Environmental Context. Tens of millions of people in developing countries are being exposed to excessive levels of arsenic in their drinking water, and this contamination is widely regarded as the largest current calamity of chemical poisoning in the world. However, arsenic can exist in many chemical forms, and these vary widely in solubility, toxicity, and in bioavailability. Therefore, it is critical to be able to measure arsenic speciation accurately and reliably in order to understand its toxicity and design effective measures of remedial action.

Abstract. Inorganic arsenic compounds are known carcinogens. The human epidemiologic evidence of arsenic-induced skin, lung, and bladder cancers is strong. However, the evidence of arsenic carcinogenicity in animals is very limited. Lack of a suitable animal model until recent years has inhibited studies of the mechanism of arsenic carcinogenesis. The toxicity and bioavailability of arsenic depend on its solubility and chemical forms. Therefore, it is critical to be able to measure arsenic speciation accurately and reliably. However, speciation of arsenic in more complex matrices remains a real challenge. There are tens of millions of people who are being exposed to excessive levels of arsenic in the drinking water alone. The source of contamination is mainly of natural origin and the mass poisoning is occurring worldwide, particularly in developing countries. Chronic arsenicosis resulting in cancer and non-cancer diseases will impact significantly on the public health systems in their respective countries. Effective watershed management and remediation technologies in addition to medical treatment are urgently needed in order to avoid what has been regarded as the largest calamity of chemical poisoning in the world.