The researchers analyzed the blood of 360 pregnant women participating in the UC Berkley project, checking for levels of DDT and DDE, one of the breakdown products. After the babies were born, researchers noted a two- to three-point decrease in mental exams at the 12- and 24-month mark, and a two-point decrease in physical tests at the 6- and 12-month mark for every tenfold increase in DDT levels measured in the mothers before birth.
The study published in the July issue of Pediatrics found that, despite the fact that DDT was transferred via breast milk, the children who were breast-fed developed more normally even if the mothers showed high levels of DDT exposure.
Ninety percent of the participants in this study were born in Mexico, where DDT was widely used until its ban in 2000. In the United States, DDT has been banned since 1972 and environmentalists have long been concerned with the pesticide's toxicity to humans. However, Dr. Walter Rogan, senior investigator in the National Institute of Environmental Health Sciences' epidemiology branch, says it is not clear that DDT has ever killed anyone.
Rogan, whose department helped pay for the study but did not participate, added that while the chemical does appears to be hazardous to some animals, DDT's effects on humans are still being studied.