Researchers from the Columbia Center for Children’s Environmental Health report evidence of a link between prenatal exposure to the insecticide chlorpyrifos and deficits in IQ and working memory at age seven. This is the first study to evaluate the neurotoxicity of prenatal chlorpyrifos exposure on cognitive development at the time of school entry. Findings are online in Environmental Health Perspectives.
Until banned for indoor residential use by the U.S. Environmental Protection Agency in 2001, chlorpyrifos, an organophosphate pesticide, was one of the most widely used insecticides for residential pest control. In a sample of 265 New York City minority children, born prior to the ban, the researchers found evidence that increases in the amount of chlorpyrifos in the babies’ umbilical cord blood were associated with decreases in performance on a measure of cognitive functioning at age 7.
Specifically, higher prenatal exposure was associated with lower scores on two different scales of the Wechsler Intelligence Scales for Children (WISC-IV). On average, for each standard deviation increase in chlorpyrifos exposure, the full-Scale IQ was reduced by 1.4% (0.94 to 1.8 points) and Working Memory was reduced by 2.8% (1.6 to 3.7 points). This means that those children who have exposures in the upper 25% of the exposure distribution will score, on average, 5.5% (or 5.3 points) lower on the test of Working memory, and 2.7% (or 2.7) points lower on Full-scale IQ, as compared to those children in the lowest quartile.
Furthermore, the decline in test scores begins at the lowest exposures and continues downward with increasing exposure levels. This suggests no evidence of a threshold, below which exposures are completely safe.
The Columbia researchers had previously reported that, prior to the ban, chlorpyrifos was detected in 100% of personal and indoor air samples, and 70% of umbilical cord blood collected from babies. They also reported that the amount of chlorpyrifos in babies’ blood was associated with neurodevelopmental problems at age three. The new findings suggest that the relationship between prenatal chlorpyrifos exposure and neurodevelopmental deficits among cohort children persists through age seven, with possible longer-term educational implications.
“These observed deficits in cognitive functioning at 7 years of age could have implications for school performance,” noted Virginia Rauh, ScD, deputy director of the Columbia Center for Children’s Environmental Health (CCCEH), and lead author of the study. “Working memory problems may interfere with reading comprehension, learning and academic achievement, even if general intelligence remains in the normal range.”
The good news, reports Robin Whyatt, DrPH, senior author on the paper, is that since the EPA ban took effect, exposure to the organophosphate has measurably declined. CCCEH scientists have found a 3-fold decrease in chlorpyrifos levels in personal and indoor air samples in the cohort and a more than 5-fold decrease in blood levels.
“However, agricultural use of chlorpyrifos is still permitted in the U.S.,” says Dr. Whyatt, professor of Clinical Environmental Health Sciences and deputy director of CCCEH. “It is vitally important that we continue to monitor the levels of exposure in potentially vulnerable populations, especially in pregnant women in agricultural communities, as their infants may continue to be at risk.”
Also published in Environmental Health Perspectives today, two other NIEHS/EPA funded Children's Environmental Health Centers present independent investigations of organophosphate pesticides and neurodevelopment. Although findings cannot be directly compared, these studies also found early cognitive and behavioral effects associated with prenatal organophosphate exposure.
The study at the Columbia Center for Children’s Environmental Health was supported by the National Institute of Environmental Health Sciences, EPA, and several private foundations.
April 21, 2011