Perfluoroalkyl acids (PFAAs) are a subset of the broad group of poly- and perfluoroalkyl substances (PFASs) that have received significant attention due to their environmental persistence and mobility. These compounds have historically been released into the environment through the use of aqueous film forming foams (AFFFs). In addition to some AFFF formulations using PFAAs directly, many AFFFs also contain a wide variety of precursor compounds capable of transforming into PFAAs. Due to a lack of commercially available analytical standards, studying PFAA precursor compounds is challenging. As a result, their reactivity and environmental fate is poorly understood. This study sought to investigate direct and indirect photochemical transformations of PFAA precursors contained in AFFF mediated by natural sunlight. Solutions containing dilute AFFF, bicarbonate and either nitrate or Suwanee River Humic Acid (SRHA) were subjected to natural sunlight at 39.7° N for two weeks. Reactivity and transformation products were assessed using liquid chromatography quadrupole time of flight mass spectrometry. Perfluorocarboxylates (PFCAs), a group of PFAAs, were observed to be the major transformation products via both indirect and direct photolysis pathways. Irradiation of AFFF in humic acid solutions showed the largest formation of PFCAs. The major PFAA precursors degraded are those of the N-dimethyl ammonio propyl perfluoralkane sulfonamido propanoic acid, or AmPr-FASA-PrA family. A relationship between degradation of AmPr-FASA-PrA compounds and their hydrophobicity in humic acid solutions suggests that microheterogeneous production of reactive transients aids in PFAA precursor degradation.

Sunlight- mediated photochemical transformations of perfluoroalkyl acid precursors in aqueous film forming foams

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.