Per- and poly-fluoroalkyl substances (PFAS) present one of the most complex environmental health challenges of the twenty-first century. Used in nonstick and water-resistant coatings since the 1950s, PFAS are now woven into the fabric of contemporary consumer life. Mobile, persistent, toxic, and prone to bioaccumulation, PFAS have been dubbed “forever chemicals,” a legacy pollutant that will be with us for generations. The frequent discovery of PFAS contamination in recent years forces communities to confront the hidden threats of once proud industrial pasts, revalued as toxic heritage. To illustrate, this chapter traces three histories of contamination related to perfluorooctane sulfonate (PFOS), one of the first PFAS substances commercialized on a mass scale. PFOS was originally in Scotchgard, a fabric coating made by the 3M company, used on iconic brands such as Hush Puppies shoes. It was also a crucial component in the development of aqueous film-forming foams to suppress oil fires. Each of these products reveals how the discovery of PFAS contamination forces a reinterpretation of the past and prompts a new orientation towards the future, with toxic heritage signifying an “emergent presence” that informs the lived experience of PFAS toxicity.