In Vitro Metabolism of 8-2 Fluorotelomer Alcohol: Interspecies Comparisons and Metabolic Pathway Refinement

Abstract

The detection of perfluorinated organic compounds in the environment has generated interest in their biological fate. 8-2 Fluorotelomer alcohol (8-2 FTOH, C(7)F(15)CF(2)CH(2)CH(2)OH), a raw material used in the manufacture of fluorotelomer-based products, has been identified in the environment and has been implicated as a potential source for perfluorooctanoic acid (PFOA) in the environment. In this study, the in vitro metabolism of [3-(14)C] 8-2 FTOH and selected acid metabolites by rat, mouse, trout, and human hepatocytes and by rat, mouse, and human liver microsomes and cytosol were investigated. Clearance rates of 8-2 FTOH in hepatocytes indicated rat > mouse > human >/= trout. A number of metabolites not previously reported were identified, adding further understanding to the pathway for 8-2 FTOH metabolism. Neither perfluorooctanoate nor perfluorononanoate was detected from incubations with human microsomes. To further elucidate the steps in the metabolic pathway, hepatocytes were incubated with 8-2 fluorotelomer acid, 8-2 fluorotelomer unsaturated acid, 7-3 acid, 7-3 unsaturated acid, and 7-2 secondary fluorotelomer alcohol. Shorter chain perfluorinated acids were only observed in hepatocyte and microsome incubations of the 8-2 acids but not from the 7-3 acids. Overall, the results indicate that 8-2 FTOH is extensively metabolized in rats and mice and to a lesser extent in humans and trout. Metabolism of 8-2 FTOH to perfluorinated acids was extremely small and likely mediated by enzymes in the microsomal fraction. These results suggest that human exposure to 8-2 FTOH is not expected to be a significant source of PFOA or any other perfluorocarboxylic acids.

Uptake, Translocation, and Metabolism of 8:2 Fluorotelomer Alcohol in Soybean (Glycine max L. Merrill)

“…The finding of 8:2 FTOH adsorbed to the rubber plug also indicated the evaporation. This result was consistent with those obtained by Wang et al 35 and Nabb et al, 16 who found that 8:2 FTOH evaporated from the aqueous fraction and migrated into the headspace in their experimental systems. No significant difference was found in soybean dry weights between those of the whole soybean systems and the blank controls at each time point (two-tailed unpaired Student's t test, P > 0.05, SI Figure S2 Table S10).…”

Methodology for studying biotransformation of polyfluoroalkyl precursors in the environment

“…To obtain knowledge on the specific microorganisms responsible for the polyfluoroalkyl precursor biotransformation processes, microbial consortium or pure bacterial cultures from soil and sewage sludge were isolated and used [30][31][32]. To elucidate the metabolism mechanism and possible adverse effects due to covalent binding of unsaturated polyfluoroalkyl intermediate metabolites to biological macromolecules, in-vitro bioassays were performed using hepatocytes, cytosol fractions and liver microsomes from mammalian and fish species [19,21]. In-vivo dietary exposure studies were also conducted to evaluate uptake, metabolism and elimination dynamics of PFASs in Sprague-Dawley rats and juvenile rainbow trout [20,33,34].…”

“…Fluorotelomer aldehydes (FTALs) are short-lived initial intermediates of fluorotelomer-based product transformation, and could be quickly oxidized into fluorotelomer carboxylic acids (FTCAs). 2,4-Dinitrophenylhydrazine (DNPH) was frequently used as the derivatization reagent for the identification of FTALs in in-vitro animal studies by mixing organic-sample extracts with DNPH solution in hydrochloric acid prior to LC-MS analysis [19][20][21]. The derivatization step was also applied to microbial incubation systems to identify 8:2 FTAL and 5:3 ketone aldehyde in 8:2 FTOH dosed soil and 6:2 FTOH dosed mixed bacterial culture, respectively [29,30].…”

“…In accurate-mass measurement, selected suspect-ion monitoring or retrospective screening of the full-scan spectrum are effective in confirming plausible analytes without using authentic standards. For example, typical phase II metabolites (glutathione, glucuronide and sulfate conjugates) of polyfluorinated alcohols, aldehydes and unsaturated telomer acids could easily be observed once deprotonated molecular ions of corresponding conjugates were monitored [19][20][21]. 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].…”

“…Elevated PFAS concentrations found in effluents compared with those in influents may further indicate contributions of polyfluorinated-precursor biodegradation in the WWTPs [18]. Covalent binding of certain intermediate transformation products (e.g., fluorotelomer unsaturated aldehydes or carboxylic acids) to nucleophilic amino acids and proteins, and formation of conjugated Phase II metabolites are also possible biological fates of polyfluoroalkyl precursors in mammals and fish [19][20][21].…”