A new research report shows health problems linked to the long-banned insecticide DDT have persisted across at least three generations, affecting even the granddaughters of women exposed to the chemical in the 1960s. 

The research, which was published April 14 in the Cancer Epidemiology, Biomarkers & Prevention Journal, is the latest in a series of findings generated from a relatively unique study that began in the 1960s, when DDT was widely used. Researchers obtained blood samples from women in their third trimester of pregnancy and also just after they gave birth to determine their DDT exposure. More than 15,000 women seeking obstetric care at the Kaiser Foundation Health Plan in the San Francisco Bay Area from 1959 to 1967 were included in the original study.

Previous findings showed that daughters of the women who had more DDT in their blood had a much heightened risk for breast cancer and increased prevalence of obesity, while sons had heightened risks for testicular cancer.  

The new analysis marks the first confirmation that the granddaughters of those women with DDT in their blood samples drawn decades ago also have a higher risk for obesity as well as early menstruation. These conditions are related to cardiometabolic problems such as insulin resistance, impaired glucose tolerance, and high blood pressure, and increased risk for breast cancer and some other cancers. 

The findings support the theory that grandmother exposures to DDT could have contributed to a dramatic increase in obesity seen today in young adult women, and that exposure to DDT just before or after birth is associated with breast cancer risk factors for at least three generations, according to the study.

The work is significant, not just for what it shows about DDT and long-term health impacts, but also because it underscores a critical need for more long-term studies of the impacts of other pesticides and chemicals we have been, and currently are, exposed to, according to study author Barbara Cohn, director and senior research scientist of the Child Health and Development Studies program at the Public Health Institute in Berkeley, California.

Along with Cohn, two other Public Health Institute researchers and a researcher from the UC Davis College of Biological Sciences authored the study.

Cohn said she fears that we won’t learn until decades from now about chemicals being used widely today that could be doing irreparable harm to our health. We are “flooding the world” with chemicals that may have the capacity to cause harm years down the road, and are not devoting enough research funding to track the impacts, Cohn said in an interview with Sierra.

“There can be these long-term effects that you can’t immediately see,” she said. “What is our DDT now?”

Julia Brody, executive director and senior scientist at the Silent Spring Institute, echoed Cohn’s sentiments. 

“This is a sign that toxic chemicals are a multigenerational issue similar to climate change,” she told Sierra. We need more and more thorough testing to exclude carcinogens from use and better protect public health, Brody said.  

The Silent Spring Institute studies the links between chemicals and women’s health with a particular focus on breast cancer. In 2020, the institute published an analysis of scientific research submitted to the EPA on 28 pesticides linked with mammary-gland tumors and found the EPA dismissed the evidence for 19 of the 28.  

Disrupting hormones

DDT (dichloro-diphenyl-trichloroethane) was introduced in the 1940s as a highly effective insecticide designed to combat the spread of malaria, typhus, and other diseases carried by insects. It also was used for eradicating insects harmful to crops and livestock, and it was embraced for use around homes and gardens as well.  

The pesticide was considered safe enough to be sprayed widely through US towns. On warm summer nights, trucks carrying DDT would roll down residential streets, fogging entire neighborhoods with the chemical to combat mosquitoes.

The EPA banned DDT in 1972 after an accumulation of research showing harmful impacts to wildlife and potential human health risks, and it’s now classified as a probable human carcinogen. Still, DDT remains in use in some countries. 

DDT is considered to be an endocrine-disrupting chemical, or an EDC, a category of chemicals that researchers find particularly worrisome because of evidence that they alter and disrupt hormones important to good health, including reproductive health, as well as neurological and immune functions. 

Twenty years ago, the National Institute of Environmental Health Sciences and the Centers for Disease Control and Prevention, along with other scientific organizations, published a study linking DDT to an “epidemic of premature births,” which is a contributing factor to infant mortality.  

Many other chemicals are now known to be EDCs, and both Cohn and Brody said we could head off many health problems by curtailing use. 

DDT exposure persists

Exposure to DDT did not end when the chemical was banned in the United States almost 40 years ago. The chemical does not easily break down and is known by scientists to accumulate in the tissues of animals. In recent years, the Food and Drug Administration has found DDT residues in food samples.

Last year, the Los Angeles Times revealed that decades ago DDT manufacturers sunk leaking barrels contaminated with DDT deep into the Pacific Ocean off the coast of California—possibly as many as half a million barrels. The contamination of fish and other sea life has persisted over decades, and a recent study linked DDT and other pollutants to aggressive cancer seen in California sea lions.

Bruce Blumberg, professor of cell and developmental biology at the University of California, Irvine, said the story of DDT underscores the failure of companies and regulators to protect public health from the dangers of many chemicals. The government needs to fund studies that extend over multiple generations and truly examine the impacts of chemicals such as DDT on human health, he said.

“The industry will have you believe that even if a chemical is toxic and you prove it . . .  you take it off the market then the harm will be gone. The fact is that is not true,” Blumberg said. “The effects continue. Once you let that genie out of the bottle, it keeps on giving.”