Trace Elements in Saanich Peninsula Agricultural Soils 1
TRACE ELEMENTS IN AGRICULTURAL SOILS OF SAANICH PENINSULA, VANCOUVER ISLAND, BRITISH COLUMBIA, CANADA
By
LEKHNATH GHIMIRE
M.Sc., Tribhuvan University, 1999
A thesis submitted in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in ENVIRONMENT AND MANAGEMENT
We accept this thesis as conforming to the required standard
...... Dr. Matt Dodd, Thesis Supervisor Royal Roads University
...... Thesis Coordinator School of Environment and Sustainability
...... Michael-Anne Noble, Director School of Environment and Sustainability
ROYAL ROADS UNIVERSITY
September 2012
© Lekhnath Ghimire, 2012
Trace Elements in Saanich Peninsula Agricultural Soils 2
Abstract
The concentrations of trace elements in 30 Saanich Peninsula agricultural soil samples were determined by acid digestion and inductively coupled plasma – optical emission spectroscopy
(ICP-OES). A comparison of the results obtained to a 1995 BC Ministry of Environment data indicated that As, Cu, Mo, Sb, Se and Sn concentrations had increased whereas the concentrations of Ba, Be, Cd, Cr, Co, Mn, Ni, Pb, V and Zn had decreased. The principal sources of the trace elements were anthropogenic sources including fertilizer and manure application, weathering of rocks and atmospheric deposition. The concentrations changes were largely influenced by the individual properties of the elements, soil texture, soil organic matter and clay content. The mobility of the trace elements in the soils was mainly controlled by clay content and followed the order Cd> B >Mo> Cr> V> Zn> Se> Co> Cr> As> Ba> Sb> Mn> Ag, Be, Hg, Ni,
Pb.
Key words
Trace elements, agricultural soils, biogeochemical cycles, weathering of rocks, phosphate fertilizer, soil pH, clay and organic matter, bioavailability and mobility
Trace Elements in Saanich Peninsula Agricultural Soils 3
Table of Contents Abstract ...... 2
List of Figures ...... 5
List of Tables ...... 6
List of Appendices ...... 6
Acknowledgements ...... 7
Introduction ...... 8
Trace Elements...... 8
The Biological Essentiality and Toxicity of Trace Elements ...... 8
Sources of Trace Elements in Agricultural Soils ...... 10
Elements of Concern (EOC) in Agricultural Soils ...... 12
Scope of the Study ...... 13
Research Questions ...... 14
Literature Review and Background ...... 15
Trace Elements in England and Wales’ Farms ...... 15
Trace Elements in Chinese Agricultural Soils ...... 15
Trace Elements in USA Farms...... 16
Trace Elements Contaminations in Canadian Farms ...... 17
Trace Elements in Saanich Peninsula Farms ...... 19
Geology and Soil Type of Saanich Peninsula Farms ...... 20
Mobility and Bioavailability of Trace Elements in Agricultural Soil ...... 22
Factors Affecting Mobility and Bioavailability of Trace Elements ...... 22
Soil pH ...... 23
Soil Organic Matter (SOM) ...... 24
Chemical Speciation ...... 25
Clay Mineral’s Nature and Content ...... 25 Trace Elements in Saanich Peninsula Agricultural Soils 4
Cation Exchange Capacity ...... 26
Oxides of Aluminium, Iron and Manganese ...... 27
Rhizosphere Chemistry ...... 27
Methodology ...... 29
Site Selection ...... 29
Soil Sampling Protocol ...... 31
Soil Sample Preparation ...... 31
Soil Characteristics ...... 31
Total Elements Analysis ...... 31
Selenium Speciation ...... 32
Water Extraction Procedure ...... 32
Statistical Analysis ...... 32
Results and Discussion ...... 33
Soil Characteristics ...... 33
Soil pH ...... 33
Soil Textures and Types ...... 33
Soil Organic Matter (SOM) ...... 34
Soil Electrical Conductivity ...... 35
Total Trace Elements in Soils ...... 36
Comparison of Current Results to the 1995 BC Ministry of Environment Data ...... 38
Antimony ...... 41
Barium ...... 42
Beryllium ...... 42
Boron ...... 42
Cadmium ...... 43
Chromium ...... 44 Trace Elements in Saanich Peninsula Agricultural Soils 5
Copper ...... 44
Cobalt ...... 45
Mercury ...... 46
Manganese ...... 46
Molybdenum ...... 46
Nickel ...... 47
Lead ...... 47
Selenium ...... 48
Tin ...... 49
Vanadium ...... 50
Zinc ...... 50
Mobility of Trace Elements in Soils (Soil Solid/Liquid Partition Coefficients, Kd) ...... 50
Conclusions and Recommendations ...... 55
Conclusions ...... 55
Recommendations and Possible Future Research Directions ...... 56
List of Figures
Figure 1: Biogeochemical cycles of trace elements in agricultural soils (adapted from Lombi et al, 1998;
Prasad, 2008)...... 11
Figure 2: Igneous and fractured rocks in Saanich Peninsula ...... 21
Figure 3: Map of Saanich Peninsula showing farming land reserves and soil sampling locations (i.e., brown spots in figure) ...... 30
Figure 4: Relationship between soil organic matter and electrical conductivity ...... 36
Figure 5: Correlation between total arsenic concentration and clay content ...... 41
Figure 6: Correlation between total Cd concentration and clay content in soil ...... 44 Trace Elements in Saanich Peninsula Agricultural Soils 6
Figure 7: Correlation between total Cu concentration in soil and soil organic matter ...... 45
Figure 8: Correlation between Cu Kd values and clay ...... 53
Figure 9: Relationship between Cd Kd values and clay content (%) ...... 54
List of Tables
Table 1: Statistical Summary for Current Soil Samples (0-15cm) ...... 37
Table 2: Statistical Summary for the 1995 BC Ministry of Environment Data (0-15cm) ...... 39
Table 3: Comparison of Current and Previous Results (Two Sample t-Tests and p-Values) ...... 40
Table 4: Water Soluble Selenium Species in Selected Saanich Peninsula Agricultural Soils ...... 49
Table 5: Kd Values for Selected Elements in Saanich Peninsula Agricultural Soils ...... 52
List of Appendices
Appendix A: Canadian Council of Ministers of the Environment (CCME) agricultural soil quality
guidelines (CCME, 2007)...... 69
Appendix B: Trace elements in agricultural soils (surface soil, 0-15cm) of Saanich Peninsula (Central
Saanich) (BC Ministry of Environment, 1995) ...... 70
Appendix C: Total metals, pH, soil organic matter (SOM), and electrical conductivity (EC) for Saanich
Peninsula agricultural soils ...... 71
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g) ...... 76
Appendix E: Soil textures and types ...... 81
Appendix F: Soil solid/liquid partition coefficients, Kd values of Saanich Peninsula Agricultural soils .. 83
Trace Elements in Saanich Peninsula Agricultural Soils 7
Acknowledgements
I would like to extend my sincere thanks to all the farmers of Saanich Peninsula who overwhelmingly supported and cooperated throughout this study. In particular this study would not have been completed in the present form if I had not got cooperation and encouragement from farmers Dr. Lynda Miller, Mike Doehnel and Terry Michell.
I am deeply indebted to my supervisor Dr. Matt Dodd for his invaluable guidance and support during this study. I appreciated his assistance with soil sampling from the different farms and his constructive suggestions in the whole thesis writing process.
I would like to express my deep gratitude to Dr. Harry Hartmann, CEO, MB Laboratory
Ltd., Sidney, BC for sponsoring this thesis and providing all the technical support including conducting the soil characteristics and total elements analysis. I am immensely thankful to Ms.
Connie Slemko and Ms. Christine Tough, MB Laboratory Ltd., Sidney, BC for their painstaking work in the total elements and Selenium speciation analysis.
I also would like to thank John Wozny and Dr. Elaine Gallagher (Professor, University of
Victoria) for helping me contact and build a network with the farmers as well as provide transportation support in this study.
Last but not the least; I am very thankful to my wife Vandana Sharma who encouraged me to pursue this research and inspired me to write different chapters and my son Rehaan
Ghimire who made my thesis writing enjoyable. Their cooperation was instrumental for me to complete this project successfully on time.
Trace Elements in Saanich Peninsula Agricultural Soils 8
Introduction
Trace Elements
Agricultural soils contain different types of metals, organic, inorganic and organometallic compounds. Among these substances, certain elements such as silver (Ag), arsenic (As), barium
(Ba), beryllium (Be), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), manganese
(Mn), molybdenum (Mo), nickel (Ni), lead (Pb), antimony (Sb), selenium (Se), and zinc (Zn) are often called trace elements as they occur in concentrations less than 100 mg/kg (He, Yang, &
Stoffella, 2005). Most of them are essential to plants and animals up to certain levels; however, they are regarded as soil pollutants or contaminants if they exceed those levels since elevated levels are detrimental to plants and animals health. Agricultural soils may act as good sinks where trace elements and other pollutants accumulate rapidly but are depleted very slowly. The accumulated metals and other contaminants can enter into living organisms through inhalation, dermal contact and ingestion and passed on into higher trophic levels through the food chain.
Since soil is one of the key components of the natural ecosystem, a healthy soil is also a symbol of good health, safe and a clean environment. Sustainable agriculture is only possible in sound and healthy agro-ecosystems with balanced trace elements and other essential nutrients
(Kabata-Pendias, 2011; Prasad, 2008; He et al., 2005). However, some soils in different regions of the world have lower concentrations of trace elements to support the growth and health of plants and animals causing a public health problem in many developing countries (Prasad, 2008, p. xxiii).
The Biological Essentiality and Toxicity of Trace Elements
Trace elements have been classified as low risk (e.g., Fe, Mn, Ni and Cr), moderate risk
(e.g., Cu and As) and high risk (e.g., Se, B, Cd, Hg, Pb and Th). High risk implies that the Trace Elements in Saanich Peninsula Agricultural Soils 9 existing concentrations can be exceeded in some time frame (Agriculture and Agri-Food Canada,
2005). Most of the trace elements are indispensable for the physiological function and growth of plants and animals and are often called “micronutrients or essential nutrients”. The role the essential elements play in biochemical reactions and metabolic processes cannot be replaced by other species. So far, 17 elements (viz., Al, B, Br, Cl, Co, Cu, F, Fe, I, Mn, Mo, Ni, Rb, Si, Ti, V, and Zn) have been recognized as essential for plants. The role of each trace element depends on the plant species, and the functions of some of the trace elements in plants are still unknown.
Young leaves wilting, melanism (brown, violet, red), stunted growth and leaf deformation are some symptoms of trace elements deficiency in plants (Kabata-Pendias, 2011).
Plants can withstand slightly elevated concentrations (chemical stress) compared to insufficient trace element levels in soil; dark green leaf, purpling of stems, leaf tip chlorosis, brown stunted roots, and degradation of protein enzymes are some common examples of trace elements toxicity in plants (Kabata-Pendias, 2011). The margin of safety between harmful and beneficial concentrations is very narrow, and at higher concentrations, trace elements may be extremely harmful for the health and development of plants as well as animals; they inhibit growth and development of plants and are cytotoxic to humans and other organisms (Bradford et al., 2008). Studies have found that elevated concentrations of trace elements in soil hinder bacterial or microbial activities, which are essential for agricultural soils, resulting in the decrease in soil fertility and agricultural productivity. Change in microbial biomass, activity and community structure as a result of trace element concentrations may also be taken as an indicator of soil contamination in agro-systems (He et al., 2005).
Trace Elements in Saanich Peninsula Agricultural Soils 10
Sources of Trace Elements in Agricultural Soils
Natural processes of weathering of rocks, aerial transport of volatile compounds (e.g.,
Hg, Se, As and Sb) and anthropogenic activities such as combustion of coal and other fossil fuels, mining and smelting of metallic ores, landfills, industrial activities, vehicles emissions, repeated use of metal-enriched fertilizers, pesticides and agro-chemicals, biosolids, sewage sludge and waste water application may introduce trace elements into agricultural soils (Singh,
1994; Prasad, 2008). One of the potential sources of trace elements is phosphate fertilizer that contains Cd, Se and other trace elements as impurities (i.e., from phosphate rocks). Copper, Se, and Zn are often added to animal feeds and are transferred to agricultural soils via animal manure
(Sheppard, Grant, & Drury, 2009). It is a challenging task to determine the relative contribution of trace elements in agricultural soils from weathering (i.e., internal sources), aerial deposition
(i.e., external sources) and other non-point sources (Rowe, Percival, & Hendershot, 2004).
Figure 1 illustrates the biogeochemical cycle of trace elements in agricultural soils and, shows the variety of sources of trace elements in the agro-ecosystems, their fate, transformation, bioaccumulation and output from the agricultural soils. Bedrock is one of the potential contributors of trace elements in agricultural soils and highly influences the surface soil’s chemical composition. The total amount of trace elements present in a soil at a particular time depends on how much metals are added to the soil from different media and how much are leached or absorbed by plants and animals (Aydinalp & Marinova, 2003).
Trace Elements in Saanich Peninsula Agricultural Soils 11
Volcanic Atmosphere activities Waste incineration Fuel combustion
Wet Dry Burning, Food chain deposition deposition Volatilization Humans & animals
Weathering, Mining Plant/Crop
Litterfall Manure , Fertilizer Biosolids Pesticides Agricultural Soils
Runoff, Leaching, Groundwater & Aquatic ecosystems
Equilibrium between free ions and chelated ions in soils
Exchangeable trace Unavailable trace elements (soil) elements (soil)
Figure 1: Biogeochemical cycles of trace elements in agricultural soils (Lombi, Wenzel, & Adriano, 1998; Prasad, 2008)
Trace Elements in Saanich Peninsula Agricultural Soils 12
Elements of Concern (EOC) in Agricultural Soils
The Canadian Council of Ministers of the Environment (CCME) published the Canadian
Environmental Quality Guidelines for various chemicals in soils based on agricultural, residential/parkland, commercial and industrial land use. The guidelines for agricultural land use are summarized in Appendix A. The Elements of Concern (EOC) for agricultural soils identified in the guidelines are Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Zn, B, Sn, Co, and
V (CCME, 2007). Additionally, these elements are frequently studied in different countries by many other researchers (He et al., Ma, Tan & Harris, 1997; Holmgren, Meyer, Chaney, &
Daniels, 1993; Chen, Ma, & Harris, 1999; Sheppard, et al., 2009; Prasad, 2008, p. 55; Mermut et al., 1996). Therefore, this study is particularly focused on these trace elements. Among these elements, Cu, Zn, Fe, Mn, Mo, and B are essential to the normal growth and development of both plants and animals including humans. On the other hand, Co, Cr and Se are not essential for plants but only necessary for animals and humans. Copper, Zn, Pb and Cd are the most studied and widely distributed trace elements in agricultural soils (He et al., 2005; Alloway, 1990).
Arsenic, Hg, Pb and Cd have no biological functions and are highly toxic even in very low concentrations and are on the United States Environmental Protection Agency (USEPA) priority pollutants list. They are the elements with the most environmental concerns because of their widespread distribution in nature and extremely detrimental effects on ecological and human receptors (Carrillo-Gonzalez, Simunek, Sauve, & Adriano, 2006).
The spatial variation in concentration and distribution of trace elements in agricultural soils depend on their input quantity, dilution, transport, plant uptake and accumulation in soils.
