6:2 and 8:2 Fluorotelomer Alcohol Anaerobic Biotransformation in Digester Sludge from a WWTP under Methanogenic Conditions

Abstract

6:2 FTOH and 8:2 FTOH [FTOHs, F(CF2)nCH2CH2OH, n = 6, 8] are the principal polyfluorinated raw materials used to manufacture FTOH-based products, which may be released to WWTPs during their product life cycle. For the first time, anaerobic biotransformation of FTOHs and key biotransformation intermediates in WWTP digester sludge under methanogenic conditions was investigated. 6:2 FTOH was transformed to 6:2 FTCA, [F(CF2)6CH2COOH, 32-43 mol %], 6:2 FTUCA [F(CF2)5CF═CHCOOH, 1.8-8.0 mol %], and 5:3 acid [F(CF2)5CH2CH2COOH, 18-23 mol %] by day 90 and day 176 in two separate studies. 8:2 FTOH was transformed by day 181 to 8:2 FTCA (18 mol %), 8:2 FTUCA (5.1 mol %), and 7:3 acid (27 mol %). 6:2 and 8:2 FTOH anaerobic biotransformation led to low levels of perfluorohexanoic acid (PFHxA, ≤0.4 mol %) and perfluorooctanoic acid (PFOA, 0.3 mol %), respectively. 6:2 FTUCA anaerobic biotransformation led to a newly identified novel transient intermediate 3-fluoro 5:3 acid [F(CF2)5CFHCH2COOH] and 5:3 acid, but not 5:2 sFTOH [F(CF2)5CH(OH)CH3] and α-OH 5:3 acid [F(CF2)5CH2CH(OH)COOH], two precursors leading to PFPeA (perfluoropentanoic acid) and PFHxA. Thus, FTOH anaerobic biotransformation pathways operated by microbes in the environment was likely inefficient at shortening carbon chains of FTOHs to form PFCAs (perfluorinated carboxylic acids). These results imply that anaerobic biotransformation of FTOH-based products may produce polyfluorinated acids, but is not likely a major source of PFCAs detected in anaerobic environmental matrices such as anaerobic digester sludge, landfill leachate, and anaerobic sediment under methanogenic conditions.

Methodology for studying biotransformation of polyfluoroalkyl precursors in the environment

“…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]. A limited number of rational molecular compositions by a combination of C, H, F, O, N elements could be further obtained with a mass accuracy of less than 5 ppm [27,39,58].…”

“…The elemental composition of cleaved functional groups (e.g., consecutive loss of CO2+2HF and HF) in given pseudo-molecular ions by collisioninduced dissociation (CID) could be accurately measured by HRMS [39]. Besides, precursor-ion scan can be used to search for transformation products structurally related to the parent compound.…”

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

“…6:2 FTI (98% purity) was obtained from Alfa Aesar (WardHill, MA). Other fluorinated metabolite standards used for quantitative analysis were the same as previously described with 96% or better purity (Ruan et al, 2013;Zhang et al, 2013 Pooled liver microsomes of male SD and WH rats, respectively, were incubated in 10 mL serum bottles containing 2 mL reaction media at 37°C under dark. Liver microsomes from male rats were able to metabolize 8:2 FTOH to form various metabolites (Nabb et al, 2007).…”

“…The LC/MS/MS quantification method for the target metabolites was similar to a previously described method (Zhang et al, 2013) with some modifications. In brief, the LC/MS/MS system consisted of a Waters (Milford, MA) Quattro Micro triple quadrupole mass spectrometry coupled with a Waters 2795 HPLC module.…”

“…For WH microsomes, 5:3 Uacid accounted for 16 mol% in NADPH-addition system versus 1.0 mol% in NADPH-regenerating system. The greater amounts of 5:3 Uacid indicate that the reducing energy source, NADPH, was nearly depleted in NADPH-addition system, since converting 5:3 Uacid to 5:3 acid needs reducing energy (Zhang et al, 2013). On the other hand, NADPH-regenerating system is more effective at regenerating NADPH from NADP via glucose oxidase electron-and-proton shuttle system, providing sufficient NAPPH to reduce 5:3 Uacid to 5:3 acid.…”