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.
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