Despite years of work in environmental cleanup, PFASs remain a serious problem. PFASs are chemicals commonly used in fire-fighting foams, but also in manufacturing to make products more stain-resistant, waterproof and/or nonstick. PFASs are harmful to humans and particularly persistent in the environment due to the strong carbon-fluorine bonds.

PFASs are usually classified into two major groups; perfluorinated sulphonic acids (PFSAs) and perfluorinated carboxylic acids (PFCAs). Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are the two perfluoroalkyl (PFAAs) that have received the most attention due to their bioaccumulation potential, persistence, toxicity, and ubiquitous presence in the environment. PFOS was shortlisted as a Persistent Organic Pollutant (POP) by the Stockholm on Persistent Organic Pollutants (POPs) in 2009, while PFOA was anticipated to be a likely carcinogen by the United States Environmental Protection Agency (USEPA).  In 2009, the USEPA established provisional health advisory (PHA) levels drinking water for PFOA and PFOS at 0.4 and 0.2 µg/L, respectively (USEPA, 2009). In May 2016, USEPA released a lifetime health advisory level for combined concentrations of PFOA and PFOS of 0.07 μg/L (parts per trillion) (USEPA, 2016a). Table 1 shows the most common PFASs, their molecular weight, and common acronyms.

PFASs Acronyms Molecular Weight (g/mol) Carbon Chain Length(n) Formula
Trifluoracetic acid TFA 114.02 2 CF3COOH
Perfluoropropanoic PFPrA 164.03 3 C2F5COOH
Perfluorobutanoic acid PFBA 214.03 4 C3F7COOH
Perfluorobutanesulfonate PFBS 300.10 4 C4HF9SO3
Perfluoropentanoic acid PFPeA 264.05 5 C4F9COOH
Perfluorohexanoic acid PFHxA 314.05 5 C5F11COOH
Perfluorohexanesulfonate PFHxS 400.11 6 C6HF13SO3
Perfluoroheptanoic acid PFHpA 364.06 7 C6F13COOH
Perfluorooctanoic acid PFOA 414.07 8 C7F15COOH
Perfluorooctanesulfonate PFOS 500.13 8 C8HF17SO3

Approximately 100,000 tons of PFASs are estimated to be present in the groundwater and drinking water across the country. None of the conventional and advanced treatments available today can degrade both PFOA and PFOS. These compounds can thus only be physically removed from water via filtration or adsorption, which are prohibitively expensive.