National Academy of Sciences

National Academy of Engineering

Institute of Medicine

National Research Council

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

Strengthening Science at the U.S. Environmental Protection Agency: Research Management and Peer Review Practices (2000)

Scientific Frontiers in Developmental Toxicology and Risk Assessment (2000)

Modeling Mobile-Source Emissions (2000)

Copper in Drinking Water (2000)

Ecological Indicators for the Nation (2000)

Waste Incineration and Public Health (1999)

Hormonally Active Agents in the Environment (1999)

Research Priorities for Airborne Particulate Matter: I. Immediate Priorities and a Long-Range Research Portfolio (1998); II. Evaluating Research Progress and Updating the Portfolio (1999)

Ozone-Forming Potential of Reformulated Gasoline (1999)

Risk-Based Waste Classification in California (1999)

Arsenic in Drinking Water (1999)

Brucellosis in the Greater Yellowstone Area (1998)

The National Research Council's Committee on Toxicology: The First 50 Years (1997)

Toxicologic Assessment of the Army's Zinc Cadmium Sulfide Dispersion Tests (1997)

Carcinogens and Anticarcinogens in the Human Diet (1996)

Upstream: Salmon and Society in the Pacific Northwest (1996)

Science and the Endangered Species Act (1995)

Wetlands: Characteristics and Boundaries (1995)

Biologic Markers (5 reports, 1989-1995)

Review of EPA's Environmental Monitoring and Assessment Program (3 reports, 1994-1995)

Science and Judgment in Risk Assessment (1994)

Ranking Hazardous Waste Sites for Remedial Action (1994)

Pesticides in the Diets of Infants and Children (1993)

Issues in Risk Assessment (1993)

Setting Priorities for Land Conservation (1993)

Protecting Visibility in National Parks and Wilderness Areas (1993)

Dolphins and the Tuna Industry (1992)

Hazardous Materials on the Public Lands (1992)

Science and the National Parks (1992)

Animals as Sentinels of Environmental Health Hazards (1991)

Assessment of the U.S. Outer Continental Shelf Environmental Studies Program, Volumes I-IV (1991-1993)

Human Exposure Assessment for Airborne Pollutants (1991)

Monitoring Human Tissues for Toxic Substances (1991)

Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991)

Decline of the Sea Turtles (1990)

Copies of these reports may be ordered from the National AcademyPress

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(202) 334-3313

www.nap.edu

IN 1997, the U.S. Environmental Protection Agency (EPA) issued two reports to the U.S. Congress on mercury (Hg) and its effects on public health. The first of these reports, the Mercury Study Report to Congress, assessed the source and amount of Hg emissions in the United States, the detrimental effects of Hg on humans and wildlife, and the feasibility of control technologies. The second report, the Utility Hazardous Air Pollutant Report to Congress, looked specifically at emissions from utility companies and cited Hg as a major contaminant, especially in emissions from coal-fired power plants. Once in the environment, Hg can be converted to methylmercury (MeHg), which bioaccumulates up the food chain. Such bioaccummulation can lead to high concentrations of MeHg in predatory fish. Because of concerns about MeHg exposure levels in the United States from the consumption of contaminated fish, particularly among sensitive populations, questions have arisen among federal agencies over what is an acceptable level of exposure to MeHg. Because of gaps in the scientific data regarding Hg toxicity, particularly MeHg, the potentially widespread implications for human health, and the high financial costs and feasibility problems associated with further regulating Hg emissions, Congress directed EPA in the House Appropriations Report for EPA's Fiscal 1999 funding to contract with the National Research Council (NRC) to prepare recommendations on the appropriate reference dose for Hg exposure.

In this report, the Committee on the Toxicological Effects of Methylmercury of the NRC independently reviewed the reference dose

for MeHg. The committee reviewed the available toxicological, epidemiological, and exposure data (from food and water) and determined the appropriateness of the critical study, end points of toxicity, and uncertainty factors used by EPA in the derivation of the reference dose for MeHg. The committee was also asked to identify data gaps and make recommendations for future research.

This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise in accordance with procedures approved by the NRC's Report Review Committee for reviewing NRC and Institute of Medicine reports. The purpose of this independent review is to provide candid and critical comments that will assist the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscripts remain confidential to protect the integrity of the deliberative process. The committee wishes to thank the following individuals, who are neither officials nor employees of the NRC, for their participation in the review of this report: Melvin Andersen, Colorado State University; Michael Aschner, Wake Forest University; Kenny Crump, ICF Consulting; Kim Dietrich, University of Cincinnati; Johanna Dwyer, New England Medical Center; John Emmerson, Eli Lilly (retired); Susan Miller, University of California at San Francisco; Charles Poole, University of North Carolina; Jonathan Samet, Johns Hopkins University; Ellen Silbergeld, University of Maryland; Christopher Whipple, Environ International Corporation; James Woods, University of Washington.

The individuals listed above have provided many constructive comments and suggestions. It must be emphasized, however, that responsibility for the final content of this report rests entirely with the authoring committee and the NRC.

The committee gratefully acknowledges the following individuals for providing background information and for making presentations to the committee: Richard Duffy of the office of Senator Patrick Leahy (Vermont); Lee Alman of the office of Congressman Alan Mollohan (West Virginia); George Lucier, National Institute of Environmental Health Sciences; William Farland, EPA; Michael Bolger, Food and Drug Administration; Christopher DeRosa, Agency for Toxic Substances and Disease Registry; E. Spencer Garrett, National Oceanic and Atmospheric Administration, Fran Sharples, Office of Science and Technology; Michael Bender, Mercury Policy Project; Jane Williams, California

Communities Against Toxics; Eric Uram, Sierra Club-Great Lakes Program; Greg Schaefer, Arch Coal, Inc.; Leonard Levin, Electric Power Research Institute; and David Michaud, Wisconsin Electric Power Company. The committee also heard from a number of researchers actively investigating issues related to MeHg exposure. Those researchers are Tord Kjellstrom, University of Auckland, New Zealand; Donna Mergler, University of Quebec at Montreal; Kenny Crump, ICF Kaiser; Ellen Silbergeld, University of Maryland; Philippe Grandjean, University of Southern Denmark; Neils Keiding and Esben Budtz-Jøergensen, both from the University of Copenhagen; and Thomas Clarkson, Christopher Cox, Gary Myers, Philip Davidson, and Mark Moss, all from the University of Rochester. In addition, the committee wants to give special thanks to individuals and groups who provided further analyses and information at the request of the committee. Those are Wayne Rosamond, University of North Carolina; Philippe Grandjean; Neils Keiding; Esben Budtz-Jørgensen; Thomas Clarkson; Christopher Cox; Tord Kjellstrom; Harvey Clewell III; Jeffrey Swartout; Cynthia Van Landingham; and Kenny Crump. The committee also gratefully acknowledges input from individuals representing the Environmental Working Group, the Dental Amalgam Mercury Syndrome (DAMS) organization and the Mercury Free Press.

The committee is grateful for the assistance of the NRC staff in preparing the report. Staff members who contributed to this effort are Carol A. Maczka, senior program director for the Toxicology and Risk Assessment Program; Michelle Catlin, research associate; Ruth E. Crossgrove, editor; Laura Holliday and Judy Estep, senior project assistants; and Mirsada Karalic-Loncarevic, information specialist.

Finally, I would like to thank all the members of the committee for their dedicated efforts throughout the development of this report.

Robert A. Goyer

Chair, Committee on the Toxicological

Effects of Methylmercury