The input of trace elements into soils may be greater than losses since most metals are not biodegradable and undergo transformation into water insoluble and soluble organometallic Trace Elements in Saanich Peninsula Agricultural Soils 13 complexes. That is why trace elements contamination in agricultural soils is increasing and likely to continue worldwide in the foreseeable future making trace elements contamination a long term problem with potential environmental and public health implications (Markert & Friese, 2000, p. vii; Kabata-Pendias, 2011, p. 22). Moreover, some of the organometallic complexes formed (e.g., methyl mercury) may be more toxic to humans and other organisms. An understanding of the biogeochemical distribution, environmental fate and behavior as well as changes in concentrations over time is vital for managing trace elements concentration and reducing environmental pollution in agro-ecosystems (Markert & Friese, 2000).
Scope of the Study
The fundamental aim of studying trace elements in agro-systems is to determine their benefits and potential toxicity to environmental and human health and prevent them from entering into the food chain through agricultural products (mainly from crops) and other sources
(Prasad, 2008). Saanich Peninsula farms have been cultivating various crops in different seasons including fruits (blueberries, apples, raspberries, strawberries, peaches, grapes, prune plums, cherries, and pears), fresh vegetables (broccoli, lettuce, beans, tomatoes, carrots, squash and pumpkins), corn and hay (Farm Fresh, 2012). Most of these farms are more than hundred years old and are among the oldest farm lands in Canada (BC Ministry of Environment, 1985).
Farmers conduct extensive farming using different types of fertilizers (viz., chemical fertilizers, farmyard manure or green manure), pesticides and insecticides. There has also been a significant increase in vehicular movement in the surrounding areas. These factors may have contributed to changes in the concentrations of trace elements in agricultural soils in the Saanich Peninsula over the past few years making the study of the fate, transport, behavior and change in the concentrations of trace elements in the region a priority. Trace Elements in Saanich Peninsula Agricultural Soils 14
The BC Ministry of Environment conducted an extensive province wide survey to establish background concentrations for various parameters in 1995. Baseline data (i.e., background concentrations) for the Saanich Peninsula were established as part of the study. This database can be very useful for detecting long-term trends for contaminants in the region (BC
Ministry of Environment, Environmental Protection division, 1995). Periodical evaluation of contaminants in agricultural soils is vital for the formulation of new environmental management policy. The concentrations and trend of trace metals in agricultural soils in the Saanich
Peninsula has not been determined since the BC Ministry of Environment study 17 years ago.
Therefore, this study was undertaken to fill that void by determining the current concentrations of trace elements of agricultural interest and their mobility and bioavailability.
Research Questions
• What are the current concentrations of trace elements in agricultural soils in the
Saanich Peninsula?
• How much has the concentration of trace elements changed over the last fifteen years
and what are the possible causes of such change?
• What are the factors that likely influence the bioavailability of trace elements in
agricultural soils in the region?
• What are the factors that affect the migration and distribution of trace elements in
these soils?
Trace Elements in Saanich Peninsula Agricultural Soils 15
Literature Review and Background
Trace Elements in England and Wales’ Farms
An inventory of heavy metals inputs to agricultural soils by Fiona et al. (2003) concluded that atmospheric deposition, livestock manure and sewage sludge were the major sources of trace elements contamination in agricultural soils in England and Wales. The elevated levels of those metals were the main cause of the reduction in crops yield and environmental degradation.
Rawlins, Lister, and Mackenzie (2002) found significantly higher concentrations of trace elements (about 40%) in more densely populated areas than low population density areas in northern England. They identified four potential sources for the trace elements dispersed in human settlements. The first two were related to the use of coal as a main source of energy in domestic dwellings as well as in industries for more than 150 years; coal combustions dispersed
As, Mo and Pb into top soils by aerial deposition. The third pathway was the extensive use of sewage sludge, wastewater and animal waste as fertilizers in 18 th and 19 th century. The fourth pathway was the release of Pb from leaded gasoline and Zn from rubber tyres.
Trace Elements in Chinese Agricultural Soils
Due to rapid industrialization, urbanization and extensive use of agrochemicals in farms, trace elements contamination was a major environmental problem in China and reduction of those potentially toxic trace elements was a strategic plan for sustainable agriculture and health
(Luo, Ma, Zhang, Wei, & Zhu, 2009). Luo et al. (2009) studied trace elements contamination in
China and found that atmospheric deposition from anthropogenic sources and livestock manure were the main sources of trace metals in Chinese agricultural soils. Electronic waste (e-waste) and coal combustion were the main sources in southern agricultural soils. For example, 45% of
Hg and a significant amount of As (100 time more than Europe) were from the combustion of Trace Elements in Saanich Peninsula Agricultural Soils 16
Chinese coal. In northern China, wastewater used for agricultural irrigation was the principal source of trace elements. Among the trace elements, Cd was the element of top priority in agricultural soils in China, because of extensive use of Cd containing fertilizers including organic and phosphate-based fertilizers, sewage sludge and biosolids.
Ping et al. (2011) studied the concentrations of Cd, Hg, As, Pb, Cr, Cu, Zn and Ni in the top soil horizon (0 to 20 cm) of greenhouses and open farmlands from agriculturally active areas of China (i.e., Shouguang, Laiyang, Jinxiang and Shandong provinces). They found 22 samples out of 149 were contaminated by Cd, Ni, Cu or Hg. The greenhouses were mainly contaminated with Cd whereas open fields farming soils were contaminated by Cu. Mercury and Pb concentrations were elevated due to anthropogenic activities such as vehicular and industrial emissions, as well as wastewater irrigation. Chromium, As and Ni were contributed mainly from the natural process of weathering in these Chinese provinces. Yu, Xin, Gang, and Qiang (2008) studied the concentrations of Cu, Pb, Cr, Hg and As in arid and irrigated agricultural soils in central Gansu Province and found that anthropogenic activities were the principal contributors of trace elements in irrigated agriculture whereas lithological factor was the main source of metals in arid agriculture.
Trace Elements in USA Farms
Shacklette and Boerngen (1984) studied the nationwide geochemical pattern and found lower concentrations of some trace elements (Al, Ba, Ca, Mg, K, Na, and Sr) in the eastern part compared to the western part of the USA. At the state level, the concentrations of trace elements in Florida soils were lower than other states. Florida soils comprise sandy and loamy marine sediments and because of the sandy nature trace elements were relatively more mobile. In Trace Elements in Saanich Peninsula Agricultural Soils 17
Minnesota, some trace metals such as Cd, Pb and Zn were higher in top-soils while Cr, Cu and
Ni were concentrated in sub-soils (Ma et al., 1997; Holmgren et al., 1993).
In another studied, Holmgren et al. (1993) conducted a USA wide screening of trace elements in agricultural soils and found higher concentration of Pb in the Mississippi, Ohio and
Missouri River valley. Maximum Cd concentrations were found in central and southern
California, and Cu concentrations were higher in Florida and Oregon. Chen et al. (1999) conducted a baseline study of 15 trace elements (Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Mo, Ni,
Pb, Sb, Se, and Zn) in Florida surface soils and found that compared to the mean USA and the world levels the concentrations were lower for all the elements except Cu. The relatively higher mean Cu concentrations were attributed to the use of Cu containing fungicides on citrus fruits in
Florida. Ma et al. (1997) studied the concentrations of trace metals in different types of agricultural soils in Florida and found that metals in soils decreased in the order of Ultisols>
Entisols> Spodosols. This was attributed to differences in clay content and Fe-Mn oxide composition.
Trace Elements Contaminations in Canadian Farms
The background concentrations of trace elements in Canadian agricultural lands are largely unknown (Sheppard et al., 2009). Atmospheric deposition from vehicles and industries and the weathering of rocks have the potential to add trace elements to Canadian agricultural soils. The extensive use of agrochemicals (chemical fertilizers, pesticides, fungicides, etc.), manure and biosolids on crops have led to the increase of trace elements in agricultural soils
(Sheppard et al., 2009). In Ontario, elevated levels of some potentially toxic trace elements (As,
Pb, Hg and Cu) were found in agricultural soils after the use of chemical fertilizers and pesticides containing these trace metals as impurity (Ma et al., 1997). The atmospheric Trace Elements in Saanich Peninsula Agricultural Soils 18 deposition of trace and major elements increased from 1942 to 1970 in the Lake Hertel area,
Quebec, Canada. They are now stabilized with the exception of Ni, Cu, Zn and Sn. Lead deposition decreased by 25% due to the use of unleaded gasoline between 1982 and 1995. Other elements such as Co, Hg, and Th also decreased slightly over the same periods. The current rates of metals emissions are very low since Canada and the USA have introduced legislation and environmental management policy to control the emissions of trace elements from industries, vehicles and fertilizers (Gelinas, Lucotte, & Schmit, 2000). In Manitoba agricultural soils, Se,
Mo and V were found to be significantly higher than the national and the world’s averages
(Agriculture and Agri-Food Canada, 1998a).
Elevated levels of some trace elements (e.g., Pb, Fe and Hg) decrease soil fertility and agricultural output of soils (Uwah, Ndahi, & Ogugbuaja, 2009). High concentrations or contaminations of trace elements in agricultural soil are becoming an issue of global concern due to their multiple sources, distribution and diverse effect on the ecosystems (Mermut et al., 1996;
Sheppard et al., 2009; Uwah, et al., 2009). The Canadian Fertilizers Act (1993) and fertilizer regulations set forth specific limits for heavy metals contained in all fertilizers (chemical fertilizers, biosolids and farm manures) marketed and used in the provinces (USEPA, 1999).
However, despite this legislation continuous use of these substances on crops many times per year is instrumental for increasing their concentrations in agricultural soils (He et al., 2005).
Recently, Canada has faced embargoes limiting international sales of selected grains because of significant concentration of trace elements, particularly Cd and Se, which clearly reflects the problem of trace elements contamination in agricultural soils in Canada (Sheppard et al., 2009). Periodic evaluations of trace elements in Canadian agricultural soils are therefore essential for the assessment of trace elements contamination, environmental monitoring, land use Trace Elements in Saanich Peninsula Agricultural Soils 19 and ecological evaluation to ensure healthy and sustainable agricultural system in Canada
(Qishlaqi & Moore, 2007).
Mermut et al. (1996) studied the correlation between the amounts of clay content and trace elements concentrations in surface and sub-surface agricultural soils in Saskatchewan. Many soil samples had less clay in surface soil than in the sub-soil horizon. They found a positive relationship between clay content and metals concentrations except for Se. In heavy clay soils, the concentrations of Cu, Zn, Se and Pb were higher in the surface soils than in the sub-soils; however, the increases in concentrations were not statistically significant. The trace elements such as Cu, Cd and Pb were depleted in soils with relatively low clay content, and their concentrations were lower compared to the parent materials. However, in soils with similar clay content in the surface and sub-soil horizon, the concentrations of trace elements (V, Cr, Co, Ni,
Zn, Cd, Sn, Sb, Tl and Pb) were higher in the surface soil than the sub-soil. This was attributed to the fact that anthropogenic sources, atmospheric deposition, impurities present in phosphate fertilizers and weathering of parent rocks add these elements to surface soil first.
Trace Elements in Saanich Peninsula Farms
In 1995, the industrial waste and hazardous contaminants branch of the BC Ministry of
Environment conducted a province wide screening of chemicals (organic chemicals and metals in agricultural as well as urban soils (BC Ministry of Environment, Environmental Protection
Division, 1995). The main purpose of the survey was to determine the contaminants concentrations in all regions of the province (i.e., determine background concentrations). A number of organic and inorganic contaminants were detected in soils from Vancouver Island.
Among these chemicals, trace elements concentrations in Saanich Peninsula’s farms (i.e., surface soils, 0-15cm) are shown in Appendix B. The trace element concentrations detected in Trace Elements in Saanich Peninsula Agricultural Soils 20 agricultural soils from the Saanich Peninsula soils were significantly lower than the CCME soil quality guidelines for agricultural land use as summarized in Appendix A (CCME, 2007).
Geology and Soil Type of Saanich Peninsula Farms
Geographically, Saanich Peninsula is located on the southern end of Vancouver Island, north of the city of Victoria . It has arable land with the mildest climate in Canada. The annual precipitation varies from 635 millimeters in Victoria (city) and increases by 45% in the northern part of the Peninsula, particularly at the airport and nearby areas (Saanich Peninsula, n.d;
Victoria, n.d.).
It is well known that the earth crust is the most important reservoir for all types of trace elements (Prasad, 2008, p. 15). The background concentrations of metals in soil are therefore dependent on the bedrock type from which the soils form. Saanich Peninsula is situated in the south eastern part of the Nanaimo lowland and Vancouver Island ranges. Its eastern side is bordered by Cordova Channel and the western side by Saanich Inlet. The Peninsula is mainly underlain by fractured and faulted volcanic and igneous rocks (i.e., lithosphere) as shown in
Figure 2 (Huntley, Bennett, Bobrowsky, & Clague, n.d; Agriculture and Agri-Food Canada,
1998b). Furthermore, the earth crust is made up of up to 95% igneous rocks and contains higher concentrations of some trace elements such as Zn, Cr, Co, Ni, Mn, and Cu which are responsible for background concentrations in the natural environment (He et al., 2005). The igneous bedrock may contribute to the background concentrations of trace elements in Saanich Peninsula farm soils.
The Peninsula has some variation in altitude; the highest point of the study area is Mount
Newton (307 m) whereas Brentwood Bay, Keating, and Island View Beach are low lying areas.
Besides volcanic and igneous bedrocks, limestone is also found in Brentwood Bay and Trace Elements in Saanich Peninsula Agricultural Soils 21 surrounding areas. Bedrock in the study area is covered by a surficial layer of sand, clay and some organic matter ranging in thickness from less than a metre on slopes and steep areas to more than forty metres in some low lying areas. The Peninsula has soils of different texture exposed in sea-cliff and wave-cut platform including sands and gravels; mud, rock; humic; gravely, sandy loam; silt, clay loam; and gravely, loamy sand. These different texture soils are classified as Regosols, saline phases; Terric Humisol; Gleyed Dystric Brunisol; Orthic Dystric
Brunisol; Duric Dystric Brunisol; Orthic Sombric Brunisol; Orthic Humic Gleysol; Terric
Humisol; Orthic Dystric Brunisol; Orthic Regosol; Orthic Regosol. Some typical local soils and soil types in the Peninsula are Metchosin, Brigantine, Shawnigan, Langford, Saanichton,
Qualicum, Shawnigan etc. (Huntley et al., n.d; Agriculture and Agri-Food Canada, 1998).
Figure 2: Igneous and fractured rocks in Saanich Peninsula
Trace Elements in Saanich Peninsula Agricultural Soils 22
Mobility and Bioavailability of Trace Elements in Agricultural Soil
Metals occur in soils in various forms including water soluble (e.g., in soil solution), exchangeable, organically bound, adsorbed on Fe, Al and Mn oxides, compounds (metal carbonate, phosphate, etc.) and structurally bound to minerals. The soluble and exchangeable fractions are highly mobile and bioavailable in agricultural soil (Kabata-Pendias, 2011). The total amounts of the metals that are available in soil for physical, chemical and biological activities
(fate, transport and bioaccumulation) are called environmentally available fraction. The total environmentally available fraction does not necessarily imply the total amount of metals that are absorbed into living beings; however, it represents the total pool of metals that are available to
(i.e., enter into) an organism at the given time. Environmental availability of a metal is specific to the environmental conditions and is a dynamic process which changes with the change in environmental conditions (USEPA, 2004; Carrillo-Gonzalez et al., 2006).
