Issue Date: May 14, 2007
CONGRESS IS POISED to intervene in a long-standing struggle over perchlorate pollution that has pitted the Environmental Protection Agency against the Pentagon and the National Aeronautics & Space Administration. A bill pending in the House of Representatives would force EPA to limit the amount of perchlorate, a component of rocket fuel, allowed in drinking water.
But EPA is asking lawmakers to hold off on the legislation. The agency says it needs forthcoming research from the Food & Drug Administration to determine whether regulating perchlorate in drinking water will have any impact on public health. That FDA work, which is targeted for release later this year, will estimate how much perchlorate taints the U.S. food supply. EPA will use this data to determine whether regulating perchlorate in drinking water would put a significant dent in the public's risk from consuming the chemical, agency officials say.
The issue of perchlorate pollution is more complex than most environmental problems and is centered within the federal government, involving an array of federal agencies. The Defense Department, NASA, and their contractors are believed to be responsible for much, though not all, of the perchlorate contamination in the U.S. EPA and FDA, respectively, have authority to regulate drinking water and food tainted with the chemical.
Meanwhile, new studies by yet another federal agency, the Centers for Disease Control & Prevention (CDC), are increasing the pressure for the government to limit perchlorate exposure. This research shows that exposure to low levels of perchlorate is widespread throughout the U.S. and potentially affects the health of tens of millions of women—but not men. The ramifications for children these women conceive could be serious, because the substance can impair development of the brains and nervous systems of fetuses and infants.
Perchlorate contaminates aquifers or rivers in at least 35 states. The chemical, which inhibits uptake of iodine by the thyroid gland, has been found in produce, including lettuce and melons. Such produce likely was irrigated with perchlorate-tainted water, or it was grown in soils where the chemical occurs naturally or that are treated with perchlorate-containing fertilizer. The substance also has been found in cows' milk, presumably because these animals drink water or eat feed contaminated with perchlorate.
EPA has considered the regulation of perchlorate for years. It has faced stiff opposition from the military and NASA, which use 90% of the perchlorate produced in the U.S. and face a potentially huge liability for cleanup if EPA regulates the substance in drinking water.
The Pentagon and NASA had previously attacked EPA's scientific basis for setting an acceptable dose of perchlorate that people can safely ingest. In 2005, the National Research Council settled the issue, saying 0.7 ??g per kg of body weight per day is a safe dose, even for the most vulnerable, that is, the unborn children carried by women who have iodine-deficient diets or whose bodies don't make enough thyroid hormone (C&EN, Jan. 17, 2005, page 13).
At a congressional hearing, held by the House Energy & Commerce Subcommittee on Hazardous Materials on April 25, Bush Administration officials gave a status report on the federal government's consideration of perchlorate regulation. The subcommittee is considering a bill, H.R. 1747, that requires EPA to regulate perchlorate in drinking water.
Benjamin J. Grumbles, EPA's assistant administrator for water, said his agency is placing a high priority on determining whether and how to regulate perchlorate.
But before EPA can decide whether to regulate the chemical, it needs to understand how much of the public's exposure to perchlorate comes from food and how much comes from drinking water, Grumbles said. Then the agency can determine whether imposing a limit on perchlorate in drinking water "presents a meaningful opportunity for health risk reduction," he said.
Rep. Albert R. Wynn (D-Md.), chairman of the subcommittee and a cosponsor of H.R. 1747, wondered aloud at the hearing whether it is prudent for the government to wait to regulate until it knows whether food or drinking water is the public's main source of perchlorate exposure.
"The agency believes the currently available food data are inadequate" for making a regulatory determination, Grumbles said.
Robert E. Brackett, director of FDA's Center for Food Safety & Applied Nutrition, testified that his agency has preliminary results on the average perchlorate exposure for the general U.S. population aged two years and older. They are based on a survey of 27 types of food and beverages, including milk, fruit and fruit juices, vegetables, and grains, as well as seafood grown in aquaculture. The results, which do not represent the complete diet of the U.S. population, are undergoing interagency review before they are made public, he said.
Later this year, FDA plans to complete a more thorough assessment of the exposure of consumers to perchlorate through foods that are the major components of the U.S. diet, Brackett said.
Meanwhile, CDC researchers recently documented widespread human exposure to perchlorate in the U.S., said James Pirkle, deputy director for science at CDC's National Center for Environmental Health. Researchers detected perchlorate in urine from each of the 2,820 participants who were at least six years old in its National Health & Nutrition Examination Study for 2001-02. They also found that concentrations of perchlorate in children were generally higher than levels found in adolescents and adults.
CDC researchers also discovered that perchlorate exposure was associated with a decreased level of thyroid hormone among women with lower than normal concentrations of iodine in their urine, Pirkle told the subcommittee. Iodine is essential to production of thyroid hormone, which regulates the body's metabolism. Perchlorate interferes with the thyroid's uptake of iodine.
An estimated 43 million women in the U.S. have iodine levels low enough to put them at increased risk of developing goiter, an enlargement of the thyroid gland due to an insufficient amount of thyroid hormone, Pirkle said.
THE LINK between perchlorate and thyroid function in women with low levels of iodine "was unexpected," on the basis of previous research, Pirkle said. "CDC researchers are planning a second study to affirm their findings and evaluate additional measures of thyroid function," he added.
Gary L. Ginsberg, a Connecticut toxicologist who specializes in children's vulnerability to toxic chemicals, told the subcommittee that the CDC finding shows that "we have many vulnerable women." If these women become pregnant, they could have babies at risk of abnormal brain development, he said. The developing nervous system is sensitive to small changes in thyroid hormone levels, he added.
An embryo is completely dependent on maternal thyroid hormone during the first trimester of a pregnancy, Anila Jacob, a practicing physician and senior scientist for the Environmental Working Group, explained at the hearing. "After that, the fetus begins to produce its own thyroid hormone but still receives about 30% of its total from the mother for the remainder of the pregnancy," she said. "Any thyroid hormone deficiency in the mother has repercussions for her fetus."
Nursing infants have a special vulnerability to neurological problems from perchlorate exposure, Ginsberg said. An infant can get a "substantial dose" of perchlorate in breast milk, he said. Plus, perchlorate in a mother's body inhibits the movement of iodine into her breast milk, he said.
"This creates double jeopardy for the nursing infant: lower iodine intake at the same time that it is getting a risky level of perchlorate," Ginsberg said.
Also at the hearing, a Pentagon official described how the military is working to replace perchlorate in some applications.
Alex Beehler, assistant deputy undersecretary of defense for environment, safety, and occupational health, said research and development efforts have identified substitutes for perchlorate in devices used in training exercises to simulate ground bursts and hand grenades. These devices have accounted for most of the perchlorate used on Army training ranges in the past, he said. The Defense Department closed two training ranges because of perchlorate contamination.
Beehler said production of the perchlorate replacement for use in simulators for military training is scheduled to begin in 2008. Meanwhile, testing is under way for alternatives that could replace perchlorate in solid rocket propellants, he said.
In addition, John B. Stephenson, director of natural resources and environment for the Government Accountability Office, told the subcommittee, "EPA does not centrally track or monitor perchlorate detections, environmental releases, or cleanup activities." GAO, the investigative arm of Congress, recommends that EPA set up a system to keep tabs on the sites where perchlorate contamination is found, he said. He added that EPA disagrees there is a need for such a system.
A spokesman for Wynn's panel said the subcommittee has no immediate plans for voting on H.R. 1747. But support for the bill seems to be growing among lawmakers as more studies document the breadth of perchlorate exposure in the U.S. and its potential threat to babies.
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