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News from the National Academies
Date: July 11, 2000
Contacts: Bob Ludwig, Media Relations Associate
Kathi McMullin, Media Relations Assistant
(202) 334-2138; e-mail <news@nas.edu>

FOR IMMEDIATE RELEASE

EPA's Methylmercury Guideline Is Scientifically Justifiable
For Protecting Most Americans, But Some May Be at Risk

WASHINGTON -- While the U.S. Environmental Protection Agency's guideline for protecting the public from a toxic form of mercury is justifiable based on the latest scientific evidence, some children of women who consume large amounts of fish and seafood during pregnancy may be at special risk of neurological problems, says a new report from the National Academies' National Research Council. Congress requested that the Research Council provide independent, scientific advice in establishing appropriate exposure limits for methylmercury.

Fish and other seafood products are the main source of methylmercury in the human diet. Fetuses are particularly vulnerable to methylmercury because of their rapid brain development, and some may currently be receiving exposures at levels that cause observable adverse neurological effects.

"Although we believe EPA's guideline on methylmercury is generally adequate to protect most people, more must be done to gain a better understanding of various risk factors for the U.S. population," said Robert A. Goyer, chair of the committee that wrote the report and professor emeritus at the University of Western Ontario, who now resides in Chapel Hill, N.C. "Trends in methylmercury exposure, including regional differences, should be analyzed, as should subpopulations whose diets are high in fish and seafood. And we need to better understand how this chemical affects brain development in fetuses and children."

Based on an analysis of available data that included exposure levels to methylmercury and food-consumption surveys, the committee said the majority of Americans are at low risk of adverse health effects. However, the committee estimated that each year about 60,000 children may be born in the United States with neurological problems that could lead to poor school performance because of exposure to methylmercury in utero.

EPA's current reference dose for methylmercury is 0.1 micrograms per kilogram of body weight per day -- the amount of methylmercury to which an individual can be exposed on a daily basis without adverse health consequences. EPA's reference dose is used to guide risk-management decisions and regulatory policies ranging from fish-consumption advisories to air-emission permits. According to EPA, the typical American consumer eats less than a third of an ounce of fish per day, and would be exposed to considerably less than its current guideline.

To draw its conclusions, the committee evaluated the range of data on which risk assessments conducted by EPA and other regulatory agencies are based. It also reviewed new findings that have emerged since the development of EPA's current reference dose in 1995 and met with researchers of major ongoing population studies. The overall weight of the evidence from this comprehensive review led the committee to conclude that EPA's reference dose is scientifically justifiable for protecting the health of the vast majority of Americans.

When the agency first developed its guideline five years ago, EPA judged data from a 1971 Iraqi poisoning incident to be the most relevant. To provide EPA with more appropriate data in formulating its reference dose, the committee analyzed population studies in the Faroe Islands, Seychelles Islands, and New Zealand. It concluded that the Faroe Islands analysis should be used by EPA as the critical study for deriving the reference dose, the report says.

Neurodevelopmental problems are the most appropriate basis for setting an exposure limit, the committee found. Strong scientific evidence exists from human and animal studies to link certain levels of methylmercury exposure and neurological problems, including poor performance on tests that measure attention and motor function. However, researchers still need to understand if there is a precise time during development when the brain is most sensitive to methylmercury and exactly how the chemical exerts its effects. Evidence also indicates that the cardiovascular and immune systems could be affected by methylmercury, the report notes. Information on whether methylmercury causes cancer in humans is still inconclusive.

Scientists do not agree on how to account for some uncertainties, such as varying individual responses to methylmercury exposure and emerging health concerns. Better data are needed to decrease the uncertainties, the report says. For example, further investigation is needed on low-dose exposure to methylmercury throughout the lifespan of humans and animals, and on carcinogenic, neurologic, reproductive, and immunologic effects, including the emergence of delayed neurological effects later in life. More research on factors that might influence responses, such as genetics, age, sex, health status, and nutrition, also is needed.

Likewise, research should be conducted to gather data on methylmercury exposure in different regions of the United States and in specific populations with high consumption of fish, the committee noted. In addition to methylmercury, research on exposure to other forms of mercury, including mercury from dental fillings, is needed to see if they affect the human body's response to methylmercury.

Mercury exists naturally in the environment and finds its way into the air through both natural processes and human activities. Power plants that burn fossil fuels, particularly coal, generate the greatest amount of mercury emissions. Once mercury is deposited in lakes, rivers, and oceans, it is converted to methylmercury by aquatic organisms. Humans are exposed to the chemical when they eat fish.

In the United States, responsibility for regulating mercury is shared by two federal agencies: EPA and the Food and Drug Administration (FDA). FDA is charged with regulating commercially sold fish and seafood. EPA monitors concentrations in the environment and regulates industrial releases of mercury to surface water and air.

The study was sponsored by the U.S. Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

Read the full text of Toxicological Effects of Methylmercury for free on the Web, as well as more than 1,800 other publications from the National Academies. Printed copies are available for purchase from the National Academy Press Web site or at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).


NATIONAL RESEARCH COUNCIL
Commission on Life Sciences
Board on Environmental Studies and Toxicology

Committee on the Toxicological Effects of Methylmercury

Robert A. Goyer, M.D. (chair)
Chairman and Professor Emeritus
Department of Pathology
University of Western Ontario (retired)
Chapel Hill, N.C.

H. Vasken Aposhian, Ph.D.
Professor
Department of Molecular and Cell Biology and Department of Pharmacology
University of Arizona
Tucson

Lenore Arab, Ph.D.
Professor
Department of Epidemiology and Department of Nutrition
School of Public Health
University of North Carolina
Chapel Hill

David C. Bellinger, Ph.D.
Associate Professor
Department of Neurology
Harvard Medical School
Boston

Thomas M. Burbacher, Ph.D.
Associate Professor
Department of Environmental Health
School of Public Health and Community Medicine
University of Washington
Seattle

Thomas A. Burke, Ph.D.
Associate Professor
Department of Health Policy and Management
School of Hygiene and Public Health, and
Co-Director
Risk Science and Public Policy Institute
Johns Hopkins University
Baltimore

Joseph L. Jacobson, Ph.D., J.D.
Professor
Department of Obstetrics/Gynecology
School of Medicine, and
Professor
Department of Psychology
Wayne State University
Detroit

Lynda P. Knobeloch, Ph.D.
Senior Toxicologist
Division of Public Health
State of Wisconsin Bureau of Environmental Health
Madison

Louise M. Ryan, Ph.D.
Professor of Statistical Science
Department of Biostatistical Science
Dana-Farber Cancer Institute, and
Professor
Department of Biostatistics
Harvard School of Public Health
Boston

Alan H. Stern, Dr.P.H.
Chief
Bureau of Risk Analysis
New Jersey Department of Environmental Protection, and
Adjunct Assistant Professor
Department of Environmental and Community Medicine
University of Medicine and Dentistry of New Jersey
Trenton

RESEARCH COUNCIL STAFF

Carol A. Maczka, Ph.D.
Study Director