Decades later, DDT is still a ‘silent’ killer

Hear the name of the pesticide DDT, and there’s a good chance you’ll immediately think of the late author Rachel Carson. Her “Silent Spring” published in 1962 – so named to evoke the impact of the toxins on birds – was a call to action on the misuse of chemical pesticides harming the planet. The classic launched what many consider the start of the modern environmental movement.

Now, 57 years later, new research points to an equally silent killer and it is still DDT. The pesticide was banned in the United States in 1972 and remains in use in the developing world for malaria-related mosquito control, but the consequences of DDT exposure may last across a lifetime in women.

Many women in the U.S. were exposed to the dichloro-diphenyl-trichloroethane, which was developed in the 1940s as the “first of the modern synthetic insecticides,” according to the Environmental Protection Agency. “It was initially used with great effect to combat malaria, typhus, and the other insect-borne human diseases among both military and civilian populations.”

That remained true on farms and in homes and gardens until Carson’s book raised awareness. Despite the eventual U.S. ban, DDT residues remain in the environment even decades later. Worse still, the breast cancer diagnoses in women appear to emerge decades after their exposures to DDT stop. It’s only now that the youngest of those women are entering the age window for heightened breast cancer risk.

The new study published in the Journal of the National Cancer Institute builds on previous research into the links between DDT and breast cancer, with findings that suggest the exposure timing is everything.

“All women exposed to high levels of DDT are at increased risk for breast cancer through age 54, but the timing of cancer risk depends on when they were first exposed,” said the team, led by Dr. Barbara Cohn at the Public Health Institute in Berkeley, California.

“We know that if harmful exposures occur at times when breast tissue is rapidly changing, such as during puberty, they impact breast development in ways that can later result in cancer,” Cohn said. “The research published today suggests that DDT affects breast cancer as an endocrine disruptor, that the period of time between first exposure and cancer risk seems to be around 40 years—and that other endocrine disrupting chemicals could potentially simulate this kind of risk pattern.”

Cohn and her colleagues from Columbia University’s Mailman School of Public Health and the Columbia Medical Center in New York City based their findings on 15,528 women and six decades’ worth of data.

Some women were exposed to the pesticide in utero up to age 14, and saw higher breast cancer risk before they turned 50. The highest risk for this earlier, premenopausal diagnosis was with DDT exposures before the age of 3. The older groups – women who were exposed to DDT after age 14 – still had a higher risk for breast cancer, but only after they turned 50.

“As you travel through life, your periods of risk change,” said Cohn. “Considering the patterns we observed, working backward to determine when a woman first came into contact with the chemical could help inform early detection and treatment of DDT-associated breast cancer.”

While the research is specific to the U.S., the use of DDT was not – raising anew what it may one day mean to communities in Africa and Asia that have consistently used the pesticide to control malaria. Studies increasingly link DDT exposure to high blood pressure, Alzheimer’s disease, autism and other conditions, even two or three generations after exposure.