Risk of internal cancers from arsenic in drinking water

The U.S. Environmental Protection Agency is under a congressional mandate t o revise its current standard for arsenic in drinking water. We present a r isk assessment for cancers of the bladder, liver, and lung from exposure to arsenic in water, based on data from 42 villages in an arseniasis-endemic region of Taiwan. We calculate excess lifetime risk estimates for several v ariations of the generalized linear model and for the multistage-Weibull mo del. Risk estimates are sensitive to the model choice, to whether or not a comparison population is used to define the unexposed disease mortality rat es, and to whether the comparison population is all of Taiwan or just the s outhwestern region. Some factors that may affect risk could not be evaluate d quantitatively: the ecologic nature of the data, the nutritional status o f the study population, and the dietary intake of arsenic. Despite all of t hese sources of uncertainty, however, our analysis suggests that the curren t standard of 50 mu g/L is associated with a substantial increased risk of cancer and is not sufficiently protective of public health.