Effects of Hydrogen Peroxide on Cyanobacterium <i>Microcystis aeruginosa</i> 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.