Fish caught in the fresh waters of the nation’s streams and rivers and the Great Lakes contain dangerously high levels of PFOS, short for perfluorooctane sulfonic acid, a known synthetic toxin phased out by the federal government, according to a study of data from the US Environmental Protection Agency.The chemical PFOS is part of a family of manufactured additives known as perfluoroalkyl and polyfluoroalkyl substances, or PFAS, widely used since the 1950s to make consumer products nonstick and resistant to stains, water and grease damage.“You’d have to drink an incredible amount of water — we estimate a month of contaminated water — to get the same exposure as you would from a single serving of freshwater fish,” Andrews said.Read more: Doctors should test levels of PFAS in people at high risk, report says More than just water It’s nearly impossible to avoid PFAS, experts say.Read more: Dangerous chemicals found in food wrappers at major fast-food restaurants and grocery chains, report says Government data Scientists at the Environmental Working Group used data from the EPA’s own monitoring programs — the National Rivers and Streams Assessment, which has been periodically testing stream conditions since 2008, and the Great Lakes Human Health Fish Fillet Tissue Study, which tests lake water every five years."