Cadmium is a ubiquitous, highly toxic element that is present at low levels throughout the environment, including food, water, and soil (1), and in most biological substrates, although it has no known biological role. Thus the primary routes of exposure to the metal are dietary in the general population and dermal contact upon sustained occupational exposure. Persistent in the environment and living organisms, the toxicology of the metal has been well documented (2). In accord with its relatively high ionization energy, Cd2+ is highly electropositive and Cd complexes have a considerably covalent character. This accounts for the antagonistic effect that cadmium has on other essential trace metals in the mammalian organism, such as copper, iron, zinc and magnesium (3-5). There is also growing evidence that cadmium interferes with bone formation (6) and increases bone resorption (7) in vivo, and that it decreases osteoblastic accumulation of calcium in vitro (8).
Due to its relatively high vapor pressure and ease of thermal volatilization, especially significant in metal smelting and refining processes, and the release of highly water-soluble cadmium salts into industrial wastewater, environmental levels of the metal are continually rising and present a considerable public health concern. The metal is seen to concentrate in certain plants, e.g., in tobacco leaves, and to accumulate in animal soft tissue, reaching potentially toxic levels (9). Dietary intake and smoking of tobacco thus are the principal sources of human exposure to cadmium. That among the general population smokers are particularly at risk was demonstrated by significantly elevated cadmium levels measured in their blood and seminal fluid, as compared with the corresponding values seen in nonsmokers (10).
The metal has been associated with malignant neoplasms in humans (11), |
and it is predicted that Cd-induced carcinogenicity might be mainly due to oxida-
tive DNA damage (12). In a model, on a relative scale of carcinogenicity based |
on human, animal, and short-term predictive data, cadmium compounds were
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