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. While some arsenic compounds (e.g., inorganic arsenite and arsenate) are very toxic, others (e.g., arsenobetaine, the major arsenic-containing compound in crustacean seafood) are much less toxic. 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. Such studies are not reliable to assess toxic effects and biochemical interactions, given that the toxicity of an element is strongly dependent on chemical forms. We are currently studying interactions between arsenic and selenium in biological systems by examining the individual forms of their biochemical interaction products.