NEUROBEHAVIORAL EFFECTS OF DEVELOPMENTAL METHYLMERCURY EXPOSURE

Methylmercury (MeHg) is a global environmental problem and is listed b y the international Program of Chemical Safety as one of the six most dangerous chemicals in the world's environment. Human exposure to MeHg primarily occurs through the consumption of contaminated food such as fish, although catastrophic exposures due to industrial pollution hav e occurred. The fetus is particularly sensitive to MeHg exposure and a dverse effects on infant development have been associated with levels of exposure that result in few, if any, signs of maternal clinical ill ness or toxicity. High levels of prenatal exposure in humans result in neurobehavioral effects such as cerebral palsy and severe mental reta rdation. Prenatal exposure to MeHg in communities with chronic low-lev el exposure is related to decreased birthweight and early sensorimotor dysfunction such as delayed onset of walking. Neurobehavioral alterat ions have also been documented in studies with nonhuman primates and r odents. Available information on the developmental neurotoxic effects of MeHg, particularly the neurobehavioral effects, indicates that the fetus and infant are more sensitive to adverse effects of MeHg. It is therefore recommended that pregnant women and women of childbearing ag e be strongly advised to limit their expo sure to potential sources of MeHg. Based on results from human and animal studies on the developme ntal neurotoxic effects of methylmercury, the accepted reference dose should be lowered to 0.025 to 0.06 MeHg mu g/kg/day. Continued researc h on the neurotoxic effects associated with low level developmental ex posure is needed.