Limited effects of fluorine-free foam alternatives on gray treefrog (<i>Hyla versicolor</i>) larval development in laboratory and mesocosm studies

Aqueous film-forming foams (AFFFs) containing per- and polyfluoroalkyl substances (PFAS) have been used extensively for decades to rapidly extinguish hydrocarbon fires. Given PFAS persistence, propensity to bioaccumulate, and potential wildlife and human health risks, focus has shifted to developing fluorine-free foam (F3) alternatives. However, the toxicity of these alternatives to wildlife is largely unknown. We assessed the toxicity of F3 alternatives to gray treefrogs using both laboratory and outdoor mesocosm studies. Overall, gray treefrogs were relatively tolerant of chronic F3 alternative exposure. Across both experimental venues, there was limited evidence that metamorphic endpoints (e.g., time to metamorphosis, size at metamorphosis, survival to metamorphosis) were negatively affected by F3 alternatives compared with the control treatments. In contrast, the PFAS-containing AFFF Buckeye Platinum Plus C6 MILSPEC 3% reduced survival and delayed metamorphosis at the highest concentration tested in the laboratory experiment. Despite minimal effects of the formulations on growth and development, behavioral observations of the outdoor mesocosm experiment found that tadpoles were using refuges more often (i.e., 19%-30% fewer tadpoles seen) with several of the F3 alternatives and the AFFF. Although this behavioral effect did not alter the growth or development of the gray treefrogs, there is the potential for such behavioral shifts to influence the outcome of ecological interactions (e.g., predation, parasitism, competition). It will be important to continue building on this work while also examining the fate and transport of these alternatives in aquatic and terrestrial ecosystems to inform ecological risk assessments.