A family of chemicals — known as PFAS and responsible for marvels like Teflon and critical to the safety of American military bases — has now emerged as a far greater menace than previously disclosed.

The chemicals once seemed near magical, able to repel water, oil and stains.

By the 1970s, DuPont and 3M had used them to develop Teflon and Scotchgard, and they slipped into an array of everyday products, from gum wrappers to sofas to frying pans to carpets. Known as perfluoroalkyl substances, or PFAS, they were a boon to the military, too, which used them in foam that snuffed out explosive oil and fuel fires.

It’s long been known that, in certain concentrations, the compounds could be dangerous if they got into water or if people breathed dust or ate food that contained them. Tests showed they accumulated in the blood of chemical factory workers and residents living nearby, and studies linked some of the chemicals to cancers and birth defects.