Effects of peroxide-based compounds on growth and toxicity of Microcystis aeruginosa

Cyanobacterial blooms are increasing worldwide, compromising water bodies and ecosystem services. Among the possible management measures are curative methods, such as hydrogen peroxide, that can suppress cyanobacteria growth. However, the rapid breakdown of H₂O₂ could limit its effectiveness; thus new formulations (liquid and solid) that are, in theory, more stable have been developed. Here, we tested three new formulations (Oximycin™ P5, Phycomycin® SCP and Lake Guard® Oxy) and traditional peroxides (H₂O₂ and CaO₂) on their capacity to end Microcystis aeruginosa bloom and their effect on microcystin dynamics. In general, all the products controlled M. aeruginosa biomass. The products were comparable mainly in the tests with lower initial Chl-a (150 µg L^-1), with slightly less effectiveness of CaO₂. At a higher initial bloom concentration (600 µg Chl-a L^-1), all the products were effective in reducing Chl-a concentration to zero at a dose of 3 mg H₂O₂ L^-1, except Lake Guard® Oxy and CaO_2, which showed an increase in Chl-a by the end of the experiment. This suggests that Oximycin^TM P5, Phycomycin® SCP, and liquid H₂O₂ may perform better at lower doses. Nonetheless, at the highest dose tested (10 mg H₂O₂ L^-1), all products were highly effective, with no signs of recovery. After one day of exposure, extracellular MC concentrations were higher in all treatments but reduced to lower levels than the control after nine days, pointing to the degradation of dissolved MCs. There is no obvious top choice in terms of overall efficiency. However, each product may be better suited for different purposes depending on the specific situation and strategy.