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A persistent chemical formerly used in Scotchgard still contaminates most fish in U.S. rivers and the Great Lakes despite a phase-out a dozen years ago, a new federal study shows.

U.S. Environmental Protection Agency researchers found perfluorooctane sulfonic acid (PFOS) in all of the 157 fish sampled from nearshore waters in the five Great Lakes and in 73 percent from 162 rivers.

The study, the largest of its kind in freshwater fish, suggests that eating bass, trout, walleye and catfish could be a major source of exposure for anglers and their families. The chemical remains widespread in wildlife, people and water around the world.

“This just shows that PFOS still dominates. Even though production stopped more than a decade ago, it’s still the main perfluorinated acid in the environment,” said Craig Butt, a Duke University chemist who was not involved in the study.

PFOS and other perfluorinated compounds are used in oil and water resistant coatings for pots and pans, clothes, paper, carpet and flame retardant foams.

The 3M Company, the major manufacturer of PFOS, voluntarily stopped its production in 2002 after scientists discovered that it was building up in water, wildlife and people.     

Nevertheless, “every single human being we test has levels of PFOS in them,” Butt said. The compound “doesn’t break down in light, it doesn’t oxidize. Once it’s in the environment it’s not going anywhere.”

Most health studies have focused on communities with drinking water contaminated by PFOS. But people are exposed in many ways, said Sarah Knox, a professor and epidemiologist at West Virginia University. “Routes of exposure are multiple – things like linings of food containers, stain resistance sprays, fire-proofing and non-stick cookware,” she said.

The EPA estimates that “contamination in food may account for more than 90 percent of human exposure to PFOS and PFOA” and that fish may be a major source of PFOS.