Published by the Students of Johns Hopkins since 1896
January 28, 2022

Pesticide exposure lowers children’s IQs

By Mo-Yu Zhou | May 5, 2011

Three studies conducted by researchers at the University of California at Berkeley, Columbia University, and the Mount Sinai School of Medicine have recently shown that children who were exposed before birth to substantial levels of neurotoxic pesticides tend to have somewhat lower IQs by the time they start school, compared to children with virtually no exposure. These differences in IQ could translate into a hampering of these children’s ability to learn and, later on, to be as competitive as their peers in the workplace.

The studies began in the late 1990s, following children from before birth up to the age of seven. More than 300 Mexican-American low-income families in Calif. are exposed to farm work, and thus pesticides. On the other hand, in New York City, families are more likely to be exposed by bug spraying in their homes or by eating pesticide-treated produce.

In the studies women were screened for compounds in their blood and urine that would indicate that they had been exposed to pesticides, in particular organophosphate pesticides like chlorpyrifos, diazinon and malathion. These pesticides kill bugs by inhibiting their brain-signaling compounds, and have been shown to be able to cross the human placenta. Their residential use was phased out by 2000, but they are still a threat as it is still legal to use them on farm fields.

Among the families in Calif., the 20 percent of children with the highest degree of pre-birth organophosphate pesticide exposure had IQs that were seven points lower on average compared with the 20 percent with the lowest exposure, according to researchers at Berkeley.

Meanwhile, a study conducted by Columbia University following low-income black and Hispanic families in New York City found that for every additional 4.6 picograms of the pesticide, chlorpyrifos, in the blood of a pregnant woman, her child was likely to have a drop in IQ by 1.4 percent. This also corresponded to a 2.8 decrease in measuring the child’s working memory function.

A more diverse group of New York City families was studied by the Mount Sinai School of Medicine. Their research showed that risk from pesticide exposure was determined largely by genetics. The mothers whose children were affected most strongly by pesticide exposure tended to carry a gene variant for the enzyme that breaks down organophosphates. These women’s version of the enzyme, present in about one-third of all Americans, acted more slowly than that of the rest of the population.

The study also showed that the harmful effects of pesticides may be a direct result of the organophosphates themselves, rather than of their breakdown products. The children who exhibited the largest impacts on their IQs came from homes that had been treated with bug spray when their mothers had been pregnant, even if the mothers’ urine did not show a higher amount of the pesticides as analysis of their urine measured the breakdown product and not the direct exposure. The breakdown products themselves are not harmful and are merely a sign of exposure to the organophosphates.

The consistency in all three studies is a cause for concern, says Bruce Lanphear of Simon Fraser Unversity, as a drop of seven IQ points is “a big deal. If fact, half of seven IQ points would be a big deal, especially when you see this across a population.” Such a deficit in IQ may add up to lost earnings over the individuals’ lifetimes, as well as to the costs of behavioral and learning problems.

Comments powered by Disqus

Please note All comments are eligible for publication in The News-Letter.

News-Letter Special Editions