Kinetics of reactions between chlorine and the cyanobacterial toxins microcystins

Apparent second-order rate constant for the chlorination of MC-LR at 20 °C varied from 475 M−1 s−1 at pH 4.8 to 9.8 M−1 s−1 at pH 8.8. From these apparent second-order rate constants, rate constants for the reactions of MC-LR with hypochlorous acid (HOCl) and hypochlorite (ClO−) were evaluated. Half-life times ranged from minutes at pH 6 to 1 h at pH 8 for a constant residual chlorine concentration of 1.0-0.5 mg l−1, typical of oxidation pre-treatment and final disinfection. Similar reactivity with chlorine was found for MC-RR and MC-YR. Therefore, chlorination is a feasible option for microcystin degradation during oxidation and disinfection processes, and can be applied in drinking water treatment in case of cyanobacterial toxin risk if the pH is kept below 8.