Page 450 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

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VetBooks.ir Chapter 24

Cadmium

Stephen B. Hooser

INTRODUCTION fields of phosphate fertilizers (which contain varying
amounts of cadmium depending on the source), and sew-
Cadmium accumulation in plants and animals from
age sludge results in cadmium deposition in the soil
several sources of environmental exposure is increasing.
(Piscator, 1985; Lane et al., 2015). Some plants readily
The application of rock phosphate (which contains vary-
extract cadmium from the soil, making it available for
ing amounts of cadmium depending on the source) and
consumption. For example, cadmium concentrations in
sewage sludge fertilizers results in cadmium deposition in
clover grown in soil fertilized with high cadmium rock
the soil of pastures (Piscator, 1985; ATSDR, 2009). In phosphate were significantly higher than the concentra-
addition to direct ingestion of soil containing cadmium,
tions in clover grown in soils treated with low cadmium
some forage plants extract cadmium from the soil.
phosphate fertilizer (McLaughlin et al., 1997). A New
Although cadmium accumulation in the soft tissues of
Zealand national survey of soils and plants, and random
livestock has been demonstrated and there is ample
testing of kidneys from grazing animals revealed that
experimental documentation of the toxicity of cadmium
there was an approximately twofold increase in soil cad-
in animals, under natural conditions, documented cases of
mium, while over a 3-year period, 14% 20% of cattle
direct toxic or carcinogenic effects of cadmium in domes-
kidneys exceeded the New Zealand maximum residue
tic livestock have been very uncommon (Dorn, 1979); no
level of 1 μg Cd/g (Roberts et al., 1994). In a study in
clinical cases have been reported in farmed ruminants
which cattle were allowed to graze pastures treated with
(Lane et al., 2015).
anaerobically digested sewage sludge for up to 8 years,
cadmium was the only metal to accumulate consistently
in increased amounts in the tissues of the cattle
BACKGROUND
(Fitzgerald et al., 1985). It has been reported that cattle
Pure cadmium is a soft, silver-white metal with an atomic grazing on sewage sludge-treated pastures consumed sig-
number of 48 and a molecular weight of 112.41. It is a nificantly more (up to three times) cadmium than cattle
divalent transition metal with chemical properties that are on control pastures (Reddy and Dorn, 1985). In addition,
similar to zinc, and is usually found as a mineral in com- a Swedish study has found a direct correlation between
bination with other elements to form cadmium oxide, cad- cadmium in feed and pig kidneys (Grawe et al., 1997).
mium chloride, or cadmium sulfate (ATSDR, 2009). A study reporting the analysis of Wisconsin dairy feeds
Since numerous compounds are formed from cadmium, it for heavy metals found that cadmium concentrations in
is used in batteries, solders, semiconductors, solar cells, complete dairy feed rations were the closest of the heavy
plastics stabilizers, and to plate iron and steel. All soil metals to United States maximum acceptable concentra-
and rocks contain some cadmium. It can enter the envi- tions, suggesting that cadmium has the greatest potential
ronment from zinc smelting and refining, coal combus- to exceed those maximum standards if the amounts of
tion, mine wastes, iron and steel production, and from the cadmium in feeds increase in the future (Li et al., 2005).
use of rock phosphate and sewage sludge as fertilizers However, several studies have failed to demonstrate any
(Klasing, 2005). adverse clinical manifestations related to increased cad-
Cadmium accumulation in plants and animals from a mium concentrations in the animals examined, and natu-
variety of sources is increasing, the most severe being rally occurring cadmium toxicity in farmed ruminants has
in the vicinity of zinc smelters. The use of cadmium- not been reported (Lane et al., 2015). In one study,
containing mineral supplements in feed (e.g., from although cattle on pasture fertilized with sewage sludge
calcium phosphate), the application on pastures and hay consumed increased amounts of cadmium and had

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