PFAS chemicals were darlings of chemical-industry leaders like 3M and DuPont for much of the 20th century following their discovery in the 1930s. PFAS were championed for their abilities to fight grease (Teflon) and repel water (Gore-Tex and Scotchgard). They were also used to make a firefighting foam used at military bases around the country.

But waste dumped from chemical-manufacturing plants can contaminate groundwater with PFAS chemicals, and they can also seep into lakes and other freshwater sources after firefighting foam gets used. PFAS are extremely persistent, so if they leech out of household products like cooking pans