Curious, I looked it up and discovered that it's in the class of chemicals that were manufactured by 3M for use in Scotchguard, among other consumer products and applications. Perfluorooctane sulfonate (PFOS) received a flurry of attention around 2000, when studies of its effects on animal and human health showed that it was bioaccumulative (meaning that it accumulates in body tissue, especially in fat where it can linger for years), persistent, and toxic to mammals.