Panel Downplays Perchlorate Risk
By J.R. Pegg
WASHINGTON, DC, January 12, 2005, (ENS) - A pollutant from rocket fuel that can adversely affect the human thyroid gland and has contaminated drinking water in 35 states is not as dangerous as federal environmental regulators previously thought, a panel of experts said Tuesday.
Humans can safely ingest some 20 times more perchlorate than the reference dose recommended by the U.S. Environmental Protection Agency (EPA), according a new report by the National Research Council.
Perchlorate, which is also found in road flares and fireworks, has recently emerged as an environmental concern across much of the nation.
The chemical inhibits the thyroid's uptake of iodide, which is essential for the production of thyroid hormones.
Insufficient iodide has been shown to harm neurological development of children.
In 2002 the EPA completed a risk assessment that proposed a daily reference dose of 0.00003 milligrams of perchlorate per kilogram of body weight.
The agency said this dose would correspond to a drinking water concentration, based on body weight and daily water consumption, of one part per billion (ppb).
Pentagon officials and arms manufacturers, who face hefty bills for cleaning up water contaminated with perchlorate, argued that any perchlorate level below 200 ppb in drinking water is safe.
In 2003 the Bush administration ordered the independent review of the EPA's recommendation by the National Research Council.
The panel agreed the reference dose used by the EPA was too high and determined daily ingestion of up to 0.0007 milligrams per kilogram of body weight can occur without adverse health effects.
That figure reflects an adjustment to protect fetuses, infants and children, according to the committee.
"We came up with a level to protect even the most sensitive individual," said Dr. Richard Corley, an environmental toxicologist with the U.S. Energy Department's Pacific Northwest National Laboratory.
The panel's reference dose roughly equates to a water quality concentration of 20 ppb, but the committee declined to confirm if their recommendation would lead to that standard.
"The water level is a matter of policy - a lot of other factors go into determining what the safe water level would be," said committee chair Richard Johnston, a professor of pediatrics at the University of Colorado School of Medicine.
Johnston said such a standard includes assumptions about body weight, water consumption and the perchlorate contamination levels found in water and food.
The chemical has recently been found in milk and lettuce and other crops that the Food and Drug Administration and others have tested.
"It is going to vary from community to community," Johnston said. "Those that make public health policy, we have tried to give them a dose that we feel is safe. They will then have to deal with how much perchlorate is consumed."
Environmentalists said that even with the panel's recommendation, it is still possible that EPA and states could set a drinking water standard for perchlorate at one to four ppb.
But some critics said the panel's findings reflected pressure from the White House and the Pentagon to avoid setting a standard that would force widespread cleanup of contaminated drinking water.
According to the Natural Resources Defense Council (NRDC), internal government documents show "uncommon, extensive involvement by White House and Pentagon officials to limit the scope of NAS' inquiry and select the panelists, as well as collaboration among the White House, Pentagon and DOD contractors to influence the panel."
Senator Barbara Boxer, a California Democrat, said the documents obtained by NRDC show that "once again, the administration has let its friendships with special interests groups stand in the way of protecting the health of the people of this country."
Bush administration officials denied the allegation and the National Research Council said the report was not subject to political influence.
"This report was subject to a vigorous peer review process and it is focused [solely] on science," said Jim Reisa, director of the National Research Council's Board on Environmental Studies and Toxicology. "It is others that will have to go the next mile and make the tough decisions about what to do on regulation and risk management."
The committee specifically disagreed with the EPA's conclusion that exposure can lead to thyroid cancer and said the agency's assessment relied too heavily on animal studies.
The 15 member panel had "more confidence in the human data than the EPA did," Johnston said.
"You can block uptake of iodide with perchlorate without affecting level of thyroid hormone production," Johnson said. "The human body has a very strong mechanism for compensating."
The committee's recommendation centers on data from one clinical study of seven healthy men and women - data it says are supported by the results in four other studies of healthy subjects, including a six-month study.
No studies have directly examined the impact of perchlorate on pregnant women, fetuses or infants, the panel said, so an uncertainty factor of 10 was used to protect these vulnerable populations.
The committee called this a "conservative, health-protective approach to perchlorate risk assessment," but acknowledged that more studies should be completed to more precisely define "safe" perchlorate exposures.
Future findings could result in the need to adjust the reference dose recommended in the report, the committee said.