RISK AND REVISIONISM IN ARSENIC CANCER RISK ASSESSMENT

Oral exposures Of nonoccupational populations to environmental Inorgan ic arsenic are associated with skin and internal cancers as well as va rious noncarcinogenic effects. Cancer risk assessments have been based largely on epidemiological studies of a large population exposed to I norganic arsenic In well water in Taiwan. Criticisms and skepticism of the use of che Taiwanese data for estimating arsenic cancer risks out side of Taiwan, including potential use by the U.S. Environmental Prot ection Agency for regulatory purposes, have been expressed on various grounds. The nature and extent of such criticisms have sharpened with recent findings in the exposed Taiwanese of increased incidence of Int ernal cancers (bladder, kidney, liver, and lungi, in addition ro alrea dy-observed skin cancer, coupled with a good likelihood that these fin dings will produce more stringent arsenic regulation in the United Sta res and elsewhere. These criticisms collectively posit a revisionist v iew that: 1) cancer Incidence among the Taiwanese was amplified by a n umber of host and environmental Factors not applicable elsewhere, 2) t he cancer dose-response curve may not be linear at the lower exposures elsewhere, and 3) there is a toxicokinetic and metabolic threshold to cancer risk that was exceeded by the Taiwanese. However, a number of the arguments against wide use of the Taiwanese data are flawed and su bject to challenge. We explore some of these arguments and their criti cal evaluation, particularly as they concern certain exposure, metabol ic, and nutritional determinants of the cancer risk of inorganic arsen ic in the Taiwanese.