Citation:

Kolanczyk, R., M. Saley, J. Serrano, S. Daley, AND M. Tapper. PFAS Biotransformation Pathways: A Species Comparison Study. Toxics. MDPI, Basel, Switzerland, 11(1):74, (2023). https://doi.org/10.3390/toxics11010074

Impact/Purpose:

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have taken on a major emphasis of worldwide concern by the international regulatory community as reflected in an explosion of recent scientific literature. PFAS are found all over the planet, do not break down in the environment, can move through soils and contaminate drinking water sources, and build up (bioaccumulate) in humans and wildlife. Toxicological concerns include various cancers, growth and development, reproduction, thyroid function, and impairment of both the immune system and liver function. While the perfluoroalkylcarboxylic acids and sulfonic acids are persistent chemicals presumed not capable of further biotransformation there is much to be learned about the PFAS precursors which may eventually breakdown to the perfluoroalkyl acids. Transitional metabolites and rate of formation of intermediates potentially play a large role in risk assessment evaluation, for example if the intermediates happen to exhibit greater toxicological effects. This research seeks to characterize the metabolites formed and compare metabolism pathways across species to better understand similarities and differences in biotransformation reactions that may lead to enhanced toxicity. Results from these efforts can then serve as a basis for predicting metabolism for untested species.

Description:

Limited availability of fish metabolic pathways for PFAS may lead to risk assessments with inherent uncertainties based only upon the parent chemical or the assumption that the biodegradation or mammalian metabolism map data will serve as an adequate surrogate. A rapid and transparent process, utilizing a recently created database of systematically collected information for fish, mammals, poultry, plant, earthworm, sediment, sludge, bacteria, and fungus using data evaluation tools in the previously described metabolism pathway software system MetaPath, is presented. The fish metabolism maps for 10 PFAS, heptadecafluorooctyl(tridecafluorohexyl)phosphinic acid (C6/C8 PFPiA), bis(perfluorooctyl)phosphinic acid (C8/C8 PFPiA), 2-[(6-chloro-1,1,2,2,3,3,4,4,5,5,6,6-dodecafluorohexyl)oxy]-1,1,2,2-tetrafluoroethanesulfonic acid (6:2 Cl-PFESA), N-Ethylperfluorooctane-1-sulfonamide (Sulfuramid; N-EtFOSA), N-Ethyl Perfluorooctane Sulfonamido Ethanol phosphate diester (SAmPAP), Perfluorooctanesulfonamide (FOSA), 8:2 Fluorotelomer phosphate diester (8:2 diPAP), 8:2 fluorotelomer alcohol (8:2 FTOH), 10:2 fluorotelomer alcohol (10:2 FTOH), and 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), were compared across multiple species and systems. The approach demonstrates how comparisons of metabolic maps across species are aided by considering the sample matrix in which metabolites were quantified for each species, differences in analytical methods used to identify metabolites in each study, and the relative amounts of metabolites quantified. Overall, the pathways appear to be well conserved across species and systems. For PFAS lacking a fish metabolism study, a composite map consisting of all available maps would serve as the best basis for metabolite prediction. This emphasizes the importance and utility of collating metabolism into a searchable database such as that created in this effort.

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