Persistent organic pollutants are chemicals that do not break down in the environment; this is why they tend to end up in food, especially in animals higher up the food chain. Many POPs have had wide consumer and industrial use in the past 50 years, which explains their ubiquitous existence in soil, water, air, and food.

The scientists looked at levels of three major groups of contaminants, PFCs, PCBs, and pesticides. Perfluourinated Compounds (PFCs) were used in aerosols and sprays until they were recently phased out by manufacturers.  Polychlorinated Biphenyls (PCBs) were used in industrial chemicals and electrical work until the 1970s, but they can still be found in humans and animals today. DDT, the miracle pesticide from the early to mid 20th century, is another type of persistent pollutant. All of these chemicals have been shown to have toxic affects, including decreased fertility, cancer, and hindered neurologic development.

All food samples were purchased from Dallas supermarkets. Thirty-one types of food, including produce, meat, and dairy, were tested for 32 pesticides, seven PCBs, and 11 different PFCs. These organic pollutants were found to be widespread in the different types of food. PFCs were found in 17 of the foods; six of the seven types of PCBs were found in salmon and canned sardines. Pesticides were found in 23 of the 31 foods tested.

The levels of chemicals varied dramatically in the different types of food. Foods with a high fat content had relatively high levels of pesticides. The highest levels of DDT were found in whole milk yogurt; the greatest numbers of PCBs found primarily in fish, especially salmon; and that there were PFOAs in more than one-half the samples, especially in olive oil. Concentrations of one type of pesticide, dieldrin, ranged from 0.028 nanograms per gram in whole milk to 2.3 ng/g in catfish fillets. When compared with produce and other types of meat, fish was usually found to have much higher levels of contaminants.

The researchers then looked at the overall consumption of different foods to calculate the daily intake of persistent organic chemicals for the average American. The total daily consumption of DDTs was 263 ng/day, mainly from dairy products. The daily consumption of other chemicals was lower, with PCBs at 33 ng/day. For all chemicals measured, however, the total daily intake was not higher than the EPA’s reference doses or the European Union’s highest acceptable level for pesticide contamination of food.

The researchers pointed out, however, that while the effects of each single chemical compound are known, there is no research on the effects of having a complicated mixture of many organic pollutants. In reality, it’s unlikely that a person would find themselves exposed to only one of these chemicals. Potentially toxic interactions between the chemicals, even when present at lower levels, is an issue that has not been researched.

For the future, scientists in the study called for better monitoring and studying of chemical contaminants in food. Previous USDA studies have not tested the same foods from year to year, so comparing data has not been possible. In other studies, only one type of food had been tested, which did not allow researchers to get an idea of how much contaminant was being ingested overall.

At the end of their paper, the researchers warned about not only watching for these known contaminants, but also considering new organic pollutants that are entering the food system: “Our study shows that U.S. food is contaminated with a wide range of chemicals, including pesticides, PFCs, and PCBs, and that expanding the current monitoring beyond pesticides to include emerging pollutants is warranted.”