ENVIRONMENTAL
NEWS
Drinking water proposal eases some health goals
E
PA's long-stalled effort to expand its purview over drinking water disinfectants and their byproducts got a push forward in late March when the agency proposed a new rule. The agency's proposal triggered "extreme concern" on the part of environmental organizations by loosening standards for chloroform based on a controversial risk assessment approach. At issue is the agency's retreat from its previous "zero tolerance" goal for the disinfection byproduct chloroform, a probable carcinogen that is also known to affect liver and kidney function. Chloroform is one of more than a dozen disinfectants and disinfection byproducts (DBPs) targeted for first-time or enhanced regulation due to suspected links with cancer, liver and kidney damage, miscarriages, and birth defects. The regulation is widely expected to meet its congressionally mandated November deadline for promulgation. With the exception of the new goal for chloroform and two other disinfectants and DBPs, the proposed rule is identical to a version EPA issued in 1994. Environmentalists are most concerned about the method used to reevaluate the relative risk of chloroform's carcinogenicity. In the past, EPA set maximum contaminant level goals (MCLGs) of zero for carcinogens. MCLGs are EPA's "health-related goals set at a level for which no known or anticipated human health effects will occur," said Tom Grubbs, DBP Regulation Manager for the Office of Groundwater and Drinking Water. "The maximum contaminant levels (MCLs) are set as close as is technically and economically possible to the MCLGs," Grubbs explained. In 1996, at EPA's request, the International Life Sciences Institute
The risks associated with chlorinating drinking water are addressed in a new rule proposed by EPA. (Courtesy American Water Works Association)
(ILSI) undertook a study re-evaluating existing data on chloroform's carcinogenicity using the disputed approach set forth in the agency's 1996 Proposed Guidelines for Carcinogen Risk Assessment. Unlike the zero tolerance approach used in the past—which assumed a linear relationship between dose and response, and therefore a risk at any dose of a carcinogen—the approach laid out in the risk assessment proposal allows a threshold dose to be set for some chemicals. The risk of doses below that threshold is considered sufficiently small as to be acceptable. The ILSI panel recommended that a threshold could be set for chloroform. Accordingly, EPA proposed increasing the MCLG for chloroform from 0 to 300 micrograms/liter (ug/L). Such threshold determinations must be made on a chemical-by-chemical basis. "This is the first time that we're aware of that EPA has weakened an existing health goal based on the threshold hypothesis," said Erik Olson, a drinking water specialist for the Natural Resources Defense
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Council (NRDC). "This is deeply troubling. We're going to be looking very carefully at their justification for it," he said. "This is what industry has been trying to push since the Reagan administration. Our concern is that an awful lot of EPA's resources are going to be pouring down this drain of determining whether there's a threshold, instead of making precautionary decisions about whether or not to regulate chemicals." "All carcinogens don't act the same," explained Michael Cox, toxicologist in the Office of Groundwater and Drinking Water, in defense of the agency's stance. "For chloroform, [the ILSI panel is] saying there was some dose below which it didn't have an effect." To observers like Olson, EPA's proposal to raise the MCLG for chloroform sets a dangerous precedent. The new goal for chloroform would be more than three times higher than the enforceable MCL set for the chemical, which is currently regulated as one of the four "total trihalomethanes." Ironically, EPA is proposing decreasing the maximum contaminant level for total trihalomethanes from 100 ug/L to 80 ug/L in the same rule in which it proposed increasing the chloroform goal to 300 pg/L. Setting drinking water MCLGs so that they are easier to attain than the MCLs does not make sense, according to the NRDC's Olson. The other two chemicals for which the MCLG goals have been increased are chlorine dioxide, a disinfectant, and chlorite, a DBP. EPA proposed a tenfold expansion of chlorite's MCLG, and it is proposing more than doubling the goal for chlorine dioxide. Whether these goals make it into the final rule depends on how they fare in the comment period that ended April 30. —KELLYN S. BETTS
0013-936X/98/0932-208A$15.00/0 © 1998 American Chemical Society
