Effects of Per- and Polyfluoroalkyl Substance Mixtures on the Susceptibility of Larval American Bullfrogs to Parasites.

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants known to adversely affect health and development in many taxa. Although PFAS generally occur as mixtures in the environment, little is known about the effects of PFAS mixtures on organisms compared to single chemical exposures. Moreover, PFAS exposure in nature occurs alongside biotic factors such as parasitism. Even though host-parasite interactions are common in natural systems, there is little information about how PFAS affect these interactions. Here, we examined the effects of PFAS mixtures on the susceptibility of larval American bullfrogs ( Rana catesbeiana ) to echinostomes. Our PFAS treatments included perfluorooctanesulfonic acid (PFOS) at 4 and 10 ppb, two mixtures without PFOS as a component at 6 and 10 ppb total PFAS, and a mixture containing PFOS at 10 ppb total PFAS. We found that a 62-day PFAS exposure increased parasite loads by 42-100% in all treatments relative to the control. Additionally, we found that the singular exposure to PFOS increased parasite loads by ∼40% compared to a mixture containing PFOS suggesting antagonism among PFAS in mixtures. Our results highlight the need for further investigation into the effects of PFAS mixtures on organisms and how PFAS affect common ecological interactions.