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About this book
About this book
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.
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. Chemistry, exposure, toxicokinetics, and toxicodynamics; physical and chemical properties; methods of chemical analysis; exposures to MeHg in the US population; toxicokinetics; mobilization of body Hg; chemical forms of Hg in toxicity; toxic effects and target organs; biochemical mechanisms of toxicity; summary and conclusions. Biological variability: age-related susceptibility; gender differences; genetics; mechanisms of nutritional influence on MeHg health effects; toxicokinetic variability. 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. Health effects of methylmercury: carcinogenicity; genotoxicity; immunotoxicity; reproductive effects; renal toxicity; cardiovasuclar effects; hematological effects; developing central nervous-systems toxicity; adult central nervous-systems toxicity. 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 exposure. Dose-response assessment: risk assessment for non-cancer 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. 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 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 conclusions.
Committee on the Toxicological Effects of Methylmercury, Board on Environmental Studies and Toxicology, National Research Council