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

Abstract

With the increase of algal blooms worldwide, drinking water resources are threatened by the release of various algal toxins, which can be hepatotoxic, cytotoxic, or neurotoxic. Because of their ubiquitous occurrence in global waters and incomplete removal in conventional drinking water treatment, oxidation/disinfection processes have become promising alternative treatment options to destroy both the structures and toxicity of algal toxins. This Review first summarizes the occurrence and regulation of algal toxins in source water and drinking water. Then, the transformation kinetics, disinfection byproducts (DBPs)/ transformation products (TPs), pathways, and toxicity of algal toxins in water oxidation/disinfection processes, including treatment by ozonation, chlorination, chloramination, ultraviolet-based advanced oxidation process, and permanganate, are reviewed. For most algal toxins, hydroxyl radicals (HO • ) exhibit the highest oxidation rate, followed by ozone and free chlorine. Under practical applications, ozone and chlorine can degrade most algal toxins to meet water quality standards. However, the transformation of the parent structures of algal toxins by oxidation/disinfection processes does not guarantee a reduction in toxicity, and the formation of toxic TPs should also be considered, especially during chlorination. Notably, the toxicity variation of algal toxins is associated with the chemical moiety responsible for toxicity (e.g., Adda moiety in microcystin-LR and uracil moiety in cylindrospermopsin). Moreover, the formation of known halogenated DBPs after chlorination indicates that toxicity in drinking water may shift from toxicity contributed by algal toxins to toxicity contributed by DBPs. To achieve the simultaneous toxicity reduction of algal toxins and their TPs, optimized oxidation/disinfection processes are warranted in future research, not only for meeting water quality standards but also for effective reduction of toxicity of algal toxins.

Water Analysis: Emerging Contaminants and Current Issues

“…Transformation of algal toxins during drinking water oxidation/disinfection processes was the focus of a new review by Dong et al 223 An overview of global algal toxin occurrence and regulation was also provided. Transformation kinetics, formation of DBPs/TPs, and reaction pathways are detailed for ozonation, chlorination, chloramination, UV-based advanced oxidation processes, and permanganate treatment of representative algal toxins (MC-LR, cylindrospermopsin, and βmethylamino-L-alanine (BMAA)).…”

Mitigation of Cyanobacterial Harmful Algal Blooms by Electrochemical Ozonation: From Bench-scale Studies to Field Applications

“…3 The surge production of hepatotoxic, cytotoxic, and neurotoxic microcystins can be expected in the HAB events. 4 Chemical oxidation (using chlorine, permanganate, H 2 O 2 , etc.) [5][6][7] and advanced oxidation processes (UV/H 2 O 2 and UV/chlorine) 8 are promising for HAB mitigation at drinking water treatment works.…”

Removal of Algae and Algal Toxins from a Drinking Water Source Using a Two-Stage Polymeric Ultrafiltration Membrane Process

“…Traditional water treatment methods cannot effectively remove MCs from water, especially sand filtration [12][13][14]. Under practical applications, ozone and chlorine might degrade most algal toxins, but disinfection by-products (DBPs)/transformation products may also form during this process [15]. Therefore, it is urgent to develop effective methods for removing microcystins from water to address the seasonal occurrence of algal bloom or sudden outbreaks of blue-green algae in water sources.…”