February 9, 2011 -- When the EPA phased out the widespread residential use of chlorpyrifos and other organophosphorus (OP) insecticides in 2000-2001 because of risks to child neurodevelopment, these compounds were largely replaced with pyrethroid insecticides. But the safety of these replacement insecticides remained unclear, as they had never been evaluated for long-term neurotoxic effects after low-level exposure. In the first study to examine the effects of these compounds on humans and the first evaluation of their potential toxicity to the developing fetal brain, scientists of the Columbia Center for Children's Environmental Health at Columbia University's Mailman School of Public Health found a significant association between piperonyl butoxide (PBO), a common additive in pyrethroid formulations, measured in personal air collected during the third trimester of pregnancy, and delayed mental development at 36 months. Findings from the study are online in the journal, Pediatrics.
The study was conducted with a subset of 725 pregnant women participating in a prospective longitudinal study of black and Dominican women living in upper Manhattan and the South Bronx underway at the Columbia Center for Children's Environmental Health (CCCEH). The insecticide permethrin was selected for the evaluation because it is one of the most common pyrethroid insecticides used in U.S. homes, as well as the most commonly sold pesticide, according to a nationally representative sample. PBO, a chemical that is added to insecticides to increase efficacy was also selected for evaluation. Any detection of PBO in air is a marker of a pyrethroid insecticide application.
In all, 342 women were studied for permethrin exposure in personal air during pregnancy; 272 for permethrin in maternal and umbilical cord plasma; and 230 were evaluated for exposure to PBO. To collect the air samples, mothers from the CCCEH Mothers and Newborns cohort wore a small backpack holding a personal ambient air monitor for 48 hours during the third trimester of pregnancy.
The children of these mothers were evaluated for cognitive and motor development at age three. CCCEH researchers used the Bayley Scales of Infant Development. In evaluating the results, researchers controlled for gender, gestational age, ethnicity, maternal education and intelligence, quality of the home environment, and prenatal exposure to environmental tobacco smoke and chlorpyrifos.
PBO was detected in the majority of personal air samples (75%). While the results demonstrate that a significant prenatal exposure to permethrin in personal air and/or plasma was not associated with performance scores for the Bayley Mental Developmental Index or the Psychomotor Developmental Index at 36 months, children who were more highly exposed to PBO in personal air samples (≥4.34 ng/m3) scored 3.9 points lower on the Mental Developmental Index than those with lower exposures.
"This drop in IQ points is similar to that observed in response to lead exposure," said Megan Horton of the Mailman School of Public Health and lead researcher. "While perhaps not impacting an individual's overall function, it is educationally meaningful and could shift the distribution of children in the society who would be in need of early intervention services".
The researchers point out that environmental and biological monitoring of pyrethroid insecticides present certain challenges. "We know most pyrethroid insecticides are difficult to measure in the air because they are not volatile and are difficult to measure in bodily fluids because they are rapidly metabolized, and these difficulties may prevent us from seeing significant associations with neurodevelopmental outcomes," noted Dr. Horton. "Because PBO is volatile and permethrin is not volatile, we would not expect to find a strong association between the two compounds. With the exception of the increased odds of motor delay in the lowest PBO exposure group, prenatal exposure to PBO seems to have an impact on cognitive rather than motor development, which is quite worrisome because mental development scores are more predictive of school readiness."
As this is the first study of these compounds, the results should be considered preliminary but, Dr. Horton notes, they do - raise a cautionary red flag about the use of these chemicals during pregnancy. And, she adds, research at the Columbia Center for Children's Environmental Health, indicates that "integrated pest management and the non-spray application of lower toxicity pesticides are viable alternatives to the use of these spray pesticides for pest control."
"This is an important study with potentially broad public health implications," according to Dr. Robin Whyatt, Mailman School professor of clinical environmental health sciences and a co-deputy director at the CCCEH. "Further, it identifies a critical need for additional research."
About the Columbia Center for Children's Environmental Health
The Columbia Center for Children's Environmental Health (CCCEH) carries out community-based research in northern Manhattan and the South Bronx to examine the health effects of prenatal and early postnatal exposures to common urban air pollutants, with the aim of preventing environmentally related disease in children. The Center is unique in the field of scientific research because it applies the results of its research to interventions that reduce toxic pesticide use; conducts a community education campaign to increase environmental health awareness among local residents, parents, health professionals and educators; and informs public interest groups, elected officials, and other policymakers who can shape policies to improve the environmental health status of underserved neighborhoods. The Center's overall mission is to improve prevention and clinical treatment, and work with community-based organizations to improve their neighborhood's environmental health. Our lead community partner is WE ACT for Environmental Justice.
About the Mailman School of Public Health
Founded in 1922 as one of the first three public health academies in the nation, Columbia University's Mailman School of Public Health pursues an agenda of research, education, and service to address the critical and complex public health issues affecting New Yorkers, the nation and the world. The Mailman School is the third largest recipient of NIH grants among schools of public health. Its 300 multi-disciplinary faculty members work in more than 100 countries around the world, addressing such issues as infectious and chronic diseases, environmental health, maternal and child health, health policy, climate change & health, and public health preparedness. It is a leader in public health education with over 1,000 graduate students from more than 40 nations pursuing a variety of master's and doctoral degree programs. The Mailman School is also home to numerous world-renowned research centers including the International Center for AIDS Care and Treatment Programs (ICAP), the National Center for Disaster Preparedness and the Center for Infection and Immunity. For more information, please visit www.mailman.columbia.edu