DESTRUCTION OF CYANOBACTERIAL PEPTIDE HEPATOTOXINS BY CHLORINE AND CHLORAMINE

Toxic cyanobacteria (blue-green algae) are becoming recognized as a greater water quality problem as blooms become more common in waters affected by increasing nutrient levels, and knowledge of the properties of the toxin increases. Of particular importance are the hepatotoxic cyclic peptides produced by certain strains of Microcystis species and by Nodularia spumigena. The effects of chlorine and chloramine on these hepatotoxins in both freeze-dried and intact material were investigated. The destruction of the toxins was monitored using HPLC analysis. In a number of cases mouse bioassays were used for confirmation of the destruction of the toxins and to ensure that toxic by-products, not detectable by HPLC, were not formed. Contrary to evidence reported in the literature, chlorine was effective in destroying toxins, as long as sufficient chlorine was used. Toxins were destroyed under conditions such that a chlorine residual of at least 0.5 mg/l was present after 30 min contact time. The destruction of toxins was pH dependent; chlorinating agents such as calcium and sodium hypochlorite were not as effective at high dose rates due to elevation of pH, Chloramination had little effect on toxins. Although the degradation mechanisms have yet to be established, the results show that chlorination may be an effective and practical method for the removal of cyanobacterial peptide toxins from drinking water.