Case studies of the impact of understanding bioavailability: arsenic.

Arsenic is a metalloid that occurs in virtually all environmental matrices. The inorganic forms of arsenic occurring as As(III) and As(V) are toxic and may pose a health risk to human population. Although exposure can occur in various settings, ingestion of contaminated ground water is more widespread. The toxicity of arsenic is dependent to a large extent on its bioavailability or its ability to be liberated from various matrices and be internalized in the target organs of the host. This article reviews the main health impacts of arsenic and the methodologies for measuring bioavailability, and interprets the bioavailability studies conducted so far. It is argued that, because the bioavailability of arsenic varies with environmental matrices, a single default value is not recommended for risk determination and management in all environmental settings. Precise site-specific knowledge of bioavailability of arsenic is critical for both setting the maximum contaminant levels and directing site-specific cleanup operation in a cost-effective manner. Finally, molecular geochemical knowledge is combined with epidemiological observation to propose a model for disease in which the bioavailability of arsenic plays a determinant role together with other host and environmental factors.