Chlorpyrifos, a common pesticide, may be subtly influencing brain development in children, according to a new study. The brain abnormalities, found among a very small population of school-aged children, may have occurred while they developed in utero.
What is troubling, according to scientists, is that relatively low levels of chlorpyrifos appear to have caused the cascade of brain changes.
"It's out there and we do not know what the longer term impact is of lower levels," said Virginia Rauh, professor of Clinical Population and Family Health at Columbia University Mailman School of Public Health, and the study's lead author. "But it does seem to be associated with cognitive damage and structural changes in brain."
In the study, 40 children, ages 6 to 11, were given MRI scans. Half of the children had relatively low levels of chlorpyrifos based on samples of their cord blood at birth, and the other half had relatively high levels.
The abnormalities found among children with higher-than-normal exposure to chlorpyrifos included overgrowth, and undergrowth, in areas of the brain associated with attention, emotion, behavior - even IQ.
"When the brain is developing and cells are migrating to various places in the brain they're intended to go, that process is being disrupted," said Rauh.
But the makers of chlorpyrifos say that the small population of children studied mars the findings.
"Because of the small number of blood samples and the small group of children evaluated, even a slight misclassification of 'high' vs. 'low' exposure classifications could drastically skew the results of the MRI imaging comparisons that are the focus of this article," said Garry Hamlin, a spokesperson for Dow AgroSciences, makers of chlorpyrifos, in an email.
Chlorpyrifos was a common household pesticide until it was phased out for residential use by the Environmental Protection Agency in 2001, according to the study. But it is still used commercially in public places and - most importantly for a wider swath of the population - in agriculture.
One theory, which is not well-studied, is that chlorpyrifos could be entering the womb by way of the fruits and vegetables consumed by pregnant women.
"The mother is exposed, the chemical crosses the placenta and essentially enters bloodstream of the fetus," said Rauh, deputy director of the Columbia Center for Children's Environmental Health. "That is a transport system to all parts of the child's body."
On its website, EPA reports that "Dietary exposures from eating food crops treated with chlorpyrifos are below the level of concern for the entire U.S. population, including infants and children."
"There is this general sense that chemicals have one known function, that they only do that one thing and not anything else," said Dr. David Carpenter, director of the Institute for Health and the Environment at the University at Albany. "This study shows that's clearly not the case... there are gross changes in the structure of brain."
"I think this is a very, very important study," he added.
The concern among environmental health experts is not just chlorpyrifos, but a host of other pesticides falling under the umbrella of organophosphates. The suggestion of studies in animals, and more recently in humans, is that during critical stages of brain development, organophosphates could be irreparably altering brain development - and that the changes may persist as the child ages.
An interesting finding of the current study, published in the journal Proceedings of the National Academy of Sciences, involves the possibility that chlorpyrifos interferes with sexual differentiation in the brain early in development.
"We have some evidence that among highly exposed children, those differences are slightly blurred," said Rauh. "Meaning... the brain of an average boy looks less like the brain of a boy, and a little more like the brain of a female."
Since the study population is still pre-pubescent, the real world implications of that finding are not known.