Replacement per- and polyfluoroalkyl substance (PFAS)-free aqueous film-forming foams impact growth more than a PFAS-containing product in the hard clam, <i>Mercenaria mercenaria</i>

Aqueous film-forming foams (AFFFs) are widely used fire suppression products that have been identified as a direct source of environmental per- and polyfluoroalkyl substances (PFAS). Per- and polyfluoroalkyl substance exposure has demonstrated chronic and sublethal effects on biota. Ongoing efforts aim to reduce and, ideally, eliminate PFAS use in AFFF products. However, there is little known about the potential toxic effects of the new PFAS-free AFFFs, specifically on benthic organisms. The objective of this study is to quantify the effects of seven AFFFs on growth in the hard clam, Mercenaria mercenaria, over a 21-day exposure period with juvenile animals. Additionally, AFFF effects are reported from algal toxicity assays and a feeding study. Five of the PFAS-free AFFFs negatively impacted growth over the exposure period, while one PFAS-free AFFF and the reference PFAS-containing AFFF had no observable effect. Median effect concentrations (EC50) for shell growth ranged from 5.81 mg/L to >100 mg/L. Clam dry and wet weights also decreased with increasing exposure concentration (p < 0.05). Algal growth was impacted over a 96-hr exposure. Impacts were observed to final standing biomass and overall growth rates at the highest exposure concentrations. However, complete lethality was only observed for one PFAS-free product, suggesting lack of food availability was likely not the primary driver of growth inhibition for all products. Net particle clearance rates in AFFF-exposed clams were not found to be impacted, suggesting there was no obvious AFFF influence on organismal feeding ability. The presented results identify chronic effects of exposure to these AFFFs in this economically and ecologically important bivalve species and are expected to inform decisions regarding PFAS replacement AFFF products.