John Wiley & Sons, Ltd.

Critical predicted no effect concentrations (PNECs) should not be based on a single toxicity test

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Courtesy of John Wiley & Sons, Ltd.

Predicted no effect concentrations (PNECs), which represent the concentration of a substance below which an unacceptable effect will most likely 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. We 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 two laboratories gave inhibitory concentration (IC20) responses to a specific ionic composition of TDS that varied from 684 to >1,510 mg/l. The concentration‐response curve was shallow, thus these differences could have been due to chance alone. We 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 three test results to adequately assess and bound test variability, especially when the concentration‐response curve is shallow. This article is protected by copyright. All rights reserved

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