Bioavailability refers to the fraction of metal that pass through the roots, skin, lung or alimentary tract and enters into the blood stream for biological activity. Metal bioavailability depends on various factors including particle size, route of entry, exposure duration, cell receptors, and frequency of exposure, metal dose and exposure matrix. The uptake by plants
(phytoavailability) entirely depends on the mobility and availability of metals in soils. Plant uptake of trace elements is of concern because of two reasons. First, trace elements may have direct phytotoxic impact on plants and reduce crop yields. Second, plants may transfer trace elements from soil-plant systems to the food chain (Uwah, Ndahi, & Ogugbuaja, 2009
Factors Affecting Mobility and Bioavailability of Trace Elements
Burt, Wilson, Mays, and Lee (2003) showed that trace elements from anthropogenic origin are more mobile than those from lithogenic origin (pedogenic processes) as lithogenic Trace Elements in Saanich Peninsula Agricultural Soils 23 metals are better correlated with the clay minerals, organic matter, oxides and carbonate compared to anthropogenic metals. The accumulated trace elements in agricultural soils through different media are gradually depleted by plant uptake, leaching, volatilization and erosion. Their mobility and bioavailability depend on their distribution between solution and solid phases in soils (solid-liquid partition coefficient, kd). Trace elements dissolved in soil solution are highly mobile, and bioavailable to plants and animals. Among the various species of trace elements
(free ions, inorganic and organometallic compounds) in soil, the free ions (cations) are the most mobile and bio or phytoavailable species whereas chelated compounds with inorganic and organic ligands (organometallic) are less mobile and bio or phytoavailable, and some are highly toxic (Han & Singer, 2007). Different factors such as soil type, pH, ionic strength, organic matter, nature of silicate clay minerals and concentration of electrolyte are responsible for the mobility of trace elements and its uptake by plants and animals (Mermut et al., 1996).
Soil pH
Generally soil pH ranges from 4 – 8.5 (Alloway, 1990, p. 9). However, the CCME guidelines for agricultural soil is pH 6 to 8 (CCME, 2007). Soil pH is one of the most important property which controls trace elements mobility and bioavailability to plants and animals as it directly influences ion pair and complex formation, as well as the solubility and precipitation of
2- - 3− carbonate ( CO 3 ), hydroxide (OH ), phosphate (PO 4 ), and other inorganic and organic materials in soils (Han & Singer, 2007; Carrillo-Gonzalez et al., 2006). Soil pH has a direct influence on the sorption of trace elements on agricultural soils. Lower pH decreases the sorption of trace elements, which consequently increase their mobility and bioavailability. For example, each 0.5 increase in pH doubled Cd sorption over the pH range from 3.8 to 4.9 in soil-systems.
High pH decreases the ionic mobility and solubility of some trace elements in soils (Rieuwerts, Trace Elements in Saanich Peninsula Agricultural Soils 24
2007; Carrillo-Gonzalez et al., 2006). The bioavailability and mobility of some trace elements such as Cu, Zn, Ni, Cd, Cr 3+ and Pb significantly decrease at pH 7 and above (alkaline medium) as these metals are present as hydrolyzed species that are highly adsorbed on soil matrix whereas
As, Se, Mo, Cr, Sb, and U adsorb on soil matrix at low pH but are highly mobile and bio-or phytoavailable at high pH. High pH also decreases the metals’ soluble and exchangeable fractions as it facilitates the adsorption of these metals on various solid phases including Al, Mn and Fe oxides in soils. Soil pH also affects the speciation of some metals such as transformation between Cr 3+ and Cr 6+ ; Cr 6+ is highly bio-or phytoavailable and mobile while Cr 3+ strongly adsorbs onto the soil matrix (Han & Singer, 2007; Carrillo-Gonzalez et al., 2006).
Soil Organic Matter (SOM)
All soils contain organic matter or debris and humus that originate from organisms (both plants and animals). The amounts and types of organic matter vary with the type of soils.
Organic matter influences the bioavailability and mobility of trace elements in soils either by changing the soil pH or by accumulating the free metal ions (cations) on the large negative charge of the organic matter (Rieuwerts, 2007). Metal mobility and bioavailability is lower in soils with high organic matter. One study in Australia indicated that high concentrations of organic matter significantly decreased bioavailability of trace elements in soils particularly Zn and Cu as they formed insoluble Zn/Cu organic complexes. These insoluble organometallic complexes as well as those of Pb, Ni, and Cd are unable to pass through root cell membranes leading to their low bioavailability. On the other hand, low molecular weight compounds such as fulvic acids increase the mobility of bound trace elements in soil (Han & Singer, 2007; Carrillo-
Gonzalez et al., 2006). Soil organic matter also reduces the toxicity of Cr 6+ by reducing it into less toxic Cr 3+ (Magdoff & Weil, 2004). Trace Elements in Saanich Peninsula Agricultural Soils 25
Chemical Speciation
Speciation is defined as the study of the amount and nature (forms and phases) of species of an element that occurs in soil samples (Kabata-Pendias, 2011). Different chemical species of the same element has different mobility and bioavailability in soil. Cr 3+ is an essential micronutrient to plants and relatively sparingly soluble in soil solution; however, Cr 6+ is highly soluble, bioavailable and toxic (Carrillo-Gonzalez et al., 2006). Divalent manganese (Mn 2+ ) is stable and bioavailable in soil solution while Mn 3+ and Mn 4+ are only stable in solid phase and are not bioavailable and mobile in agricultural soils (Nadaska, Lesny, & Michalik, n.d).
Selenium (Se) has three chemical species: selenite (Se 4+ ), selenate (Se 6+ ) and selenides (Se 2-).
The chemistry and mobility of these species are significantly different in soil. Selenate (Se 6+ ) is less adsorbed onto soil and has greater mobility and bio-or phytoavailability than Selenite (Se 4+ ) which leaches into groundwater (Alloway, 1990). Selenium is mostly found as selenite (Se 4+ ) in humid soil. Microbial methylation of inorganic Se species in soil converts it into dimethyl selenide which is highly volatile and may be lost to the atmosphere (Kabata-Pendias, 2011, p.
372).
Sequential extraction techniques have been used to determine metal speciation in soils.
Based on the physico-chemical properties of metals, the highest proportions of metals are found in the Fe-Mn oxide fraction in both natural and contaminated soils. The association of metals such as Cd and Ni is lowest in organic matter while Cu, Pb, Ni, and Zn are mainly bound to cation exchange sites of organic matter in soil (Kabata-Pendias, 2011).
Clay Mineral’s Nature and Content
In agricultural soils, clay minerals are one of the most important sinks for trace elements and influence their mobility and bioavailability. Weathering of parent rocks and pedogenic Trace Elements in Saanich Peninsula Agricultural Soils 26 processes mix clay minerals into soil systems and these minerals have marked effects on physical, chemical and biological properties of soils. The percentage of clay minerals, silt and sand-sized particles determine the soil’s texture (Kabata-Pendias, 2011; Alloway, 1990). Clay rich soils generally have higher sorption capacity due to the relatively large surface areas and permanent negative charges of the clay minerals. Soil pH and electrode potential (Eh) also influence the adsorption of trace elements onto clay minerals (Kabata-Pendias, 2011; Alloway,
1990).
Cation Exchange Capacity
Agricultural soils contain different types of cations such as calcium (Ca 2+ ), magnesium
2+ + + 2+ (Mg ), potassium (K ), ammonium (NH 4 ), and iron (Fe ). Clay minerals and organic matter having large negative charge on their surfaces adsorb these cations. The capacity of soils to adsorb and exchanges cations in soil-systems is referred to as the cation exchange capacity
(CEC). As a whole, soil is electrically neutral as all cations are held and neutralized by negatively charged clay and organic matter. The adsorbed cations are not easily lost from leaching and are retained as nutrient reservoirs for plant uptake; however, they can be replaced or exchanged from the soil by other cations (exchangeable) and made available for plant uptake.
The availability of cations depends on how strongly they are bound onto the clay and organic
3+ 2+ 2+ + + + matter. In soil, the adsorption of cations follow the order Al > Ca > Mg > K = NH 4 > Na
(Camberato, 2001; Tree Fruit Research and Extension Centre, 2004). CEC is dependent on soil texture (clay content) and organic matter. It is higher for soils with higher clay and organic matter content since the greater negative charges attract more cations. Low pH decreases the
CEC in soil as the high concentrations of H + ions replace the cations from clay and organic matter. Small loses of essential plant micronutrients in soil from leaching or surface runoff are Trace Elements in Saanich Peninsula Agricultural Soils 27 compensated through the CEC in soils which act as a buffer capacity of soil micronutrients in agricultural soils (Cation Exchange Capacity, 2007).
Oxides of Aluminium, Iron and Manganese
Large number of oxides and hydroxides such as silicon oxide, iron oxide, manganese oxide, aluminium oxide and hydroxides are formed during weathering and pedogenic processes.
They are the most common constituents in soils and often produce soil color or pigment (mainly
Fe oxides). Soil pH and redox potential (Eh) facilitate oxidation-reduction reactions in soils and change the oxidation state of some oxides, for example, Fe 3+ into Fe 2+ and Mn 4+ into Mn 2+ .
These oxides and hydroxides are important for the mobility and bioavailability of trace elements in soils as they have a strong tendency to adsorb metals. Several studies have indicated that soil’s
As, Cr and Ni have an affinity toward Fe-hydroxides whereas Co, Mn, Ni, and Pb and have an affinity for Fe/Mn oxides; however, Cu and Mo adsorb weakly on Fe/Mn oxides. The sequence of adsorption of trace elements on Fe is V > Cr > Pb > As > Se. The sorption capacity of soil also depends on the soil pH; the maximum sorption of oxides and hydroxides have been found at pH
4 and 5(Kabata-Pendias, 2011, p. 71).
Rhizosphere Chemistry
The rhizosphere is the interface between plant roots and the soil that surround the roots. It influences pH, Eh, CEC and microbial activity in soil. Changes in these properties in soil change the ionic equilibrium in the interface. The elements in low concentration in soil solution are likely to be depleted faster by plant uptake, which affect the nutrients and metals bioavailability in plants. Changes in pH, Eh and microbial activity also affect the speciation of some elements such as Cr, Mn, Fe and Se. Various oxides and hydroxides are also soluble in the acidic and reducing conditions of the rhizosphere which increase the trace elements solubility and Trace Elements in Saanich Peninsula Agricultural Soils 28 bioavailability. The rhizosphere also has a strong influence on CEC in soil-systems (Han &
Singer, 2007). The H + generated by root hair may replace the cations that are adsorbed or bound on the organic matter and clay minerals releasing them into the soil solution and making them available for plant uptake and microbial activities (Tree Fruit Research and Extension Centre,
2004). The strong organic chelators released by rhizosphere increase the bioavailability of Fe,
Zn, Ni and Cd. At the same time, the availability of one trace element (cations) in soil solution influences the bioavailability of another trace element (antagonistic relationship). For example, in some soil, the plant uptake of K is inhibited by high concentration of Ca (Han & Singer,
2007).
Trace Elements in Saanich Peninsula Agricultural Soils 29
Methodology
Site Selection
Saanich Peninsula is located on the southern end of Vancouver Island and comprises
North Saanich, Central Saanich, Saanich, and Sidney. The study area has 60 different farms; however, 30 soil samples from 10 farms were collected based on the history, types and number of crops produced per year, use of chemical fertilizers and farm manure, location, distance from the highway and industries as well as spatial variation to cover the Peninsula. The history and type of crops produced in the priority region were obtained from the BC Ministry of
Environment’s report and Farm Fresh magazine (annual magazine of Southern Vancouver Island
Direct Farm Marketing Association) and personal communication with the local farmers respectively (BC Ministry of Environment, Environmental Protection Division, 1996; Farm
Fresh, 2012; Farmers, personal communication, March 2, 2011). Details regarding Saanich
Peninsula agricultural land reserves and soil sampling locations are shown in Figure 3. Trace Elements in Saanich Peninsula Agricultural Soils 30
Figure 3: Map of Saanich Peninsula showing farming land reserves and soil sampling locations (i.e. , brown spots in figure) (Copyright © Province of British Columbia. All rights reserved. Reprinted with permission of the Province of British Columbia. www.ipp.gov.bc.ca )
Trace Elements in Saanich Peninsula Agricultural Soils 31
Soil Sampling Protocol
Soil samples were collected from the topsoil (0–15 cm) with a stainless steel trowel. The trowel was cleaned thoroughly by washing with laboratory grade detergent followed by rinsing with distilled water, and dried by paper towel between each sample to avoid cross contamination.
The samples were placed in plastic bags, stored in a cooler with ice and transported to the MB
Laboratory, Sidney BC for laboratory analysis.
Soil Sample Preparation
The samples were dried, ground and passed through 2 mm stainless steel sieve to remove larger particles, rocks, roots and other impurities. The air dried samples were kept in polyethylene bag at 5ºC for acid digestion as per MB Laboratory Ltd’s protocol.
Soil Characteristics
Soil pH was determined by using Standard Methods 4500-H B; soil diluted 1:2 with distilled water (American Public Health Association, 1998). Soil particles size was determined using Environment Canada Sediment Survey Section IWD-HQ-WRB-SS-84-5 procedures for sediment analysis (Environment Canada, 1988). Standard Methods 2510 B which involved the1:2 dilution of the soil with distilled water was used to the measurement of soil conductivity
(American Public Health Association, 1992). Soil Organic Matter was estimated from Loss on
Ignition method (Heiri, Lotter, & Lemcke, 1999).
Total Elements Analysis
Total metals in soil samples were determined after acid digestion using the US EPA
Method 3010A (USEPA, 1992) while Method 3050 B was used for volatile elements such as mercury (USEPA, 1996). Total elements in the digestates were determined by either Inductively
Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) as per US EPA method 200.7 Trace Elements in Saanich Peninsula Agricultural Soils 32
(USEPA, 1994), or Graphite Furnace Atomic Absorption Spectroscopy (GFAA). Cold vapour flow injection atomic absorption spectroscopy (FIAS-AA) was used for mercury analysis
(USEPA method 3050B).
Selenium Speciation
Selenium extraction was carried out as per Martens and Suarez (1997) method and was measured using FIAS-Hydride-AA spectroscopy (Perkin Elmer Analyst 700) and GFAA and
EPA method 7740 (USEPA, 1986).
Water Extraction Procedure
Five grams of the dried, ground soil was placed into a 40-mL centrifuge tube. A 25 mL aliquot of distilled H 2O was added, and the sample was capped and shaken at 130 oscillations per minute on a horizontal shaker for 1 hour. The sample was then centrifuged for 10 minutes, and the supernatant was collected in a separate 40-mL centrifuge tube as per MB Laboratory Ltd protocols. The extract was analyzed as per the total elements analysis procedures.
Statistical Analysis
Two sample t-tests often called student’s t-tests and p-values were calculated from MS
Excel software to compare the current concentrations of trace metals with previous concentrations.
