Because DDT and DDE are so similar, scientists were surprised that DDT seemed to harm brain development while the other had little impact. That suggests that the mental abilities of U.S. children born between World War II and the early 1970s -- when DDT was routinely sprayed -- could have been affected, but not those born years later and exposed to old residue in the environment.
Nevertheless, the researchers reported that breastfeeding is beneficial to babies even when the milk contains large doses of DDT. The children's test scores increased with every month of nursing even for the most contaminated mothers.
Doctors know that breastfeeding boosts a baby's intelligence, yet they have long wondered if contaminants in the milk erase that benefit. The new study "provides additional evidence that breastfeeding may help to compensate for the subtle perinatal insult associated with DDT/DDE exposure," the authors wrote. The insecticide's damage probably occurs in the womb, not during breastfeeding.
The researchers tested the women for other pesticides, but only DDT was connected to neurological effects.
The study is part of a federally funded UC Berkeley project that assesses whether agricultural chemicals in the Salinas Valley, one of the world's most intensely farmed areas, are harming children.