Combined Exposure to Hydrogen Peroxide and LightSelective Effects on Cyanobacteria, Green Algae, and Diatoms

The selective toxicity of H2O2 was investigated to develop a potential tool for limiting cyanobacterial blooms and to better understand the occurrence of cyanobacteria and other phytoplankton species in relation to reactive oxygen species in surface waters. The cyanobacterium Microcystis aeruginosa, the green alga Pseudokirchneriella subcapitata, and the diatom Navicula seminulum were tested under pulse exposure to H2O2 in the dark and at various irradiances. H2O2 was decomposed at rates depending on algal species and was proportional to irradiance. The cyanobacterium was affected by H2O2 at 10 times lower concentrations than green alga and diatom, and a strong light-dependent toxicity enhanced the difference. The inhibition was measured as photosynthetic yield (Fv/Fm) in pulse amplitude modulated fluorometry, and was confirmed by changes in minimal fluorescence (F0) and photosynthetic oxygen evolution. Single doses of 0.27 mg L-1 of H2O2 caused 50% inhibition to M. aeruginosa at high irradiance. Such concentration overlaps with the highest levels of 0.34 mg L-1 observed in natural waters, suggesting that H2O2 may act as a limiting factor for cyanobacterial growth.