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Executive Summary
Pages 1-12

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From page 1...
... , one organic form of Hg, can accumulate up the food chain in aquatic systems and lead to high concentrations of MeHg in predatory fish, which, when consumed by humans, can result in an increased risk of adverse effects In highly exposed or sensitive populations. Consumption of contaminated fish is the major source of human exposure to MeHg in the United States.
From page 2...
... 2A reference dose is defined as an estimate of a daily exposure to the human population (including sensitive subpopulations) that is likely to be without a risk of adverse effects when experienced over a lifetime.
From page 3...
... 3The point of departure represents an estimate or observed level of exposure or dose which is associated with an increase in adverse effects in the study population. Examples of points of departure include NOAELs, LOAELs, BMDs, and BMDLs.
From page 4...
... There is also evidence in humans and animals that exposure to MeHg can have adverse effects on the developing and adult cardiovascular system (blood-pressure regulation, heart-rate variability, and heart disease)
From page 5...
... in light of those considerations and more recent epidemiological studies, the committee concludes that the Iraqi study should no longer be considered the critical study for the derivation of the RfD. Results from the three large epidemiological studies—the Seychelles, Faroe Islands, and New Zealand studies—have added substantially to the body of knowledge on brain development following long-term exposure to small amounts of MeHg.
From page 6...
... . However, on the basis of an analysis of the data, the committee concluded that the adverse effects found in the Faroe Islands study, including those seen in the Boston Naming Test,s were not attributable to PCB exposure and that PCB exposure did not invalidate the use of the Faroe Islands study as the basis of risk assessment for MeHg.
From page 7...
... individual responses to MeHg exposure are variable and a key source of uncertainty. Factors that might influence the responses include genetics, age, sex, health status, nutritional supplements, nutritional influences, including dietary interactions, and linking the time and intensity of MeHg exposure to the critical periods of brain development.
From page 8...
... The adverse effects observed In the Faroe islands study were most sensitively detected when using cord blood as the biomarker. Based on cord-blood analyses from the Faroe islands study, He lowest BMD for a neurobehavioral end point the committee considered to be sufficiently reliable is for the Boston Naming Test.
From page 9...
... In the interim, the best method of maintaining fish consumption and minimizing Hg exposure is the consumption of fish known to have lower MeHg concentrations. In the derivation of an RfD, the benchmark dose is divided by uncertainty factors.
From page 10...
... data-base insufficiencies. On the basis of the available scientific data, the committee concludes that a safety factor of 2-3 will account for biological variability in dose estimation.
From page 11...
... Based on cordblood analyses from the Farce Islands study, the lowest BMD for a neurobehavioral end point the committee considered to be sufficiently reliable is for the Boston Naming Test. For that end point, dose-response data based on Hg concentrations in corcI blood should be modeled using
From page 12...
... As stated earlier, given those considerations, an uncertainty factor of at least 10 is supported by the committee. The committee further concludes that the case of MeHg presents a strong illustration of the need for harmonization of efforts to establish a common scientific basis for exposure guidance and to reduce current differences among agencies, recognizing that risk-management efforts reflect the differing mandates and responsibilities of the agencies.


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