Effects of Hydrogen Peroxide on Cyanobacterium Microcystis aeruginosa in the Presence of Nanoplastics

Hydrogen peroxide (H₂O₂) is a common control measure for cyanobacterial harmful algal blooms (cyanoHABs), but local contaminants may alter its effects. Here, we aim to understand the control of cyanoHABs by H₂O₂ in light of nanoplastic contamination using a multistressor framework. We utilized a high-throughput full-factorial experiment to capture the multistressor impacts of H₂O₂, nanoplastics, temperature, and light on a toxigenic strain of the freshwater cyanobacterium Microcystis aeruginosa. In addition to revealing independent inhibitory effects of H₂O₂ and nanoplastics on cell abundance and microcystin production, our high-throughput system also identified non-additive, interactive effects. Specifically, we found that nanoplastics weakened the inhibitory effects of H₂O₂ on cell abundance and microcystin production. In addition, we discovered that nanoplastics restricted the degradation of H₂O₂, partially explaining this non-additive effect. Because combined H₂O₂ and nanoplastic still curbed growth, we expect H₂O₂ will remain an effective control measure even with background nanoplastic pollution. Our findings illustrate the importance of taking local stressors, including anthropogenic contaminants such as nanoplastics, into account before H₂O₂ is applied to control cyanoHABs.