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 Perchlorate drinking water recommendation dropsA long-awaited U.S. EPA draft toxicological report issued on January 18 finds that perchlorate is likely to be more harmful to human health than previously thought. In response to the report's conclusion that perchlorate concentrations of less than 1 part per billion (ppb) are safe for human consumption in drinking water, the California Department of Health reduced its advisory action level from 18 ppb to 4 ppb. The state, which is currently in the process of setting its own drinking water standard, is one of the southwestern states most affected by perchlorate-contaminated groundwater.Perchlorate salts, which are used in solid rocket fuel, fireworks, and auto air bags, have been found in ground and surface water throughout the United States. Perchlorate can cause adverse effects by blocking the uptake of iodine by the thyroid, and scientists have been struggling for more than a decade to determine whether exposure to minute amounts of the compound in drinking water can have a long-term detrimental effect on human health. Since 1992, EPA has recommended safe levels ranging from 4 to 18 ppb. The recommendation is being greeted with a mixture of surprise, caution, and approval by scientists involved with the issue. "I'm surprised; this is completely impractical because it's lower than the current detection limit," said one academic scientist, voicing a common reaction. The detection limit for ion chromatography, the best commonly available analytical method, is 4 ppb. "If this recommendation is right, we should be seeing effects in the general population. But widespread adverse effects do not occur," said a chemist, referring to the report's finding that low-level exposure to perchlorate causes neurobehavioral effects during development. The new draft report is a revision of a 1998 draft review prepared by EPA's National Center for Environmental Assessment that supported a 32-ppb standard concentration (Environ. Sci. Technol. 1999, 33, 110A). The neurodevelopmental effects that were first noted in the 1998 review form the basis for the new draft reference dose. In particular, brains of rat pups whose mothers drank perchlorate-laced water were found to be different in size and shape from control rats even at the lowest dose, 0.01 mg/kg-day. This lowest observed adverse effect level is 10 times lower than the level reported in the 1998 review. The newer report also incorporates a higher safety factor of 300, which is 3 times the safety factor used in the 1998 review. These two factors drive down the new reference dose to 0.00003 mg/kg-day. But other scientists applaud the new review, "This is state-of-the-science toxicology," said Kevin Mayer, the coordinator for perchlorate issues for the U.S. EPA Region 9, which includes California."For those of us in the field dealing with this problem, it gives us a greater level of confidence in the recommendations, knowing the level of effort and sophistication embodied in this work," Mayer says. "This is a big step forward by the EPA, confirming the latest scientific research that shows perchlorate is toxic even at very low doses," says Environmental Working Group analyst Renee Sharp. In a report issued last year, the environmental group criticized EPA's previous draft recommendations. EPA officials say that once the report is finalized, it will be a major factor in the possible development of federal regulatory standards, a process likely to take several years. The first step is external peer review and public comment. A public peer review workshop on the draft assessment has been scheduled for March 5-6 in Sacramento, and the final assessment is expected in late summer. Copyright © 2003 American Chemical Society < Back |
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