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