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PH08 Metals in the Environment: Aquatic Biological Perspectives
(PH099) Field test of the Biotic Ligand Model in Colorado Rocky Mountain streams.
Schmidt, T1, Meyer, J2, Clements, W1, 1 Colorado State University, Fort Collins, CO, USA2 University of Wyoming, Laramie, WY, USA
ABSTRACT- The U.S. Environmental Protection Agency (USEPA) plans to implement the Biotic Ligand Model (BLM) to develop site-specific aquatic life criteria for some cationic metals (e.g., Ag, Cd, Cu, Zn). However, the BLM's ability to predict trace-metal toxicity to indigenous aquatic communities has not been evaluated in natural systems. We used the Regional Environmental Management Assessment Program (REMAP) dataset collected by USEPA throughout the mountainous region of Colorado to compare the community-level predictive abilities of the BLM and its predecessor, the USEPA hardness-adjustment equations for calculating criterion continuous concentrations (CCCs). Because dissolved Ag wasn't detected at any of the REMAP sites, we calculated gill-metal accumulations for Cd, Cu and Zn (the dominant metals at these sites). Then, because the BLM does not predict gill-metal accumulation for metals mixtures, we created an index of joint-metal toxicity -- the Continuous Chronic Criterion Metal Accumulation Ratio (CCCMAR = (site-specific BLM predicted gill-metal concentration ÷ BLM-predicted gill-metal concentration at the CCC in USEPAs standard water condition), summed for Cd, Cu and Zn. For the current USEPA method, we calculated CCCs for Cd, Cu and Zn at the site-specific water hardness and then calculated the Cumulative Criterion Units (CCU = (total dissolved metal ÷ (hardness-adjusted CCC based on total recoverable metal × conversion factor)), again summed for Cd, Cu and Zn. As expected, benthic community structure (total species richness, total species abundance, and EPT richness (= sum of mayfly, stonefly and caddisfly species)) was negatively correlated with CCU (r2 = 0.31, 0.48, 0.16, respectively; p < 0.001). However, the same indices were more strongly negatively correlated with CCCMAR (r2 = 0.47, 0.63, 0.42, respectively; p < 0.001). The remaining variability not accounted for (especially at sub-chronic metal concentrations) may be caused by other factors not included in the BLM, such as physical habitat, other waterborne contaminants, and diet-borne metals.
Key words: benthic macroinvertebrates, Biotic Ligand Model, Cumulative Criterion Units, trace metals
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