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Today's Science Insight
Apr 28, 2011
On April 21, the highly regarded journal Environmental Health Perspectives published online the results of three studies carried out at three different universities, using three different methods exploring the same phenomenon the impacts of prenatal exposures to organophosphate (OP) insecticides on the neurological development of children.
The three studies reached the same, sobering conclusion exposure to OPs during pregnancy leads to IQ deficits in school-age children.
All three studies involved groups of pregnant women whose health status and exposures to OP insecticides were monitored during pregnancy and at the time of childbirth, via testing of umbilical cord blood. The women were broken into low, moderate, and high OP exposure groups, and then the intellectual development of their children was tracked for up to seven to nine years.
The study carried out by a team at the Columbia University Center for Children's Environmental Health focused on children born to a group of 265 mothers living in in low-income, public housing. By age seven, children born to mothers in the highest exposure group scored 5.5% lower on a common test of working memory and 2.7% lower in terms of IQ, compared to children born to mothers in the low-exposure group. There was no evidence of a threshold in the observed adverse impact on intelligence, suggesting that even very low exposures might lead to some reduction in mental abilities.
A study carried out by U.C. Berkeley scientists, in cooperation with the Center for the Health Assessment of Mothers and Children of Salinas, measured urinary metabolites of OP insecticides during pregnancy, and then from children at six months of age, and periodically through age five. A variety of intelligence and learning tests were used to measure the mental abilities of 329 children at age seven. Children born to the most heavily exposed mothers had an IQ deficit of seven points, or about 7%, compared to the low exposure quintile.
The senior author of this study, Brenda Eskenazi, told CNN.com that the impacts on intelligence found in their study were similar in magnitude to the adverse impacts associated with high lead exposures, and were comparable to a child performing six-months behind average in a school population.
While the implications of this study are most directly applicable -- and worrisome -- for the Latino farmworker community in the Salinas Valley, the research team also reported that about 25% of pregnant women in the general U.S. population are exposed to OP insecticides at levels comparable to the average Latino women included in this study.
The third study was carried out at the Mount Sinai School of Medicine and measured prenatal OP metabolite levels in urine and blood samples from 404 pregnant women. This team also analysed the impact of a genetic polymorphism that reduces the level of the enzyme paraoxonase (PON1). This enzyme plays a key role in the metabolism of the OP chlorpyrifos. About 30% of the women in the study population bear this genetic trait, and hence they, and especially their babies, were at higher risk following exposures to OP insecticides.
Children born to mothers bearing the PON1 genotype with impaired enzyme function suffered a 4 point decline in one measure of mental function, while children born to mothers with the normal PON1 gene showed "essentially no effect."
Dr. Phil Landrigan, Director of the Mt. Sinai Children's Environmental Health Center called the findings of the three studies "shocking" in a New York Times health blog (Tara Parker-Pope, April 21, 2011). He went on to say
"Babies exposed to the highest levels [of OPs] had the most severe effects. It means these children are going to have problems as they go through life."
"When we took lead out of gasoline, we reduced lead poisoning by 90 percent, and we raised the I.Q. of a whole generation of children four or fine points. I think these findings about pesticides should generate similar controversy, but I'm cautiously optimistic that they will have the effect of having the EPA sharply reduce the use of organophosphate pesticides."
The diet is now by far the major ongoing source of exposure to OP insecticides. The Organic Center's latest comprehensive assessment of total dietary risk from pesticides relies on the most recent data from USDA's "Pesticide Data Program" (PDP), and covers OP residues found in foods tested in 2008. In all foods tested by the PDP, just two OPs, chlorpyrifos and methamidophos, accounted for about 50% of total pesticide risk via the diet. The OPs as a class accounted for a remarkable 64% of total risk.
In 2008 (the last year for which PDP are available), chlorpyrifos was found in a total of 555 samples of 19 foods. Aggregate "Dietary Risk Index" (DRI) values for chlorpyrifos across the 19 foods was 153.6 by far the highest of any pesticide.
Back in 1996, the year the Food Quality Protection Act (FQPA) was passed, OPs accounted for 80% of overall risk, largely as a result of the huge risks associated with methyl and ethyl parathion. These are the only two high-risk OPs that the EPA has strictly regulated in an attempt to remove all residues in common foods.
In 2000-2001, the EPA completed a contentious regulatory review of chlorpyrifos, the market-leader OP with significant agricultural and in-the-home uses. The agency's risk assessment at the time showed that exposure levels were highest in people living in treated structures, and that exposures in living spaces, especially bedrooms and nurseries, were posing unacceptable developmental risks for infants and children.
Dow AgroSciences, the chlorpyrifos manufacturer, was vigorously opposing any new regulatory restrictions, but the EPA was determined to quickly end at least the home uses of chlorpyrifos, and so the agency and Dow cut a deal. In return for Dow agreeing to voluntarily cancel the home uses of chlorpyrifos (immediate risk reduction), the EPA allowed most agricultural uses to continue with little or no risk reduction measures (minimizing market disruption, here and abroad, for Dow's major agricultural insecticide). In the EPA-Dow agreement, only one high-risk farm use was banned tomatoes.
At the time this deal went down, I was among the people strongly critical of the compromise and EPA's failure to impose the broader restrictions needed to sharply reduce dietary exposures in dozens of other key children's foods. These compelling new studies provide a sober accounting of the continuing consequences of the EPA's failure to act back in 2000-2001.
But since the EPA has pledged to base all regulatory decisions on sound science, surely the consistent findings across these three studies, and the opportunity to increase IQs 4% to 7%, will compel the agency to get OPs out of foods commonly consumed by pregnant women, infants, and children.
Would such a move make dollars and sense? I contacted Phil Landrigan and asked what scientists had concluded about the economic benefits of minimizing the early-life loss of IQ from lead exposures. Phil explained that
"An IQ point has a monetary value over a lifetime of about $10,000. The economic gains that resulted from the removal of lead from gasoline amount to about $200 billion in each annual birth cohort since 1980. As we continue to poison America's children with organophosphates, we are jeopardizing America's leadership position in today's world."
Let's do the math. While the three new studies suggest adverse impacts from OP exposures of the same magnitude as lead (4 to 5 point decline), suppose that the average impact of OP exposures across the whole population is two IQ points, or $20,000 in lifetime earning capacity and contributions to the economy.
There were about 4.2 million babies born in 2010. The average loss of two IQ points across these children over their lives would cost the national economy $84 billion.
Fresh fruits and vegetables account for nearly all dietary exposures to OPs. Because of ample Integrated Pest Management alternatives, the cost of banning these OP uses on fruits and vegetables would be negligible (almost certainly less than $50 million, and the cost would decline rapidly over 2-5 years as growers adopted and refined alternatives, or converted to organic).
The cost would be zero for the approximate 12% of fruits and vegetables already grown organically.
$84 billion in annual benefits at a cost of less than $50 million. I guess we need another study.
Sources: Rauh, V., et al., "7-Year Neurodevelopmental Scores and Prenatal Exposure to Chlorpyrifos, a Common Agricultural Insecticide," Environmental Health Perspectives, online April 21, 2011
Bouchard, M.E., et al., "Prenatal Exposure to OP Pesticides and IQ in 7-Year Old Children," Environmental Health Perspectives, online April 21, 2011
Engel, S.M., et al., "Prenatal Exposure to OPs, Paraoxonase 1, and Cognitive Development in Children," Environmental Health Perspectives, online April 21, 2011