Characterization of Human Health and Wildlife Risks from Mercury Exposure in the United States
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United States EPA-452/R-97-009 Environmental Protection December 1997 Agency Air Mercury Study Report to Congress Volume VII: Characterization of Human Health and Wildlife Risks from Mercury Exposure in the United States Office of Air Quality Planning & Standards and Office of Research and Development c7o032-1-1 MERCURY STUDY REPORT TO CONGRESS VOLUME VII: CHARACTERIZATION OF HUMAN HEALTH AND WILDLIFE RISKS FROM MERCURY EXPOSURE IN THE UNITED STATES December 1997 Office of Air Quality Planning and Standards and Office of Research and Development U.S. Environmental Protection Agency TABLE OF CONTENTS Page U.S. EPA AUTHORS ................................................................iii SCIENTIFIC PEER REVIEWERS ......................................................iv WORK GROUP AND U.S. EPA/ORD REVIEWERS ...................................... vii LIST OF TABLES .................................................................. viii LIST OF FIGURES ..................................................................ix LIST OF SYMBOLS, UNITS AND ACRONYMS ......................................... x 1. INTRODUCTION ...........................................................1-1 2. HUMAN HEALTH EFFECTS: HAZARD IDENTIFICATION AND DOSE- RESPONSE ................................................................2-1 2.1 Health Hazards Associated with Mercury Exposure ...........................2-1 2.2 Dose-Response to Methylmercury ........................................2-3 2.2.1 Calculation of Methylmercury RfD .................................2-3 2.2.2 Human Dose-Response Issues .....................................2-7 2.3 Uncertainty in the Human Health RfD for Methylmercury ....................2-15 2.3.1 Qualitative Discussion of Uncertainties in the RfD for Methylmercury Alternate Analyses .............................................2-15 2.3.2 Quantitative Analysis of Uncertainty in the Methylmercury RfD ......... 2-18 3. RISK CHARACTERIZATION FOR WILDLIFE ...................................3-1 3.1 Scope of the Risk Assessment ............................................3-1 3.2 Exposure of Piscivorous Wildlife to Mercury ................................3-1 3.2.1 Estimation of Current Average Exposure to Piscivorous Wildlife on a Nationwide Basis ...............................................3-2 3.2.2 Estimation of Mercury Deposition on a Regional Scale (40 km grid) and Comparison of These Deposition Data with Species Distribution Information 3-2 3.2.3 Estimation of Mercury Exposure on a Local Scale in Areas Near Emissions Point Sources .......................................................3-4 3.3 Effects Assessment for Mercury ..........................................3-5 3.4 Risk Assessment for Mercury ............................................3-5 3.5 Risk of Mercury from Airborne Emissions to Piscivorous Avian and Mammalian Wildlife ................................3-7 3.5.1 Lines of Evidence ...............................................3-7 3.5.2 Risk Statements ................................................3-7 4. CHARACTERIZATION OF FATE OF ENVIRONMENTAL MERCURY .............. 4-1 4.1 The Modeling Analysis .................................................4-1 4.1.1 Study Design of the Modeling Analysis..............................4-1 4.1.2 Long-Range Atmospheric Transport Analysis .........................4-5 4.1.3 Analysis of Local-Scale Fate of Atmospheric Mercury .................. 4-5 4.1.4 Assessment of Watershed and Water Body Fate .......................4-5 4.2 Important Uncertainties Identified in Environmental Fate Modeling .............. 4-6 4.2.1 Emissions Uncertainties ..........................................4-6 4.2.2 Atmospheric Reactions of Emitted Mercury ..........................4-7 i TABLE OF CONTENTS (continued) Page 4.2.3 Deposition of Atmospheric Mercury ................................4-7 4.2.4 Mercury Concentrations in Water and Aquatic Biota ................... 4-9 4.3 Summary ...........................................................4-10 5. CHARACTERIZATION OF EXPOSURE ........................................5-1 5.1 Individual Human Results ...............................................5-2 5.1.1 Predicted Inhalation Exposures ....................................5-2 5.1.2 Predicted Terrestrial Food Chain Results .............................5-2 5.1.3. Predicted Soil Ingestion Results ....................................5-2 5.1.4 Fish Ingestion Scenarios ..........................................5-3 5.2 Other Sources of Human Mercury Exposure ................................5-4 5.3 Characterizing Wildlife Exposures ........................................5-5 5.3.1 Modeled Wildlife Exposures ......................................5-5 5.3.2 Measured Exposures to Methylmercury ..............................5-6 5.3.3 Avian Species Exposure to Methylmercury ...........................5-7 5.4 Human Intake of Methylmercury Estimated through Dietary Surveys and Mercury Residue Data .............................................5-11 5.4.1 Estimates Based on Total Diet Studies ..............................5-11 5.4.2 Estimates Based on Food Consumption Surveys ......................5-12 5.4.3 Mercury Concentrations in Fish and Shellfish ........................5-16 5.4.4 Subpopulations of Concern Based on Physiological Sensitivity to Adverse Developmental Effects of Methylmercury ...........................5-17 5.5 Comparison of Dietary Exposure Estimates with Hair Mercury Concentrations .... 5-26 5.5.1 General Population .............................................5-26 5.5.2 Subpopulations with Higher Exposures to Fish/ Shellfish and Mercury .... 5-27 5.5.3 Comparison with Dietary Intake of Mercury .........................5-27 5.6 Estimates of Sizes of At-Risk Populations .................................5-28 5.6.1 Number of Human Subjects in At-Risk Subpopulation in the United States . 5-28 6. INTEGRATIVE ANALYSIS FOR METHYLMERCURY ............................6-1 6.1 Characterization of Risk: Quantitative Integration of Human and Wildlife Exposure and Dose-Response .......................................................6-1 6.1.1 Introduction ....................................................6-1 6.1.2 Description of Critical Terminology for this Section .................... 6-1 6.2 Integration of Modeled Methylmercury Exposure Estimates for Humans and Wildlife with the Dose-Response Assessments ...........................6-2 6.2.1 Methylmercury Intake by Humans and Wildlife Based on the IEM-2M Modeling ..............................................6-3 6.2.2 Comparison of Dose-Response Estimates Across Species ............... 6-8 6.2.3 Integration of Modeled Methylmercury Exposure Through Fish Consumption with Health Criteria ............................................6-11 6.3 Comparison with Other Recommendations .................................6-13 6.3.1 Reference Values for Biological Monitoring .........................6-13 6.3.2 Recommendations Based on Grams of Fish Consumed Per Day .......... 6-22 6.3.2 Population-Based Projections of the Number of Women Consuming Fish/Shellfish in Excess of 100 Grams per Day ......................6-24 ii 6.3.3 Subpopulations of Anglers, Subsistence Fishers ...................... 6-28 6.4. Recommendations Based on Micrograms of Methylmercury Per Day ............ 6-28 6.4.1 Comparison with U.S. EPA's RfD and Benchmark Dose ............... 6-28 6.4.2 Children’s Exposures to Methylmercury ............................6-31 6.4.3 Comparison with Populations Consuming Large Amounts of Fish ........ 6-32 6.4.4 Freshwater Fish Consumption ....................................6-32 6.5 Wildlife Species ......................................................6-38 6.5.1 Comparison with Great Lakes Water Quality Initiative Criteria .......... 6-38 6.5.2 Estimates for the Size of the Piscivorous Wildlife Population ............ 6-39 7. CONCLUSIONS ............................................................7-1 8. RESEARCH NEEDS .........................................................8-1 9. REFERENCES ..............................................................9-1 iii U.S. EPA AUTHORS Principal Authors Kathryn Mahaffey, Ph.D. National Center for Environmental Assessment- Washington Office of Research and Development Washington, DC Glenn E. Rice National Center for Environmental Assessment- Cincinnati Office of Research and Development Cincinnati, OH Rita Schoeny, Ph.D. Office of Water Washington, DC Contributing Authors Jeff Swartout National Center for Environmental Assessment- Cincinnati Office of Research and Development Cincinnati, OH Martha H. Keating Office of Air Quality Planning and Standards Research Triangle Park, NC iv SCIENTIFIC PEER REVIEWERS Dr. William J. Adams* Dr. John A. Dellinger* Kennecott Utah Corporation Medical College of Wisconsin Dr. Brian J. Allee Dr. Kim N. Dietrich* Harza Northwest, Incorporated University of Cincinnati Dr. Thomas D. Atkeson Dr. Tim Eder Florida Department of Environmental Great Lakes Natural Resource Center Protection National Wildlife Federation for the States of Michigan and Ohio Dr. Donald G. Barnes* U.S. EPA Science Advisory Board Dr. Lawrence J. Fischer* Michigan State University Dr. Steven M. Bartell SENES Oak Ridge, Inc. Dr. William F. Fitzgerald University of Connecticut Dr. David Bellinger* Avery Point Children’s Hospital, Boston A. Robert Flaak* Dr. Nicolas Bloom* U.S. EPA Science Advisory Board Frontier Geosciences, Inc. Dr. Katharine Flegal Dr. Mike Bolger National Center for Health Statistics U.S. Food and Drug