title: Application of the target lipid model for deriving predicted no-effect concentrations for wastewater organisms.
abstract: The target lipid model (TLM) was applied to literature data from 10 microbial toxicity assays to provide a quantitative effects assessment framework for wastewater treatment plant organisms. For the nonpolar organic chemicals considered, linear relationships between the logarithm of the median effect concentrations (EC50) and log(K(OW)) conformed to the TLM for all endpoints with the exception of nitrification inhibition. Additional experimental data for the nitrification inhibition endpoint were generated for 16 narcotic chemicals using a procedure that allowed testing of volatile substances. Results obtained from the present study demonstrated that the nitrification inhibition endpoint was not adequately described by the TLM consistent with previous literature data. Acute to chronic ratios (ACRs) defined as the ratio of the EC50 to the 10% effect concentration (EC10) were available for two of the endpoints investigated and ranged from 1.1 to 2.3 for the Tetrahymena growth assay and from 2.4 to 24.1 for the nitrification inhibition endpoint. No inhibitory effects for any of the microbial endpoints investigated were observed for compounds with log(K(OW)) >5. The critical target lipid body burdens (C(L)(*)) were calculated for the nine microbial toxicity endpoints conforming to the TLM and ranged from 252 to 2,250 micromol/g octanol. The Microtox light inhibition (C(L)(*) = 252 micromol/g octanol) and Tetrahymena pyriformis growth (C(L)(*) = 254 micromol/g octanol) assays were found to be the most sensitive endpoints. The predicted no-effect concentration (PNEC) derived using the HC5 (hazardous concentration to 5% of test organisms) statistical extrapolation procedure was calculated using TLM parameters for substances with log(K(OW)) from 0 to 5. Results from this analysis demonstrate PNECs for narcotic compounds are protective of wastewater organisms excluding nitrifying bacteria. Further model improvement is needed if protection of nitrifying bacteria in wastewater treatment systems is required.
authors.affiliation: HydroQual-East Syracuse, East Syracuse, New York 13057, USA. aredman@hydroqual.com
authors.forename: Aaron
authors.initials: A
authors.lastname: Redman
authors.forename: Joy
authors.initials: J
authors.lastname: McGrath
authors.forename: Eric
authors.initials: E
authors.lastname: Febbo
authors.forename: Thomas
authors.initials: T
authors.lastname: Parkerton
authors.forename: Dan
authors.initials: D
authors.lastname: Letinski
authors.forename: Martin
authors.initials: M
authors.lastname: Connelly
authors.forename: Douglas
authors.initials: D
authors.lastname: Winkelmann
authors.forename: Dominic Di
authors.initials: DD
authors.lastname: Toro
mesh_terms: D000465:Algorithms; D000818:Animals; D001419:Bacteria / Q000187:drug effects* / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects* / Q000502:physiology; D008954:Models, Biological; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D019055:No-Observed-Adverse-Effect Level; D018570:Risk Assessment; D013769:Tetrahymena pyriformis / Q000187:drug effects* / Q000254:growth & development; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D009573:Nitrites; D014874:Water Pollutants, Chemical