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Spheres of Influence
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Chloroform: An EPA Test Case Charles W. Schmidt Abstract
In March 1998, the U.S. Environmental Protection Agency (EPA) published a proposal to raise the drinking water maximum contaminant level goal (MCLG) for chloroform, a suspected human carcinogen, from zero to 300 parts per billion. The proposal marked a departure from the agency's traditional reliance on linear dose-response models in performing risk assessment, and reflected the new thinking contained in the 1996 draft update to the agency's cancer risk assessment guidelines. The updated guidelines emphasize mechanisms of action and descriptions of the conditions under which carcinogenic hazards are likely to be expressed. By proposing to raise the MCLG, the EPA opened a dialogue among stakeholders, possibly setting a precedent for the future evaluation of chemical carcinogens based on mechanistic data. But the dialogue that ensued proved highly contentious, with opponents charging that the EPA was not considering all the evidence. The EPA eventually elected to put the proposal on hold, pending additional review. How the chloroform debate plays out is seen as a critical issue that will define policy under both the updated guidelines and the Safe Drinking Water Act. It is therefore being watched closely by major research and policy organizations and high-level government officials. The EPA Science Advisory Board will review the chloroform risk assessment this summer ; a revised MCLG for chloroform may yet see the light of day.
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