When Rachel Carson’s “Silent Spring” first sounded the alarm on DDT and its devastating effects on birds and fish, our understanding of how this pesticide affected humans was just beginning. Chemicals can take years to reveal their insidious power, and so for decades, scientists have been piecing together — study by study — the reasons why DDT still haunts us today.
First it was breast cancer in women who were exposed to this hormone-disrupting chemical in the 1950s and ‘60s. Then their daughters, who had been exposed in the womb. Researchers over the years have also linked DDT exposure to obesity, birth defects, reduced fertility and testicular cancer in sons.
Now, a team of toxicologists, molecular biologists and epidemiologists at the University of California, Davis and the Public Health Institute in Oakland have confirmed for the first time that granddaughters of women who were exposed to DDT during pregnancy also suffer from significant health threats: higher rates of obesity and menstrual periods that start before age 11.
Both factors, scientists say, may put these young women at greater risk of breast cancer — as well as high blood pressure, diabetes and other diseases.
“This is further evidence that not only is a pregnant woman and her baby vulnerable to the chemicals that she’s exposed to — but so is her future grandchild,” said Barbara Cohn, director of the Public Health Institute’s Child Health and Development Studies, a multigenerational research project in California that has followed more than 15,000 pregnant women and their families since 1959.
“This is something that people had always thought was possible,” she said, “but there had never been a human study to support the existence of that link.”
The findings come at a time of renewed public interest in DDT, a problem that had been largely tucked into a fading chapter of history. Concerns have intensified since the Los Angeles Times reported last fall that the nation’s largest manufacturer of DDT once dumped as many as half a million barrels of its waste into the deep ocean.
The pesticide, now banned, is so stable it continues to poison the environment and move up the food chain. Significant amounts of DDT-related compounds are still accumulating in Southern California dolphins, and a recent study linked the presence of these persistent chemicals to an aggressive cancer in sea lions.
As for humans, “there’s a clear line you can track of what’s happening,” said Linda Birnbaum, who, as the former director of the National Institute of Environmental Health Sciences and the National Toxicology Program, has been following these multigenerational studies with great interest.
“A lot of people want to think that the problems with DDT have gone away, because Congress banned it in 1972. Well, they haven’t,” said Birnbaum, who is now a scholar in residence at Duke University. "By the time the daughters got pregnant with the granddaughters, that was long after DDT had been banned — and yet they were carrying within them the seeds of these problems.”