Pesticides Shown to Affect Children’s IQ

04 Jun, 2012

by Elizabeth Grossman, via Yale Environment 360

New York City’s low-income neighborhoods and California’s Salinas Valley, where 80 percent of the United States’ lettuce is grown, could hardly be more different. But scientists have discovered that children growing up in these communities—one characterized by the rattle of subway trains, the other by acres of produce and vast sunny skies—share a pre-natal exposure to pesticides that appears to be affecting their ability to learn and succeed in school.

Three studies undertaken independently, but published simultaneously last month, show that prenatal exposure to organophosphate pesticides—sprayed on crops in the Salinas Valley and used in Harlem and the South Bronx to control cockroaches and other insects—can lower children’s IQ by an average of as much as 7 points. While this may not sound like a lot, it is more than enough to affect a child’s reading and math skills and cause behavioral problems with potentially long-lasting impacts, according to the studies.

“This is not trivial,” said Virginia Rauh, one of the study authors, speaking from Columbia University, where she is deputy director of the university’s Center for Children’s Environmental Health and professor of population and family health. What is particularly significant, she said, is that these studies involved so many children from such different communities, yet produced consistent evidence of the pesticides’ effects on cognitive skills and short-term memory.

Rauh said that the new studies were prompted by the long-standing awareness of the neurotoxicity of these pesticides on animals and the chemicals’ widespread use. Given science’s growing knowledge about the measurable effects of neurotoxic chemicals and elements, such as lead, on children’s cognition and behavior, the three recent studies were a logical next step in such research, Rauh explained.

The studies in New York and California were a continuation of research that has been ongoing for 12 years. Two of the studies, led by researchers at Columbia University and the Mount Sinai School of Medicine in New York City, looked at more than 660 children, ages six to nine, living in the South Bronx, Harlem, and other inner city neighborhoods. The New York mothers were exposed primarily indoors, as they lived in buildings where these pesticides were used in public areas and inside apartments. Previous studies of pregnant women in the same New York City neighborhoods had found organophosphate pesticides in all indoor air samples and in the majority of umbilical cord blood taken from these women when they gave birth.

Rauh and her colleagues began studying the New York City mothers before they gave birth. Organophosphate pesticide levels in several hundred pregnant women were measured and ranked, with the lowest levels being those where the pesticides were non-detectable. The researchers then evaluated their children’s cognitive and motor skills at one, two, and three years of age, finding that prenatal exposure to a common pesticide was associated with neurodevelopmental problems in the three-year-olds. The most recent study then tested the children at age seven. All the children were otherwise healthy and born to healthy, non-smoking mothers who were exposed to these pesticides while pregnant.

The New York studies found that for every increased increment of prenatal organophosphate pesticide exposure, the IQs of the children studied dropped by 1.4 percent and their working memory scores dropped by 2.8 percent. A key finding of the Columbia University study was that the relationship between pesticide exposure and IQ and working memory scores was linear and showed “no evidence for a threshold.” In other words, the greater the exposure, the greater the impact on cognition.

The third study, led by researchers at the University of California, Berkeley, looked at 329 children living in agricultural communities in the Salinas Valley, in Monterey County, the country’s top vegetable-producing region. The California mothers were predominantly Latino farmworkers, and their exposure resulted from living and working near where these chemicals were used agriculturally; when sprayed on crops, organophosphate pesticides can easily drift with the wind beyond their intended fields.

In 1999 and 2000, the California researchers measured levels of organophosphate pesticides in the blood of 601 pregnant women and initiated a long-term study that would follow their children at regular intervals. In those two years, more than half-a-million pounds of organophosphate pesticides were used in the Salinas Valley. More than 3.5 million pounds of organophosphate pesticides are used annually in California alone, sprayed on corn, strawberries, lettuce, broccoli, oranges, grapes, and almonds, among other products. The study authors note that in addition to ambient air exposures, both groups, in New York and California, were also likely exposed through pesticide residues in the food they ate.

As with the New York study, when researchers measured the IQ of the California children at age seven, those with the highest prenatal exposure scored as much as 7 points lower than the children with the lowest prenatal levels of pesticide exposure.

Bruce Lanphear, director of the Children’s Environmental Health Center at Cincinnati Children’s Hospital Medical Center, said in an interview that organophosphate pesticide exposure can impair development of the brain’s prefrontal cortex. Such damage actually shrinks this area of the brain and can lead to behavioral problems that include ADHD and later-life learning and social problems, including criminal behaviors, he said. This is also the part of the brain where short-term memory and instant gratification responses lie.

The study results are significant because they help show that while these children’s social circumstances—they came from low-income communities and families—can put them at an educational disadvantage, they also appear to be starting life with a preventable physiological disadvantage.

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