By Janet Raloff, Science News
Children exposed in the womb to substantial levels of neurotoxic pesticides have somewhat lower IQs by the time they enter school than do kids with virtually no exposure. A trio of studies screened women for compounds in blood or urine that mark exposure to organophosphate pesticides such as chlorpyrifos, diazinon and malathion.
These bug killers, which can cross the human placenta, work by inhibiting brain-signaling compounds. Although the pesticides’ residential use was phased out in 2000, spraying on farm fields remains legal.
The three new studies began in the late 1990s and followed children through age 7. Pesticide exposures stem from farm work in more than 300 low-income Mexican-American families in California, researchers from the University of California, Berkeley and their colleagues report. In two comparably sized New York City populations, exposures likely trace to bug spraying of homes or eating treated produce.
Among the California families, the average IQ for the 20 percent of children with the highest prenatal organophosphate exposure was 7 points lower compared with the least-exposed group.
A Columbia University study followed low-income black and Hispanic families. Here, each additional 4.6 picrograms of chlorpyrifos per gram of blood in a woman during pregnancy correlated with a drop of 1.4 percent in her youngster’s IQ and 2.8 percent in a measure of the child’s working memory.
Findings from a more diverse group of New York City families recruited by the Mount Sinai School of Medicine point to genetics as a major determinant of risk from pesticide exposure. Children who showed the biggest cognitive impacts tended to have mothers carrying a gene variant for a slow-acting version of the enzyme that breaks down organophosphates. This variant is present in roughly one-third of all Americans, observes study leader Stephanie Engel, now at the University of North Carolina at Chapel Hill.
Another observation from her study: Children exhibited bigger IQ deficits if they came from homes that had been treated with organophosphates while their moms were pregnant—even if the women’s urine at the time wasn’t higher in breakdown products than that of parents whose kids had more normal cognitive scores. Organophosphate breakdown products aren’t toxic, just a putative marker of exposure to the toxic parent pesticide, Engel notes. So the presence of organophosphate breakdown products in mothers of the less-affected kids may reflect the mother’s exposure primarily to breakdown products, not the parent organophosphates.
Findings from all three studies appear online April 21 in Environmental Health Perspectives.
“There was an amazing degree of consistency in the findings across all three studies,” notes Bruce Lanphear of Simon Fraser University in Vancouver. And that’s concerning, he says, because a drop of seven IQ points “is a big deal. In fact, half of seven IQ points would be a big deal, especially when you see this across a population.”
Each IQ-point drop will add up to extra costs in lost earnings over an individual’s lifetime, he says—and even, potentially, to higher education and other costs to deal with behavioral and learning problems that may occur during childhood.
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