Neurobehavioral effects of developmental methylmercury exposure.

Abstract

Methylmercury (MeHg) is a global environmental problem and is listed by 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 have occurred. The fetus is particularly sensitive to MeHg exposure and adverse effects on infant development have been associated with levels of exposure that result in few, if any, signs of maternal clinical illness or toxicity. High levels of prenatal exposure in humans result in neurobehavioral effects such as cerebral palsy and severe mental retardation. Prenatal exposure to MeHg in communities with chronic low-level exposure is related to decreased birthweight and early sensorimotor dysfunction such as delayed onset of walking. Neurobehavioral alterations have also been documented in studies with nonhuman primates and rodents. 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 age be strongly advised to limit their exposure to potential sources of MeHg. Based on results from human and animal studies on the developmental neurotoxic effects of methylmercury, the accepted reference dose should be lowered to 0.025 to 0.06 MeHg pg/kg/day. Continued research on the neurotoxic effects associated with low level developmental exposure is needed. -Environ Health Perspect 103(Suppl 6): 135-142 (1995)

Exposure analysis of five fish-consuming populations for overexposure to methylmercury

“…Stern (1993) considered the available human and animal study data addressing developmental endpoints and suggested that the weight of evidence indicated the reference dose ( RfD ) to be 0.07 g /kg /day. With the understanding that the fetus and infant are more sensitive to adverse effects from methylmercury exposure, Gilbert and Grant -Webster (1995 ) used the Iraq episode data (Amin -Zaki et al, 1981;Marsh et al, 1987 ), supported by data on neurobehavioral effects in animals, to develop an RfD range of 0.025 to 0.06 g/kg/ day. Zelikoff et al ( 1995 ) considered various approaches for establishing an RfD based on prenatal methylmercury exposure effects in small mammals, nonhuman primates and humans.…”

Dietary and tissue selenium in relation to methylmercury toxicity

“…Mercury (Hg) is listed by the International Program of Chemical Safety as one of the most dangerous chemicals in the environment (Gilbert and Grant-Webster, 1995). Humans typically encounter methylmercury (MeHg) from eating fish and seafoods.…”

Aging unmasks adverse effects of gestational exposure to methylmercury in rats

“…Difficulties in detecting such damage could be due to the nervous system's extraordinary compensatory ability or because the threshold for neural damage has not been crossed. Delayed neurotoxicity, a necessary element of the hypothesis, is clearly established with methylmercury, especially in sensory± motor domains [4,10,32].In reports that may have prompted the original hypothesis, mice exposed during gestation to high levels of methylmercury showed progressive deterioration in swimming ability and other motor endpoints as they aged [34 ± 36]. These early reports have been supplemented by more recent studies with nonhuman primates [32].…”

“…Difficulties in detecting such damage could be due to the nervous system's extraordinary compensatory ability or because the threshold for neural damage has not been crossed. Delayed neurotoxicity, a necessary element of the hypothesis, is clearly established with methylmercury, especially in sensory± motor domains [4,10,32].…”