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The effect of binary mixtures of Zn, Cu, Cd, and Ni on the growth of the freshwater diatom Navicula pelliculosa and comparison with mixture toxicity model predictions

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We investigated the effect of binary mixtures of Zn, Cu, Cd, and Ni on the growth of a freshwater diatom Navicula pelliculosa. A 7 × 7 full factorial experimental design (49 combinations in total) was used to test each binary metal mixture. A 3‐d fluorescence microplate toxicity assay was used to test each combination. Mixture effects were predicted by concentration addition (CA) and independent action (IA) models based on single metal concentration‐response relationship between relative growth rate and the calculated free metal ion activity. Although the CA model predicted the observed mixture toxicity significantly better than the IA model for the Zn‐Cu mixture, the IA model predicted the observed mixture toxicity significantly better than the CA model for the Cd‐Zn, Cd‐Ni, and Cd‐Cu mixtures. For the Zn‐Ni and Cu‐Ni mixtures, it was unclear which of both models was better. Statistical analysis concerning antagonistic/synergistic interactions showed that the CA model is generally conservative (with the Zn‐Ni mixture being the sole exception), indicating that the CA model would be useful as a method for a conservative first tier screening level risk analysis of metal mixtures. This article is protected by copyright. All rights reserved

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