Sensitivity of Cyanobacteria to Herbicides Commonly Used in Aquatic Systems: Implications for Controlling Harmful Algal Blooms

Authors: BARRICK, ANDREW - Auburn University; AHMED, SAYEM - Auburn University; ORDONEZ HINZ, FRANCISCA - University Of Florida; WILSON, PATRICK - University Of Florida; Beck, Benjamin; HOANG, THAM - Auburn University

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Water quality and eutrophication are major drivers of harmful cyanobacterial blooms. Issues arising from nutrient loads, water circulation, and temperature influence blooms of toxic cyanobacteria, such as Anabaena and Microcystis, which can be detrimental to aquatic organisms in natural and aquaculture systems. Copper sulfate, an EPA-approved algicide, has been commonly used to control cyanobacterial blooms, especially in aquaculture systems. While effective, repeated annual use of copper can result in copper accumulation in aquatic systems over time. Organic herbicides, which can degrade after application, used in aquaculture systems for weed control may also limit cyanobacterial blooms; however, their efficacy towards different cyanobacterial species is not well defined. Anabaena spp. and Microcystis aeruginosa were exposed to 15 herbicides (2,4-Dichlorophenoxyacetic acid (2, 4-D), bispyribac sodium, copper sulfide, diquat dibromide, diuron, endothall, hydrogen peroxide, imazapyr, imazamox, fluridon, flumioxazin, glyphosate, penoxsulam, topramezone, and triclopyr) commonly used in aquaculture systems to characterize their effects on cyanobacteria. Dose-response testing was conducted for each herbicide to measure growth rates, chlorophyll, and phycocyanin concentrations to derive median effect concentrations (EC50s). Results demonstrated that M. aeruginosa growth was inhibited by copper, diuron, diquat, hydrogen peroxide, and penoxsulam, with diuron having the lowest EC50, indicating it was the most effective chemical for controlling M. aeruginosa. Anabaena spp. growth was inhibited by bispyribac sodium, copper, diuron, diquat dibromide, H2O2, and penoxsulam, with both diuron and penoxsulam having lower EC50 values than copper. The research provides a comprehensive look at how commonly used herbicides influence Anabaena spp. and M. aeruginosa, providing insight into alternative management strategies; however, additional research is needed to characterize the long-term efficacy of organic herbicides.

Technical Abstract: Water quality and eutrophication are major drivers of harmful cyanobacterial blooms. Issues arising from nutrient loads, water circulation, and temperature influence blooms of toxic cyanobacteria, such as Anabaena and Microcystis, which can be detrimental to aquatic organisms in natural and aquaculture systems. Copper sulfate, an EPA-approved algicide, has been commonly used to control cyanobacterial blooms, especially in aquaculture systems. While effective, repeated annual use of copper can result in copper accumulation in aquatic systems over time. Organic herbicides, which can degrade after application, used in aquaculture systems for weed control may also limit cyanobacterial blooms; however, their efficacy towards different cyanobacterial species is not well defined. Anabaena spp. and Microcystis aeruginosa were exposed to 15 herbicides (2,4-Dichlorophenoxyacetic acid (2, 4-D), bispyribac sodium, copper sulfide, diquat dibromide, diuron, endothall, hydrogen peroxide, imazapyr, imazamox, fluridon, flumioxazin, glyphosate, penoxsulam, topramezone, and triclopyr) commonly used in aquaculture systems to characterize their effects on cyanobacteria. Dose-response testing was conducted for each herbicide to measure growth rates, chlorophyll, and phycocyanin concentrations to derive median effect concentrations (EC50s). Results demonstrated that M. aeruginosa growth was inhibited by copper, diuron, diquat, hydrogen peroxide, and penoxsulam, with diuron having the lowest EC50, indicating it was the most effective chemical for controlling M. aeruginosa. Anabaena spp. growth was inhibited by bispyribac sodium, copper, diuron, diquat dibromide, H2O2, and penoxsulam, with both diuron and penoxsulam having lower EC50 values than copper. The research provides a comprehensive look at how commonly used herbicides influence Anabaena spp. and M. aeruginosa, providing insight into alternative management strategies; however, additional research is needed to characterize the long-term efficacy of organic herbicides.