Perchlorate health goals could have doubled based on NAS report
findings
California’s public health goal for perchlorate could have doubled to 12 parts per billion had the state relied solely on the findings of a National Academies of Science report that will be used to set a federal drinking water standard, a California environmental official said this week.
Dr. George Alexeeff, a deputy director for the Office of Environmental Health Hazards Assessment, said his agency took a different view of the key study – the so-called Greer study – cited in the NAS report and derived a lower benchmark dose, which is used to measure risk exposure.
The agency first set the health goal at 6 parts per billion last year and reconfirmed it in April after reviewing the NAS report that was published in January. The public health goal is important because polluters must clean up to state standards, even if federal standards are more relaxed.
The NAS report did not set a drinking water standard or health goal, or advocate a policy position. The committee instead set a reference dose, or the amount of perchlorate a 155-pound man could ingest safely each day.
Depending on who’s doing the math, the reference dose translates into a standard of as low as 1 part per billion, as argued by environmental groups, or 24.5 part per billion, which, the U.S. Environmental Protection Agency said in February, is the level that protects all humans, even pregnant women and babies, from the thyroid damage attributed to perchlorate.
“Depending on the factors you use, you could come up with a different water standard,” Alexeeff said. “In the National Academies report, they concluded that there was no effect at the lowest dose [in the Greer study]. In our report, we didn’t make a conclusion one way or another.”
And the NAS conclusion has been criticized by public health officials in the latest edition of the scientific journal Environmental Health Perspectives. In the article, Dr. Gary Ginsberg, a toxicologist with the Connecticut Department of Public Health, and Dr. Deborah Rice, of the Maine Bureau of Health, say that the Greer study is not sufficient to set a safe dose because the NAS focused on only seven subjects who displayed a wide range of responses to perchlorate.
The authors also say that the NAS committee should have considered the contaminant’s initial observable effect on humans – the inhibition of iodide uptake to the thyroid – to be adverse, and they urge the U.S. Environmental Protection Agency to take another look at the study before adopting the NAS report as the basis for a national water standard.
“I don’t think they properly identified the [effect level] from this one particular study,” Ginsberg said in an interview. “You can’t ask questions about risk, but you can ask whether or not the [dose] has been set properly. Our review suggests that it merits careful reconsideration because there are factors that would tend to make it lower.”
Dr. Richard Corley, a staff scientist at the Pacific Northwest National Laboratory in Washington state and a member of the NAS committee, defended the report. He said there’s no evidence that a disruption of iodide uptake of less than 75 percent is in itself harmful, and resisted the suggestion that the committee based its findings solely on the seven Greer subjects.
“The committee absolutely feels that the effect we’re looking at is not adverse,” Corley said. “The results from Greer were not taken in isolation. They were consistent with other studies on humans, with ongoing studies. We were very careful. But any time you have a single-number reference dose there are going to be critics on both sides.”
Alexeeff stopped well short of criticizing the NAS report, but he does agree that the seven subjects studied in Greer do not make a particularly persuasive case and said that initial EPA number, the drinking water equivalent level, or DWEL, is too high for the most vulnerable populations.
“The problem is that there are only seven, and there’s a lot of variation, so it’s not a very powerful point,” Alexeeff said. “We don’t know how the EPA will come out, but if the [drinking water standard] is equivalent to the DWEL, that means they didn’t take into account body weight.”
The EPA has several complex formulas it uses to determine the relative sources of contaminants, but it defaults to a ratio that assumes 20 percent of contaminant comes through drinking water, meaning a federal water standard based on the NAS report could actually fall as low as 5 parts per billion. California assumes that 60 percent of perchlorate comes from water.
But Ginsberg said the NAS reference dose, and in turn, the DWEL, should be divided by a factor ranging from three to 10, and that the DWEL should be in the range of 2.5 to 8 parts per billion.
“There’s a greater degree of uncertainty regarding human risks than what the panel decided to attribute,” he said. “It’s a professional judgment kind of call. I see a greater degree of uncertainty.”
The EPA has placed perchlorate on its contaminant candidate list, but it can not issue a national standard unless it demonstrates that doing so will cause a significant reduction of a public health threat. About 150 of the 3,000 sites monitored by the EPA have tested for perchlorate at or above 4 parts per billion. Those sites provide water for about 11 million people, but there are substantially fewer sites that test at 10 or 20 parts per billion.
The final drinking water standard, or maximum contaminant level, has huge impacts for the companies, most of them in the aerospace and defense industries, who would have to clean their sites of perchlorate to the level of a national standard.
California sites, however, are governed by state regulations, meaning that each of the sites in this state must be cleaned to at least 6 parts per billion or lower if the EPA’s final standard is below 6. The state Department of Health Services is in the process of setting a state drinking water standard. By law, the standard can not fall below the health goal.
The Olin Corp., which is responsible for the 9.5-mile plume flowing south and east of the company’s former road-flare factory on Railroad Avenue in Morgan Hill, has been ordered by the Central Coast Regional Water Resources Control Board to clean that plume to background levels. However, Olin still disputes that it is responsible for the portion of the plume flowing north and east of the site.
Matt King covers Santa Clara County for The Times. He can be reached at 847-7240 or [email protected].
