Dr. Holsen is currently director of the Center for Air Resources Engineering and Science (CARES) and past co-director of Clarkson’s Center for the Environment (CEE). The focus of the Center for Air Resources Engineering and Science (CARES) is to provide a better and more complete scientific basis for air quality management including the understanding of the sources, transport, and chemistry that give rise to indoor and outdoor exposure to air pollutants including noise, their potential health and welfare effects, and ways in which these effects can be reduced or eliminated.
Evaluation of Current Use C6 AFFF: What Do They Really Contain?
INTRODUCTION: Aqueous film forming foam (AFFF) is a highly efficient fire suppressant agent used to extinguish flammable liquids that has been widely used at industrial and military sites. AFFF contains large concentrations of fluorinated surfactants including per- and polyfluoroalkyl substances (PFAS) which are persistent in the environment and associated with adverse health effects. In an effort to decease their persistence and toxicity, current AFFF formulations are being advertised as containing only C6 and smaller perfluorinated surfactants and low molecular weight polymers. To evaluate this claim and better characterize a currently available AFFF solution, AFFF Ansulite 6% (AFC-6MS-C) was obtained and analyzed using mass spectroscopy before and after oxidation using the total oxidizable precursor assay (TOP).
METHODS: Twelve perfluoroalkyl acids (PFAAs) and 10 precursor concentrations were measured in negative ionization mode using a UPLC-QToF-HRMS (Xevo G2-XS, Waters Corp.). All samples were spiked with 2 ng of labeled internal standards to allow for quantification using C-13 isotopic dilution methods. A detailed description of the analytical methods, QA procedures and individual detection limits have been published previously (Singh et al., 2019). Total oxidizable precursors (TOP) were measured using a modified persulfate oxidation method developed by Houtz and Sedlak (2012). Specifically, significantly higher concentrations of persulfate were required to oxidize all the precursors present.
RESULTS AND DISCUSSION: Analysing AFFF for PFAAs and precursors is difficult and requires significant dilutions so as not to saturate the instrument detector. These dilutions raise detection limits into the mg/L range. In the sample analysed, PFBA had the highest concentration (270 mg/L) followed by PFHxA (130 mg/L) (Figure 1). Measurable concentrations of >C6 acids were also found including PFHpA, PFOA, PFNA, PFOS, PFDA, and PFDS. Of these, PFOA and PFOS had the highest concentrations (71 and 42 mg/L, respectively). 6:2 FTS was the only precursor identified (at 130 mg/L). The TOP assay as developed by Houtz and Sedlak (2012) was only partially effective at oxidizing the precursors so increased doses and reaction times were used. Even after doses of up to 240 mM persulfate and reaction times of 6 hours concentrations of PFAAs and 6:2 FTS continued to increase indicating that higher doses and longer reaction times are needed to completely oxidize the precursors present. Although 6:2 FTS was the only precursors found, its increased concentration upon persulfate addition indicated there are significant amounts of other precursors present that can be oxidized to 6:2 FTS. Concentrations of individual PFAAs and precursors produced by oxidation with persulfate generally increased with increasing dose and reaction time. For the highest dose and longest reaction time (240 mM and 6 hrs) PFHxA was found at highest concentration (1290 mg/L) followed by shorter chain PFAAs, PFBA and PFPeA (520 and 360 mg/L, respectively). PFOA concentrations approximately doubled to 130 mg/L after oxidation.
CONCLUSIONS: Current formulations of AFFF were found to contain measureable concentrations of >C6 PFAAs and PFAA precursors. We are continuing these experiments with other suppliers and exploring other oxidation techniques and plasma destruction technologies for AFFF treatment.