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From December 18, 2001

Toxics Impair Neurological Development of Children

Extensive clinical and laboratory studies of neurological toxicants have shown the unique vulnerability of the developing brain to contaminants in the ambient environment at exposure levels that have no lasting effect on adults, according to the December 2001 Environmental Health Perspectives article "Toxic Threats to Neurologic Development of Children." Interest was sparked by the increasing incidence of developmental disabilities in the United States, including learning disabilities, attention deficit hyperactivity disorder, developmental delays and emotional and behavioral problems.

While genetic, environmental and social factors interact in complex ways to determine cognitive development and behavior, no one factor is sufficient to explain populationwide increases in neurodevelopmental abnormalities. As much as 50% of the variance of cognitive, behavioral and personality traits among individuals can be attributed to environmental influences.

The study reports that limited data are available describing the effects of developmental exposures to neurotoxic pesticides on subsequent brain function. In rodents a single low-level exposure to an organophosphate pesticide or a pyrethroid on day 10 of life causes permanent decreases in brain cholinergic receptors and hyperactivity when the animal is tested at 4 months of age. The general lack of neurodevelopmental toxicity data for agricultural chemicals is of particular concern because of their widespread use and ubiquitous exposures. Population-based studies in the United States show that over 90% of children have detectable urinary residues of just one of the neurotoxic organophosphate pesticides. Specimens analyzed for residues of 30 pesticides showed that more than 50% of the population contained at least six.

The science of neurodevelopment is slowly evolving and bringing forth questions about preventive actions. Comparisons of animal and human data for lead, mercury and PCBs show that laboratory animal studies tend to underestimate human neurodevelopmental sensitivity by 2-4 orders of magnitude. Neurological data are lacking for the majority of the suspected or known neurotoxicants and regulatory agencies have failed to require neurodevelopmental testing of chemicals before they are marketed. No voluntary testing program proposed by the chemical industry in the US includes neurodevelopmental testing.

To view the full article, see: http://ehpnet1.niehs.nih.gov/docs/2001/suppl-6/813-816schettler/abstract.html