Neurobehavioral dysfunction as a possible sentinel of methylmercury exposure

The main concern regarding methylmercury neurotoxicity relates to adverse e ffects on the brain during development. Many environmental chemicals may ac t as developmental neurotoxicants, but solid documentation from epidemiolog ical studies exists only on methylmercury, lead, and polychlorinated biphen yls (PCBs). Neurobehavioral tests may reveal subtle dysfunctions, but the t ests chosen must be valid and appropriate for the setting. In a prospective study in the Faroe Islands, the main neuropsychological functions affected by prenatal methylmercury exposure were attention, language and memory. De ficits in visuospatial function were mainly related to postnatal exposures. These associations were stable after adjustment for confounders and exclus ion of the children with the highest exposures to methylmercury and PCBs. T ests with good psychometric properties were more likely to show an associat ion with mercury exposure. Greater sensitivity was also seen with tests adm inistered by specialized academic staff rather than a trained technician. D espite highly significant effects on nervous system function, the deficits were subtle, and mercury exposure explained only a small part of the variat ion. Available evidence suggests that neurotoxicity may have severe implica tions on public health, but current methods are not amenable to application as sentinels of adverse health effects in environmental health surveillanc e.