Food in the U.S. Is Still Tainted with Chemicals That Were Banned Decades Ago

In a photograph from a 1947 newspaper advertisement, a smiling mother leans over her baby's crib. The wall behind her is decorated with rows of flowers and Disney characters. Above the photo, a headline reads "Protect Your Children From Disease Carrying Insects."

The ad, for wallpaper impregnated with DDT, captures a moment of historical ignorance, before the infamous insecticide nearly wiped out many birds and turned up inside the bodies of virtually everyone on Earth.

The story of DDT teaches a lesson about the past. But experts say it also provides a glimpse into the future.

Thirty-eight years after it was banned, Americans still consume traces of DDT and its metabolites every day, along with more than 20 other banned chemicals. Residues of these legacy contaminants are ubiquitous in U.S. food, particularly dairy products, meat and fish.

Their decades-long presence in the food supply underscores the dangers of a new and widely used generation of chemicals with similar properties and health risks. "They're manmade, and they're toxic, and they bio-accumulate," said Arnold Schecter, a professor at the University of Texas School of Public Health who has been studying human exposure to chemicals for more than 25 years. "So the fact that they're still around a long time after they've been banned isn't surprising."

Recent studies sketch a complex profile of legacy contaminants in U.S. food - a profusion of chemicals in trace amounts, pervasive but uneven across the food supply, occurring sometimes by themselves, but more often in combination with others. Included are DDT and several lesser-known organochlorine pesticides as well as industrial chemicals such as polychlorinated biphenyls, or PCBs, which were used until the late 1970s in electrical equipment.

This picture raises a host of equally complicated questions: Are small amounts of these chemicals dangerous, by themselves or in mixtures? Why are they still around and how are they getting into our food?

Think of these chemicals like sand in your shoes after a trip to the beach. Despite our efforts to rid ourselves of it, we discover more later - sometimes that evening, sometimes years later - when we put on the same pair of summer shoes and feel the grains between our toes.

Like those grains of sand, many chemicals stick around. They belong to a class called "persistent organic pollutants" or POPs - which take decades to break down in sediment and soil and can travel globally on wind and water, ending up in regions as remote as the Arctic. These migratory POPs, when ingested, take up semi-permanent residence in the fat tissue of living organisms. In animals, and sometimes in humans, many of them can raise the risk of cancer or other diseases, alter hormones, reduce fertility or disrupt brain development.

The good news is that DDT and other organochlorine pesticides, PCBs and industrial byproducts called dioxins have declined significantly in food and the environment since they were banned or restricted decades ago. A few have dipped below detectable levels. "We don't expect the levels in food or people to go down abruptly, we expect them to go down over time. And that's what we're seeing," Schecter said.

Precise trends of chemicals in food are hard to identify because both government and independent studies have focused on different foods in different places at different times. However, levels in human breast milk indicate that, by 1990, DDT had dropped to one-tenth of 1970 levels, according to a 1999 report in the International Journal of Epidemiology. Similar trends exist for PCBs and dioxins. In most places, POPs are a mere fraction of what they were.

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.