Decades-banned pesticides apparently continue to interfere with fetal growth during U.S. pregnancies, a new study reports.
DDT was banned in 1972 in the United States, but low levels of it and other organic chemical pollutants can still be found in the blood of pregnant American women, researchers reported online Dec. 30 in JAMA Pediatrics.
Women carrying even low levels of these pollutants had slightly smaller fetuses than women whose exposure to the chemicals was less, results showed.
The most consistent effects seemed to come from DDT and related pesticides, said study co-author Pauline Mendola, an investigator at the U.S. National Institute of Child Health and Human Development.
"Bones seem to be more affected," she said. "Head circumference and femur length were more often impacted than other growth measures."
This study looked at persistent organic pollutants -- chemicals once used in agriculture, pest control, manufacturing and industrial processes. These include DDT and dioxins like PCBs.
Although most of these chemicals are banned or rarely used in the United States, they are slow to break down and are still present in the food chain, said Dr. Rahul Gupta, chief medical and health officer for the March of Dimes.
"More than 90% of human exposure is through food," he said.
To see whether these chemicals continue to affect human pregnancy, Mendola's team took blood samples and performed ultrasound scans during the pregnancies of 2,284 women from a variety of racial and ethnic backgrounds.
"The pregnancies were all low-risk, so we could look at normal fetal growth over the course of each pregnancy," Mendola said.
The blood samples were tested for the presence of 76 persistent organic pollutants, and ranked against one another in terms of levels from each chemical class.
DDT and other organochlorine pesticides were associated with the most dramatic growth delay, researchers found.
The fetuses of women with higher blood levels of pesticide had head circumferences an average 4.7 millimeters smaller; abdominal circumference 3.5 mm smaller; and thigh bones 0.6 mm shorter. (For reference, 5 mm is about 0.20 inch.)
PCBs, a dioxin-like chemical, also appeared linked to slower fetal growth. Fetuses of women with higher levels of the chemicals had an average head circumference 6.4 mm smaller and an abdominal circumference 2.4 mm smaller.
"Although there's much less exposure in the United States, it continues to have an impact on the developing fetus," said Gupta, who wasn't part of the study.
What's most disturbing is that the elevated blood levels associated with these effects were still relatively small, Mendola pointed out.
"Their levels were really low. These are clearly healthy people, with no particular exposures other than just general exposures you'd get through daily living," she said.
Researchers noted that the blood levels of persistent organic pollutants in these women were lower than in women tested in 2003 and 2004.
It's unclear whether these infants will go on to have other health problems associated with the chemicals, but there don't seem to be widespread illnesses or birth defects, Mendola said.
"We just don't know, but if these things were causing major population-level effects we would see it, and we don't," she said.
The jury is still out, given that these chemicals are known to cause cancer and immune system problems, Gupta said.
"I think it's less well-known as to what will happen to these infants beyond the effects on the growth of their bones," he said. "These effects could be transient, but others could be longer-lasting."
Other parts of the world still use these chemicals, but Mendola said human exposure hopefully will continue to decline in the United States.
"We see slowly the levels are coming down in the population for most of these persistent chemicals," she said. "But it takes generations and generations for them to be dissipated. The half-life is really long for most of these chemicals."
The U.S. Environmental Protection Agency has more about DDT.