Environmental neurotoxicants and developing brain.

The brain of infants and children is uniquely sensitive to environmental neurotoxicants at levels far below those that are known to harm adults. There are multiple windows of vulnerability during which environmental exposures can interfere with normal development. The timing and duration of neurotoxicant exposures during development can give rise to a broad spectrum of structural and functional deficits. Only about 200 chemicals out of more than 80,000 registered with the United States Environmental Protection Agency have undergone extensive neurotoxicity testing, and many chemicals found in consumer goods are not required to undergo any neurodevelopmental testing. The cumulative effects of co-contaminants and the difficulties in analyzing biomarkers of exposure in human tissues have complicated comprehensive risk assessment. Furthermore, population-based studies that measure subtle effects on neurobehavioral outcomes are challenging to interpret and costly to conduct. Despite the fact that developmental neurotoxicity may be more severe and irreversible compared with adult toxicity, there is a relative paucity of toxicological data on developing systems for many high-production chemicals. This article provides an overview of the adverse neurological, cognitive, and behavioral outcomes associated with environmental exposures, with an emphasis on human studies.