According to study author Brenda Eskenazi, a professor of epidemiology and maternal and child health at the University of California, Berkeley, the potential benefits of DDT use to reduce malaria must be considered by policymakers along with the new findings.
Dr. Walter Rogan, senior investigator in the National Institute of Environmental Health Sciences' epidemiology branch said that while DDT appears hazardous to some animals, DDT's health effects on humans are still being studied.
The researchers examined blood levels of DDT and one of the breakdown products -- known as DDE -- in 360 pregnant women from California's Central Valley who are participating in a long-term UC Berkeley project called the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS).
Ninety percent of these women were born in Mexico, where DDT was widely used in agriculture during the 1970s, then used to control mosquitoes until 1995. It was only in 2000 that a complete ban of DDT went into effect.
Mental and physical skills of these women's infants at 6, 12 and 24 months of age were tested. It was found that the babies of mothers with the highest DDT exposure showed signs of delayed mental development at 12 months and 24 months.
For each tenfold increase in DDT levels measured in the mother, the researchers found a corresponding two- to three-point decrease in the child's mental development scores at 12 and 24 months. In physical skills exams, there were two-point decreases in children's scores at 6 months and 12 months for each tenfold increase in DDT levels in the mothers. No decrease was found at 24 months.
While changes in individual children due to DDT exposure might not be readily noticeable, Eskenazi said 'if this association is uniform across the population, you would see more children with problems in the population.' The results of the research are published in the July issue of Pediatrics.
Breast-feeding seemed to help the infants of mothers who were heavily exposed to DD, showing more normal development, although DDT is transmitted through breast milk.
People are typically exposed to DDT by coming into contact with the pesticide spray or by eating food that has been sprayed.
The physical effects of DDT on the brains of infants whose mothers are exposed to it are not entirely understood nor is it known if the developmental effects in infants will be permanent.
As for countries considering the use of DDT to fight malaria, Rogan said, "They have to entertain the idea that DDT is not an entirely innocuous compound. If you think about it, it's implausible that it would be," he said, adding that, after all, DDT is a poison designed to kill living things.