Trace Elements in Saanich Peninsula Agricultural Soils 33
Results and Discussion
Soil Characteristics
Soil pH
The soil pH for all the samples which are presented in Appendix C indicated that Saanich
Peninsula’s agricultural soil was slightly acidic with an average pH of 5.85. Generally, soil below pH 6.5 is called acidic soil (Kabata-Pendias, 2011). The pH in the current study varied from 4.89 to 6.93 whereas in the BC Ministry of Environment study, the average soil pH was 4.7 with a range of 4.6 to 4.8 (BC Ministry of Environment, 1995). The average soil pH increased by
1.15 (i.e., 24.46%) over the 17-year period. The average pH of 5.85 obtained in this study is slightly lower the CCME guidelines for agricultural soil, which is 6 to 8 (CCME, 2007). The soil pH at latitude 48°-35 -31.6˝ and longitude 123°-24 -38.7˝, which is near the previous BC
Ministry of Environment study site was 5.68, indicating an increase of 0.93 pH units compared to the previous data. However, this increase was not statistically significant ( p > .05 ).
Soil Textures and Types
The details experimental results for the soil textures and types are shown in Appendix E.
Saanich Peninsula agricultural soils contained gravel (both coarse and fine gravel), sand, slit and clay. The soil types in the Peninsula were sand, loamy sand, sandy loam and loam. A large percentage of Saanich Peninsula soils (average 75.55%) were sandy which implied that the soils had low water and nutrients holding capacity and weak structure making the soils highly prone to erosion and leachability of nutrients. Clay which makes soil sticky and holds water and nutrients was significantly lower in Saanich Peninsula soils. Many soils samples had 0% clay contents which implied that the soil’s trace elements adsorbing and retaining capacity was relatively low; however, in the high rainfall climate such as the Saanich Peninsula, perhaps this saves time and Trace Elements in Saanich Peninsula Agricultural Soils 34 money through drainage of unwanted water from agricultural fields (Agriculture and Agri-Food
Canada, 2011).
Soil Organic Matter (SOM)
SOM is one of the major indicators of soil quality and health in agro-ecosystems; however, very few studies have been done to determine its threshold value in agricultural soils
(i.e. minimum required level and maximum harmful levels) (Grain Research and Development
Corporation [GRDC], 2004). Crop residues (green manure) and animal or farmyard manure were the principal sources of soil organic matter in Saanich Peninsula agricultural soils (Farmers,
Personal communication, March 8, 2012); however, climatic factors such as precipitation and temperature could also be contributing factors for SOM in Saanich Peninsula’s soils (Magdoff &
Weil, 2004). SOM has numerous physical, chemical and biological benefits to agricultural soils.
Physical benefits include improved water infiltration and increase in water holding capacity, soil aeration, reduction in stickiness and surface crusting; chemical benefits include increase in CEC and buffer capacity, and accelerate soil minerals decomposition; while biological benefits include an increase in microbial biodiversity and decrease runoff as microorganisms enhance pore spaces.
There are no generic Canadian guidelines for SOM in agricultural soils. The optimum amount of SOM in agricultural soils depends on the soil type. For example, 1.2% Soil Organic
Carbon (SOC) is sufficient for Ultisols whereas the same amount is insufficient for Mollisols.
Soil organic matter of 3 to 6% (in 0-15 cm soil) is required for most agricultural soils below which the crops yields are significantly reduced (Soil Organic Matter, 2008). However, 2% SOC
(equivalent to 3.4% SOM) is the threshold value in dry land sites of Alberta (GRDC, 2004). Trace Elements in Saanich Peninsula Agricultural Soils 35
The SOM content in Saanich Peninsula agricultural soils is given in Appendix C. The
Saanich Peninsula soils contained relatively higher SOM than some threshold values for agricultural soils. The SOM varies from 5.96 to 54.3% with a mean of 16.24%. Beside organic manure, the percentage of silt and clay in soil and annual rainfall were the main contributing factors for the somewhat high SOM in the Peninsula agricultural soils. Slit and clay hold more water and nutrients and accelerate plant biomass production; however, it inhibits free circulation of air which facilitates aerobic decomposition of biomass resulting in higher amounts of SOM in soils. As SOM adsorbs trace elements and forms water insoluble organometallic complexes in soils, it decreases the metals mobility with increases in its amounts; however, sometimes it forms water soluble complexes and increases the trace elements mobility in soils (Magdoff & Weil,
2004).
Soil Electrical Conductivity
Agricultural soil’s electrical conductivity depends on physico-chemical properties including soil cations concentration (salinity), soil organic matter, clay content, bulk density, water content and soil temperature. The inorganic solutes that are dissolved in the aqueous phase
+ + +2 +2 - - - -2 - in soil (Na , K , Mg , Ca , Cl , HNO 3 , NO 3 , SO 4 and CO 3 ) are also responsible for electrical conductivity (EC) of soil (Corwin & Lesch, 2005). Clay content mainly influences the electrical conductivity of agricultural soils and, therefore, EC is higher in soil with greater amounts of clay.
High EC soil is more productive and suitable for most crops (Roberson, 2006). The EC results obtained are given in Appendix C. The data indicated that soil conductivity in the test area was relatively low and below the CCME guidelines (2ds/m). The lowest EC was 0.0326ds/m (Sample
25); the highest was 0.508ds/m (Sample 12) and the average was 0.175 ds/m.). The lower amounts of clay contents and higher amounts of sand as shown in Appendix E could be one of Trace Elements in Saanich Peninsula Agricultural Soils 36
the main reasons behind the fairly low EC. The soil organic matter content and the low soil pH
were also contributing factors. Figure 4 illustrates the positive correlation between EC and soil
organic matter suggesting that organic matter could be contributing to the EC.
600
500
400
300 y = 1.8517x + 144.64 R² = 0.0498 200
100 Electrical conductivity conductivity uS/cm Electrical 0 0 10 20 30 40 50 60 Soil organic matter
Figure 4: Relationship between soil organic matter and electrical conductivity Total Trace Elements in Soils
Overview of Current Results
Total elements concentrations in the 30 soil samples analyzed are given in Appendix C and a
statistical summary is provided in Table 1. Some of the trace element concentrations exceeded the CCME soil quality guidelines for agricultural soil (Appendix A). Arsenic concentrations in soil Sample 1 and
Sample 9 (Appendix C) were higher than the guideline (12µg/g); however, the mean was below the
CCME guideline. Boron concentrations in all 30 soil samples exceeded the CCME guideline (2µg/g).
Copper concentration was higher than the guideline (63µg/g) in Sample 1 and Sample 15 (Appendix C), but the mean concentration was below the guideline. In one farm (Sample 1), molybdenum concentration was higher than the guideline. Selenium concentrations in Sample 1 (6.14 1µg/g) also exceeded the
CCME guideline (1 µg/g) along with samples from four other farms (Samples 14, 16, 17 and 21). The concentration of tin in all the samples exceeded the CCME guideline. Trace Elements in Saanich Peninsula Agricultural Soils 37
Table 1: Statistical Summary for Current Soil Samples (0-15cm)
th th Elements Minimum Maximum Mean Standard 95 99 Percentile Deviation percentile Aluminium 7240 29100 14226 3878 18840 25932 Antimony 0.06 480 14.7 82.2 0.34 326 Arsenic 2.28 20 5.84 3.99 14.1 19.3 Barium 35.2 207 107 38.2 414 561 Beryllium 0.19 0.71 0.36 0.09 0.48 0.64 Boron 25.7 39.3 32.5 3.18 37.8 38.8 Cadmium 0.002 0.032 0.0066 0.0056 0.013 0.026 Calcium 1820 17000 5853 2917 8890 14433 Chromium 13.9 43 26.2 6.98 38.8 42.4 Cobalt 2.26 12.1 7.85 2.02 10.8 11.9 Copper 18.7 114 37.4 19.8 64.7 101 Gold <0.100 <0.100 n/a n/a n/a n/a Iron 10400 22400 15836 2830 20360 22112 Lanthanum 3.69 17.4 7.46 2.86 12.7 16.3 Lead <0.001 6.82 2.72 1.91 5.60 6.57 Magnesium 1490 5520 4032 899 5252 5440 Manganese 126 907 495 205 770 887 Mercury 0.004 1.81 0.11 0.309 0.18 1.30 Molybdenum 1.48 6.51 1.94 0.86 2.53 5.30 Nickel 8.33 31.4 18.18 4.82 25.3 29.9 Phosphorous 307 2370 1149 507 2030 2261 Potassium 384 3870 1561 830 3256 3729 Scandium 1.1 8.54 3.92 1.61 6.40 7.85 Selenium <0.001 6.14 0.87 1.01 1.50 4.70 Silicon 38 270 107 60.8 233 267 Silver <0.100 <0.100 n/a n/a n/a n/a Sodium <0.100 259 70.7 78.1 206 248 Strontium 11.9 71.2 31.3 14.4 58.6 70.3 Tin 7.13 22.6 13.2 3.77 20.1 22.3 Titanium 381 1150 602 166 840 1054 Tungsten 0.063 1.02 0.59 0.223 0.89 0.98 Vanadium 28.8 99.3 47.2 12.5 62.2 88.8 Zinc 21.7 88.3 61.8 17.0 87.1 88.1 Notes: n/a = not calculated as all concentrations are below the detection limit. Data in bold represent concentrations that exceeded the CCME agricultural soils quality guidelines.
Trace Elements in Saanich Peninsula Agricultural Soils 38
Comparison of Current Results to the 1995 BC Ministry of Environment Data
The concentrations of all the EOCs in the 1995 study (Appendix B) including Ag, As, Ba,
Be, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Zn, B, Sn, Co, V were below the CCME guidelines for agricultural soil (Appendix A). A statistical summary of the data is shown in Table 2.
Trace Elements in Saanich Peninsula Agricultural Soils 39
Table 2: Statistical Summary for the 1995 BC Ministry of Environment Data (0-15cm)
th th Elements Minimum Maximum Mean Standard 95 99 Percentile Deviation percentile Silver < 1 <1 n/c n/c n/c n/c Aluminum 32800 45100 41300 5829 45100 45100 Arsenic 3.80 5.70 5 0.83 5.65 5.69 Barium 168 256 228 40.6 254 255 Beryllium 0.70 0.90 0.82 0.09 0.90 0.90 Bismuth < 2 <2 n/c n/c n/c n/c Calcium 5830 7580 7295 1041 8183 8268 Cadmium 0.2 0.6 0.37 0.17 0.57 0.59 Cobalt 14.5 17.9 16.7 1.60 17.90 17.9 Chromium 26.2 41 32.9 6.22 39.9 40.8 Copper 30.2 34 32.3 1.62 33.8 33.9 Iron 29200 39500 36175 4773 39425 39485 Mercury < 0.05 <0.05 n/c n/c n/c n/c Potassium 2450 3770 3310 600 3755 3767 Magnesium 7740 8690 8037 446 8580 8668 Manganese 777 1240 1074 206 1231 1238 Molybdenum < 0.4 1.8 1.8 n/c 1.8 1.8 Sodium 346 444 401 47.6 443 443 Nickel 30.8 36.2 33.9 2.33 36.0 36.1 Phosphorous 908 1440 1212 222 1414 1434 Lead 3 9 6 2.58 8.70 8.94 Sulphur 203 305 274 47.9 303 304 Antimony < 1.5 3.3 2.26 0.89 3.15 3.27 Selenium < 0.2 <0.2 n/c n/c n/c n/c Tin < 2 6 4.66 1.15 5.8 5.96 Strontium 53 72.7 64.2 8.62 72.1 72.5 Tellurium < 2 <2.0 n/c n/c n/c n/c Titanium 1890 2280 2135 189 2288 2289 Thallium < 2.0 <2.0 n/c n/c n/c n/c Vanadium 80.4 92.3 87.1 5.62 92.1 92.2 Zinc 80.5 107 98.1 12.0 106 106 Zirconium 1.5 8.8 5.2 3.08 8.41 8.72 Notes: n/c = not calculated as most concentrations were below the detection limit. Data in bold represent concentrations that exceeded the CCME agricultural soils quality guidelines. Trace Elements in Saanich Peninsula Agricultural Soils 40
There were increases in the concentrations of As, Hg, Mo, Cu, Se, Sb, and Sn, in the current study compared to the 1995 data while Ba, Be, Cd, Co, Cr, Pb, Mn, Ni and Zn concentrations decreased. The t-test values and the statistical significance (p-values) of the changes in concentrations are indicated in Table 3.
Table 3: Comparison of Current and Previous Results (Two Sample t-Tests and p-Values)
Elements Current Mean 1995 Mean Difference % Change t-test p-value Arsenic 5.84 5.00 0.84 16.8 0.40 0.68 Barium 107 228 120 52.7 5.83 1.29E-06 Beryllium 0.36 0.82 0.46 56.0 9.33 4.98E-11 Boron 32.55 n/a Cadmium 0.006 0.37 0.36 97.2 13.83 9.40E-16 Chromium 26.24 32.95 6.71 20.3 1.80 0.08 Copper 37.3 32.3 5.0 15.4 0.49 0.62 Cobalt 7.85 16.72 8.87 53.0 8.40 6.41E-10 Mercury 0.11 Manganese 495 1074 578 53.8 5.31 6.21E-06 Molybdenum 1.94 1.8 0.14 7.77 2.66 0.01 Nickel 18.18 33.95 15.7 46.4 6.39 2.37E-07 Lead 2.72 6 3.28 54.6 4.12 0.00022 Antimony 14.70 2.26 12.4 550 0.30 0.76 Selenium 0.87 Tin 13.19 4.66 8.83 189 4.76 3.22E-05 Vanadium 47.23 87.12 39.9 45.7 6.21 3.99E-07 Zinc 61.8 98.1 36.3 37 4.11 0.00022 Notes: () = no significant values; however, in case of Ba no previous data were available. n/a data not available Data in bold represents statistically significant change (p- values) in concentration.
Arsenic
The average concentration of As in the earth crust is 1.8 mg/kg (Kabata-Pendias, 2011).
The principle source of As in agricultural soils is from the weathering of parent rocks, waste water irrigation and impurities present in phosphate fertilizer, insecticides and pesticides (Duker, Trace Elements in Saanich Peninsula Agricultural Soils 41
Carranza, & Hale, 2005). The possible sources of As in Saanich Peninsula soils include livestock manure, fertilizers, fungicides and pesticides (Farmers, personal communication, March 2,
2012). Arsenic concentrations are given in Appendix C while the statistical summary is included in Table 1. The mean value increased by 0.84 µg/g over the 17-year period; however, this increase was not statistically significant (Table 3). Soil As concentrations were positively correlated with clay contents (correlation coefficient, r = 0.38). High concentrations of As were observed in soil Samples 9, 15, 16 and 17 which contain relatively higher amounts of clay
(Appendix E). Figure 5 demonstrates the relationship between As and clay content in Saanich
Peninsula soils.
25
20
15 y = 0.4135x + 5.3991 R² = 0.1516 10 Arsenic µg/g Arsenic
5
0 0 5 10 15 20 25 Clay %
Figure 5: Correlation between total arsenic concentration and clay content
Antimony
The main source of Sb in agricultural soils is the natural weathering of rocks as well as industrial (coal combustion) and vehicular emissions (Nakamaru, Tagami, & Uchida, 2006).
