For example, the toxicity of arsenic to animals varies from the more toxic arsenite, to the moderately toxic methylated arsenicals, to the essentially non-toxic arsenobetaine. Metabolic and Toxicological Studies of Arsenic, Selenium and Mercury Arsenic is present in the natural environment and in all living organisms. Recently, arsenic in drinking water has become a concern and exposure guidelines have become more stringent. Thus it is essential to identify and quantify individual chemical forms of an element in studying biochemical effects of the element. Biochemical interactions between trace elements are extremely important, but are poorly understood.
Selenium is an essential trace element, but excess selenium is toxic to biological systems.
Furthermore, when some very toxic arsenic and selenium compounds are present together, their toxicity is dramatically reduced. Similarly, selenium reduces the toxicity of several mercury, cadmium, and lead compounds. Such antagonistic effects between toxic compounds have been observed in many types of organisms. Research has been directed to understanding these effects, but overall mechanisms still remain unclear. Most of the previous studies have been based on the measurement of total element concentrations without differentiating chemical forms of the element.