A new EPA conclusion on how chloroform causes cancer will likely lead to a new "goal" for the amount of this substance in drinking water. The move could lead to loosened standards for several carcinogenic chemicals, including formaldehyde and some pesticides.

Chloroform is a by-product of the disinfection of drinking water with chlorine. It does not cause cancer by directly interacting with DNA. Instead, it causes cell damage and regrowth.

On Oct. 19, EPA revised its risk information on chloroform, saying there exists a threshold below which exposure to the substance does not cause cancer. For other carcinogens, EPA assumes that risk of cancer increases linearly with exposure.

Getting EPA to change risk information on chloroform has been a major thrust of the American Chemistry Council's Long-Range Research Initiative.

By classifying chloroform as a so-called threshold carcinogen, EPA has taken a major step toward setting a goal higher than zero for the amount of chloroform acceptable in drinking water. Such a move would break a long-standing agency policy against setting a maximum contaminant level goal (MCLG) of more than zero for any carcinogen. MCLGs are the highest concentrations at which a contaminant in drinking water is judged to be safe. These goals, however, are not regulatory standards.

C. T. (Kip) Howlett Jr., executive director of the Chlorine Chemistry Council, applauds the agency's move. He says EPA's decision on chloroform will likely affect the agency's risk characterizations for other chemicals for which there are data indicating they are threshold carcinogens. These include formaldehyde and some chlorinated solvents, he tells C&EN.

The decision could also affect atrazine and other pesticides, says Erik D. Olson, senior attorney for the Natural Resources Defense Council. Classifying a substance as a threshold carcinogen might eventually translate into looser regulation of these substances. "There's a lot of money at stake," Olson says.

Olson is critical of EPA's move on chloroform on several counts. He says EPA ignored information that chloroform is mutagenic and that it may cause cancer through a mechanism other than cell damage and proliferation. Plus, chloroform is not the only substance people are exposed to in drinking water. "It always comes as part of a toxic package" with other disinfection by-products, he says.

Jeffrey T. Solan, director of disinfection policy at the Chlorine Chemistry Council, says EPA's new risk characterization indicates that liver toxicity is the health risk of greatest concern. So the new chloroform MCLG likely will be based on protecting public health from liver effects, not cancer.

The agency is expected to issue the new MCLG for chloroform as part of a final rule on the by-products of drinking water disinfection, due in May 2002. Olson says if the MCLG for chloroform is above zero, environmental activists likely will sue EPA.

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