Transformation of Algal Toxins during the Oxidation/Disinfection Processes of Drinking Water: From Structure to Toxicity

With the increase of algal blooms worldwide, drinkingwater resourcesare threatened by the release of various algal toxins, which can behepatotoxic, cytotoxic, or neurotoxic. Because of their ubiquitousoccurrence in global waters and incomplete removal in conventionaldrinking water treatment, oxidation/disinfection processes have becomepromising alternative treatment options to destroy both the structuresand toxicity of algal toxins. This Review first summarizes the occurrenceand regulation of algal toxins in source water and drinking water.Then, the transformation kinetics, disinfection byproducts (DBPs)/transformationproducts (TPs), pathways, and toxicity of algal toxins in water oxidation/disinfectionprocesses, including treatment by ozonation, chlorination, chloramination,ultraviolet-based advanced oxidation process, and permanganate, arereviewed. For most algal toxins, hydroxyl radicals (HO & BULL;) exhibit the highest oxidation rate, followed by ozone and freechlorine. Under practical applications, ozone and chlorine can degrademost algal toxins to meet water quality standards. However, the transformationof the parent structures of algal toxins by oxidation/disinfectionprocesses does not guarantee a reduction in toxicity, and the formationof toxic TPs should also be considered, especially during chlorination.Notably, the toxicity variation of algal toxins is associated withthe chemical moiety responsible for toxicity (e.g., Adda moiety inmicrocystin-LR and uracil moiety in cylindrospermopsin). Moreover,the formation of known halogenated DBPs after chlorination indicatesthat toxicity in drinking water may shift from toxicity contributedby algal toxins to toxicity contributed by DBPs. To achieve the simultaneoustoxicity reduction of algal toxins and their TPs, optimized oxidation/disinfectionprocesses are warranted in future research, not only for meeting waterquality standards but also for effective reduction of toxicity ofalgal toxins.

Automated summary

With the increasing occurrences of algal blooms worldwide, the release of algal toxins threatens drinking water resources. Oxidation/disinfection processes have shown promise in removing algal toxins, however, the transformation of these toxins does not guarantee a reduction in toxicity. The formation of toxic transformation products (TPs) should also be considered, especially during chlorination. Further research is necessary to optimize oxidation/disinfection processes for effective reduction of toxicity.