Adult zebrafish completely regenerate their caudal fins following partial amputation. Fin regrowth can easily be monitored in vivo and regenerating tissues can be used to study this dynamic developmental process. In this study we determined that fin regeneration is significantly affected by exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Zebrafish caudal fins were partially amputated, and the fish received intraperitoneal (ip) injection of 2.8, 14, or 70 ng/g weight TCDD or vehicle control. By 7 days postamputation, fish exposed to the highest concentration of TCDD regenerated 15% of their fin compared to 65% regrowth in control fish. To determine if this effect was stage specific, zebrafish were exposed to 70 ng/g TCDD on 1, 2, 3, or 4 days postamputation. Fin regeneration was significantly inhibited at all time points following TCDD exposure. TCDD exposure also induced hyperpigmentation in de novo tissue. Zebrafish were dosed with BrdU, following fin amputation and TCDD exposure, to study changes in cell proliferation. By 4 days postamputation, cell proliferation rates were significantly lower in TCDD-exposed fish. TCDD toxicity is mediated through the aryl hydrocarbon receptor (AHR), and RT-PCR experiments confirmed AHR2, ARNT2b, and TCDD-dependent CYP1A expression in the regenerating tissue. These results demonstrate that zebrafish caudal fin regeneration is a unique model to investigate molecular mechanism(s) of TCDD toxicity.

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Evaluation of chemical risks to threatened and endangered species is a requirement for Superfund ecological risk assessments; however, screening levels to evaluate the potential for toxicity associated with ecological receptor exposure to per‐ and polyfluoroalkyl substances (PFAS) are lacking. Therefore, PFAS risk‐based screening levels (RBSLs) were developed. Wildlife RBSLs were developed using surrogate receptors selected to be representative of threatened and endangered species with different habitat types, feeding guilds, and trophic levels. Published uptake and toxicity data were combined with receptor exposure factors to derive RBSLs for terrestrial and aquatic wildlife for several PFAS, including perfluorononanoic acid, perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorohexanoic acid, perfluorobutanesulfonic acid, and pentafluorobenzoic acid. Uptake information for surrogate PFAS were considered to calculate RBSLs for PFAS with toxicity data and insufficient bioaccumulation data to develop an RBSL. Both no‐observed–adverse effect level (NOAEL)– and lowest‐observed–adverse effect level–based wildlife RBSLs were calculated to allow for a range of risk estimates appropriate to individual threatened and endangered species and populations of nonlisted wildlife receptors, respectively. Recommended water quality RBSLs protective of aquatic life were developed for 23 PFAS based on published literature reviews and peer‐reviewed aquatic toxicity studies and Great Lakes Initiative methodology. For wildlife receptors, NOAEL RBSLs ranged from to 0.013 to 340 mg/kg for soil, 0.0014 to 370 mg/kg for sediment, and 0.000075 to 1600 mg/L for surface water. For aquatic life, chronic RBSLs ranged from 0.00022 to 3.4 mg/L. For terrestrial plants and soil invertebrates, the no‐observed‐effect concentration screening levels range from 0.084 to 642 mg/kg and from 1 to 50 mg/kg, respectively. Environ Toxicol Chem 2021;40:921–936. © 2020 SETAC

The use of aqueous film forming foam (AFFF) in the United States has caused concern about the potential effects of per‐ and polyfluoroalkyl substances (PFAS) on ecological resources. Moreover, the limited availability of scientific information and a lack of guidance have collectively resulted in significant challenges for ecological risk assessors supporting site‐specific investigations and management decisions at PFAS‐impacted sites. To address these needs, the environmental science and technology program of the Department of Defense (DoD), the Strategic Environmental Research and Development Program (SERDP), began funding four desktop review projects in 2018. Project teams were tasked with developing strategic guidance for assessing ecological risk at AFFF‐impacted DoD sites. The projects focused specifically on ecological risk assessment practices for threatened and endangered (T&E) species; however, the recommendations and approaches presented in the projects are also applicable and adaptable to common species. The present review provides risk assessors and site managers an overview of how the resources provided in these projects can support ecological‐risk‐based management decisions at AFFF and other PFAS‐impacted sites. Additionally, we synthesize perspectives offered by the four projects on a path forward for PFAS ecological risk assessment, including research needs that we recommend should be prioritized by the scientific community. Integr Environ Assess Manag 2021;17:746–752. © 2021 SETAC

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