Antimony is non-essential and an element of concern in the USEPA and EU list (Kabata- Trace Elements in Saanich Peninsula Agricultural Soils 42
Pendias, 2011). The current mean concentration (Table 1) was below the CCME guideline. There was an increase in concentration over the 17-year period; however this change was not statistically significant (Table 3). Antimony is relatively less mobile and bio- or phyto-available than other trace elements in agricultural soils. It is strongly adsorbs in Al and Fe hydroxides and adsorption increases with a decrease in pH (strong adsorption occurs below pH 7) (Nakamaru et al., 2006; Alloway, 1990). The concentration increase of Sb in Saanich Peninsula soils may be related with slightly acidic soils (average pH 5.85), and Fe and Al hydroxides concentrations.
Barium
There was a statistically significant decrease in the Ba concentration over the 17-year period as shown in Table 3. The main sources of Ba include weathering of igneous rocks, industrial activities such as brick production, glass, ceramics, paint and synthetic rubber industries (Kabata-Pendias, 2011). The decrease in Ba concentration in Saanich peninsula agricultural soils may be attributed to low clay content and sandier soils with greater leachability.
Beryllium
Industrial activities such as brick production, glass and ceramics, paint and synthetic rubber industries are the main sources of Be in the agricultural soils (Kabata-Pendias, 2011).
However, because of controlled production of these materials and improvement in environmental management practices, the concentration of this element in the current investigation showed a statistically significant decrease compared to the 1995 results.
Boron
Boron concentrations in the soil samples were elevated; however, there were no data available from the 1995 study for comparison. The main sources of B in the peninsula soils may Trace Elements in Saanich Peninsula Agricultural Soils 43 be from the use of borate and borax fertilizers by farmers (Farmers, personal communication,
March 2, 2012).
Cadmium
Cadmium is one of the most ecologically toxic metals in the environment and has adverse effects on plants, animals, humans and food quality (Kabata-Pendias, 2011). Phosphate fertilizers are the main sources of Cd in agricultural soils worldwide and may be the major sources of cadmium in Saanich Peninsula soils since Canadian phosphate fertilizers contain about 2.5 - 6.29 mg/kg Cd (Mermut et al., 1996). Other Cd sources included farmyard and livestock manure and other agricultural waste (Farmers, personal communication, March 5, 2012). The concentration of Cd was positively correlated with the clay content as shown in Figure 6. Cadmium concentrations showed a statistically significant decrease (Table 3). Cadmium is more mobile and plant available than other trace elements and as such can be removed from agricultural soils by plant uptake, leaching and erosion. A study in Australia revealed that about 95% Cd was soluble or plant available in acidic soils (Mann, Rate, & Gilkes, 2002; Alloway, 1990). The observed decrease in Cd concentrations may be due to the nature of the Saanich Peninsula soils which are slightly acidic, have sandy texture and receive high precipitation.
Trace Elements in Saanich Peninsula Agricultural Soils 44
0.035
0.03
0.025
0.02
0.015
Cadmium µg/g Cadmium 0.01 y = 0.0001x + 0.0065 R² = 0.0068 0.005
0 0 5 10 15 20 25 Clay %
Figure 6: Correlation between total Cd concentration and clay content in soil
Chromium
Chromium impairs the plant’s growth and development by affecting photosynthesis.
The mean concentration of total Cr obtained in this study (26 mg/kg) is lower than the mean level in Canadian soils (43 mg/kg) (Shanker, Cervantesb, Loza-Taverac & Avudainayagam,
2005). Impurities in phosphate fertilizers (30 – 3000 mg Cr/kg) may be the principal source of total Cr in Saanich Peninsula soils. There was no statistically significant change in Cr concentration over the study period (Table 3).
Copper
The concentrations of Cu did not show significant changes over the 17-year period (Table
3) and the mean concentration was below the CCME guideline. The major sources of Cu in
Peninsula soils may be CuSO 4 fertilizers and Cu containing pesticides and fungicides. The minor sources of Cu in soils may be from atmospheric deposition from industrial activities (textiles, paints, electrical conductors, pipes, coins and cooking utensils), and Cu mining. Copper has a Trace Elements in Saanich Peninsula Agricultural Soils 45 tendency to strongly adsorb to soil particles and is relatively less mobile compared to other trace elements leading to its accumulation in soils (CCME, 1997). Factors which influence the adsorption include pH, CEC, soil organic matter and Fe, Mn and Al oxides. Soil organic matter strongly binds Cu (one fifth to one half Cu occurs in soil organic matter) and influences its mobility (CCME, 1997, Alloway, 1990). The correlation coefficient between soil organic matter and Cu was positive (Figure 7).
120
100
80 y = 0.9294x + 22.217 R² = 0.3109 60
Copper µg/g Copper 40
20
0 0 10 20 30 40 50 60 Soil organic matter
Figure 7: Correlation between total Cu concentration in soil and soil organic matter
Cobalt
Cobalt is an essential element for animals (vitamin B 12 synthesis). The major sources in
Saanich Peninsula soil include weathering (pedogenesis) and impurities present in phosphate fertilizers and manure (Kabata-Pendias, 2011; Alloway, 1990). This study indicated that Co concentration decreased significantly over the 17-year period (Table 3) and the mean concentration was below the CCME guideline. Trace Elements in Saanich Peninsula Agricultural Soils 46
Mercury
Mercury is a non-essential element and elevated concentrations in agricultural soils are of concern since mercury is renal and neurotoxic and also highly toxic to invertebrates, microbes and plants (Tipping, Wadsworth, Norris, Hall, & Ilyn, 2011). Mercury concentrations were below the detection limit in the 1995 BC Ministry of Environment studies (Appendix B) whereas the levels in the current study (Appendix C) were all below the CCME soil quality guideline for agricultural land use (6.6µg/g).The possible sources of Hg in Saanich Peninsula agricultural soils include (phosphate fertilizers, organic manures and Hg containing fungicides and pesticides
(Farmers, personal communication, March 5, 2012). Atmospheric deposition is also a major source of Hg in agricultural soils whereas weathering of rocks is minor as igneous rocks contain fairly low levels of Hg ) (Grimaldi et al., 2008).
Manganese
Manganese is one of the most abundant trace elements in the lithosphere and mostly concentrated in loamy and calcareous soils. Anthropogenic sources of Mn in soils include MnSO 4 fertilizer and gasoline additives. Manganese is relatively more mobile in soil media than some other trace elements. In Saanich Peninsula agricultural soil, the decrease in concentration was statistically significant over the 17-year period (Table 3). The decrease in concentration may be attributed to the slightly acidic pH of the Saanich Peninsula soils since Mn is leachable in acidic soils (Kabata-Pendias, 2011).
Molybdenum
Molybdenum is one of the essential trace elements for plants. Elevated concentrations (up to 24 mg/kg) exceeding the CCME guidelines (5µg/g) has been found in some parts of British
Columbia (Kabata-Pendias, 2011). The concentrations of Mo obtained in this study were all below the CCME guideline and showed slight increase compared to the 1995 results. The major Trace Elements in Saanich Peninsula Agricultural Soils 47 sources of Mo in Saanich Peninsula soils were impurities in fertilizers, weathering of rocks and atmospheric deposition. Contrary to other micronutrients, Mo adsorption to soil decreases with increasing pH and maximum adsorption occurs at pH 4 and 5. Saanich Peninsula agricultural soils were very suitable for Mo adsorption because of the pH range and desorption was fairly low.
Nickel
Natural weathering of rocks is the main source of Ni in the soil environment (Kabata-
Pendias, 2011). Atmospheric deposition (from metal mining and refining activities) may also introduce the metal into agricultural soils. The concentrations obtained in this study (Table 1) were all below the CCME guideline. The mean concentration decreased compared to the previous study (as shown in Table 3). This change in concentration over the 17-year period was statistically significant. Soil pH, soil types and clay contents were responsible for Ni mobility in agricultural soils. Saanich Peninsula agricultural soils were light acidic with very small amount of clay which was a favorable environment for Ni mobility or leaching from soils (CCME,
1999).
Lead
Lead has a long residence time in soils compared to other trace elements. It is a highly toxic metal and cause mental impairment in young children (Alloway, 1990). The current mean concentration was lower than the previous data as shown in Table 3: the change was statistically significant. The main sources of lead in soils include the weathering of rocks, impurities in phosphate fertilizer and atmospheric deposition mainly from vehicles and industries (lead acid batteries, paints and leaded gasoline) (Kabata-Pendias, 2011). However, since Canada and the Trace Elements in Saanich Peninsula Agricultural Soils 48
USA banned the use of leaded gasoline, its concentration in the environment has been significantly decreasing and is reflected in this study.
Selenium
Selenium is an essential micronutrient for animals including humans, and so far no biochemical functions in plants have been identified. It is an EOC in agricultural soils as its beneficial and harmful range is extremely narrow (0.10 mg/kg is required in food to prevent white muscle disease) (Alloway, 1990). Natural process of weathering, impurities present in phosphate fertilizers, atmospheric deposition (coal and fossil fuels combustions in vehicles and industries as well as volcanic emissions), livestock manure and deliberate addition of Se containing fertilizers (sodium selenite, Na 2SeO 3) and sometimes insecticides and foliar spray were the sources of Se in Saanich Peninsula agricultural soils (CCME, 2009; Farmers, personal communication, March 2, 2012). ). The concentrations of Se were below the detection limit
(Appendix B) in the 1995 BC Ministry of Environment study whereas in the current study; the levels ranged from 0.25µg/g to 6.16µg/g with a mean of 0.87µg/g (Tables 1 and 3). The concentrations in five soil samples (viz., Samples 1, 14, 16, 17 and 21) exceeded the CCME Soil quality guidelines for agricultural land use.
The speciation of Se affects its mobility and toxicity. Elemental selenium (Se°) is not mobile and non-toxic in agricultural soils whereas its mobility increases with ionization: mobility increases with increasing oxidation state in the order selenide (Se 2-), selenite ( Se 4+ ) and selenate
( Se 6+ ). Due to the potential health risks associated with the speciation of Se, four samples (viz.,
Samples 1, 5, 9 and 16 (Appendix C) with concentrations in excess of the CCME soil quality guidelines were subjected to speciation analysis to determine the composition of Se 2-, Se 4+ and
Se 6+ . The water extractable Se concentrations (i.e., speciation) as shown in Table 4 were very Trace Elements in Saanich Peninsula Agricultural Soils 49 low compared to the total soil Se concentrations (Appendix C) suggesting that the mobility (or phyto-availability) of the Se in the soils was very low. The low mobility of the Se in the Saanich
Peninsula soils was attributed to the lightly acidic pH nature of the soils (average pH of 5.85) since Se is highly adsorbed to soil particles in acidic medium particularly between pH 3 to 5
(Kabata-Pendias, 2011; Alloway, 1990).
Table 4: Water Soluble Selenium Species in Selected Saanich Peninsula Agricultural Soils
Selenium Species (µg/g) Sample 1 Sample 5 Sample 9 Sample 16 Se 4+ 0.013 0.0012 0.007 0.001 Se 6+ 0.001 0.004 0.004 0.003 Se 2- 0.046 0.016 0.017 0.0310 Se 2- + Se 4+ + Se 6+ 0.0602 0.0210 0.027 0.0345
Tin
The concentrations of Sn in Saanich Peninsula agricultural soils are shown in Appendix
C. The mean value (Table 1) was higher than the CCME guideline (5µg/g) and was also higher than the mean (Table 2) for the 1995 investigation. The increase in Sn concentration was statistically significant (Table 3). Weathering of igneous rocks (particularly acidic igneous rock), coal combustion, waste incineration and impurities in fertilizers are some of the major sources of
Sn in agricultural soils (Kabata-Pendias, 2011). However, except for the role of igneous rock the source of the increasing Sn levels in Saanich Peninsula agricultural soils could not be determined. In higher concentrations, Sn can form organotin complexes with SOM which are very toxic to animals and human beings (Nakamaru & Uchida, 2006).
Trace Elements in Saanich Peninsula Agricultural Soils 50
Vanadium
Vanadium is a non-essential trace element to higher plants and animals but is essential for some microorganism and algae (Kabata-Pendias, 2011). There was a statistically significant decrease in the mean V concentration compared to the previous data (Table 3). Soil type, pH, and SOM influenced the mobility of V in agricultural soils. In addition, Mandiwana and
Panichev (2009) found that soil ammonia and carbon dioxide also play significant roles in leaching V from agricultural soils. However, the measurement of soil ammonia and carbon dioxide levels was beyond the scope of this project.
Zinc
Zinc is an essential element to both plants and animals and occurs as Zn 2+ ion in soil solution (soluble fraction). Weathering of parent rocks, atmospheric deposition, Zn fertilizers and impurities in other fertilizers are the main sources of Zn in agricultural soils (Kabata-Pendias,
2011; Alloway, 1990). This study indicated that Zn concentrations decreased in Saanich
Peninsula agricultural soils. The concentration changes were statistically significant (Table 3).
As with other trace elements, Zn adsorption and desorption is influenced by soil pH and soil types as well as total Zn present in soils. It is highly soluble in mildly acidic and sandy soils.
Saanich Peninsula agricultural soils are mildly acidic with sandy textures which facilitated Zn leaching from the soils resulting in the decrease (CCME, 1999; Kabata-Pendias, 2011).
Mobility of Trace Elements in Soils (Soil Solid/Liquid Partition Coefficients, Kd)
Depending on speciation, only a fraction of the total element in a soil sample (as determined by aqua regia digestion) is mobile or bioavailable. The environmental fate, transport and bioavailability of trace elements in soils may be described using the soil solid/liquid partition coefficients (Kd) (Sheppard et al., 2009; Serne, 2007). Soil Kd values are very useful for Trace Elements in Saanich Peninsula Agricultural Soils 51 environmental impacts assessments and risk assessment (Sheppard, Long, Sanipelli, &
Sohlenius, 2009)
Concentration in aqua regia extraction mg/kg Kd L/kg Concentration in pore water mg/L
The leaching of trace elements in soil-systems is negligible at soil Kd values greater than
1000 Lkg -1 but below this value leaching occurs (Sheppard et al., 2009). Soil Kd values depend on environmental factors such as soil pH, SOM, clay content and oxides of Fe, Mn and Al.
Increase in the amount of clay minerals and SOM increases the adsorption of trace elements onto soil particles resulting in high Kd values. Since most of the elements are weakly adsorbed at low pH and strongly adsorbed at high pH (except Se and Mo), soil Kd values are lower in the acidic environment compared to the alkaline environment (Luo, Zhou, Liu, & Wang, 2006).
The Kd values for selected EOC in agro-systems in the Saanich Peninsula soil samples are given in Appendix F. A statistical summary of the data is given in Table 5.
Trace Elements in Saanich Peninsula Agricultural Soils 52
Table 5: Kd Values for Selected Elements in Saanich Peninsula Agricultural Soils
Element Minimum Maximum Mean Correlation Correlation with clay with pH Arsenic 58.6 1915 485 -0.06 -0.09 Barium 173 1361 540 0.008 -0.07 Beryllium Boron 2 5.27 3.63 -0.09 -0.04 Cadmium 0.5 6 2.56 -0.23 0.34 Chromium 137 1104 380 -0.22 0.08 Copper 52.9 398 112 -0.19 0.66 Cobalt 57.9 570 331 0.005 -0.33 Mercury Manganese 86.2 57045 2924 0.4 -0.08 Molybdenum 4.61 8.28 5.65 -0.09 0.41 Nickel Lead Antimony 5.45 80000 2700 -0.05 -0.02 Selenium 46.1 1020 284 0.49 0.04 Tin Vanadium 86.1 342 216 -0.31 -0.12 Zinc 48.1 683 220 -0.19 -0.24 Notes: () = no significant values as their concentration were below the detection limit in water extraction. Data in bold represents very low and very high Kd values of elements.
