by Elizabeth Grossman
“Organic, schmorganic,” wrote New York Times foreign editor and International Herald Tribune editor-at-large Roger Cohen, summing up his “takeaway” from the study by Stanford University researchers that examined studies comparing the nutritional value and pesticide residues in organic and “conventionally” grown food. The study concluded that evidence was lacking to show that organic food is more nutritious than conventionally grown food, but that organic food did have about 30 percent fewer pesticide residues. “I’d rather be against nature and have more people better fed,” wrote Cohen, “And I trust the monitoring agencies to ensure pesticides are used at safe levels – a trust the Stanford study found to be justified.”
Those pesticide residues and what constitutes safe levels of exposure, however, take on new significance in light of the recent research by Virginia Rauh and colleagues at the Columbia University Mailman School of Public Health. Rauh, who presented her latest study during a September 12 webinar hosted by the US Environmental Protection Agency (EPA) and National Institute of Environmental Health Sciences (NIEHS), has found a strong association between prenatal pesticide exposure and adverse impacts on behavior, brain structure, cognitive ability, and neurodevelopment. Her research also indicates that the brain abnormalities triggered by this pesticide exposure appear to occur at levels below the current EPA threshold for toxicity.
Rauh and colleagues have been studying the effects of prenatal exposure to the pesticide known as chlorpyrifos on New York City children living in Harlem and the South Bronx whose mothers likely encountered the chemical when it was used in indoor pest control. Chlorpyrifos, which belongs to a class of pesticides known as organophosphates, has been on the US market for more than 40 years. It is used worldwide, and kills insects by affecting their nervous systems. Chlorpyrifos has been used in indoor pest control, in commercial agriculture, in lawn care products, for termite control, and in domestic pet flea and tick collars. Concern over chlorpyrifos and other organophosphates’ potential health effects, particularly on children, led to an EPA ban on the use of several, including chlorpyrifos, for indoor use beginning in 2001.The children in Rauh’s study were exposed before the ban took effect.
Organophosphates in the fields
While now off the market for use indoors, chlorpyrifos and other organophosphate pesticides continue to be used agriculturally. In the US in 2002, 10 million pounds of chlorpyrifos were used in agriculture; in 2009, more than one million pounds of chlorpyrifos were used in California alone. In that state’s Salinas Valley, University of California scientists have been studying children prenatally exposed to these chemicals. Both the Columbia and California researchers found these children’s IQ to be notably reduced by organophosphate exposure; that the higher the exposure, the lower the IQ score. Both also found there was no threshold or base measured level of pesticide exposure that did not produce an effect.
In their latest research, Rauh and colleagues have looked at how this exposure is affecting children’s brains physically. Their study is the first to use MRI (magnetic resonance imaging) to identify structural evidence for cognitive deficits in humans, though this has been done previously in animal studies. Strikingly, what they saw in physical brain alterations – thinning in some areas and abnormal enlargement in others – is consistent with effects that would produce the IQ reductions measured in the children who Rauh’s study has been following since birth. The brain alterations observed, explained Rauh, are in the parts of the brain linked to working memory function, language, and behavior including emotion, reward, and inhibition control, and attention.
Last spring researchers at the Mailman School reported that these children, who were exposed to chlorpyrifos prenatally through the pesticide’s use indoors, had reduced IQ scores at age 7. “These observed deficits in cognitive functioning at 7 years of age could have implications for school performance,” Rauh explained in a Columbia University newsletter. “Working memory problems may interfere with reading comprehension, learning and academic achievement, even if general intelligence remains in the normal range,” said Rauh.
The new research examining chlorpyrifos exposure’s impact on physical brain development also indicates that this exposure may also eliminate or reverse the male-female differences ordinarily present in the brain – at least at a time well before puberty. “The brain abnormalities suggest that prenatal chlorpyrifos exposure, even at very low levels that would be consistent with standard agricultural use, show a significant association with structural changes in the developing brain, including sex-specific effects that persist into middle childhood,” explained Rauh during the EPA/NIEHS webinar.
Rauh also explained that the EPA’s current safety standards for chronic exposure to chlorpyrifos at 30 nanograms per kilogram of bodyweight are based on a particular mechanism through which chlorpyrifos inhibits an enzyme vital to healthy brain development. The adverse impacts to brain development Rauh and colleagues documented, however, appear to be happening at lower levels of exposure than EPA considers safe. As appeared to be the case with IQ score effect, the brain alterations appear to be occurring levels of exposure so low that Rauh and colleagues say there may be no threshold below which exposure does not alter brain or neurodevelopment. This means other mechanisms besides this particular enzyme may be involved. It also means, said Rauh, that the EPA standards for chlorpyrifos exposure may be too high to be protective, at least where prenatal and children’s exposure is concerned.
Despite the indoor use ban and a recent drop in overall organophosphate pesticide use, chlorpyrifos continues to be widely used not only in agriculture, but also on highway medians, golf courses, some parks, and as a wood treatment. People can be exposed as the chemical drifts during use but also, say the Columbia researchers, by eating treated fruits and vegetables.
The “organic ideology is an elitist, pseudoscientific indulgence shot through with hype,” wrote Roger Cohen in his New York Times op-ed, “a class-driven decision that demonstrates how much you love your offspring but whose overall impact on society is debatable.” The low-income parents of the elementary school children in Harlem, the South Bronx, and California’s Central Valley agricultural communities might beg to differ, knowing that pesticide exposure is making it harder for their children to succeed in school.
Elizabeth Grossman is the author of Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry, High Tech Trash: Digital Devices, Hidden Toxics, and Human Health, and other books. Her work has appeared in a variety of publications including Scientific American, Salon, The Washington Post, The Nation, Mother Jones, Grist, and the Huffington Post. Chasing Molecules was chosen by Booklist as one of the Top 10 Science & Technology Books of 2009 and won a 2010 Gold Nautilus Award for investigative journalism.