(Beyond Pesticides, April 22, 2011) Three independent investigations published in the journal Environmental Health Perspectives (EHP) have reached similar conclusions, associating prenatal exposure to organophosphate (OP) pesticides with IQ deficits in school-age children. The fact that three research groups reached such similar conclusions independently adds considerable support to the validity of the findings.
The three studies were conducted at the School of Public Health at the University of California, Berkeley, the Mailman School of Public Health at Columbia University, and Mount Sinai School of Medicine. All three involved cohorts of women enrolled during pregnancy. The Berkeley and Mount Sinai investigators measured OP pesticide breakdown products in the pregnant women’s urine, while the Columbia investigators measured the OP pesticide chlorpyrifos in umbilical cord blood. Intelligence tests were administered to children of these mothers between ages 6 and 9 years at Mount Sinai and at age 7 years at Berkeley and Columbia.
Although the study findings are not directly comparable, all three investigations found evidence linking prenatal OP pesticide exposures with adverse effects on cognitive function that continued into early childhood.”¨”¨“It is well known that findings from individual epidemiologic studies may be influenced by chance and other sources of error. This is why researchers often recommend their results be interpreted with caution until they are supported by similar findings in other study populations,” said EHP Editor-in-Chief Hugh A. Tilson. “As a group, these papers add substantial weight to the evidence linking OP pesticides with adverse effects on cognitive development by simultaneously reporting consistent findings for three different groups of children.”
The Berkeley study, examining families in the intensive agricultural region of Salinas Valley, California, found that IQ levels for children with the most OP exposure were a full seven IQ points lower than those with the lowest exposure levels. This is a very significant drop. According to USA Today, lead poisoning can result in a drop of less than half that amount, usually about two to three IQ points, which is still cause for grave concern. The Berkeley team also found that every tenfold increase in measures of organophosphates detected during a mother’s pregnancy corresponded to a 5.5 point drop in overall IQ scores in the 7-year-olds.
The findings of the three studies support the suggestions of recent research on a phenomenon known as “inverse dose response.” This refers to the idea that it is often the timing of chemical exposure that is most important, rather than the actual degree of exposure. The studies found that exposure to OPs while a child was still in the womb correlated to lower IQ scores, but exposures during early childhood, even at higher amounts, did not result in similar findings.
Organophosphates, derived from World War II nerve agents, are a common class of chemicals used in pesticides and are considered to be among the most likely pesticides to cause an acute poisoning. Many are already banned in several European countries. Organophosphate pesticides are extremely toxic to the nervous system, as they are cholinesterase inhibitors and bind irreversibly to the active site of an enzyme essential for normal nerve impulse transmission. In finally responding to concerns stemming from this information, EPA reached agreements with chemical manufacturers to phase out residential use of two common organophosphate pesticides, chlorpyrifos and diazinon, in 2000 and 2002 respectively. However, these pesticides remain registered for other uses, including in agricultural production.
One of the researchers involved in the recent studies, Dana Boyd Barr, PhD, recently spoke at Beyond Pesticides 29th Annual National Pesticide Forum. Video of her presentation at the forum will soon be available on our website.
The three articles are available online from EHP, free of charge:
“Prenatal Exposure to Organophosphates, Paraoxonase 1, and Cognitive Development in Childhood.” Study coauthors include Stephanie M. Engel, James Wetmur, Jia Chen, Chenbo Zhu, Dana Boyd Barr, Richard L. Canfield, and Mary S. Wolff.
“Prenatal Exposure to Organophosphate Pesticides and IQ in 7-Year-Old Children.” Study coauthors include Maryse F. Bouchard, Jonathan Chevrier, Kim G. Harley, Katherine Kogut, Michelle Vedar, Norma Calderon, Celina Trujillo, Caroline Johnson, Asa Bradman, Dana Boyd Barr, and Brenda Eskenazi.
“7-Year Neurodevelopmental Scores and Prenatal Exposure to Chlorpyrifos, a Common Agricultural Pesticide.” Study coauthors include Virginia Rauh, Srikesh Arunajadai, Megan Horton, Frederica Perera, Lori Hoepner, Dana B. Barr, and Robin Whyatt.