At the molecular level, they are made up of a chain of linked carbon and fluorine atoms, forming a very strong bond that does not degrade easily. The two most common and studied PFAS are perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Other types of PFAS exist and are often found in combination. While their use has been discontinued in many forms of manufacturing, they are suspected to be present at some level in the blood of nearly every American.  Acute and chronic exposure is linked to cancer, liver damage, weakened immunity, risks to pregnant women and babies and other health problems. PFAS can also accumulate over time in the environment and human body, compounding risks. “The science is clear…long term exposure from PFAS is linked to significant health impacts,” Jennifer McLain of the Environmental Protection Agency said during a recent webinar explaining a proposal to regulate PFAS in drinking water.