Aug. 31, 2018

Harmful to living things

DDT was one of the first chemicals in widespread use as a pesticide. Following World War II, it was promoted as a wonder-chemical, the simple solution to pest problems large and small. In the United States alone, an estimated 1.35 billion pounds were sprayed to wipe out mosquitoes and agricultural pests over a period of about 30 years. Today, nearly 40 years after DDT was banned in the U.S., we continue to live with its long-lasting effects. The science on the impact of DDT on human health has continued to mount over the years, with recent studies showing harm at very low levels of exposure. Studies show a range of human health effects linked to DDT and its breakdown product, DDE:


  • male infertility (rats become sterile with DDT)
  • miscarriages & low birth weight
  • developmental delay
  • nervous system & liver damage

A recent study has linked DDT with autism. When they measured DDT by-product levels in blood samples, they found that mothers with high concentrations of this chemical—those in the top quartile—were 32% more likely than women with lower DDT levels to give birth to children who developed autism. The likelihood that a child with autism accompanied by intellectual disability was twice as high in mothers with elevated DDT levels compared to those with lower levels. We know that DDT works on insects by disorganizing the nervous system (interfering with normal nerve impulses) autism is a nervous system problem.

DDT is considered to be a persistent organic pollutant, POP, which can raise the risk of cancer or other diseases, alter hormones, reduce fertility or disrupt brain development. We know that DDT concentrates as it moves up the food chain. A fancy science word for that is bio-accumulation. Thirty-eight years after DDT was banned, Americans still consume trace amounts of the infamous insecticide every day, along with more than 20 other banned chemicals.

Last year, as part of an ongoing study of POPs in the food supply, Schecter and his colleagues collected and analyzed more than 300 samples from supermarkets around Dallas, Texas. The samples were combined into 31 food types, such as yogurt, chicken and peanut butter, and tested for old contaminants as well as newer ones. “Every food within this study contained multiple pesticides,” the authors wrote in a paper published in February in the journal Environmental Health Perspectives. The DDT metabolite DDE was the most prevalent, occurring in 23 of the 31 foods sampled.

Other banned pesticides that have lingered in food for decades include dieldrin, toxaphene, chlordane, hexachlorocyclohexane and hexachlorobenzene. Although lesser known, they pose risks similar to the infamous DDT and PCBs. These chemicals are prevalent in fish, salmon, catfish and sardines.

Rachel Carson highlighted the dangers of DDT in her groundbreaking 1962 book Silent Spring. Carson used DDT to tell the broader story of the disastrous consequences of the overuse of insecticides, and raised enough concern from her testimony before Congress to trigger the establishment of the Environmental Protection Agency. Research has found that people consume more DDT than any other persistent organic pollutant. Its relative abundance in food today is due to its widespread historical use. 

We're just not that good about understanding the longterm affects of chemicals on our health or in our ecosystems.