The study is the first to find gender differences in how the chlorpyrifos insecticide harms prenatal development. Scientists say the finding adds to evidence that boys’ brains may be more vulnerable to some chemical exposures.
“This suggests that the harmful effects of chlorpyrifos are stronger among boys, which indicates that perhaps boys are more vulnerable to this type of exposure,” said Virginia Rauh, a perinatal epidemiologist at Columbia University and co-author of the study published in July.
Chlorpyrifos is an organophosphate insecticide, a powerful class of pesticide that has toxic effects on nervous systems. It was widely used in homes and yards to kill cockroaches and other insects, but in 2001 the U.S. Environmental Protection Agency banned its residential use because of health risks to children. Since then, levels inside U.S. homes have dropped, but residue remains in many homes. In addition, many developing countries still use the pesticide indoors.
Known by the Dow trade name Lorsban, chlorpyrifos is still sprayed on some crops, including fruit trees and vegetables, and also is used on golf courses and for mosquito control. About 10 million pounds of chlorpyrifos are applied to agricultural fields annually, according to the EPA.
“There’s mounting evidence now from epidemiological studies that prenatal exposure to organophosphate pesticides, and chlorpyrifos in particular, may be associated with detriments with IQ in children,” said Kim Harley, an environmental epidemiologist with the University of California, Berkeley who has studied effects of pesticide exposure on children in California farm towns. She was not involved in the New York City study.
The 335 pairs of mothers and children in the new study were not farmworkers, but were part of a large group of Latino and African American children from low-income neighborhoods of Northern Manhattan and the South Bronx. Columbia University researchers have been tracking more than 700 of these kids since they were born, between 1998 and 2006. Children there have a history of health problems, including asthma rates that are among the nation’s highest, and low birth weight. Many were born before the residential ban on chlorpyrifos.
An earlier study of the children found that chlorpyrifos was linked to delayed mental and motor skill development even after controlling for poverty, dilapidated housing and other community factors. The scientists, in a more detailed follow-up, then found that IQs and memories were reduced in 7 year olds with higher prenatal exposure. Those with the highest exposures scored on average 5.3 points lower on a short-term memory test, and 2.7 points lower on an IQ test, than children with the lowest exposures.
In the new study, published last month in the journal Neurotoxicology and Teratology, umbilical cord blood was collected from the newborns, who were born before and slightly after the 2001 chlorpyrifos restrictions. When the kids were 3 years old, the researchers studied how well the mothers nurtured and educationally stimulated them. Then, at age 7, the children’s short-term memory ¬¬¬was tested, for example, by having them repeat a sequence of numbers. Memory is an important component of IQ tests.
Chlorpyrifos exposure had a larger association with working memory scores in the boys, who averaged three points lower than the girls with similar exposures, the study found.
“There are adverse effects overall, but you see that the effects are bigger in boys,” Rauh said. “The notion is that boys might be more vulnerable, for whatever reason.”
Why chlorpyrifos might affect boys more than girls is not fully understood, but a 2012 study of rats found that the pesticide reduced testosterone, which has a critical role in male brain development.
The new study is the first to measure chlorpyrifos in umbilical cord blood, which unequivocally shows if a mother and her fetus were exposed. Researchers do not know how those kids’ exposures, which occurred between 1998 and 2006, compare with levels in kids today because there are no data for comparison.
Virginia Ruiz, director of occupational and environmental health for Farmworker Justice, said chlorpyrifos is one of the most dangerous pesticides that farmworkers are exposed to. Her group is pushing for an end to all uses as soon as possible.
Lawsuits are also currently pending, as the environmental group Earthjustice has sued the EPA in an effort to ban all remaining uses of chlopyrifos.