Bioconcentration and toxicity of perfluoroalkyl substances (PFAS) in embryonic stages of the ecologically and commercially relevant Olive Flounder (Paralichthys olivaceus), and the zebrafish (Danio rerio) embryo model system.

Abstract

Polyfluoroalkyl substances (PFAS) are ubiquitous in aquatic habitats, and there are emerging concerns that these chemicals may pose risks to organisms in these ecosystems. The present study investigated bioconcentration and toxicity of PFAS including the "legacy" congener, perfluorooctanoic acid (PFOA), and seven long- and short-chain perfluoroether carboxylic acids (PFECA) in embryonic stages of both zebrafish (Danio rerio), as an established laboratory model, and Olive Flounder (Paralichthys olivaceus), as a relevant marine fish species. Bioconcentration factors were determined for both species with BCF values ranging from 22 to 1741 L kg^-1. At high exposure concentrations (i.e., 1 mg L^-1), BCF values were significantly higher for zebrafish compared to flounder. Notably, however, PFAS were also measured in untreated media used for both species, and at these lower concentrations (0.2 to 29 ng L^-1 and 0.4 to 9 ng L^-1, respectively) approaching environmentally relevant levels, calculated BCF values were significantly higher for flounder (215-1741 L kg^-1) compared to zebrafish (120-327 L kg^-1) embryos. At low exposure concentration (i.e., 1 µg L^-1), as well as in exposure to control media, BCF values were significantly correlated with chain length and octanol/water partition coefficients (i.e., log K_OW), suggesting a role of relative lipophilicity in uptake in both species. Median lethal concentrations (LC₅₀), and corresponding critical body residues (CBR), in the zebrafish embryo model, ranged from 0.05 to 50 mg L^-1, and 0.005 to 25 µmol g^-1, respectively, and significantly correlated with PFAS chain length. However, while acute toxicity for PFOA was similar between zebrafish and flounder (20 and 21 mg L^-1, respectively), no significant acute toxicity was observed for flounder embryos, over the same concentration range, and corresponding CBR values were, thus, significantly higher, for all PFECA. These findings suggest differences in both uptake and relative toxicity of PFAS in these two species. Phylogenetic differences with respect to molecular targets, as well as physicochemical factors (i.e., freshwater versus saltwater), in relation to uptake and toxicity, are discussed.