffl White Nile 3.2.4 Fish Analysis
The concentrations of elements by XRF Table (3.23) in samples offish from the BN and WN show high concentration of K, Cu, Rb and Pb in samples from the BN compared to the WN, Br and Ca show equal concentrations but Zn and Fe were high at the WN. The AAS results (Table 3.24) gave high Cr, Fe and Cu at the BN where Mn, Co, Ni, Zn and Pb were high at the WN. The concentrations of K by XRF and flame photometry were similar (Fig. 3.10). The concentrations of Fe by AAS, XRF and UV spectrometry were identical. The results of Fe, Zn and Pb were nearly similar by both AAS and XRF but Cu was high by XRF.
The elemental concentrations in fish samples from the two areas were compared by a T-test where the concentrations of Co, Cr, Cu, Mn, Ni, Pb andZn were found to be significantly similar while Fe was significantly different in the two groups.
When the data for fish from Eastern Africa (was compared with this study : Mn, Fe, Cu and Pb were high for fish from the Nile at Khartoum but Zn was comparable. The concentration of
Mn, Fe, Cu, Zn and Pb were all higher in Khartoum than Lake Victoria, Kenya. Zn in Tilapia Niloticus from Egypt(47) which was found to be 15.4 ppm were in a good agreement with the concentration of Zn in this work.. The concentrations of Zn and Cu in Lake Tanganyika were lower than the concentration of the two elements in this study. When these results were compared with those of the marine fish(48'49) , the difference can be clearly observed where Ca, Fe, Mn, Ni and Rb were high at the marine fish but Pb, Zn and Cu were similar.
71 Table (3.23) Mean & range of elemental concentration in fish by XRF
Element BN WN Mean Range Mean Range K % 1.48 1.23-1.80 0.97 0.80-1.14 Ca % 0.57 0.44 - 0.66 0.57 0.44 - 0.79 Fe ppm 293.5 238.0 - 359.0 321.0 231.0-411.0 Cu ppm 39.3 24.3-67.3 34.2 24.8-43.6 Zn ppm 26.8 15.8-46.1 38.6 37.7-39.5 Br ppm 9.6 6.5-12.6 9.4 7.7-11.0 Rb ppm 11.4 8.5-15.7 6.4 6.0-6.8 Pb ppm 4.6 4.2-4.6 2.7 2.3-3.0
Table (3.24) Mean & range of elemental concentration in fish by AAS
Element BN WN Mean Range Mean Range Cr ppm 15.7 4.8-27.1 15.4 4.8-51.6 Mn ppm 4.2 0.5-6.5 5.5 3.3-9.9 Fe ppm 299.2 203.0-430.0 216.8 190.0-237.0 Co ppm 3.3 1.1 -5.9 3.6 1.9-5.2 Ni ppm 6.6 2.8-11.0 6.9 0.9-16.5 Cu ppm 3.8 2.7-5.7 3.6 1.8-5.8 Zn ppm 37.4 29.2-41.7 58.5 27.7 -107.8 Pb ppm 3.9 1.9-5.3 5.3 2.2-7.5
72 Table (3.25) Mean & range of K, Na and P in fish
Element BN WN Mean Range Mean Range Na % 0.33 0.30-0.37 0.40 0.34-0.51 K % 1.4 1.30-1.60 1.38 1.01 - 1.67 P % 0.42 0.32 - 0.49 0.23 0.09 - 0.49
Table (3.26) Comparison of results of fish with literature data
BN WN eas.Afr.(82) Saad(83) L. Victr(*2)
K % 1.48 0.97 Ca % 0.57 0.57 Mn ppm 4.2 5.5 0.7-1.8 0.1-0.7 Cr ppm 15.7 15.4 0.5-4.7 Fe ppm 299 217 3.8-5.4 257 Co ppm 3.3 3.6 Ni ppm 6.6 6.9 Cu ppm 3.8 3.6 0.2- 2.0 23 0.2-0.5 Zn ppm 37.4 58.5 2.2 - 22 59 2.2- 7.0 Br ppm 9.6 9.4 Rb ppm 11.4 6.4 Pb ppm 3.8 5.3 0.2-1.1 0.4-1.1 Na % 0.33 0.40 P % 0.42 0.23
73 Fig (3.10 a ) Potassium concentration as determined by XRF & Flame Photometry in fish from the BN
49%
51%
EK(xrf) HK(fl.phot)
Fig. (3.10 b ) Potassium concentration as determined by XRF & Flame Photometry in fish from the WN
41%
59%
EK(xrf) • K(fl.phot.)
