Geology Reference
In-Depth Information
vitamin D intake, and calcium deficiency, suffered a condition known as
Itai-Itai (Ouch-Ouch) disease, with symptoms ranging from lumbago-
type pains to multiple fractures of softened bones. The cause was
irrigation water from a river (Jintsu) chronically contaminated with
dissolved cadmium from a zinc mining and smelting operation. Con-
taminated rice from the irrigated paddy fields was eaten and the Ca
21
in
bones replaced by Cd
21
, an ion of the same charge and size.
Although this is a particularly extreme example of acute effects
resulting from high exposure to this non-essential element, concern
has been expressed about chronic effects (e.g. kidney damage, hyperten-
sion) from possible enhanced exposure of humans through increased
application of sewage sludge to agricultural land, in view of EC-
enforced cessation of dumping at sea by 1999. Compared with other
heavy metals, cadmium exhibits an especially high mean sludge con-
centration (20 mg kg
1
) relative to mean soil concentration (0.4 mg
kg
1
).
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In acidic soils the concentration of Cd
21
available for uptake by
plants can be substantial,
84
as it adsorbs only weakly onto clays, whereas
at pH 47 it readily precipitates, e.g. as CdCO
3
for which the solubility
product, K
SP
ΒΌ
1.8
10
14
, is indicative of the advantages of liming.
Similarly, in drinking water, the presence of dissolved carbonate at a
concentration of 5
10
4
mol L
1
can reduce the solubility of cadmium
from 637 to 0.11 mg L
1
, in line with evidence that hard water, with a
high calcium content, can protect against cadmium.
85
3.3.2.4 Selenium in Irrigation Water. In 1983, high rates of embryo-
nic deformity and death, attributed to selenium toxicosis, were found in
wild aquatic birds at the Kesterson National Wildlife Refuge in the San
Joaquin Valley of California.
86
Kesterson Reservoir was a regional
evaporation pond facility where drainage waters, often containing high
level of salts and trace elements (including selenium), from irrigated
farmland had been collected since 1978.
With evapotranspiration, greatly in excess of precipitation, bringing
soluble salts to the surface of farmland in the arid climate of the west-
central San Joaquin Valley, and crop productivity, after irrigation,
threatened by shallow saline groundwater near the root zone, grids of
sub-surface tile drains were constructed to divert the saline waters to a
collective drain (San Luis), which flowed into Kesterson Reservoir. It
was the geologic setting of the San Joaquin Valley as well as the climate,
however, which led not only to the soil salinization but also to the
presence of selenium (in the form of SeO
4
2
) in Kesterson inflow waters
at concentrations well in excess of the USEPA designation of 1000 mg
L
1
for selenium as a toxic waste, never mind its 10 mgL
1
limit for