Based on the data obtained (Table 5) Be, Hg, Ni, Pb, Sb and Sn were all relatively immobile. Cadmium was highly mobile with Kd values ranging from 0.5 Lkg -1 to 6 Lkg -1 and a mean 2.56 Lkg -1 as shown in Table 5; Cd concentrations were however very low. Boron had elevated concentrations that exceeded the CCME guidelines and also had low Kd values as shown in Table 5 indicative of high mobility. Special precaution is therefore required to control and reduce boron concentrations to the CCME guidelines (2µg/g). Arsenic mobility in the soils was relatively low and therefore, environmental concerns associated with the slight increase of
As concentration in the Saanich Peninsula soils was minor. Trace Elements in Saanich Peninsula Agricultural Soils 53
The Kd values for Cr, Cu and Co implied the lower mobility in the Saanich Peninsula soil-systems. Despite an increase in Se levels in the Saanich Peninsula agricultural soils, its mobility was very low with a mean Kd value of 284 Lkg -1.
Kd values generally increase with increasing soil clay content due to the adsorption of the trace elements on their surfaces. This relationship was true for about half of the trace elements studied as shown in Table 5. The positive correlation between Cu and Cd Kd values and soil clay content are shown in Figure 8 and 9 respectively. For the remaining elements it appears other factors such as pH, SOM, and Al, Fe and Mn oxides may predominant and influence the Kd values.
450 400 350 y = 12.549x + 95.719 R² = 0.4413 300 250 200 150 Cu Kd values values Kd Cu 100 50 0 0 5 10 15 20 25 Clay %
Figure 8: Correlation between Cu Kd values and clay
Trace Elements in Saanich Peninsula Agricultural Soils 54
7
6
5 y = 0.1229x + 2.395 R² = 0.1127 4
Cd kd Cd 3
2
1
0 0 5 10 15 20 25 Clay content (%)
Figure 9: Relationship between Cd Kd values and clay
Trace Elements in Saanich Peninsula Agricultural Soils 55
Conclusions and Recommendations
Conclusions
This study indicated that the pH of Saanich Peninsula agricultural soils was below the
CCME soil quality guideline for agricultural land use (pH 6 to 8). However, soil pH increased at a very slow rate compared to the 1995 BC Ministry of Environment study and the mean soil pH was mildly acidic (pH = 5.85). The mean soil electrical conductivity was also below the CCME guideline (i.e., 2ds/m). Trace elements such as Zn, Mn, Cu, Fe, Co and B were highly leachable in light acidic soil whereas Mo and Se were immobile in light acidic medium and only mobile or leachable in alkaline medium in Saanich Peninsula agricultural soils. Therefore, soil pH was one of the major factors for the retention and mobility of trace elements in the soils. Other factors included soil electrical conductivity, soil textures and soil organic matter.
The soils had sandier texture (average 75% sand) with variable clay content (0 – 20%).
This implied that the soils’ nutrients and water holding capacity were fairly low and could be the reason behind the low soil electrical conductivity. Soil organic matter was somewhat higher in
Saanich Peninsula soil, higher than dry land site of Alberta (i.e., 3.4%) and general soils guidelines (i.e., 3 to 6%). This aided in adsorption and absorption of water, nutrients and minerals despite the sandier textures. The application of manure, silt and clay content, precipitation and temperature were the main contributing factors for the elevated soil organic matter in Saanich Peninsula agricultural soils.
There were statistically significant increases in the concentrations of As, B, Cu, Se, Sn,
Hg and Sb compared to the 1995 BC Ministry of Environment data. Among these elements, B and Sn levels in the 30 samples analyzed exceeded the CCME soil quality guidelines for agricultural land use. Arsenic, Se and Cu concentrations in some of the samples also exceeded Trace Elements in Saanich Peninsula Agricultural Soils 56 the CCME guidelines. Barium, Be, Cd, Cr, Co, Mn, Ni, Pb, V and Zn concentrations decreased compared to the previous BC Ministry of Environment data. Soil Kd values indicated different trace elements mobility in the soil systems, which followed the order Cd > B >Mo > Cr > V> Zn >
Se > Co > Cr > As > Ba > Sb > Mn> Ag, Be, Hg, Ni, Pb.
Since most of the trace elements were below the CCME guidelines and elements balance
(i.e., increase or decrease in concentrations) were not pronounced within the 17-year period, this study concluded that Saanich Peninsula farmers have been practicing sound agricultural management practices and moving towards sustainable agricultural production. However, this study found that some moderate (i.e., Cu, As) and high risk (i.e., Se, B, Hg) trace elements for
Canadian agricultural soils (Agriculture and Agri-Food Canada, 2005) were slowly increasing in the Peninsula soil. Although except Boron they were not harmful as their concentrations in most of the soil samples were below the CCME agricultural soil quality guidelines. It is utmost importance to study their sources and changes in concentration over time to maintain the present agricultural management practices in the Peninsula soils.
Recommendations and Possible Future Research Directions
1. The background concentrations, concentration change and leachability (solid/liquid partition
coefficient, Kd) of trace elements in the Canadian agricultural soils are largely unknown.
Therefore, periodical study of trace elements in agricultural soils should be done to monitor
their levels in soils and environmental management of agricultural lands.
2. This study only focused on the total metals and their mobility in soil-systems (0 to 15cm).
Since plants can also absorb trace metals from soils and the surrounding environments, the
total metals content in fruits and vegetables in Saanich Peninsula could be analyzed to
determine potential food chain uptake and ensure sustainable agriculture. Trace Elements in Saanich Peninsula Agricultural Soils 57
3. This study only focused on the trace elements present on the surface soil (0-15cm) and detail
study of trace elements in different layers of soils such as surface and subsurface and their
mobility in these levels should be determined.
4. Different types of fertilizers, chemicals as well as farmyard manure, insecticides and
pesticides currently used in the Saanich Peninsula should be analyzed in order to determine
their contributions to trace elements loading in agricultural soils.
5. The sources and causes of the increase in concentrations of metals such as As, Bo, Hg, Se
and Sn identified in this study should be determined.
6. To better inform farmers regarding the effects of trace elements on food quality, food safety
and environmental contamination, some training or workshop on trace elements in agro-
chemicals and fertilizers and their management on farm lands should be provided.
7. How climate change is influencing biogeochemical cycling of trace elements and nutrients in
agricultural lands should be studied.
Trace Elements in Saanich Peninsula Agricultural Soils 58
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Trace Elements in Saanich Peninsula Agricultural Soils 69
APPENDICES
Appendix A: Canadian Council of Ministers of the Environment (CCME) agricultural soil quality guidelines (CCME, 2007).
Trace Elements Soil Quality Guidelines in mg.kg -1( dry weight) Arsenic (As) 12 Antimony (Sb) 20 Barium (Ba) 750 Beryllium (Be) 4 Boron (B) 2 (hot water soluble boron) Cadmium (Cd) 1.4 Total Chromium (Cr) 64 Chromium Hexavalent 0.4 Copper (Cu) 63 Cobalt (Co) 40 Mercury (Hg) 6.6 Lead (Pb) 70 Molybdenum (Mo) 5 Nickel (Ni) 50 Selenium (Se) 1 Silver (Ag) 20 Tin (Sn) 5 Uranium (U) 23 Vanadium (V) 130 Zinc (Zn) 200 Soil Conductivity (ds/m) 2 Soil pH 6 to 8 Sulphur (S) 500 Total Fluoride (F) 200
Trace Elements in Saanich Peninsula Agricultural Soils 70
Appendix B: Trace elements in agricultural soils (surface soil, 0-15cm) of Saanich Peninsula (Central Saanich) (BC Ministry of Environment, 1995)
Parameter Detectable Unit Sample 1 Sample 2 Sample 3 Sample 4 Silver 1 µg/g 1 1 1 1 Aluminum 2 µg/g 45100 32800 45100 42200 Arsenic 0.2 µg/g 5.4 3.8 5.7 5.1 Barium 0.1 µg/g 256 168 249 240 Beryllium 0.1 µg/g 0.9 0.7 0.9 0.8 Bismuth 2 µg/g 2 2 2 2 Calcium 1 µg/g 7480 5830 8290 7580 Cadmium 0.1 µg/g 0.6 0.3 0.4 0.2 Cobalt 0.3 µg/g 16.6 14.5 17.9 17.9 Chromium 0.2 µg/g 30.7 41 26.2 33.9 Copper 0.1 µg/g 34 30.2 32.2 33.1 Iron 0.3 µg/g 39500 29200 39000 37000 Mercury 0.05 µg/g 0.05 0.05 0.05 0.05 Potassium 40 µg/g 3670 2450 3770 3350 Magnesium 2 µg/g 8690 7760 7960 7740 Manganese 0.2 µg/g 1100 777 1180 1240 Molybdenum 0.4 µg/g 1.8 0.4 0.4 0.4 Sodium 1 µg/g 444 346 438 377 Nickel 0.8 µg/g 36.2 30.8 35.1 33.7 Phosphorus 4 µg/g 1230 908 1440 1270 Lead 2 µg/g 5 3 9 7 Sulphur 3 µg/g 305 203 293 297 Antimony 1.5 µg/g 3.3 1.7 1.8 1.5 Selenium 0.2 µg/g 0.2 0.2 2 0.3 Tin 2 µg/g 4 2 6 4 Strontium 0.1 µg/g 68.9 53 72.7 62.4 Tellurium 2 µg/g 2 2 2 2 Titanium 0.3 µg/g 2280 1890 2290 2080 Thallium 2 µg/g 2.0 2.0 2.0 2.0 Vanadium 0.3 µg/g 92.3 80.4 91.2 84.6 Zinc 0.2 µg/g 104 80.5 107 101 Xirconium 0.3 µg/g 4.3 8.8 1.5 6.2
Trace Elements in Saanich Peninsula Agricultural Soils 71
Appendix C: Total metals, pH, soil organic matter (SOM), and electrical conductivity (EC) for Saanich Peninsula agricultural soils
Parameter Units SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 1 2 3 4 5 6 pH 6.22 6.73 6.93 6.61 6.03 5.6 SOM % 43 17.8 14.6 15.2 13.3 7.82 EC (uS/cm) 294 143 144 256 164 124 Aluminium Al µg/g 15900 13700 14800 11300 12700 10300 Antimony Sb µg/g 0.427 0.279 0.255 0.23 0.225 0.15 Arsenic As µg/g 18 2.93 5.51 4.55 5.53 4.9 Barium Ba µg/g 101 104 104 96.1 99.5 86.2 Beryllium Be µg/g 0.478 0.321 0.389 0.245 0.347 0.255 Boron B µg/g 26.8 32.5 36.2 37.8 33.5 33.4 Cadmium Cd µg/g 0.015 0.005 0.006 0.007 0.009 0.012 Calcium Ca µg/g 17000 7680 7270 5980 4450 2950 Chromium Cr µg/g 43 25.9 26.9 18.9 28.6 19.2 Cobalt Co µg/g 7.45 6.09 8.97 6.12 8.65 6.02 Copper Cu µg/g 114 36.4 40.3 32.9 31.2 54.5 Gold Au µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Iron Fe µg/g 10400 13100 17000 13400 17200 13700 Lanthanum La µg/g 8.34 6.11 7.48 4.21 6.41 3.69 Lead Pb µg/g 4.1 5.3 6.82 5.19 3.27 1.2 Magnesium Mg µg/g 3610 3970 4550 3860 4150 3360 Manganese Mn µg/g 292 254 502 487 606 663 Mercury Hg µg/g 0.156 0.066 0.071 0.069 0.062 0.059 Molybdenum Mo µg/g 6.51 1.85 1.93 1.76 1.74 1.73 Nickel Ni µg/g 22.4 14.6 18 13.7 16.9 13.6 Phosphorus P µg/g 1880 1220 1270 1630 1330 2030 Potassium K µg/g 1700 2610 3140 1760 2150 1340 Scandium Sc µg/g 5.83 4 3.94 2 3.16 2.13 Selenium Se µg/g 6.14 0.738 0.828 0.569 0.634 0.431 Silicon Si µg/g 184 174 157 114 84.9 169 Silver Ag µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Sodium Na µg/g 259 153 <0.100 3.58 <0.100 19.2 Strontium Sr µg/g 68.4 36.4 38.9 27.2 24 17.8 Tin Sn µg/g 22.6 13.4 13.6 9.28 14.3 9.93 Titanium Ti µg/g 593 430 737 449 460 381 Tungsten W µg/g <0.050 0.868 0.672 0.791 0.911 0.815 Vanadium V µg/g 99.3 39.6 50.8 34.6 48.2 34.8 Zinc Zn µg/g 54.4 66 79.5 67.1 84.7 66.3 Trace Elements in Saanich Peninsula Agricultural Soils 72
