Development of Fluoride Protective Values for Aquatic Life Using Empirical Bioavailability Models

The derivation of protective values for aquatic life can be enhanced by the development and use of bioavailability models. Recent advances to metals bioavailability modeling are applicable to other analyte groups and should be widely considered. In this study, we conduct a meta-analysis of available aquatic toxicity literature for fluoride to evaluate the utility of hardness, alkalinity, and chloride as toxicity modifying factors (TMFs) in empirical bioavailability models of freshwater taxa. The resulting optimal multiple linear regression (MLR) model predicting acute fluoride toxicity to the invertebrate Hyalella azteca included all three TMFs (Observed versus Predicted LC50, R 2 = 0.88) and the optimal model predicting toxicity to the fish Oncorhynchus mykiss included alkalinity and hardness (R 2 = 0.37). At >20 mg/L chloride, the preliminary final acute values (FAVs) for fluoride were within one order of magnitude and ranged from approximately 18.1 to 56.3 mg/L, depending on water chemistry. Sensitivity of H. azteca to low chloride conditions increased model uncertainty when chloride