USE OF A MODEL OF METAL BIOAVAILABILITY FOR DEVELOPING SITE-SPECIFIC WATER QUALITY CRITERIA

摘要

Water quality criteria (WQC) are intended to define, on the basis of sound scientificrninformation and toxicological principles, concentrations of specific chemicals in waterrnthat are protective of aquatic life and human health. Meaningful WQC are needed tornserve as a basis for development of watershed-based control programs that willrnprotect the aquatic environment, while also being cost effective to implement. Thernimportance of explicitly considering bioavailability in the development of water qualityrncriteria for metals is gaining increased recognition by regulatory authorities. AlthoughrnWQC for several metals include adjustments for hardness, it is known that other waterrnquality characteristics influence metal bioavailability. Bioassay based methods suchrnas the water effect ratio (WER) procedure have been developed to account for thesernwater chemistry-based effects on metal bioavailability and toxicity in the evaluation ofrnsite-specific WQC. The biotic ligand model (BLM) has recently been receivingrnconsiderable attention as a computational alternative to the Wer procedure forrnevaluating site-specific WQC for metals. The BLM considers the effect of waterrnchemistry on metal bioavailability and toxicity. By simulating metal accumulation at thisrnsite of action, defined as the biotic ligand, the BLM equates a given toxicity end pointrn(e.g., an LC50) with metal accumulation beyond a critical threshold. BLM predictionsrnfor copper and silver toxicity to freshwater fish and invertebrates will be compared tornresults from bioassays to demonstrate the utility of the BLM approach. Comparisonsrnof BLM results with measured data show excellent agreement, with nearly allrnpredictions within a factor of two of the measured results.