Appendix C: Total metals, pH, s oil organic matter (SOM), and electrical conductivity (EC) for Saanich Peninsula agricultural soils (Continued)
Elements Units Sample Sample Sample Sample Sample Sample 7 8 9 10 11 12 pH 5.6 6.04 6.39 5.9 5.23 5.87 SOM % 7.73 7.6 13 10.5 16.7 13.5 EC (uS/cm) 112 65.6 176 89.7 180 508 Aluminium Al µg/g 10300 7240 17600 18000 10900 12800 Antimony Sb µg/g 0.15 0.106 0.121 0.103 0.071 0.083 Arsenic As µg/g 4.9 2.57 20 4.82 2.28 2.55 Barium Ba µg/g 86.2 35.2 188 121 45.5 46.8 Beryllium Be µg/g 0.255 0.194 0.383 0.413 0.343 0.38 Boron B µg/g 33.4 31.2 38 32.7 33.6 37.7 Cadmium Cd µg/g 0.012 0.002 0.007 0.005 0.008 0.006 Calcium Ca µg/g 2950 2360 7820 6140 6180 5630 Chromium Cr µg/g 19.2 13.9 37.3 30.3 15 17.4 Cobalt Co µg/g 6.02 2.26 10.4 9.17 5.03 5.25 Copper Cu µg/g 54.5 20.1 42.9 56.7 19 24 Gold Au µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Iron Fe µg/g 13700 14000 21500 15200 12200 12800 Lanthanum La µg/g 3.69 3.73 6.8 9.45 5.81 7.39 Lead Pb µg/g 1.2 2.06 <0.001 <0.001 1.1 <0.001 Magnesium Mg µg/g 3360 1880 4830 4540 3460 3490 Manganese Mn µg/g 663 147 169 450 180 196 Mercury Hg µg/g 0.059 0.012 0.077 0.043 0.093 0.092 Molybdenum Mo µg/g 1.73 1.64 2.73 1.73 1.64 1.72 Nickel Ni µg/g 13.6 8.33 26.9 21.9 12.1 12.9 Phosphorus P µg/g 2030 307 1240 708 999 658 Potassium K µg/g 1340 384 3430 1420 944 1020 Scandium Sc µg/g 2.13 1.1 6.41 6.4 2.47 3.15 Selenium Se µg/g 0.431 0.257 0.982 0.858 0.46 0.46 Silicon Si µg/g 169 134 84 80.4 45.3 38 Silver Ag µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Sodium Na µg/g 19.2 98.4 <0.100 83.4 <0.100 <0.100 Strontium Sr µg/g 17.8 11.9 41.9 33.9 31.7 27.7 Tin Sn µg/g 9.93 7.13 21.8 15.2 8.36 9.27 Titanium Ti µg/g 381 451 709 553 832 748 Tungsten W µg/g 0.815 0.19 0.427 0.402 0.512 0.497 Vanadium V µg/g 34.8 28.8 47.9 50.9 36.9 38.3 Zinc Zn µg/g 66.3 21.7 73.6 52.3 57.5 73.6 Trace Elements in Saanich Peninsula Agricultural Soils 73
Appendix C: Total metals, pH, s oil organic matter (SOM), and electrical conductivity (EC) for Saanich Peninsula agricultural soils (Continued)
Parameters Units Sample Sample Sample Sample Sample Sample 13 14 15 16 17 18 pH 5.63 5.75 5.68 5.13 4.89 6.69 SOM % 14.8 21 18.9 52.9 54.3 13.4 EC (uS/cm) 146 130 145 140 220 182 Aluminium Al µg/g 19200 29100 14500 11700 11100 9760 Antimony Sb µg/g 0.085 0.06 480 0.132 0.223 0.145 Arsenic As µg/g 4.42 5 11.5 11.4 10.9 3.52 Barium Ba µg/g 150 207 87.1 69.8 69.6 88.1 Beryllium Be µg/g 0.495 0.717 0.359 0.367 0.337 0.277 Boron B µg/g 35.7 39.3 35.1 30.8 32.2 30.8 Cadmium Cd µg/g 0.005 0.004 0.007 0.01 0.007 0.003 Calcium Ca µg/g 6230 7830 7890 8110 8480 7230 Chromium Cr µg/g 30.9 41 27.6 22 21.5 17.6 Cobalt Co µg/g 9.2 11.4 12.1 5.98 7.04 6.73 Copper Cu µg/g 33.5 52.1 75.7 52.6 50.1 26.4 Gold Au µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Iron Fe µg/g 18500 22400 18700 12300 12500 13300 Lanthanum La µg/g 14 17.4 7.46 7.94 6.07 5.14 Lead Pb µg/g <0.001 <0.001 <0.001 0.968 <0.001 3.07 Magnesium Mg µg/g 4280 5170 4980 1490 2700 4330 Manganese Mn µg/g 644 845 720 126 174 463 Mercury Hg µg/g 0.062 0.084 0.127 0.229 0.15 0.022 Molybdenum Mo µg/g 1.53 1.65 1.87 2.13 2.41 1.69 Nickel Ni µg/g 21.8 31.4 23.4 24.3 21 14 Phosphorus P µg/g 790 1240 1020 1490 1110 929 Potassium K µg/g 2810 3870 1520 811 914 1420 Scandium Sc µg/g 5.92 8.54 5.78 4.46 4.32 2.66 Selenium Se µg/g 0.878 1.39 <0.001 1.5 1.52 0.458 Silicon Si µg/g 51.6 60.9 77.1 270 39.7 68.1 Silver Ag µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Sodium Na µg/g <0.100 <0.100 8.95 <0.100 29.7 <0.100 Strontium Sr µg/g 52 71.2 37.5 45 50.7 29.8 Tin Sn µg/g 14.3 19 13.9 10.5 10.5 9.72 Titanium Ti µg/g 852 1150 646 503 533 634 Tungsten W µg/g 0.339 <0.050 0.063 <0.050 <0.050 0.586 Vanadium V µg/g 54.6 66.7 53.2 40.4 40.9 34.4 Zinc Zn µg/g 72.6 88.3 45 30.8 36.2 56.3 Trace Elements in Saanich Peninsula Agricultural Soils 74
Appendix C: Total metals, pH, s oil organic matter (SOM), and electrical conductivity (EC) for Saanich Peninsula agricultural soils (Continued)
Elements Units Sample Sample Sample Sample Sample Sample 19 20 21 22 23 24 pH 5.37 6.11 6.21 5.82 5.49 5.06 SOM % 10.1 12.1 13.6 8.93 11.8 9.29 SEC (uS/cm) 218 183 172 152 79.5 129 Aluminium Al µg/g 17300 13600 18600 14300 17300 14100 Antimony Sb µg/g 0.165 0.105 0.062 0.118 0.127 0.166 Arsenic As µg/g 5.14 3.37 3.83 3.68 4.09 3.87 Barium Ba µg/g 185 117 137 96.6 135 138 Beryllium Be µg/g 0.434 0.333 0.441 0.376 0.421 0.39 Boron B µg/g 29.9 29.7 32.7 30.1 29.8 30.4 Cadmium Cd µg/g 0.003 0.003 0.004 0.002 0.002 0.002 Calcium Ca µg/g 3390 5020 6280 3870 3580 1820 Chromium Cr µg/g 30.4 25.6 30.7 26.4 31.4 23.5 Cobalt Co µg/g 9.94 8.74 7.81 8.17 9.92 7.66 Copper Cu µg/g 25.7 26.5 32.3 20.5 20.1 23.3 Gold Au µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Iron Fe µg/g 19200 16900 18200 17300 19600 16300 Lanthanum La µg/g 11.9 6.68 10.3 6.63 7.82 7.9 Lead Pb µg/g <0.001 0.455 <0.001 <0.001 <0.001 4.24 Magnesium Mg µg/g 4560 4490 4110 4040 4730 3510 Manganese Mn µg/g 907 656 500 435 624 657 Mercury Hg µg/g 1.81 0.012 0.053 0.047 0.036 0.014 Molybdenum Mo µg/g 1.54 1.61 1.59 1.52 1.53 1.54 Nickel Ni µg/g 22.4 17.6 21.2 16.7 20.7 15.4 Phosphorus P µg/g 1090 962 967 462 651 625 Potassium K µg/g 1090 1510 1430 830 976 510 Scandium Sc µg/g 4 3.38 5.32 3.53 3.43 2.87 Selenium Se µg/g 0.666 0.565 1.02 0.549 0.599 0.437 Silicon Si µg/g 80.9 55.7 48.2 67.2 91.1 114 Silver Ag µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Sodium Na µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Strontium Sr µg/g 24.7 29.6 39.5 22.2 25.6 12.5 Tin Sn µg/g 15.4 13.8 14.8 15 17.9 10.7 Titanium Ti µg/g 736 692 544 576 767 539 Tungsten W µg/g 0.638 0.623 0.671 0.472 0.435 0.433 Vanadium V µg/g 57.6 47.8 48.6 49.2 59.2 46.9 Zinc Zn µg/g 79.8 67.4 78.7 56.6 66.5 48.6
Trace Elements in Saanich Peninsula Agricultural Soils 75
Appendix C: Total metals, pH, s oil organic matter (SOM), and electrical conductivity (EC) for Saanich Peninsula agricultural soils (Continued)
Elements Sample Sample Sample Sample Sample Sample 25 26 27 28 29 30 pH 5.31 6.45 5.91 5.48 5.75 5.67 SOM % 8.02 13.3 6.04 5.96 13.2 18.9 SEC (uS/cm) 32.6 144 103 76.1 427 306 Aluminium Al µg/g 15100 9390 13300 14200 14500 14800 Antimony Sb µg/g 0.178 0.098 0.17 0.165 0.229 0.282 Arsenic As µg/g 5.5 3.87 4.23 4.48 5.8 5.7 Barium Ba µg/g 141 73.5 94.8 92.9 105 112 Beryllium Be µg/g 0.366 0.273 0.354 0.386 0.382 0.404 Boron B µg/g 29.7 33.5 28.7 25.7 32.5 36.6 Cadmium Cd µg/g 0.004 0.002 0.003 0.003 0.032 0.011 Calcium Ca µg/g 2580 3510 2540 2360 7280 8980 Chromium Cr µg/g 26.5 24.2 19 22.8 36.3 31.6 Cobalt Co µg/g 6.33 6.98 6.92 7.52 9.71 9.44 Copper Cu µg/g 25.2 27 18.7 19.9 30.7 32.6 Gold Au µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Iron Fe µg/g 18700 14300 14500 15300 17400 17400 Lanthanum La µg/g 8.18 4.19 6.1 6.46 7.38 8.91 Lead Pb µg/g 0.72 <0.001 <0.001 <0.001 0.968 3.59 Magnesium Mg µg/g 4620 3740 3400 3480 5240 5520 Manganese Mn µg/g 712 477 483 574 549 594 Mercury Hg µg/g 0.009 0.007 0.004 0.013 0.005 0.012 Molybdenum Mo µg/g 1.48 1.83 1.87 1.88 2.08 2.12 Nickel Ni µg/g 20.1 15.9 13.7 14.5 19.7 18.3 Phosphorus P µg/g 941 728 726 1020 2370 2030 Potassium K µg/g 1210 1660 694 695 2080 2020 Scandium Sc µg/g 3.47 2.28 2.75 3.29 3.64 4.37 Selenium Se µg/g 0.401 0.353 0.399 0.578 0.887 0.843 Silicon Si µg/g 103 114 214 262 83.1 69.2 Silver Ag µg/g <0.100 <0.100 <0.100 <0.100 <0.100 <0.100 Sodium Na µg/g <0.100 22.2 <0.100 <0.100 <0.100 <0.100 Strontium Sr µg/g 18.8 16.8 14.6 13.7 29.8 34.5 Tin Sn µg/g 14 9.49 9.44 9.43 18.4 13.7 Titanium Ti µg/g 646 445 728 710 565 528 Tungsten W µg/g 0.83 0.723 0.494 0.542 1.02 0.796 Vanadium V µg/g 49.2 36.6 43.1 44.5 55.2 50.2 Zinc Zn µg/g 61.5 43.3 37.9 45.9 87.6 86.8
Trace Elements in Saanich Peninsula Agricultural Soils 76
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g)
ELEMENTS SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 1 2 3 4 5 6
Aluminium Al 11.0 9.75 16.4 7.74 95.1 10.3 Antimony Sb 0.019 0.011 0.003 <0.001 0.007 0.027 Arsenic As 0.137 0.05 0.037 <0.001 0.043 0.043 Barium Ba 0.208 0.217 0.194 0.159 0.555 0.111 Beryllium Be <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Boron B 9.52 10.3 10.1 9.71 11.6 10.2 Cadmium Cd 0.004 0.002 0.002 <0.000 0.003 0.002 Calcium Ca 258 130 81 80.8 55.8 31.9 Chromium Cr 0.095 0.067 0.087 0.049 0.191 0.083 Cobalt Co 0.036 0.032 <0.020 <0.020 0.044 <0.020 Copper Cu 0.484 0.401 0.636 0.517 0.505 0.56 Gold Au 0.061 0.067 0.059 0.049 0.064 0.052 Iron Fe 4.93 8.38 8.63 3.99 55.6 3.76 Lanthanum La <0.020 <0.020 <0.020 <0.020 <0.020 <0.020 Lead Pb <0.001 <0.001 <0.001 <0.001 0.024 <0.001 Magnesium Mg 52.6 32.8 17.1 17.7 21.8 6.46 Manganese Mn 1.66 1.15 0.088 0.127 1.14 1.15 Mercury Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Molybdenum Mo 0.786 0.367 0.351 0.374 0.329 0.338 Nickel Ni <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Phosphorus P 5.16 30.5 16.4 25.0 23.1 38.0 Potassium K 86.1 165 140 187 112 90.4 Scandium Sc <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Selenium Se 0.027 <0.001 <0.001 <0.001 0.003 <0.001 Silicon Si 15.3 23.2 27.6 13.8 95.5 9.34 Silver Ag <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Sodium Na 92.2 41.4 27.5 29.6 32.1 24.6 Strontium Sr 0.682 0.348 0.239 0.194 0.192 0.102 Tin Sn <0.010 <0.010 <0.010 <0.010 0.043 <0.010 Titanium Ti 0.217 0.463 0.736 0.258 4.36 0.234 Tungsten W <0.050 0.058 <0.050 <0.050 <0.050 <0.050 Vanadium V 1.10 0.46 0.373 0.264 0.426 0.216
Trace Elements in Saanich Peninsula Agricultural Soils 77
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g) (Continued)
ELEMENTS SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 7 8 9 10 11 12 Aluminium Al 5.23 7.34 7.65 28.6 6.58 6.29 Antimony Sb 0.013 0.012 0.015 0.013 0.005 0.006 Arsenic As 0.009 0.01 0.039 0.028 0.009 0.003 Barium Ba 0.17 0.203 0.169 0.241 0.184 0.165 Beryllium Be <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Boron B 6.51 11.8 8.38 7.02 8.27 8.97 Cadmium Cd 0.002 0.002 0.003 0.002 0.003 0.002 Calcium Ca 64.5 65.1 85.4 62.5 51.9 71.4 Chromium Cr 0.061 0.046 0.113 0.06 0.087 0.127 Cobalt Co 0.021 0.039 <0.020 <0.020 0.021 0.021 Copper Cu 0.39 0.38 0.25 0.317 0.356 0.34 Gold Au 0.051 0.053 0.043 0.053 0.041 0.045 Iron Fe 2.63 2.91 3.37 13.4 1.08 1.65 Lanthanum La <0.020 <0.020 <0.020 <0.020 <0.020 <0.020 Lead Pb <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Magnesium Mg 6.89 6.69 23.1 19.6 9.94 19.1 Manganese Mn 0.396 0.078 1.96 0.148 0.255 0.259 Mercury Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Molybdenum Mo 0.315 0.296 0.341 0.318 0.322 0.305 Nickel Ni <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Phosphorus P 1.03 1.08 6.72 5.73 35.1 12.5 Potassium K 14.6 18.7 22.9 14 86.8 105 Scandium Sc <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Selenium Se <0.001 0.001 0.001 0.002 0.004 <0.001 Silicon Si 9.58 11.3 28.4 51.4 11.6 11.4 Silver Ag <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Sodium Na 23.9 26.7 34.7 41.3 36.8 31.1 Strontium Sr 0.215 0.201 0.259 0.268 0.233 0.33 Tin Sn <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Titanium Ti 0.126 0.213 0.182 1.18 0.073 0.104 Tungsten W <0.050 <0.050 <0.050 0.059 0.072 <0.050 Vanadium V 0.165 0.153 0.144 0.252 0.213 0.21 Zinc Zn 0.307 0.189 0.361 0.216 0.95 0.25