74 Fig (3.12) Average elemental concentrations in fish from BN & WN
1.6 /Z7 1.4 1.2 g 1 0.8 - & ] > 0.6 Io 1 O 0.4 - 0.2 0 Na K Ca Fe • Blue Nile Element E White Nile
60
50
Ea. a. 40 c 30 ati o *~ "S o 20 o O 10 • Blue Nile E White Nile 0 Co Cu Ni Br Rb Pb 3.2.5 Water Analysis :
Table (3.27) shows the recoveries of elements from water which was spiked with the elements under study. The recoveries of Mn were low at pH 4, a similar result was reached by Eltayeb(84) who found that the precipitation of Mn started at pH 8 and was completed at pH 11. The high recoveries of Zn and Cu may be due to poor fitting at the low concentrations. The other elements showed reasonable recoveries, thus making this method of coprecipitation a reliable one. Table (3.27) The percentage recoveries of elements using APDC
Element 2ppm 4ppm 6ppm 8ppm lOppm Cr 100 64 31 47 23 Mn 62 47 35 15 15 Fe 109 101 97 79 65 Co 82 104 99 85 79 Ni 81 50 60 53 57 Cu 110 105 100 90 85 Zn 110 101 107 100 95 Se 63 60 52 62 88 Pb 110 91 104 79 80
The water under study was found to be alkaline (Table 3.28). No variation between the BN and the WN stations were observed. The analysis revealed that there was a high concentration of K and Na in both areas.
76 Table(3.28) water sample pH values
Station 1 2 3 4 5 6 7 8 9 pH 7.95 7.95 8.00 8.00 8.05 8.05 7.50 8.10 8.30
In Tables (3.29) and (3.30) of the XRF and the AAS results respectively where a good agreement between the concentrations of Fe, Ni and Cu was obtained while Co was low by AAS. Zn was high by the XRF a fact may be attributed to fitting problems in the analysis or to some impurities in the blank (distilled water). The concentration of Pb by XRF was high. This may be reasoned as a calibration problem in the sensitivity of the L-lines of Pb in the system which might not be accurately calculated or performed. The range of K concentration in both flame photometry and AAS were almost similar while the range at the BN was different. When the elemental concentration at the BN and the WN were compared (Fig. 3.13), Fe was high at the BN while Cr, Cu, Co, Na and P were high at the WN. The data determined by the National Chemical Laboratory, Khartoum (54) in the eighties showed a good agreement with this work for Na and K while the concentration of Pb have increased since then. The results reached by Elkhatim(47) for drinking water from the Nile is comparable with this work. When these results of the environmental water and the maximum allowable limits set by the WHO(85) were compared, the levels of concentration of the Nile water was much higher.
