Re-evaluation of the reference dose for methylmercury and assessment of current exposure levels.
Methylmercury (Me-Hg) is widely distributed through freshwater and saltwater food chains and human consumption of fish and shellfish has lead to widespread exposure. Both the U.S. EPA Reference Dose (0.3 micrograms/kg/day) and the FAO/WHO Permissible Tolerable Weekly Intake (3.3 micrograms/kg/week) are currently based on the prevention of paraesthesia in adult and older children. However, Me-Hg exposure in utero is known to result in a range of developmental neurologic effects including clinical CNS symptoms and delayed onset of walking. Based on a critical review of developmental toxicity data from human and animal studies, it is concluded that current guidelines for the prevention of paraesthesia are not adequate to address developmental effects. A dose of 0.07 micrograms/kg/day is suggested as the best estimate of a potential reference dose for developmental effects. Data on nationwide fish consumption rates and Me-Hg levels in fish/seafood weighted by proportion of the catch intended for human consumption are analyzed in a Monte Carlo simulation to derive a probability distribution of background Me-Hg exposure. While various uncertainties in the toxicologic and exposure data limit the precision with which health risk can be estimated, this analysis suggests that at current levels of Me-Hg exposure, a significant fraction of women of childbearing age have exposures above this suggested reference dose.
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Division of Science and Research, New Jersey Department of Environmental Protection and Energy, Trenton 08625.
D000818:Animals; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006197:Hair / Q000737:chemistry; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008452:Maximum Allowable Concentration; D008767:Methylmercury Compounds / Q000009:adverse effects / Q000032:analysis; D008895:Milk, Human / Q000737:chemistry; D009010:Monte Carlo Method; D010292:Paresthesia / Q000139:chemically induced; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012016:Reference Values
D008767:Methylmercury Compounds