Babies and toddlers of California farmworkers exposed to the insecticide DDT have neurological effects that are severe enough in some cases to slow their mental and physical development, according to research by UC Berkeley scientists published today.
The federally funded research involving the children of women who recently emigrated from Mexico to the Salinas Valley is the first in the United States to indicate that the pesticide harms human brain development.
"This suggests that ... DDT has effects that no one even thought to test for back when it was in use," said Dr. Walter Rogan, an epidemiologist with the National Institute of Environmental Health Sciences. He was not involved in the new study, published in the journal Pediatrics.
Because DDT was banned more than 30 years ago in the United States and most developed countries, the findings have particular relevance for the ongoing, controversial use in Africa to combat malaria.
UC Berkeley scientists measured levels of various pesticides in 360 pregnant women, nearly all of whom were born in Mexico, and tested the mental and motor skills of their infants and toddlers, who were born in the Salinas Valley.
For every tenfold rise in DDT exposure, the children's scores on mental tests dropped 2 to 3 points. Their motor skills were also reduced. In the worst cases, the highest DDT doses were associated with a 7- to 10-point drop in the mental scores of 24-month-old children compared with those who were not exposed.
Those drops are significant, because the average score in the study was 86 at that age and anything below 85 indicates a developmental delay and potential learning disability. The tests measure the children's ability to learn and think, including memory and problem-solving skills.
"If you had a whole population with a downward shift like this, you'd be seeing more kids with developmental problems," said Brenda Eskenazi, a UC Berkeley professor of maternal and child health and epidemiology, who directed the project.
The Salinas Valley women had very high exposures, eight times higher than average levels in the U.S. population reported recently by the Centers for Disease Control and Prevention. They were probably exposed in Mexico, because most of them had lived in the United States for less than five years. Mexico allowed the use of DDT on farms until 1995 and for mosquito control until 2000. All uses in the United States ended in 1972.
