Abstract
Abstract
The aquatic herbicide ProcellaCOR (florpyrauxifen-benzyl) is increasingly used for invasive plant control; however, its effects on non-target freshwater phytoplankton have only recently gained scientific attention, particularly under the major co-occurring stressor road salt. To our knowledge, no studies have evaluated their interactive effects on primary producers. We conducted a microcosm study to assess the individual and combined effects of florpyrauxifen-benzyl (10 µg L⁻¹ and 50 µg L⁻¹), road salt (860 mg L⁻¹ NaCl), and their mixtures on the green alga
Scenedesmus obliquus
and the cyanobacterium
Synechococcus elongatus
. ProcellaCOR alone did not affect the growth of either taxon. Salinity was the primary driver of responses in green algae, significantly reducing chlorophyll, lipid content, biomass, and cell abundance, with no indication of interactive effects with ProcellaCOR. In cyanobacteria, chlorophyll was affected by the ProcellaCOR × salinity interaction, with a significant reduction observed only in the 50 µg L⁻¹ ProcellaCOR × 860 mg L⁻¹ NaCl. Salinity also reduced lipid content and biomass in cyanobacteria, whereas cell abundance remained unaffected. Overall, salinity exerted stronger effects than ProcellaCOR on both taxa, and mixture effects were limited to chlorophyll at the highest ProcellaCOR concentration. Across all growth endpoints, cyanobacteria exhibited greater tolerance to salinity than green algae. These findings provide the empirical evidence needed to understand the effects of florpyrauxifen-benzyl on freshwater phytoplankton under environmentally relevant salinity conditions and support the incorporation of multiple stressors into ecological risk assessments.