Sublethal Exposure of Per- and Polyfluoroalkyl Substances of Varying Chain Length and Polar Functionality Results in Distinct Metabolic Responses in Daphnia magna.

ABSTRACT

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent organic pollutants used in industrial applications because of their physicochemical properties, which results in their ubiquitous presence across environmental matrices. To date, legacy PFAS have been well studied; however, the concentration of alternative PFAS may exceed the concentration of legacy pollutants, and more information is needed regarding the sublethal toxicity at the molecular level of aquatic model organisms, such as Daphnia magna. Perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic acid (PFNA) are four widely detected PFAS alternatives of varying chain length and polar functionality that are quantified in aquatic environments. The present study examines the metabolic perturbations of PFAS with varying chemistries to D. magna using targeted mass spectrometry-based metabolomics. Daphnia were acutely exposed to sublethal concentrations of PFBA, PFHxA, PFHxS, and PFNA before the polar metabolite profile was extracted from single organisms. Multivariate analysis demonstrated significant separation between the sublethal concentrations of PFHxA, PFHxS, and PFNA relative to the controls; in sum, longer chain lengths demonstrated greater overall perturbations to the extracted metabolic profiles. Univariate statistics revealed significant perturbations in the concentrations of several amino acids, nucleotides/nucleosides, and neurotransmitters with exposure to PFAS. These metabolic perturbations are consistent with disruptions in energy metabolism (pantothenate and coenzyme A metabolism, histidine metabolism) and protein synthesis (aminoacyl-transfer RNA biosynthesis and amino acid metabolism), which were identified through biochemical pathway analysis. These results provide evidence that although PFAS chemistry (chain length and polar functional group) invokes unique metabolic responses, there is also an underlying toxic mode of action that is common with select PFAS exposure. Overall, the present study highlights the capabilities of environmental metabolomics to elucidate the molecular-level perturbations of pollutants within the same chemical class to model aquatic organisms, which can be used to prioritize risk assessment of substituted PFAS alternatives. Environ Toxicol Chem 2023;42242-256. © 2022 SETAC.