Response of juvenile chinook salmon ( oncorhynchis tshawytscha ) to the aquatic, florpyrauxifen-benzyl

Florpyrauxifen-benzyl (ProcellaCOR®) is an aquatic herbicide commonly used to control Eurasian watermilfoil (Myriophyllum spicatum) and other invasive aquatic plants. Previous studies have demonstrated effective Eurasian watermilfoil control under low aqueous concentrations (<10 µg L−1) and short exposure times (<24 hr). While florpyrauxifen-benzyl possesses an excellent environmental profile and its acute toxicity has been assessed in freshwater model organisms, there has been no work to examine toxicity of this herbicide in salmonids. Therefore, the objective of this study was to evaluate the acute toxicity to Endangered Species Act (ESA)-listed Chinook salmon (Oncorhynchis tshawytscha). Chinook fry and smolts were exposed to florpyrauxifen-benzyl at 50 and 100 µg L−1 for 96 hr under a 24-hr static renewal protocol at 12 °C. Daily observations included fish startle response, position in the water column, and signs of overt toxicity. No adverse effects of the herbicide were observed at either concentration in both Chinook fry and smolts. Our results indicate that the maximum US-labeled application rate of florpyrauxifen-benzyl (48 µg L−1 ai) did not result in overt toxicity to juvenile salmonids under the exposure scenarios used in this study.