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DDT has long been suspected of causing cancer in humans, but concrete evidence has been lacking. Now, a new study published in the Journal of Clinical Endocrinology & Metabolism takes a step closer to confirming the suspicion.

The study, conducted as a collaboration between the California Public Health Institute, the University of California–Davis, and the California Department of Toxic Substances Control, found that daughters of women who had high levels of DDT in their bodies during gestation were 3.7 times more likely to get breast cancer than daughters of women who had low levels of the pesticide.

Via: Tom Grundy | Shutterstock

Study author Barbara A. Cohn told the Washington Post that the research is “the first to provide direct evidence that chemical exposures for pregnant women may have lifelong consequences for their daughters’ breast cancer risk.”

Pesticides are designed to be killers, and the evidence shows that many of them are toxic to humans as well as insects. Although some insecticides may ostensibly not cause harm to humans in low doses, there are a number of reasons to be wary of widespread pesticide use. We are still ignorant of the effects of ingesting them over a long period of time, and many of the studies that proclaim the safety of pesticides are funded by pesticide manufacturers, creating an obvious conflict of interest.

What’s more, chemicals we once thought were safe have later proven harmful, DDT being the most prominent example. The chemical dichlorodiphenyltrichloroethane became popular as an insecticide starting in 1939 when it proved useful for controlling mosquito-born diseases like malaria. It quickly was adopted by farmers and was used indiscriminately as an agricultural pesticide in the ’40s and ’50s.

Photo: Rachel Carson

However, people started to ask questions about how much we really understood about the chemical. Biologist Rachel Carson published her famous book Silent Spring in 1962, which pointed the finger at DDT for decimating bird populations as well as playing a role in cancer formation in humans. In 1972, the United States banned its use, and it was later prohibited in agricultural production worldwide.

To some extent, the damage was already done however. Remnants of DDT are still found in our food and our bodies. Even the EPA says DDT “is classified as a probable human carcinogen by U.S. and international authorities…[and is] known to be very persistent in the environment, will accumulate in fatty tissues, and can travel long distances in the upper atmosphere.” And the new research shows the effects can be generational — over 40 years after DDT was banned, we are seeing breast cancer cases pop up in the children of the people originally affected.

DDT is still around, if not as ubiquitous as it once was. Some countries still use it to spray houses to kill mosquitoes that carry the malaria virus, a noble goal but one that could have unintended consequences. A review of studies about the pesticide published in the Lancet found that “exposure to DDT at amounts that would be needed in malaria control might cause preterm birth and early weaning, abrogating the benefit of reducing infant mortality from malaria” and that hormone mimickers in the chemical could also potentially cause disruptions in menstruation, gestation, lactation and semen production.

“Our findings don’t change the perception of benefits, but they do change the perception of risks,” Cohn told the Washington Post. “We are hoping that policymakers will use this information as they continue to debate the use of DDT around the world.”