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Stability of microcystins from cyanobacteria--IV. Effect of chlorination on decomposition
1Kanagawa Prefectural Public Health Laboratories, Yokohama, Japan.
Abstract:
Microcystins, the cyclic heptapeptide toxins produced by cyanobacteria such as Microcystis, show tumor-promoting activity through inhibition of protein phosphatases 1 and 2A. They potentially threaten human health, and are increasing the world-wide interest in the health risk associated with cyanobacterial toxins. In this study, the effect of chlorination on the decomposition of microcystins-LR and -RR was examined. The toxins were easily decomposed by chlorination with sodium hypochlorite, and the decomposition depended on the free chlorine dose. In this operation, many reaction products were formed, one of which was determined to be dihydroxymicrocystin formed through the chloronium ion at the conjugated diene of Adda [3-amino-9-methoxy-10-phenyl-2,6,8-trimethyl-deca-4(E), 6(E)-dienoic acid], followed by hydrolysis. Other products may be its stereoisomers and/or regioismers. No noxious products were detected from the chlorination process of microcystin-LR. Although these results suggested that chlorination at an adequate chlorine dose is very effective for the removal of microcystin in raw water, preoxidation of the cell itself with chlorine must be avoided, because it frequently causes toxin release from algae and produce trihalomethanes during water treatment.
Insights
Chlorination effectively decomposes harmful microcystins (cyanobacterial toxins) in water, with effectiveness depending on chlorine dose. Avoid pre-oxidizing algae cells to prevent toxin release and harmful byproducts.
Area of Science:
- Environmental Chemistry
- Toxicology
- Water Treatment
Background:
- Cyanobacteria produce microcystins, cyclic heptapeptide toxins that inhibit protein phosphatases 1 and 2A, posing health risks.
- Increasing global interest in cyanobacterial toxins necessitates effective removal strategies in water treatment.
Purpose of the Study:
- To investigate the efficacy of chlorination in decomposing microcystins-LR and -RR.
- To identify reaction products and assess potential hazards associated with microcystin chlorination.
Main Methods:
- Examined the decomposition of microcystins-LR and -RR using chlorination with sodium hypochlorite.
- Analyzed reaction products, including the identification of dihydroxymicrocystin.
Main Results:
- Chlorination readily decomposed microcystins, with decomposition rate dependent on free chlorine dose.
- Dihydroxymicrocystin was identified as a major product, formed via a chloronium ion intermediate at the Adda residue.
- No noxious byproducts were detected from the chlorination of microcystin-LR.
Conclusions:
- Adequate chlorination effectively removes microcystins from raw water.
- Pre-oxidation of cyanobacterial cells with chlorine should be avoided to prevent toxin release and trihalomethane formation.