Inactivation Kinetics of the Cyanobacterial Toxin Microcystin-LR by Free Chlorine

Worldwide, the increasing occurrence of toxins produced by cyanobacteria in water bodies used as source waters for drinking water has become an important public health issue. Microcystin-LR is one of the most commonly found cyanotoxins. A detailed evaluation of the free chlorine induced inactivation kinetics of extracellular microcystin-LR is presented in this study. Rate constants needed for chlorine inactivation of the toxin were derived from the data. The effects of varied pH, chlorine dose, toxin concentration, and temperature on the rate of inactivation were evaluated. Batch chlorination experiments were run using carbonate-buffered Milli-Q water at three different initial toxin concentrations (1, 2, and 8 mg/L), three different chlorine doses (1, 3, and 9 mg/L), and three different pH values (6.0, 7.5, and 9.0) at 11, 20 and 29°C. The study showed that extracellular microcystin-LR was inactivated by free chlorine and the inactivation rate was affected by pH. The highest inactivation rates were observed at pH 6.0 and the lowest at pH 9.0.