Agriculture Reference
In-Depth Information
Table 7.5
Global emissions of trace metals to the atmosphere and concentrations
in freshwater
Emissions
(
kt year
−
1
)
a,b
Concentration in
freshwater
(
µ
gL
−
1
)
c
Natural
Anthropogenic
Total
Mean (range)
Antimony
2.6
3.5
6.1
0.2 (0.01-5)
Arsenic
12
19
31
0.5 (0.2-230)
Cadmium
1.4
7.6
9.0
0.1 (0.01-3)
Chromium
43
31
74
1 (0.1-6)
Cobalt
6.1
35
41
0.2 (0.04-8)
Copper
28
332
360
3 (0.2-30)
Lead
12
38
50
3 (0.06-120)
Manganese
317
3.6
320
8 (0.02-130)
Mercury
2.5
52
54
0.1 (0.0001-2.8)
Molybdenum
3.0
6.3
9.3
0.5 (0.03-10)
Nickel
29
5.1
34
0.5 (0.02-27)
Selenium
10
5.1
15
0.2 (0.02-1)
Vanadium
28
86
114
0.5 (0.01-20)
Zinc
45
132
177
15 (0.2-100)
Sources
:
a
Nriagu (1989).
b
Nriagu and Pacyna (1988).
c
Bowen (1979).
complexes increases in the order (Chapter 3):
Cd
<
Zn
<
Co
Ni
=
Cu
<
Hg
and the tendency to form strongly sorbed, inner-sphere complexes with oxides
and clays increases in the order:
Cd
<
Ni
<
Co
<
Zn
Cu
<
Hg
The tendency to co-precipitate in secondary minerals also differs. Typical co-
precipitates are (Sposito, 1983):
Fe oxides
V, Mn, Ni, Cu, Zn, Mo
Mn oxides
Fe, Co, Ni, Zn, Pb
Ca carbonates
V, Mn, Fe, Co, Cd
Clay minerals
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb
These differences are exemplified in Figure 7.5 which shows the results of an
experiment in which Cd
2
+
,
Zn
2
+
,
Ni
2
+
and Cu
2
+
salts were applied on the surface
of an acid soil, with and without lime, and the soil leached with 0
.
01MCaCl
2
for
several hours (McBride, 1994). In the unlimed soil, Cd
2
+
,
Zn
2
+
and Ni
2
+
moved
readily to depth, but Cu
2
+
remained near the surface because it was strongly
sorbed on soil solids. In the limed soil, with pH 6.5, increased sorption and
