[10] In 1999, the U.S. Environmental Protection Agency began investigating perfluorinated compounds after receiving data on the global distribution and toxicity of PFOS, the key ingredient in Scotchgard.

[18] Telomerisation involves constructing the PFOS molecule using short chain (often 2-carbon) precursors and adding a sulfonate group as a final step.

2000 teenagers from 9 European countries with most samples collected in years 2016-2018 found higher blood concentrations of several PFOS’s in those, who consumed more seafood, eggs or offal, as well as in those from North and West (versus the South and East) Europe.

[29] Much higher levels of blood PFOS (12,830 ppb) have been reported in people with occupational exposure [30]—or possibly 1,656 parts per billion[31]—in a consumer.

[34] PFOS has been detected in U.S. freshwater fish,[35][36] as well as in municipal wastewater[37] and drinking water samples,[38] worldwide, at concentrations ranging between few ng/L and some μg/L.

A variety of wildlife species have had PFOS levels measured in egg, liver, kidney, serum, and plasma samples and some of the highest recorded values as of January 2006 are listed below.

[44] There has been some evidence to suggest that PFOS levels in pregnant women have been associated with preeclampsia, preterm labor, low birth weight and gestational diabetes.

[48] Additionally, PFOS exposure has been shown to be related to the downregulation genes corresponding to growth factors, pregnancy-related signal transducers, and maternal hormones.

[53] The Agency for Toxic Substances and Disease Registry (ATSDR) concluded that breastfeeding benefits continue to outweigh potential risks associated with PFOS in breastmilk.

[63] Serum levels of PFOS were found to be associated with increased risk of chronic kidney disease in the general US population.

[64] "This association was independent of confounders such as age, sex, race/ethnicity, body mass index, diabetes, hypertension, and serum cholesterol level.

[46] As of November 2023, the International Agency for Research on Cancer (IARC) has classified PFOS as possibly carcinogenic to humans (Group 2b) based on “strong” mechanistic evidence.

[67][68] PFOS affects the immune system of male mice at a blood serum concentration of 91.5 parts per billion, raising the possibility that highly exposed people and wildlife are immunocompromised.

[4] Originally, parties agreed on acceptable proposes (time-unlimited exemptions) for the following uses—in addition to a range of specific exemptions (time-limited):[70] In 2019, it was decided to only keep one acceptable purpose:[71] In 2023, the Government of Canada is considering addressing PFAS as a class rather than as individual substances or in smaller groups.

[73] However, PFOS use for industrial applications (e.g. photolithography, mist suppressants for hard chromium plating, hydraulic fluids for aviation) was exempted.

[75] In 2018 the State of Michigan established a legally enforceable groundwater cleanup level of 70 ppt for both PFOA and PFOS.

[76] In 2020 the Michigan Department of Environment, Great Lakes, and Energy (EGLE) adopted stricter drinking water standards in the form of maximum contaminant levels (MCLs), lowering acceptable levels from the 2018 enforceable groundwater cleanup levels of 70 ppt to 8 ppt for PFOA and 16 ppt for PFOS and adding MCLs for 5 previously unregulated PFAS compounds PFNA, PFHxA, PFHxS, PFBS, and HFPO-DA.

[80] In October 2021 the EPA proposed to designate PFOA and PFOS as hazardous substances in its PFAS Strategic Roadmap.

[81][82] In September 2022 the EPA proposed to designate as hazardous substances under the Superfund Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA).