Per- and polyfluoroalkyl substances (PFAS)-free aqueous film forming foam formulations: Chemical composition and biodegradation in an aerobic environment

Abstract

Per- and poly-fluoroalkyl substances (PFAS) have been historically used in fire-suppression activities, including aqueous film-forming foam (AFFF), given their unique structures and characteristics. However, the same properties that make them durable, resistant, and valuable also make them persistent, bioaccumulative, and toxic. This has led to recent investigations on alternative PFAS-free AFFF formulations for suppression of hydrocarbon-based fires. Such foams should contain certain classes of chemicals to remain effective, while being more environmentally friendly; part of the latter involves thoroughly characterizing the constituents and performing necessary biodegradability and toxicity studies. As part of the Department of Defense’s Strategic Environmental Research and Development Program (SERDP), we performed comprehensive constituents’ characterization and assessed the biodegradability of seven PFAS-free AFFF and a reference PFAS-based AFFF. We discovered that most of PFAS-free formulations share similar constituents with similar biodegradability through a 28-day reaction period. In PFAS-based AFFF, 4:2 and 6:2 fluorotelomer sulfonates (6:2 FTS) were identified with 6:2 FTS concentration at ∼ 9000 ng/mL. In biodegradation studies, the concentrations of 4:2 FTS and 6:2 FTS decreased while generating some perfluoroalkyl acids (PFCAs). These results increase the current knowledge on the biodegradability of AFFF alternatives but also highlight the need for future efforts on development of novel PFAS-free AFFF formulations that are more biodegradable than PFAS-based AFFF.