Mercury is widespread in our environment. Methylmercury, one organic form of mercury, can accumulate up the aquatic food chain and lead to high concentrations in predatory fish. When consumed by humans, contaminated fish represent a public health risk.

Combustion processes, especially coal-fired power plants, are major sources of mercury contamination in the environment. The U.S. Environmental Protection Agency (EPA) is considering regulating mercury emissions from those plants.

Toxicological Effects of Methylmercury reviews the health effects of methylmercury and discusses the estimation of mercury exposure from measured biomarkers, how differences between individuals affect mercury toxicity, and appropriate statistical methods for analysis of the data and thoroughly compares the epidemiological studies available on methylmercury. Included are discussions of current mercury levels on public health and a delineation of the scientific aspects and policy decisions involved in the regulation of mercury.

This report is a valuable resource for individuals interested in the public health effects and regulation of mercury. The report also provides an excellent example of the implications of decisions in the risk assessment process for a larger audience.

Contents

• THE NATIONAL ACADEMIES
• COMMITTEE ON THE TOXICOLOGICAL EFFECTS OF METHYLMERCURY
• BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
• COMMISSION ON LIFE SCIENCES
  • Staff
• OTHER REPORTS OF THE BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
• PREFACE
• EXECUTIVE SUMMARY
  • THE CHARGE TO THE COMMITTEE
  • THE COMMITTEE'S APPROACH TO ITS CHARGE
  • THE COMMITTEE'S EVALUATION
  • RESEARCH NEEDS
  • RECOMMENDATIONS
• 1. INTRODUCTION
  • SOURCES OF Hg
  • FATE AND TRANSPORT
  • HEALTH EFFECTS
  • EXPOSURE EVENTS AND STUDIES
  • SUMMARY OF RISK ASSESSMENTS FOR MeHg
  • SCIENTIFIC CONTROVERSIES AND SOURCES OF UNCERTAINTY
  • ORGANIZATION OF THE REPORT
  • REFERENCES
• 2. CHEMISTRY, EXPOSURE, TOXICOKINETICS, AND TOXICODYNAMICS
  • PHYSICAL AND CHEMICAL PROPERTIES
  • METHODS OF CHEMICAL ANALYSIS
  • EXPOSURES TO MeHg IN THE U.S. POPULATION
  • TOXICOKINETICS
  • MOBILIZATION OF BODY Hg
  • CHEMICAL FORMS OF Hg IN TOXICITY
  • TOXIC EFFECTS AND TARGET ORGANS
  • BIOCHEMICAL MECHANISMS OF TOXICITY
  • SUMMARY AND CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 3. BIOLOGICAL VARIABILITY
  • AGE-RELATED SUSCEPTIBILITY
  • GENDER DIFFERENCES
  • GENETICS
  • MECHANISMS OF NUTRITIONAL INFLUENCE ON MeHg HEALTH EFFECTS
  • TOXICOKINETIC VARIABILITY
  • CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 4. DOSE ESTIMATION
  • DIETARY ASSESSMENT
  • BIOMARKERS OF EXPOSURE
  • ANALYTICAL ERROR IN BIOMARKER MEASUREMENTS
  • EXPOSURE AND DOSE ASSESSMENT IN THE SEYCHELLES, FAROE ISLANDS, AND NEW ZEALAND STUDIES
  • SUMMARY AND CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 5. HEALTH EFFECTS OF METHYLMERCURY
  • CARCINOGENICITY
  • GENOTOXICITY
  • IMMUNOTOXICITY
  • REPRODUCTIVE EFFECTS
  • RENAL TOXICITY
  • CARDIOVASCULAR EFFECTS
  • HEMATOLOGICAL EFFECTS
  • DEVELOPING CENTRAL-NERVOUS-SYSTEM TOXICITY
  • ADULT CENTRAL-NERVOUS-SYSTEM TOXICITY
  • CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 6. COMPARISON OF STUDIES FOR USE IN RISK ASSESSMENT
  • ASSESSMENT OF PRENATAL Hg EXPOSURE: CORD BLOOD VERSUS MATERNAL HAIR AND TIMING OF EXPOSURE
  • DIFFERENCES IN THE NEUROBEHAVIORAL END POINTS ASSESSED AND THE CHILDREN'S AGES AT ASSESSMENT
  • STABLE VERSUS EPISODIC PATTERN OF EXPOSURE
  • STUDY DIFFERENCES IN CONTROL FOR CONFOUNDERS
  • POPULATION DIFFERENCES IN VULNERABILITY
  • RANDOM VARIATION IN THE DETECTABILITY OF EFFECTS AT LOW EXPOSURES
  • CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 7. DOSE-RESPONSE ASSESSMENT
  • RISK ASSESSMENT FOR NONCANCER END POINTS
  • BENCHMARK-DOSE CALCULATIONS FOR CONTINUOUS OUTCOMES
  • SOME SPECIFIC CONSIDERATIONS FOR MeHg
  • COMPARING BENCHMARK DOSES
  • CHOOSING A CRITICAL DOSE FOR A POINT OF DEPARTURE
  • AN INTEGRATIVE ANALYSIS
  • MODEL CHOICE ISSUES
  • SUMMARY AND CONCLUSIONS
  • RECOMMENDATIONS
  • REFERENCES
• 8. RISK CHARACTERIZATION AND PUBLIC HEALTH IMPLICATIONS
  • THE CURRENT EPA REFERENCE DOSE
  • EVALUATING THE RfD–END POINTS OF MeHg TOXICITY
  • SELECTION OF THE END POINT FOR THE RfD
  • EXAMINATION OF THE CRITICAL STUDIES FOR THE RfD
  • BMD CONSIDERATIONS: SELECTING A POINT OF DEPARTURE
  • SELECTION OF THE CRITICAL STUDY AND POINT OF DEPARTURE FOR THE REVISED RfD
  • SOURCES OF UNCERTAINTY: CONSIDERATION FOR UNCERTAINTY FACTORS
  • IMPLICATIONS FOR PUBLIC HEALTH AND RISK MANAGEMENT
  • COMMITTEE FINDINGS AND RECOMMENDATIONS
  • REFERENCES
• APPENDIX TO CHAPTER 7
• GLOSSARY

This project was supported by Grant Agreement No. X 827238-01 between the National Academy of Sciences and the Environmental Protection Agency. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project.

NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.