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<p>The use of peroxide-based algaecides is a promising approach for controlling cyanobacterial harmful algal blooms (cyanoHABs) though more information is needed to guide operational use toward achieving management objectives while minimizing potential unintended ecological impacts. This study investigated the influence of initial cell density of <i>Microcystis aeruginosa</i> on the dissipation and efficacy of a peroxide (H<sub>2</sub>O<sub>2</sub>)-based algaecide (Oximycin® P5). Experiments were conducted to measure peroxide concentrations over time, assess cell density changes post-treatment, model peroxide degradation, and develop an exposure-effect relationship. <i>Microcystis aeruginosa</i> at different initial cell densities of 1 × 10<sup>6</sup>, 5 × 10<sup>6</sup>, and 1 × 10<sup>7</sup> cells mL<sup>−1</sup> were exposed to a range of initial concentrations of the algaecide (1, 2, 3.5, 7, and 14&#xa0;ppm H<sub>2</sub>O<sub>2</sub>). Peroxide degradation rates differed with application concentration and cell density. Higher peroxide degradation was found with greater initial cell densities. Linear models indicated that degradation rate increased with peroxide concentration but decreased with increasing application rate at lower densities. Cell density reduction was significantly affected by both initial cell density and algaecide application concentration. Peroxide effectiveness declined sharply at higher initial cell densities due to rapid degradation. It required ≥ 7&#xa0;ppm H₂O₂ to elicit &gt; 90% control at 1 × 10⁷ cells/mL whereas 1&#xa0;ppm H₂O₂ was able to elicit the same level of control with 1 × 10<sup>6</sup> initial cell density. Some concentrations of peroxide that provided control at lower cell densities resulted in growth with higher initial cell densities. With the lowest initial cell density, peroxide was still detectable in the 1&#xa0;ppm treatment 1&#xa0;h after treatment and able to elicit significant control, whereas the 1&#xa0;ppm peroxide treatment in the 5 × 10<sup>6</sup> density and 1 and 2&#xa0;ppm in the 1 × 10⁷ treatment all dissipated to non-detect after 1&#xa0;h and growth of <i>M. aeruginosa</i> was measured. These findings highlight the critical role of cyanobacterial cell density for peroxide algaecide effectiveness and advance the development of more targeted and efficient cyanoHAB treatment strategies.</p>

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Influence of Microcystis aeruginosa (Cyanobacteria) Cell Density on Peroxide Algaecide Dissipation and Efficacy

  • 期刊论文

  • 发表日期：

    2025年11月17日

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  • H. Dail Laughinghouse IV,
  • Maximiliano Barbosa,
  • West M. Bishop

摘要

The use of peroxide-based algaecides is a promising approach for controlling cyanobacterial harmful algal blooms (cyanoHABs) though more information is needed to guide operational use toward achieving management objectives while minimizing potential unintended ecological impacts. This study investigated the influence of initial cell density of Microcystis aeruginosa on the dissipation and efficacy of a peroxide (H2O2)-based algaecide (Oximycin® P5). Experiments were conducted to measure peroxide concentrations over time, assess cell density changes post-treatment, model peroxide degradation, and develop an exposure-effect relationship. Microcystis aeruginosa at different initial cell densities of 1 × 106, 5 × 106, and 1 × 107 cells mL−1 were exposed to a range of initial concentrations of the algaecide (1, 2, 3.5, 7, and 14 ppm H2O2). Peroxide degradation rates differed with application concentration and cell density. Higher peroxide degradation was found with greater initial cell densities. Linear models indicated that degradation rate increased with peroxide concentration but decreased with increasing application rate at lower densities. Cell density reduction was significantly affected by both initial cell density and algaecide application concentration. Peroxide effectiveness declined sharply at higher initial cell densities due to rapid degradation. It required ≥ 7 ppm H₂O₂ to elicit > 90% control at 1 × 10⁷ cells/mL whereas 1 ppm H₂O₂ was able to elicit the same level of control with 1 × 106 initial cell density. Some concentrations of peroxide that provided control at lower cell densities resulted in growth with higher initial cell densities. With the lowest initial cell density, peroxide was still detectable in the 1 ppm treatment 1 h after treatment and able to elicit significant control, whereas the 1 ppm peroxide treatment in the 5 × 106 density and 1 and 2 ppm in the 1 × 10⁷ treatment all dissipated to non-detect after 1 h and growth of M. aeruginosa was measured. These findings highlight the critical role of cyanobacterial cell density for peroxide algaecide effectiveness and advance the development of more targeted and efficient cyanoHAB treatment strategies.