Comparative Toxicity of Aquatic Per‐ and Polyfluoroalkyl Substance Exposure in Three Species of Amphibians

Abstract

Per-and polyfluoroalkyl substances (PFAS) are contaminants of concern due to their widespread occurrence in the environment, persistence, and potential to elicit a range of negative health effects. Per-and polyfluoroalkyl substances are regularly detected in surface waters, but their effects on many aquatic organisms are still poorly understood. Species with thyroid-dependent development, like amphibians, can be especially susceptible to PFAS effects on thyroid hormone regulation. We examined sublethal effects of aquatic exposure to four commonly detected PFAS on larval northern leopard frogs (Rana [Lithobates] pipiens), American toads (Anaxyrus americanus), and eastern tiger salamanders (Ambystoma tigrinum). Animals were exposed for 30 days (frogs and salamanders) or until metamorphosis (toads) to 10, 100, or 1000 μg/L of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), or 6:2 fluorotelomer sulfonate (6:2 FTS). We determined that chronic exposure to common PFAS can negatively affect amphibian body condition and development at concentrations as low as 10 µg/L. These effects were highly species dependent, with species having prolonged larval development (frogs and salamanders) being more sensitive to PFAS than more rapidly developing species (toads). Our results demonstrate that some species could experience sublethal effects at sites with surface waters highly affected by PFAS. Our results also indicate that evaluating PFAS toxicity using a single species may not be sufficient for accurate amphibian risk assessment. Future studies are needed to determine whether these differences in susceptibility can be predicted from species' life histories and whether more commonly occurring environmental levels of PFAS could affect amphibians.

An Environmentally Relevant Mixture of Perfluorooctanesulfonic Acid and Perfluorohexanesulfonic Acid Does Not Conform to Additivity in Northern Leopard Frogs Exposed Through Metamorphosis

“…Therefore, it represents an ecologically relevant endpoint because energy reserves are crucial for longterm survival and reproduction. These results agree with a previous study on R. pipiens, which also reported declines in SMI after PFOS and PFHxS exposure, with a lowest-observedeffect concentration (LOEC) of 10 ppb, the lowest concentration tested in that study (Flynn et al, 2022).…”

“…It is plausible that PFAS are interacting with PPARα and potentially other isoforms of this nuclear receptor in R. pipiens, which would be consistent with the literature. Our laboratory is currently testing this hypothesis in a study looking at the effects of PFOS and PFHxS on the PPAR signaling pathway in amphibians because changes in SMI in amphibians exposed to PFAS have been consistently observed in other studies (Abercrombie et al, 2021;Flynn et al, 2022).…”

Is Mixtures’ Additivity Supported by Empirical Data? A Case Study of Developmental Toxicity of PFOS and 6:2 FTS in Wildtype Zebrafish Embryos

“…Future studies with PFOS and 6:2 FTS can build upon this study by focusing on the dose range between 100 and 2000 μg/L (PFOS equivalents) to determine whether there is a predictable threshold effect within this range where the interaction shifts from less-than-additive to more-than-additive, and whether that threshold changes with ratios different from the approximate range 1:10–1:30 (PFOS to 6:2 FTS) examined in this study. In addition, concurrent evaluations of gene expression [ 33 , 34 ] would further elucidate potential modes of action that may explain the interactions observed with mixtures of PFOS and 6:2 FTS.…”

Toxicity of per- and polyfluoroalkyl substances to aquatic vertebrates

“…Certain amphibian species could experience sublethal effects at sites where the surface waters are highly affected by PFAS because the negative impact on their body condition and development is more easily triggered than in fish (Flynn et al, 2022). LC50, EC50, and minimum concentration to inhibit growth (MCIG) of Xenopus laevis for PFOS were 51.46, 108.20, and 35 mg/L, respectively (Wei et al, 2012) (Table 3).…”

“…The eight-carbon backbone of PFOS and PFOA are two of the most widely used PFASs, and their ecotoxicity in the aquatic environment has been the focus of many studies (Flynn et al, 2022). In the general categorization of toxicity data, PFOS is moderately-acutely toxic and slightly chronically toxic to aquatic organisms (Hu, 2009), whereas PFOA is both acutely and chronically practically non-toxic (Van Rijn et al, 1995;Hekster et al, 2003;Shi et al, 2017b).…”