Biodegradation of Polyfluoroalkyl Phosphates as a Source of Perfluorinated Acids to the Environment

Abstract

Wastewater treatment plants (WWTPs) have been identified as a major source of perfluorocarboxylates (PFCAs) to aqueous environments. The observed increase in PFCA mass flows from WWTP influent to effluent suggests the biodegradation of commercial fluorinated materials within the WWTP. Commercial fluorinated surfactants are used as greaseproofing agents in food-contact paper products as well as leveling and wetting agents. As WWTPs are likely the major fate of these surfactants, their biodegradation may be a source of PFCA production. One class of commercial surfactants, the polyfluoroalkyl phosphates (PAPs), have been observed in WWTP sludge. While PAPs have been shown to degrade into PFCAs in a rat model, the present study investigates their microbial fate to determine whether the biodegradation of PAPs within a WWTP-simulated system will contribute to the load of PFCAs released. PAPs are applied commercially in mixed formulations of different chain lengths and substitution at the phosphate center. The effect of chain length and phosphate substitution on the biodegradation of PAPs was investigated by incubating mixtures of 4:2, 6:2, 8:2, and 10:2 monosubstituted PAPs (monoPAPs) in an aerobic microbial system and by separately incubating the 6:2 monoPAP and 6:2 disubstituted PAP (diPAP) for 92 days. Headspace sampling revealed production of the fluorotelomer alcohols (FTOHs) from the hydrolysis of the PAP phosphate ester linkages. Analysis of the aqueous phase revealed microbial transformation of the PAPs to the final PFCA products was possible. The majority of the oxidation products observed were consistent with previous investigations that have suggested fluorotelomer precursor compounds degrade predominantly via a beta-oxidation-like mechanism. However, in this study, the detection of odd-chain PFCAs suggests that other pathways may be important. The present study demonstrated microbially mediated biodegradation of PAPs to PFCAs. This observation, together with the diPAP concentrations observed in WWTP sludge, suggest PAPs-containing commercial products may be a significant contributor to the increased PFCA mass flows observed in WWTP effluents.

Methodology for studying biotransformation of polyfluoroalkyl precursors in the environment

“…One or two C18 SPE cartridges were inserted into the headspace as the conduit and to capture volatile parent and potential volatile transformation products [25,27]. To mimic continuous exchange of PFASs in surface soil or active sludge with surrounding air, flow-through systems using purge-and-trap methods were used to study 6:2 FTOH and 6:2 polyfluoroalkylphosphate biotransformation [26,28]. Wang et al [29] found that the molar yield of perfluorooctanoic acid (PFOA) in the flowthrough system was only half of that in semi-static closed bottles.…”

“…In semi-static systems, the headspace was usually purged through C 18 SPE cartridges at the beginning of sample preparation to trap volatile precursors and transformation products [25,27]. XAD adsorbents were also chosen to monitor the formation of FTOHs from the degradation processes of mono-PAPs and di-PAPs by aerobic microbes from a WWTP in flow-through systems [28]. Meanwhile, polydimethylsiloxane solid-phase microextraction materials were expediently used in enrichment and identification of novel transformation intermediates and products in headspace and to quantify the gas-fraction concentrations of analytes [27,40,41].…”

C6-Perfluorinated Compounds: The New Greaseproofing Agents in Food Packaging

“…However, unlike the longchain PFCs, the C6-PFCs do not appear to be used in the manufacture of non-stick cookware. It should also be noted that long-chain PFCs usually comprise a mixture of fluorotelomers varying in perfluorinated carbon length from C6 to C12 [2]; additionally, these mixed-chain-length telomers can be transformed in mammals [7] and in the environment [8,9] to PFHxA and to perfluoroheptanoate (PFHpA). As such, it should be emphasized that levels of PFHxA measured in various media, including human bodily fluids and tissues, could originate from a variety of sources, including C6-and long-chain PFCs and FTOHs, and the presence of PFHxA in these media can only rarely be directly extrapolated to direct exposure to PFHxA itself.…”

6:2 Fluorotelomer iodide in vitro metabolism by rat liver microsomes: Comparison with [1,2-14C] 6:2 fluorotelomer alcohol

“…In addition, 6:2 FTI biotransformation in soil also yielded PFHpA (16 mol%) via a pathway still yet to be elucidated (Ruan et al, 2013). Low levels of PFHpA (<1.5 mol%) were also observed along with PFHxA and 5:3 acid in activated sludge dosed with 6:2 fluorotelomer phosphates (Lee et al, 2010). Similarly, PFPeA, PFHxA, and 5:3 acid were observed during microbial biotransformation of 6:2 FTOH-based ethoxylates and 6:2 fluorotelomer sulfonic acid [6:2 FTSA, F(CF2) 6 CH 2 CH 2 SO 3 H] (Frömel and Knepper, 2010;Wang et al, 2011).…”