John Wiley & Sons, Ltd.

Comparative toxicity of twenty herbicides to five periphytic algae and the relationship with mode of action

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We used 5 species periphytic algae to conduct toxicity assays of twenty herbicides. The 5 tested species represent riverine primary producers most likely to be affected by herbicides. A fluorescence microplate toxicity assay was used as an efficient and economical high‐throughput assay. Toxicity characteristics were analyzed, focusing on their relationship to herbicide mode of action (MoA). The relative differences between 50% and 10% effect concentrations depended on herbicide MoA, rather than tested species. Moreover, the clear relationship between sensitive species and herbicide MoA was also observed. Green alga was most sensitive to herbicides of 2 MoA groups (inhibitors of protoporphyrinogen oxidase and very long‐chain fatty acid synthesis). Diatoms were most sensitive to herbicides of a MoA group (4‐hydroxyphenyl‐pyruvate‐dioxygenase inhibitors). Cyanobacterium was most sensitive to herbicides of a MoA group (inhibitors of acetolactate synthase). The species sensitivity distribution (SSD) based on obtained data was also analyzed. The slopes of the SSD significantly differed among MoA, suggesting that difference in species sensitivity is specific to the MoA. In particular, the differences in species sensitivity were markedly large for inhibitors of acetolactate synthase, protoporphyrinogen oxidase, and very long‐chain fatty acid synthesis. Our results clearly showed that a single algal species cannot represent the sensitivity of an algal assemblage. Therefore, the multispecies algal toxicity data is essential for substances with specific modes of action. This article is protected by copyright. All rights reserved

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