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

Area of Science:

• Environmental Toxicology
• Aquatic Chemistry
• Ecotoxicology

Background:

• Bioavailability models enhance protective value derivation for aquatic life.
• Metals bioavailability modeling advances offer applicability to other analyte groups.
• Fluoride toxicity in freshwater ecosystems requires better understanding.

Purpose of the Study:

• Evaluate hardness, alkalinity, and chloride as toxicity-modifying factors (TMFs) in fluoride bioavailability models.
• Assess the utility of TMFs for predicting acute fluoride toxicity in freshwater taxa.
• Determine if existing protective values for fluoride are overly conservative.

Main Methods:

• Conducted a meta-analysis of aquatic toxicity literature for fluoride.
• Developed multiple linear regression models to predict acute fluoride toxicity.
• Included water chemistry parameters (hardness, alkalinity, chloride) as TMFs.
• Derived chronic values using an acute-to-chronic ratio (ACR) approach.

Main Results:

• Optimal model for Hyalella azteca included hardness, alkalinity, and chloride (R²=0.88).
• Optimal model for Oncorhynchus mykiss included alkalinity and hardness (R²=0.37).
• Preliminary acute values for fluoride ranged from 18.1 to 56.3 mg/L at >20 mg/L chloride.
• Model uncertainty increased at chloride concentrations below 20 mg/L.

Conclusions:

• Toxicity-modifying factors significantly influence fluoride bioavailability and toxicity.
• Existing protective values for fluoride may be overly conservative.
• Further toxicological studies are needed to refine bioavailability models for inorganic anions like fluoride.