John Wiley & Sons, Ltd.

Evaluation and comparison of the relationship between NOEC and EC10/EC20 values in chronic Daphnia toxicity testing

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Hypothesis‐based no effect concentration (NOEC) and regression‐based x% effect concentration (ECx) values are common statistical approaches to summarize ecotoxicological effects. Controversy over the NOEC model has prompted movement towards discontinuation of NOEC in favor of ECx, but the best x% effect surrogate for NOEC has not yet been determined. Historically, 10% and 20% effect concentrations have been treated as NOEC analogues. Given these measurements' importance to ecotoxicology, further understanding of relationships between NOEC and EC10 or EC20 is crucial. In this study, a metadataset of daphnid chronic toxicity tests was compiled to analyze strength and significance of NOEC:EC10 and NOEC:EC20 relationships. Impact of endpoint (e.g., mortality, reproduction) and test condition parameters (e.g., pH, temperature) on NOEC:EC10 and NOEC:EC20 was evaluated. Mortality endpoints were most sensitive 51% of the time with growth and reproductive endpoints constituting the remainder, underscoring the value of using multiple endpoints to evaluate toxic effect rather than reliance on reproduction as the a priori most sensitive endpoint. When test condition parameters were less restricted (e.g., pH, hardness) NOEC:EC20 association was more robust, suggesting that variability introduced by test implementation increased variability in ECx calculation. This analysis revealed that overall EC10 was a more suitable analogue for NOEC than EC20. Recommendations included refinement and mandatory reporting of test parameters pH and hardness to minimize variability in ECx calculation. This article is protected by copyright. All rights reserved

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