A federal ban on two insecticides has resulted in a significant reduction in their impact on newborns' birth weight and length, according to a new study funded by the National Institute of Environmental Health Sciences of the National Institutes of Health, the U.S. Environmental Protection Agency, and other private foundations.

The results of the study -- the first one to demonstrate the benefits of the ban during pregnancy in human subjects -- will be published in "Environmental Health Perspectives", the monthly peer-reviewed journal of the NIEHS. It is now available online at http://ehp.niehs.nih.gov.

The study, released by the Columbia Center for Children's Environmental Health, part of the Mailman School of Public Health at Columbia University, measured the impact on faetal growth of two insecticides -- chlorpyrifos and diazinon --whose use in households was banned by the federal government starting in 2000. The insecticides had been among the most commonly-used agents for residential pest control.

In the study, researchers measured the levels of the two insecticides in blood drawn from the umbilical cords after delivery, both before and after the ban, and correlated those levels with the babies' birth weight and length. All blood samples were frozen and stored at -70 degrees Centigrade in order to ensure the stability of the pesticides. Subsequent analyses were performed on frozen samples at three different times -- spring 2001, summer 2002 and fall 2002.

They found that prior to January 2001, newborns with combined insecticide exposures in the highest 26th percentile had birth weights averaging almost 200 grams (almost half a pound) less than infants with no detectable pesticide levels. The researchers also noted a highly significant inverse association between the combined exposures and newborn birth length. However, when they looked at the relationship between insecticide exposures and faetal growth after January 2001, the exposure levels had been reduced substantially, and the impact on weight and length was no longer apparent.

"This human study confirms the developmental impact, shown previously in animal studies, of these insecticides," said Dr. Robin M. Whyatt, an Assistant Professor at the Mailman School and principal author of the study. "It also demonstrates the positive effect of the federal ban, which has substantially reduced exposures and benefitted human health."

"The differences in fetal growth seen here are comparable to the differences between babies whose mothers smoke during pregnancy and babies whose mothers don't," said Whyatt. "The fact that the ban was associated with such an immediate change in birth weight and length provides considerable evidence of cause and effect."

According to the study investigators, the widespread use of the two pesticides makes them good candidates for a residential study of this kind. Chlorpyrifos, for instance, was the most frequently used residential insecticide in New York City prior to the ban. Both compounds are still widely used in agriculture and continue to be found in the food supply.

"This study is good news for our nation's children," said Dr. Frederica P. Perera, Director of the Center and the study team leader. "The evidence that birth weight increased following the Environmental Protection Agency's regulatory action implies important benefits for the children's future health and development. At the same time, the results highlight the need to address continuing prenatal exposures to these and other toxic pesticides." The study is part of a broader, multi-year research project, "The Mothers & Children Study In New York City," started in 1998, which examines the health effects of exposure of pregnant women and babies to air pollutants from vehicle exhaust, the commercial burning of fuels, and tobacco smoking, as well as from residential use of pesticides and allergens. The present study included a sample of 314 infants of African American and Dominican women in Washington Heights, Central Harlem and the South Bronx.

Other co-authors of this study include Dr. Virginia Rauh from the Columbia Center, Dr. Dana Barr from the Centers for Disease Control and Prevention, and David Camann from Southwest Research Institute.