The researchers tested the urine of pregnant Mexican-American women living in California's Salinas Valley, a major agricultural region, for pesticide metabolites. Their children were then followed for five years, being regularly tested for pesticide metabolites and attention disorders. Attention was evaluated through parental questionnaires and standardized tests.
The researchers found that while only a weak connection between attention problems and prenatal pesticide exposure was observed by age three, by age five a significant correlation was observed.
A tenfold higher concentration of organophosphate metabolites in a mother's urine corresponded to a 500 percent increase in her child's risk of being diagnosed with attention deficit hyperactivity disorder (ADHD). A higher concentration of metabolites in a child's urine was also correlated with an increased risk of diagnosis, though not as strongly.
A previous study found that children with high levels of organophosphate metabolites in their urine were nearly 100 percent more likely to be diagnosed with ADHD as children with no detectable metabolites. Organophosphates and other pesticides have also been linked to other nervous system disorders, such as Parkinson's disease.
"There has been a linkage between early pesticide exposure and a later loss of dopamine-producing cells in the substantia nigra, a pathology associated with Parkinson's disease," write Peter J. Whitehouse and Daniel George in their book The Myth of Alzheimer's.
A connection between pesticide exposure and nerve-related disorders is not surprising, since many pesticides -- including organophosphates -- are designed to disrupt insect nervous systems. One of the neurotransmitters that they target, acetylcholine, is also found in the human brain.
Approximately 40 different organophosphate pesticides are currently approved for use in the United States.
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