Does salinity mediate the toxicity of perfluorooctanesulfonic acid (PFOS) in an estuarine fish?

Perfluorooctanesulfonic acid (PFOS) is detected in estuarine environments, where salinity levels fluctuate regularly. We investigated the effects of salinity on the toxicity of PFOS in embryos and larvae of Cyprinodon variegatus. We crossed six PFOS treatments (0, 1-10,000 µg/L) with two salinities (10, 30 ppt). Larvae exposed to the highest concentration of PFOS under high salinity accumulated over twice the amount of PFOS compared to larvae maintained under low salinity. Embryonic survival was unaffected by PFOS, salinity, or their interaction. PFOS delayed time to hatch and increased salinity reduced time to hatch regardless of PFOS treatment; however, no salinity by PFOS interactions were observed. Conversely, PFOS and salinity interacted in the larval stage, with decreased survival at 30 ppt salinity. This is one of the first studies evaluating interactive effects of PFOS and high salinity and highlights the importance of assessing PFAS toxicity across life stages.

Toxicities of Legacy and Current-Use PFAS in an Anuran: Do Larval Exposures Influence Responses to a Terrestrial Pathogen Challenge?

Legacy polyfluoroalkyl substances (PFAS) [perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA)] are being replaced by various other fluorinated compounds, such as hexafluoropropylene oxide dimer acid (GenX). These alternatives are thought to be less bioaccumulative and, therefore, less toxic than legacy PFAS. Contaminant exposures occur concurrently with exposure to natural stressors, including the fungal pathogen Batrachocytrium dendrobatidis (Bd). Despite evidence that other pollutants can increase the adverse effects of Bd on anurans, no studies have examined the interactive effects of Bd and PFAS. This study tested the growth and developmental effects of PFOS, PFOA, and GenX on gray treefrog (Hyla versicolor) tadpoles, followed by a Bd challenge after metamorphosis. Despite PFAS exposure only occurring during the larval stage, carry-over effects on growth were observed post metamorphosis. Further, PFAS interacted with Bd exposure to influence growth; Bd-exposed animals had significantly shorter SVL [snout-vent length (mm)] with significantly increased body condition, among other time-dependent effects. Our data suggest that larval exposure to PFAS can continue to impact growth in the juvenile stage after exposure has ended. Contrary to predictions, GenX affected terrestrial performance more consistently than its legacy congener, PFOA. Given the role of Bd in amphibian declines, further investigation of interactions of PFAS with Bd and other environmentally relevant pathogens is warranted.

Chronic Exposure to a PFAS Mixture Resembling AFFF-Impacted Surface Water Decreases Body Size in Northern Leopard Frogs (Rana pipiens).

Per- and polyfluoroalkyl substances (PFAS) occur in the environment as mixtures, yet mixture toxicity remains poorly understood. Aqueous film-forming foams (AFFFs) are a common source of PFAS. Our objective was to examine chronic effects of a complex PFAS mixture on amphibian growth and development. We tested toxicity of a five-chemical PFAS mixture summing to 10 µg/L and that accounts for >90% of the PFAS in AFFF-affected surface waters: perfluorooctane sulfonate (PFOS, 40%), perfluorohexane sulfonic acid (PFHxS, 30%), perflurooctanoic acid (PFOA, 12.5%), perfluorohexanoic acid (PFHxA, 12.5%), and perfluoropentanoic acid (PFPeA, 5%). We also included treatments to determine whether PFOS drove mixture toxicity and whether PFOS and mixture components act additively. We exposed Northern leopard frog (Rana pipiens) larvae through metamorphosis (∼130 d) in outdoor mesocosms. After 21 days of exposure, the larval body condition fell ∼5% relative to controls in the 4 µg/L PFOS treatment and mixtures lacking PFOS. At metamorphosis, the full 5-component 10 µg/L PFAS mixture reduced mass by 16% relative to controls. We did not observe effects on development. Our results indicate that toxicity of PFOS and other PFAS mixtures typical of AFFF sites act additively and that PFOS is not more inherently toxic than other mixture components.