Environmental neurotoxic illness: research for prevention.

Recognition of the deleterious neurological effects of chemicals has evolved from anecdotal observation to studies of illness in persons exposed to high doses. Now, the more subtle effects of exposures to environmental neurotoxicants are being documented: reduction in intelligence, impairment in reasoning ability, shortening of attention span, and alteration of behavior. Substances to which millions of persons are exposed occupationally and in the general environment that can result in such deficits include lead, organophosphorus pesticides, certain chlorinated hydrocarbons, carbon disulfide, solvents, and mercury. The first step in the prevention of neurological impairments due to environmental exposures is to assess the toxicity of chemicals. Fewer than 10% of the 70,000 chemicals in commercial use have been evaluated for neurotoxicity. This knowledge gap needs to be narrowed by building on existing systems of toxicity testing. Concurrent with assessment of chemicals will be tiers of in vivo screening tests to measure functional and structural changes following exposures in vitro. Epidemiologic surveillance of populations at high risk will continue to inform on the ranking of suspect or known neurotoxicants. Research and researchers must become more sophisticated in the development and application of refined biologic markers so the findings can be used to detect absorption of toxicants and early neurological or neurobehavioral dysfunction before disability occurs and to protect human health and the environment.