Citation:

Kolanczyk, R., L. Roach, M. Saley, M. Tapper, S. Daley, AND J. Serrano. PFAS biotransformation pathways (v.3.3.1 and v.3.4.0) in MetaPath application (v.5.3.1.16). U.S. Environmental Protection Agency, Washington, DC, 2022. https://doi.org/10.23645/epacomptox.25122113

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 perfluoroalkyl carboxylic 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 ecological risk assessments with inherent uncertainties based upon the parent chemical only or the assumption that the biodegradation or mammalian metabolism map data will serve as an adequate surrogate. A MetaPath database of 302 PFAS maps was compiled from the open literature. The database was created under version.3.3.1 and 3.4.0 with MetaPath application version.5.3.1.16. It contains metabolism and biodegradation pathways for a diverse set of species or test systems covering 97 different PFAS parent chemicals. Fish species covered in the database were rainbow trout, perch, carp, medaka, zebrafish, loach, gudgeon, barbel, turbot, and gilthead bream. The mammalian species including human, monkey, dog, sheep, pig, rat, mouse, beluga whale, ringed seal, and polar bear were compiled. Metabolic maps for the plant species carrot, wheat, pumpkin, alfalfa, soybean, lettuce, radish, mung bean, corn, and ryegrass were found. Other species such as mussels, earthworms, and chicken were also provided. Biodegradation was reported in aerobic and anaerobic soil, sediment, and wastewater treatment plant sludge as well as bacterial and fungal microbes. The process presented herein represents a rapid and transparent approach to comparing metabolism across species using MetaPath and associated evaluation tools built to facilitate analyses of metabolic pathways. Further, the compilation of biotransformation pathways in an organized structural database with supporting data evaluation tools will serve to support risk assessment and provide intrinsic data to support development of metabolic simulators.

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