77 Table (3.29) Mean & range of elemental concentrations in water by XRF
Element BN WN Mean Range Mean Range Cr ppm 0.7 0.5-0.9 2.4 0.6-3.2 Fe ppm 9.3 0.4-20 8.1 0.2-10.9 Coppm 0.5 0.2-0.8 1.0 0.0-2.0 Ni ppm 0.3 0.1-0.4 0.3 0.0-0.5 Cuppm 0.4 0.2-0.7 0.2 0.1-0.3 Zn ppm 0.5 0.1-1.4 0.9 0.1-1.7 Seppm 0.15 0.1-0.2 0.15 0.0-0.3 Pbppm 1.4 0.1-5.3 0.85 0.4-1.3
78 Table (3.30) Mean & range of elemental concentration in water by A AS
Element BN WN Mean Range Mean Range K ppm K>.03 ±3.4 2.5-11.0 10.50 ±0.6 9.9-11.0 Fe ppm 1C1.03 ±2.1 0.03 - 48.4 08.00 ±3.0 5.9-11.4 Co ppm 00 08 ±0.06 0.01 - 0.24 00.44 ±0.13 0.31-0.57
Zn ppm 00 11 ±0.06 0.03 - 0.22 00.17 ±0.02 0.15-0.18 Cu ppm 00 31 ±0.13 0.12-0.44 00.55 ± 0.02 0.52 - 0.57
Ni ppm 00 41 ±0.15 0.17-0.56 00.80 ±0.1 0.72 - 0.93 Pb ppm 00 02 ±0.00 0.00 - 0.02 00.03 ± 0.01 0.02 - 0.04
Table (3.31 ) Mean & range of elemental concentration of Na, K and P in water
Element BNile WN Mean Range Mean Range Na ppm 29.4 17.5-57.0 34.3 31.0-37.5 K ppm 5.2 3.6-13.5 , 12.5 5.4-18.9 P ppm 1.0 0.4-1.3 2.0 1.1-2.7
79 Table (3.32) Comparison of results of water analysis with data from literature Element BN WN Elkhatim(40) WHO(S6) Cr 0.7 2.4 0.05 Cu 0.31 0.55 0.35 1.5 Co 0.08 0.44 Fe 10.03 8.0 0.907 1.0 Ni 0.41 0.8 0.525 Zn 0.11 0.17 0.017 15 Pb 0.02 0.03 0.05 0.05 Se 0.15 0.15 0.01 K 5.2 12.5 5.0 Na 29.4 34.3 21.0 P 1.0 2.0 pH 8.0 8.0 <9.2>6.5
80 Fig. (3.12 ) Average elemental concentrations in water from the BN & WN
Se Blue Nile White Nile
E B'.ue Nile Jonclusion rhe comparison of the analytical results obtained by XRF and AAS for elements determined by both methods showed good agreement with the exception of Zn and Pb indicating that the data was reliable. The results of the analysis of elements determined by flame photometry, colorimetry or UV spectrometry were also comparable. The soil and water of the BN and WN were both alkaline according to the pH measurements. Generally, the elemental concentrations of soil and sediments from the BN were higher than the WN. The plants of the WN have the elements slightly concentrated than those of the BN. No great variation in the elemental content of fish or water between the two areas of study were observed. The average elemental concentration order was: soil : Fe > Ca > Ti > K > Na > P > Mn > Zr > Sr > Zn > Co > Cr > Pb > Ni > Cu > Rb > Y > Br sediments: Fe > Ca > Ti > K > Na > P > Mn > Sr > Zr > Zn > Cr > Co > Ni > Pb > Cu > Rb > Y > Br plants : K > Ca > P > Na > Fe > Mn > Zn > Sr > Cu > Br > Rb > Pb > Ni > Co fish : K > Ca > P > Na > Fe > Zn > Cr > Rb > Br > Ni > Mn > Cu > Pb > Co water : Na > Fe > K > P > Cr > Ni > Cu > Zn > Se > Co The comparison of the average values of soil and sediment analysis with data reported by other workers revealed a good agreement with data from Sudan
(19,7,20) ^ some differences were found when comparing the data of this work with the international data (77J8J9'63) The extent of pollution was determined by calculating the enrichment factors in sediments where some elements were slightly enriched at some sites. The accumulation factors in plants showed that some elements were accumulated by
82 factors other than soil or water. The data for fish analysis showed no high elemental concentration at the BN or WN either. The comparison of the water analysis data with the WHO guidelines showed that the concentrations many elements were slightly high. Generally we can conclude that the extent of pollution with heavy metals at the BN and WN around Khartoum state is not a serious environmental problem so far but still more samples are required to be analyzed annually to establish a rich base-line data.
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