A new study that checked American women's breast milk for PFAS contamination detected the toxic chemical in all 50 samples tested, and at levels nearly 2,000 times higher than the level some public health advocates advise is safe for drinking water. "These harmful chemicals are contaminating what should be nature's perfect food," said Erika Schreder, a co-author. PFAS, or per and polyfluoroalkyl substances, are a class of about 9,000 compounds that are used to make products like food packaging, clothing and carpeting water and stain resistant. They are called "forever chemicals" because they do not naturally break down and have been found to accumulate in humans. They are linked to cancer, birth defects, liver disease, thyroid disease, plummeting sperm counts and a range of other serious health problems. The peer-reviewed study ... found PFAS at levels in milk ranging from 50 parts per trillion (ppt) to more than 1,850ppt. The federal Agency for Toxic Substances and Disease Registry ... recommends as little as 14ppt in children's drinking water. Studies of older children and adults have linked the chemicals to hormonal disruptions and suggests PFAS harm the immune system. Among steps that the authors recommend pregnant women and mothers take to protect themselves are avoiding greaseproof carryout food packaging, stain guards like ScotchGard, waterproof clothing that uses PFAS, and cooking products with Teflon or similar non-stick properties.