title: Critical predicted no effect concentrations (PNECs) should not be based on a single toxicity test.
abstract: Predicted no-effect concentrations (PNECs), which represent the concentration of a substance below which an unacceptable effect most likely will not occur, are widely used for risk assessment and in environmental policy and regulation. They are typically based on single-species laboratory toxicity tests; often, a single test result for the most sensitive endpoints drives the derivation of a PNEC. In the present study, the authors provide a case study emphasizing the importance of determining the reliability of those most sensitive endpoints. Five 21-d Daphnia magna toxicity tests conducted using the same procedures by 2 laboratories gave 20% inhibitory concentration responses to a specific ionic composition of total dissolved solids that varied from 684 mg/L to more than 1510 mg/L. The concentration-response curve was shallow; thus, these differences could have been attributable to chance alone. The authors strongly recommend that the most sensitive endpoints that determine PNECs not be based on a single toxicity test result but rather on the geometric mean of at least 3 test results to adequately assess and bound test variability, especially when the concentration-response curve is shallow.
authors.affiliation: Golder Associates, Vancouver, British Columbia, Canada.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Chapman
authors.forename: James R
authors.initials: JR
authors.lastname: Elphick
mesh_terms: D000818:Animals; D003621:Daphnia / Q000187:drug effects; D019055:No-Observed-Adverse-Effect Level; D011786:Quality Control; D018570:Risk Assessment / Q000379:methods* / Q000592:standards*; D018675:Toxicity Tests / Q000592:standards*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical
keywords: Ecotoxicology; Hazard/risk assessment; PNECs; Response curves; Species sensitivity distribution