Algicidal activity of phthalocyanines--screening of 31 compounds.

Phthalocyanines and their analogues show great potential as photodynamic agents producing reactive oxygen species (ROS), especially in medicine. However, their biocidal effects may also be employed to inhibit various undesirable organisms. This study explores their potential algicidal effects. The laboratory tests concern the effects of various phthalocyanine derivatives on the green alga Pseudokirchneriella subcapitata and cyanobacterium Synechococcus nidulans. Their effects on one example of the sensitive nontarget aquatic organism-crustacean Daphnia magna were also screened. Among 31 tested compounds, the cationic phthalocyanines substituted with heterocycle exhibited the strongest effects on phytoplankton species, some of them even below the level of 1 mg/L, while effects on crustaceans ranged from 3.6 to more than 50 mg/L. These results show that some phthalocyanine derivatives can act as potent algicides.

Combined exposure to hydrogen peroxide and light--selective 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 H202 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 H202 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 H202 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 H202 may act as a limiting factor for cyanobacterial growth.