Immediate and long-term impacts of potassium permanganate on photosynthetic activity, survival and microcystin-LR release risk of Microcystis aeruginosa

The immediate and long-term impacts of potassium permanganate (KMnO ₄) as pre-oxidant on Microcystis aeruginosa and microcystin-LR (MC-LR) release risk were investigated. The cell density and the integrity of M. aeruginosa were determined by a flow cytometry, and typical photosynthetic parameters were measured by a pulse amplitude modulated fluorometer. The photosynthetic parameters were reduced to different degrees, accompanied with slight cytoclasis and complete degradation of extracellular MC-LR immediately after various dosages KMnO ₄ oxidation (2-20mgL ^-1). In a 6-d cultivation following 5mgL ^-1 KMnO ₄ oxidation, the cell density decreased from 3.9×10 ⁶ to 0.6×10 ⁶cellsmL ^-1, and then increased to 0.9×10 ⁶cellsmL ^-1, while the extracellular MC-LR increased from 0 to 51.2μgL ^-1. In the cultivation after 10mgL ^-1 KMnO ₄ treatment, the intracellular MC-LR and cell activity significantly declined, while significant cytoclasis (cell density from 3.8×10 ⁶ to 0cellsmL ^-1) and MC-LR release (increase from 0 to 15.2μgL ^-1) were observed. The photosynthetic parameters were found to be useful tools to predict the recovery tendency of M. aeruginosa cells, and the MC-LR release risk should be considered during KMnO ₄ pre-oxidation in water-treatment plants.