Aerobic Soil Biotransformation of 6:2 Fluorotelomer Iodide

Abstract

6:2 FTI [F(CF 2 ) 6 CH 2 CH 2 I] is a principal industrial raw material used to manufacture 6:2 FTOH [F(CF 2 ) 6 CH 2 CH 2 OH] and 6:2 FTOH-based products and could enter aerobic environments from possible industrial emissions where it is manufactured. This is the first study to assess 6:2 FTI aerobic soil biotransformation, quantify transformation products, and elucidate its biotransformation pathways. 6:2 FTI biotransformation led to 6:2 FTOH as a key intermediate, which was subsequently biotransformed to other significant transformation products, including PFPeA [F-(CF 2 ) 4 COOH, 20 mol % at day 91], 5:3 acid [F-(CF 2 ) 5 CH 2 CH 2 COOH, 16 mol %], PFHxA [F(CF 2 ) 5 COOH, 3.8 mol %], and 4:3 acid [F(CF 2 ) 4 CH 2 CH 2 COOH, 3.0 mol %]. 6:2 FTI biotransformation also led to a significant level of PFHpA [F(CF 2 ) 6 COOH, 16 mol % at day 91], perhaps via another putative intermediate, 6:2 FTUI [F(CF 2 ) 6 CHCHI],whose molecular identity and further biotransformation were not verified because of the lack of an authentic standard. Total recovery of the aforementioned per-and polyfluorocarboxylates accounted for 59 mol % of initially applied 6:2 FTI by day 91, in comparison to 56 mol % when soil was dosed with 6:2 FTOH, which did not lead to PFHpA. Thus, were 6:2 FTI to be released from its manufacture and undergo soil microbial biotransformation, it could form PFPeA, PFHpA, PFHxA, 5:3 acid, and 4:3 acid in the environment.

Methodology for studying biotransformation of polyfluoroalkyl precursors in the environment

“…Aeration is achieved by pumping ambient air into the headspace when the oxygen content is below 10%. 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].…”

“…For volatile precursors, such as FTOHs, FOSAs and FOSEs, with the tendency to move into the headspace, concentration procedures were performed over long-term incubation periods [40,41]. 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].…”

“…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].…”

“…Negative electrospray ionization (ESI) was the most suitable LC-MS interface, and anionic PFASs were obtained as the deprotonated ([M-H] -) ions. Pre-column formation of analyte adducts by adding additives to the LC mobile phases, such as acetate-adducts ([M+59] -) of FTOHs, sFTOHs and FT ketones, could avoid LC-peak broadening and offer sufficient sensitivity for the neutral FT alcohols and ketones (instrument detection limits, IDLs: 0.14-0.22 ng on column) along with anionic PFCAs and PFSAs (IDLs: 4.0-42 pg on column) [27,29,30]. Moreover, LC-atmospheric pressure photoionization (APPI)-MS proved to be effective in direct ionization of FTOHs and FOSAs with excellent IDLs less than 1 pg on column [53].…”

“…When searching for plausible unknown metabolites without a priori information, exact mass filtering is also one principal step in the so-called "non-target screening" strategy [57]. As the accurate mass of fluorine (m/z = 18.998) is very close to its nominal mass, mass-defect filtration (-50 to +10 mDa) of nominal masses could eliminate the majority of irrelevant information in the full-scan MS spectrum [27]. Comparison of differences in full-scan chromatograms of paired live and matrix samples could also help find signals that might represent potential transformation products that existed in live samples only [38].…”