THURSDAY, April 21, 2011 (Health.com) — Children whose mothers are exposed to high amounts of certain pesticides while pregnant appear to have lower IQs than their peers when they reach school age, according to three government-funded studies released today.
The pesticides, known as organophosphates, are commonly sprayed on food crops and can be found in trace amounts on berries, green beans, and other fruits and vegetables sold in stores. The pesticides have also been used in homes and gardens, although their indoor use has been widely restricted due to safety concerns.
Organophosphates, which kill pests by attacking the nervous system, have previously been linked to developmental delays and attention problems in young children who were exposed in the womb. Now, researchers in two different locations have found that a child’s IQ tends to decrease in proportion to the mother’s exposure while pregnant.
One of the studies followed hundreds of mostly Latino mothers and children in California’s Salinas Valley, a center of commercial agriculture. Many of the women were farmworkers, or had family members who worked on farms.
When the women were pregnant, the researchers tested their urine for several chemical by-products of organophosphates—a standard means of gauging exposure. The mothers with the highest levels of by-products (known as metabolites) had children whose IQs at age 7 were seven points lower, on average, than the children whose mothers had the lowest levels of exposure. (The average score is 100.)
“That’s not unlike the decreases we see in children with high lead exposure,” says the senior study author, Brenda Eskenazi, Ph.D., a professor of epidemiology and maternal and child health at the University of California, Berkeley. “It’s equivalent to performing six months behind the average.”
The children’s own metabolite levels were not linked to their IQs, however, which suggests that prenatal—rather than childhood—exposure is largely responsible for the trend, Eskenazi says. Organophosphates, which pass from the mother to fetus through the placenta and umbilical cord, may be more damaging to developing fetuses than to children, the study notes.
Similar trends are likely to be found outside farming communities, the researchers suggest. While the average metabolite levels of the pregnant women in the study were substantially higher than the national average, as many as 25% of pregnant women in the general population have levels above the study average.
Moreover, the findings are echoed by a second study released today, which was conducted in New York City and followed 265 black and Dominican mothers and children from low-income families.
Next page: More evidence from New York