MP6 Quantitative Structure Activity Relationships (QSARs)
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(RED-1117-827178) Application of the Narcosis Target Lipid Model to Wastewater Treatment Plant Microogranisms.

Redman, A¹, McGrath, J¹, Parkerton, T², Di Toro, D³, ¹ HydroQual, Inc.² ExxonMobil³ University of Delaware

ABSTRACT- The narcosis target lipid model (NTLM) was developed to predict the toxicity of chemicals that act via narcosis to aquatic organisms. The model accounts for variations in toxicity due to species sensitivities and chemical differences. The model is based on the hypothesis that lipid is the site of action within the organism. Previous work has focused on the application of this model to fish, algae and invertebrates. The objective of this study was to determine if this model could logically be extended to predict toxicity endpoints for microorganisms common to wastewater treatment plants (WWTPs). Toxicity datasets were gathered for twelve different species, including MICROTOX, ciliated protozoa, nitrifying bacteria and several microbial consortia derived from WWTP activated sludge. Linear relationships between Log(EC50) and Log(K_ow) were derived for fourteen individual datasets. For twelve datasets, the slopes of the individual log(EC50)-log(K_ow) relationships were found to be not statistically different from the universal narcosis slope derived from earlier analysis of toxicity data for aquatic organisms. The universal narcosis slope was applied to the individual data sets and critical target lipid body burdens (CTLBB) were determined for each WWTP species. No difference in species sensitivity was found. Acute to Chronic Ratios (ACR) were derived from available data and were found to overlap the previously reported range of ACRs. These data were used to calculate the Hazardous Concentration to 5% of the tested species, a statistical extrapolation comparable to a predicted-no-effect concentration (PNEC).

Key words: Narcosis target lipid model, WWTP, bacteria, toxicity