Trace Elements in Saanich Peninsula Agricultural Soils 78
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g) (Continued)
ELEMENTS SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 13 14 15 16 17 18 Aluminium Al 16 23.6 8.97 10.3 21 7.42 Antimony Sb 0.007 0.011 0.006 0.018 <0.001 0.018 Arsenic As 0.003 0.01 0.022 0.036 0.096 0.025 Barium Ba 0.202 0.152 0.156 0.151 0.241 0.191 Beryllium Be <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Boron B 6.85 7.57 6.65 10.2 9.48 12.1 Cadmium Cd 0.002 0.002 0.002 0.002 0.002 0.002 Calcium Ca 41.8 42.6 74 79.5 90 54.7 Chromium Cr 0.155 0.089 0.105 0.041 0.069 0.072 Cobalt Co <0.020 <0.020 0.032 0.058 0.037 0.03 Copper Cu 0.322 0.198 0.453 0.132 0.581 0.416 Gold Au 0.045 0.073 0.05 0.052 0.08 0.071 Iron Fe 8.14 11.5 4.11 4.01 9.28 2.52 Lanthanum La <0.020 <0.020 <0.020 <0.020 <0.020 <0.020 Lead Pb <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Magnesium Mg 9.95 12.1 16.4 11.5 21.5 16.7 Manganese Mn 0.28 0.54 1.33 0.616 0.827 0.447 Mercury Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Molybdenum Mo 0.305 0.303 0.298 0.311 0.323 0.366 Nickel Ni 0.067 <0.050 <0.050 <0.050 <0.050 <0.050 Phosphorus P 4.84 2.04 1.84 0.918 2.52 8.88 Potassium K 36 18.9 27.1 52.5 30.3 112 Scandium Sc <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Selenium Se 0.002 0.004 0.003 0.008 <0.001 <0.001 Silicon Si 18.8 30.7 19.4 9.47 24.9 10.9 Silver Ag <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Sodium Na 33.3 26.9 37.5 29.4 29.9 33.4 Strontium Sr 0.273 0.291 0.28 0.29 0.343 0.186 Tin Sn <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Titanium Ti 0.489 0.781 0.214 0.109 0.613 0.185 Tungsten W <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Vanadium V 0.169 0.205 0.183 0.241 0.3 0.254 Zinc Zn 0.33 0.22 0.536 0.323 0.357 0.536
Trace Elements in Saanich Peninsula Agricultural Soils 79
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g) (Continued)
ELEMENTS SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 19 20 21 22 23 24 Aluminium Al 35 8.44 11.9 9.01 7.74 7.53 Antimony Sb 0.017 0.013 0.01 0.016 0.002 0.009 Arsenic As 0.009 0.018 0.002 0.003 <0.001 0.008 Barium Ba 0.427 0.234 0.188 0.202 0.167 0.252 Beryllium Be <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Boron B 9.65 8.51 8.49 6.34 9.68 8.74 Cadmium Cd 0.006 0.002 0.002 0.002 0.002 0.002 Calcium Ca 42.4 49.7 67.7 33.2 34.6 25.7 Chromium Cr 0.082 0.082 0.11 0.09 0.034 0.089 Cobalt Co <0.020 <0.020 <0.020 <0.020 0.023 <0.020 Copper Cu 0.418 0.413 0.276 0.337 0.241 0.297 Gold Au 0.043 0.046 0.077 0.054 0.056 0.043 Iron Fe 20.2 3.95 5.08 4.74 3.45 2.13 Lanthanum La <0.020 <0.020 <0.020 <0.020 <0.020 <0.020 Lead Pb 0.018 <0.001 <0.001 <0.001 <0.001 0.001 Magnesium Mg 8.4 12.6 14.6 7.59 4.9 5.12 Manganese Mn 2.13 1.09 0.298 0.145 0.609 0.985 Mercury Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Molybdenum Mo 0.326 0.327 0.31 0.303 0.292 0.317 Nickel Ni <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Phosphorus P 3.51 4.13 1.27 2.29 0.644 0.561 Potassium K 5.13 55.4 13 7.02 4.05 7.09 Scandium Sc <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Selenium Se 0.005 0.006 0.001 0.003 0.013 0.004 Silicon Si 36.3 13.8 19.4 12.8 15.3 12.1 Silver Ag <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Sodium Na 32.2 26.8 33.6 26.6 37.2 29.8 Strontium Sr 0.205 0.213 0.318 0.161 0.173 0.152 Tin Sn <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Titanium Ti 1.77 0.269 0.369 0.284 0.31 0.206 Tungsten W 0.063 <0.050 <0.050 <0.050 <0.050 <0.050 Vanadium V 0.226 0.187 0.142 0.166 0.176 0.167 Zinc Zn 0.916 0.186 0.536 0.194 0.153 0.191
Trace Elements in Saanich Peninsula Agricultural Soils 80
Appendix D: Water extraction of metals from Saanich Peninsula agricultural soils (µg/g) (Continued)
ELEMENTS SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE SAMPLE 25 26 27 28 29 30 Aluminium Al 5.73 7.61 8.66 11.2 9.08 7.79 Antimony Sb 0.016 <0.001 0.011 0.013 0.012 0.028 Arsenic As 0.008 0.037 0.003 <0.001 0.044 0.037 Barium Ba 0.196 0.244 0.277 0.237 0.2 0.169 Beryllium Be <0.003 <0.003 <0.003 <0.003 <0.003 <0.003 Boron B 8.63 13.1 12.2 12.5 8.83 9.43 Cadmium Cd 0.002 0.002 0.003 0.002 0.007 0.003 Calcium Ca 25.8 56.5 47.7 33.3 110 101 Chromium Cr 0.024 0.113 0.058 0.03 0.063 0.109 Cobalt Co <0.020 0.032 <0.020 <0.020 0.025 0.025 Copper Cu 0.216 0.461 0.211 0.204 0.285 0.374 Gold Au 0.059 0.048 0.043 0.067 0.055 0.058 Iron Fe 2.26 9.01 2.85 4.72 5.23 4.1 Lanthanum La <0.020 <0.020 <0.020 <0.020 <0.020 <0.020 Lead Pb <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Magnesium Mg 6.07 16.7 3.54 3.48 33.5 29.1 Manganese Mn 1.18 2.94 0.333 0.589 1.89 1.34 Mercury Hg <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Molybdenum Mo 0.292 0.342 0.303 0.311 0.332 0.336 Nickel Ni <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Phosphorus P 0.951 15.5 0.756 1.28 63.7 52.1 Potassium K 21.8 202 35.2 27.2 133 127 Scandium Sc <0.050 <0.050 <0.050 <0.050 <0.050 <0.050 Selenium Se 0.003 0.003 <0.001 0.007 <0.001 <0.001 Silicon Si 16.2 15.8 13.2 17.5 20.9 17.5 Silver Ag <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Sodium Na 33.4 46.7 33.2 25.3 35.4 32.1 Strontium Sr 0.151 0.222 0.227 0.169 0.267 0.278 Tin Sn <0.010 <0.010 <0.010 <0.010 <0.010 <0.010 Titanium Ti 0.175 0.257 0.261 0.438 0.402 0.224 Tungsten W <0.050 <0.050 <0.050 0.062 <0.050 0.056 Vanadium V 0.151 0.305 0.191 0.177 0.274 0.242 Zinc Zn 0.09 0.468 0.335 0.121 0.39 0.276
Trace Elements in Saanich Peninsula Agricultural Soils 81
Appendix E: Soil textures and types
Particle Size Sample > 1/4' > 2000 > 850 > 250 > 106 > 63 < 63 > 2 µm 2µm # µm µm µm µm µm µm COARSE FINE SAND SAND SILT CLAY CLASS GRAVEL GRAVEL 1 0.00% 5.48% 7.36% 54.00% 19.66% 7.77% 5.74% 0.00% 5.48% 88.79% 5.74% 0.00% SAND 2 0.00% 14.14% 35.12% 30.23% 15.55% 3.12% 1.85% 0.00% 14.14% 84.02% 1.85% 0.00% LOAMY SAND 3 6.44% 26.29% 18.61% 31.04% 12.06% 4.82% 0.75% 0.00% 32.73% 66.53% 0.75% 0.00% SANDY LOAM 4 6.24% 13.71% 25.13% 38.46% 11.55% 3.14% 1.77% 0.00% 19.95% 78.28% 1.77% 0.00% LOAMY SAND 5 0.00% 5.50% 25.02% 49.66% 15.90% 3.27% 0.64% 0.00% 5.50% 93.85% 0.64% 0.00% SAND 6 8.99% 27.58% 11.08% 34.22% 14.64% 3.00% 0.51% 0.00% 36.57% 62.94% 0.51% 0.00% SANDY LOAM 7 0.00% 1.50% 2.17% 13.80% 59.03% 11.31% 5.02% 6.82% 1.50% 86.31% 11.84% 0.36% SAND 8 0.00% 6.25% 5.23% 52.02% 30.65% 3.55% 1.32% 0.98% 6.25% 91.45% 2.30% 0.00% SAND 9 0.00% 7.10% 14.31% 40.84% 19.65% 7.28% 4.92% 2.95% 7.10% 82.08% 7.87% 2.95% LOAMY SAND 10 0.00% 6.60% 13.76% 4.68% 20.44% 12.21% 33.92% 5.59% 6.60% 51.09% 39.51% 2.80% SANDY LOAM 11 7.35% 14.14% 14.17% 53.16% 6.89% 1.38% 1.72% 1.20% 21.49% 75.60% 2.92% 0.00% LOAMY SAND 12 0.00% 14.76% 15.60% 51.94% 10.82% 2.89% 2.01% 1.98% 14.76% 81.25% 3.99% 0.00% LOAMY SAND 13 2.85% 8.48% 30.76% 18.07% 23.85% 7.05% 5.19% 0.94% 11.33% 79.73% 6.13% 2.81% LOAMY SAND 14 11.28% 14.29% 32.11% 25.38% 8.38% 5.18% 3.01% 0.38% 25.57% 71.05% 3.39% 0.00% LOAMY SAND 15 0.00% 2.30% 13.30% 22.14% 12.75% 8.40% 32.00% 8.19% 2.30% 56.59% 40.19% 0.91% SANDY LOAM 16 0.00% 2.85% 8.00% 18.08% 13.92% 8.73% 18.36% 10.02% 2.85% 48.73% 28.38% 20.05% LOAM 17 0.00% 9.00% 10.82% 16.39% 13.56% 8.69% 27.97% 4.07% 9.00% 49.46% 32.04% 9.50% LOAM 18 0.00% 4.87% 19.58% 16.81% 45.79% 8.92% 2.76% 1.26% 4.87% 91.10% 4.02% 0.00% SAND Trace Elements in Saanich Peninsula Agricultural Soils 82
19 0.00% 13.16% 10.50% 39.44% 31.98% 0.97% 3.96% 0.00% 13.16% 82.89% 3.96% 0.00% LOAMY SAND 20 0.00% 12.67% 16.08% 38.53% 18.34% 5.61% 5.80% 2.98% 12.67% 78.56% 8.78% 0.00% LOAMY SAND 21 4.63% 2.29% 37.71% 31.92% 12.29% 5.76% 3.53% 1.58% 6.92% 87.68% 5.11% 0.30% SAND 22 0.00% 6.02% 18.10% 50.46% 14.93% 9.10% 1.39% 0.00% 6.02% 92.59% 1.39% 0.00% SAND 23 0.00% 5.82% 11.55% 39.57% 28.44% 7.79% 4.17% 2.67% 5.82% 87.35% 6.84% 0.13% SAND 24 0.00% 13.44% 20.36% 40.49% 19.39% 5.72% 0.60% 0.00% 13.44% 85.96% 0.60% 0.00% SAND 25 0.00% 7.67% 10.48% 31.17% 18.03% 7.61% 24.06% 0.99% 7.67% 67.29% 25.05% 0.00% SANDY LOAM 26 8.81% 28.51% 10.92% 25.18% 16.32% 5.08% 3.23% 0.98% 37.32% 57.50% 4.21% 0.98% SANDY LOAM 27 4.99% 19.03% 14.29% 47.51% 10.62% 2.13% 1.43% 0.00% 24.02% 74.55% 1.43% 0% LOAMY SAND 28 21.61% 22.32% 11.03% 30.14% 9.97% 4.15% 0.77% 0.00% 43.93% 55.29% 0.77% 0% SANDY LOAM 29 0.00% 5.84% 16.24% 18.87% 23.12% 9.61% 20.40% 5.92% 5.84% 67.84% 26.32% 0% SANDY LOAM 30 0.00% 9.16% 17.90% 38.06% 30.00% 4.44% 0.46% 0.00% 9.16% 90.40% 0.46% 0 SAND
Trace Elements in Saanich Peninsula Agricultural Soils 83
Appendix F: Soil solid/liquid partition coefficients, Kd values of Saanich Peninsula Agricultural soils
Elements 9 10 11 12 13 14 15 16 Silver Arsenic 512.82 172.14 253.33 850 1473.33 500 522.72 316.66 Barium 1112.42 502.07 247.28 283.63 742.57 1361.84 558.33 462.25 Beryllium Boron 4.53 4.65 4.06 4.2 5.21 5.19 5.27 3.01 Cadmium 2.33 2.5 2.66 3 2.5 2 3.5 5 Chromium 330.08 505 172.41 137 199.35 460.67 262.85 536.58 Copper 171.6 178.86 53.37 70.58 104.03 263.13 167.1 398.48 Cobalt 520 458.5 239.52 250 460 570 378.12 103.1 Mercury Manganese 86.22 3040.54 705.88 776.75 2300 1564.81 541.35 204.54 Molybdenum 8 5.44 5.09 5.63 5.01 5.44 6.27 6.84 Nickel Lead Antimony 8.06 7.92 14.2 13.83 12.14 5.45 80000 7.33 Selenium 982 429 115 439 347.5 187.5 Tin Vanadium 332.63 201.98 173.23 182.38 323.07 325.36 290.71 167.63 Zinc 203.87 242.12 60.52 294.4 220 401.36 83.95 95.35
Elements 17 18 19 20 21 22 23 24 Silver Arsenic 113.54 140.8 571.11 187.22 1915 1226.66 483.75 Barium 288.79 461.25 433.25 500 728.72 478.21 808.38 547.61 Beryllium Boron 3.39 2.54 3.09 3.49 3.85 4.74 3.07 3.47 Cadmium 3.5 1.5 0.5 1.5 2 1 1 1 Chromium 311.59 244.44 370.73 312.19 279.09 293.33 923.52 264.04 Copper 86.23 63.46 61.48 64.16 117.02 60.83 83.4 78.45 Cobalt 190.27 224.33 497 437 390.5 408.5 431.3 383 Mercury Manganese 210.39 1035.94 425.82 601.83 1677.85 3000 1024.63 667 Molybdenum 7.46 4.61 4.72 4.92 5.12 5.01 5.23 4.85 Nickel Lead Antimony 223 8.05 9.7 8.07 6.2 7.37 63.5 18.44 Selenium 133.2 94.16 1020 183 46.07 109.25 Trace Elements in Saanich Peninsula Agricultural Soils 84
Tin Vanadium 136.33 135.43 254.86 255.61 342.25 296.38 336.36 280.83 Zinc 101.4 105.03 87.11 362.36 146.82 291.75 434.64 254.45
Elements 25 26 27 28 29 30 Silver Arsenic 687.5 104.59 1410 131.81 154.05 Barium 719.38 301.22 342.23 391.98 525 662.72 Beryllium Boron 3.44 2.55 2.35 2.05 3.68 3.88 Cadmium 2 1 1 1.5 4.57 3.66 Chromium 1104.16 214.15 327.58 760 576.19 289.9 Copper 116.66 58.56 88.62 97.54 107.71 87.16 Cobalt 316.5 218.12 346 376 388.4 377.6 Mercury Manganese 603.38 162.24 1450.45 974.53 290.47 443.28 Molybdenum 5.06 5.35 6.17 6.04 6.26 6.3 Nickel Lead Antimony 11.12 98 15.45 12.69 19.08 10.07 Selenium 133.66 117.66 82.57 Tin Vanadium 325.82 120 225.65 251.41 201.45 207.43 Zinc 683.33 92.52 113.13 379.33 224.61 314.49