Perfluorooctanoic acid dominates the molecular-level effects of a mixture of equal masses of perfluorooctanoic acid and perfluorooctane sulfonic acid in earthworm.

Per- and polyfluoroalkyl substances (PFAS) are an important class of emerging contaminants in the environment. Most studies on the impact of PFAS mixtures considered phenotypic endpoints, which may not adequately reflect the sublethal effects on organisms. To fill this knowledge gap, we investigated the subchronic impact of environmentally relevant concentrations of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)-as individual compounds and a mixture (PFOS+PFOA)-on earthworm (Eisenia fetida), using phenotypic and molecular endpoints. PFAS decreased the survival (12.2-16.3%), biomass (9.0-9.8%), and reproduction (15.6-19.8%) of E. fetida after 28 d of exposure. The bioaccumulation of PFOS after 28 d increased (from 2790.7 ng/g-dw to 5224.9 ng/g-dw) while that of PFOA decreased (from 780.2 ng/g-dw to 280.5 ng/g-dw) when E. fetida was exposed to the mixture compared to the individual compounds. These bioaccumulation trends were partly attributed to changes in the soil distribution coefficient (Kd) of PFOS and PFOA when present in the mixture. Eighty percent of the (p and FDR < 0.05) altered metabolites after 28 d were similarly perturbed by both PFOA and PFOS+PFOA. The pathways dysregulated are related to the metabolism of amino acids, energy, and sulfur. We showed that PFOA dominates the molecular-level impact of the binary PFAS mixture.