TABLE 5.1 Trace Element Concentrations (mg kg−1dry weight) in Agricultural Soils and Food Crops

Element

Common Range for Agricultural Soils

Selected Average for Soils

Typical Range for Food Crops

Arsenic (As)

<1−95

5.8

0.009−1.5

Barium

19–2368

500

1–198

Boron

1–467

9.5–85

1.3–16

Cadmium

0.01–2.5

0.06–1.1

0.13–0.28

Cobalt

0.1–70

7.9

8–100

Chromium

1.4–1300

54

0.013–4.2

Copper

1–205

13–24

1–10

Fluorine

10–1360

329

0.2–28.3

Mercury

0.05–0.3

0.03

0.0026–0.086

Molybdenum

0.013–17

1.8

0.07–1.75

Nickel

0.2–450

20

0.3–3.8

Lead

3–189

32

0.05–3.0

Selenium

0.005–3.5

0.33

0.001–18

Silver

0.03–0.9

0.05

0.03–2.9

Tin

1–11

0.2–7.9

Vanadium

18–115

58

0.5–280

Zinc

17–125

64

1.2–73

SOURCE: Alloway (2005).

age sludge and fertilizers and atmospheric deposition from industrial sources. Because of differences in the mineralogy of the parent materials and the variable levels and broad range of contamination from anthropogenic sources, soils are found with a wide range of trace metal concentrations. Trace element concentrations in agricultural soils can vary by two to three orders of magnitude (see Table 5.1).

Chaney (1983) classified trace elements in agricultural soils that received sewage sludge and other wastes according to their potential for risk. At a soil pH of 6-8, the low solubilities or strong adsorptions of silver (Ag), gold (Au), chromium (Cr), fluorine (F), galium (Ga), mercury (Hg), lead (Pb), palladium (Pd), platinum (Pt), silicon (Si), tin (Sn), titanium (Ti), and zirconium (Zr) essentially preclude significantly increased concentrations in plants even when the soils are greatly enriched in these elements. Increased concentrations of aluminum (Al), arsenic (As), boron (B), barium (Ba), beryllium (Be), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), vanadium (V), and zinc (Zn) in plants are insufficient to adversely affect animals because the element causes phytotoxicity, the element is well tolerated by animals, and/or the maximum increased level in plants is lower than the toxic level to animals. Elements that are easily



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