Perfluorooctane sulfonate (PFOS)

3M invented PFOS-based chemistry in the 1950s and commercialized Scotchgard fabric protector using it in 1956 [1]. PFOS was also the key component of aqueous film-forming foam (AFFF), the firefighting foam adopted by the US military in the 1970s after a series of catastrophic aircraft carrier deck fires in the 1960s demonstrated the need for a more effective foam. AFFF was used in training exercises and emergency responses at military bases for decades, soaking into soil and groundwater at thousands of installations [2]. By 2000, 3M knew that PFOS was present in the blood of virtually all Americans tested and was accumulating in wildlife worldwide. In a largely voluntary phase-out negotiated with the EPA, 3M began discontinuing PFOS production in 2000. But the contamination was already everywhere — in soil, groundwater, sediment, fish, and human blood [3]. More than 700 military installations have confirmed PFAS contamination in surrounding communities' drinking water.

Military base water contamination is the highest-concentration source: communities that draw drinking water from wells or aquifers near military installations often have PFOS concentrations orders of magnitude above the new EPA limits [1]. The EPA's 2024 drinking water rule set maximum contaminant levels for PFOS at 4 ppt — a level many base-adjacent communities were far exceeding. Beyond military contamination, PFOS is widely present in background drinking water at lower levels [2]. Food packaging and non-stick cookware are dietary routes. PFOS bioaccumulates in fish — especially freshwater sport fish from contaminated lakes and rivers — and in meat and dairy from animals in PFAS-contaminated areas. Stain-resistant fabric and carpet treatments based on PFOS release it into house dust, providing ongoing low-level exposure [3].

PFOS, like PFOA, persists in the human body for approximately 5 years (half-life) and accumulates with ongoing exposure [1]. Its health effects overlap with PFOA's: immunosuppression (reducing children's vaccine-generated antibody levels), thyroid disruption, elevated cholesterol, reproductive effects, and liver toxicity. PFOS is classified as possibly carcinogenic to humans (Group 2B) — the evidence is less complete than for PFOA but accumulating [2]. The immune system effects are particularly concerning: studies in children with higher PFOS exposures show significantly reduced antibody responses to vaccines, meaning their immunization is less effective. PFOS also disrupts thyroid hormone levels, affecting brain development in infants and metabolic regulation in adults [3].

People who live in communities near military bases, airports with AFFF use history, or industrial facilities that used PFOS-based products face the highest drinking-water exposures [1]. EWG maintains an interactive map of PFAS-impacted sites. Infants and young children who consume infant formula prepared with PFOS-contaminated water receive especially high doses relative to body weight [2]. People who regularly eat sport fish from contaminated waterways, or who consume dairy and meat from animals raised near PFAS-contaminated land, have dietary contributions. Workers who fought fires or conducted firefighting training using AFFF carry elevated body burdens.

Look up your community's water quality data using EWG's Tap Water Database at ewg.org — search by zip code to see reported PFAS levels [1]. If PFOS is detected above 4 ppt (or any level if you have an infant or are pregnant), install a certified reverse-osmosis system or certified point-of-use carbon block filter. Stainless steel water bottles and filtered water pitchers certified for PFAS removal (NSF/ANSI 58) are practical alternatives [2]. Reduce consumption of locally caught freshwater fish if your waterways are near PFAS contamination sources. Vacuum with a HEPA filter and wet-wipe surfaces to reduce PFAS-containing house dust. Avoid products labeled with "stain-resistant," "water-repellent," or "grease-resistant" finishes — choose PFAS-free alternatives for furniture, carpets, and cookware [3].