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(P637) Use of the Biotic Ligand Model to Evaluate Bioavailability of Copper in Arid West Watercourses.
Santore, Robert*,1, Sopher, Elizabeth2, Mathew, Rooni3, Paquin, Paul3, Gensemer, Robert4, Naddy, Rami4, Medine, Allen2, Curley, Ed5, Sierra, Karen5, 1 HydroQual, Inc, Camillus, NY, US2 HydroQual, Inc., Boulder, CO, US3 HydroQual, Inc., Mahwah, NJ, US4 ENSR International, Fort Collins, CO, US5 Pima County Wastewater Management, Tucson, AZ, US
ABSTRACT- Copper bioavailability and toxicity to aquatic organisms is known to be affected by water chemistry and especially by factors such as pH, hardness, alkalinity, and organic matter concentration. Waters draining arid ecosystems in the Western United States are typically elevated in pH, hardness, and alkalinity. Furthermore, many of these water bodies are naturally characterized by low or ephemeral flows with the result that wastewater treatment effluents and associated organic matter can easily dominate existing flows. This combination of chemical and hydrologic conditions makes a unique environment for assessing copper bioavailability. The U.S. ambient water quality criterion for copper is typically overprotective under these conditions resulting in the need to develop site-specific water quality criteria for waters in the arid west. The Biotic Ligand Model (BLM) was recently developed as a regulatory tool to aid in the development of site specific criteria for metals and specifically considers the effects of water chemistry on metal bioavailability. The ability of the BLM to develop meaningful site-specific copper criteria for waters in arid west ecosystems was verified in a study conducted by the Arid West Water Quality Research Project. This study compared model predictions with measured copper toxicity to Ceriodaphnia dubia in high hardness waters typical of selected watersheds. The BLM was then used with U.S.G.S. monitoring data for several arid west rivers to characterize copper bioavailability at these sites. The results indicate that the unique chemistry at these sites has significant effects on copper bioavailability and that site-specific copper criteria are typically justified in these watersheds.
Key words: copper, arid ecosystems, water quality criteria, biotic ligand model
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