M7 PM Metals in the Environment: Aquatic Biological Perspectives
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 327-329

(VAN-1117-847344) Validation of Biotic Ligand Model performance in extremely hard surface waters of the arid southwest.

Van Genderen, E¹, Gensemer, R¹, Santore, R², Ramage, K³, Curley, E³, Meyerhoff, R⁴, ¹ Parametrix, Inc., Albany, OR, USA² HydroQual, Inc., Camillus, NY, USA³ Pima County Wastewater Management, Tuscon, AZ, USA⁴ Camp, Dresser & McKee, Denver, CO, USA

ABSTRACT- Municipal wastewater treatment facilities in the arid western U.S. often face difficulties in complying with their NPDES discharge permits resulting from the unique hydrologic and geochemical conditions of effluent-dependent waters (i.e., river flow generated entirely from effluent discharge). In part, this is because the scarcity of upstream flows limits discharge mixing zones; but also because of the unique geochemical characteristics of these waters. Acute copper water-effect ratios (WER) were derived with three species of aquatic organisms (Pimephales promelas, Ceriodaphnia dubia, and Daphnia pulex) using seven effluent-dependent waters ranging in hardness from 150 to over 1000 mg/L (as CaCO₃) under base stream flow conditions. Additional WERs were derived using only C. dubia for three of the sites during elevated flow conditions. The results of this study were used to quantify the influence of extremely hard waters on metal toxicity, and to help validate the Biotic Ligand Model (BLM) for use in predicting acute copper toxicity and WERs under the unique ionic composition of these test waters. WER values ranged from 2 to 15 under base flow conditions and were typically greater for C. dubia and D. pulex compared to P. promelas. Base flow WERs were typically two-times greater than WERs produced in site waters collected during elevated flow conditions. Flow related effects on WER values were likely due to dilution of water quality constituents such as hardness, alkalinity and dissolved organic carbon. A majority of BLM predictions of median-lethal concentrations and WERs were within acceptable deviations of observed values for all species. However, improvements to model predictions were noted by including Mg-biotic ligand interactions for invertebrates and copper complexation by suspended solids.

Key words: copper, Water Effect-Ratio, hardness, Biotic Ligand Model