Several studies show that algal toxins, such as domoic acids (DAs) or cyanotoxins (particularly microcystins), may be subject to photolysis. In the marine environment, the planktonic diatom Pseudo-nitzschia spp. is a known producer of DA, a tricarboxylic amino acid with neurotoxic properties; its occurrence has been linked to fish kills, poisoning of marine mammals and birds, and human poisoning through ingestion of contaminated shellfish and finfish. DA may be photodegraded directly as well as indirectly. The direct photolysis degrades this potent toxin on a timescale of days. However, Fe(III) and dissolved organic matter are significant promoters of DA photodegradation - indicating that photo-Fenton reactions are involved.
Microcystins, potent freshwater toxins, are stable in deionized water when exposed to natural sunlight. However, they can indirectly be photodegraded, when extracted algal pigments or humic material, serving as photosensitizers, are added to the irradiation solutions. With HS, the aromaticity was the most powerful molecular predictor of the indirect photodegradation. Since its rates are yet comparably low, this purification process alone cannot explain the frequently observed low persistence - neither does the microbial decomposition alone. Hence, the combination of photolytic cleavage and microbial decomposition is possibly the way that micro-cystins disappear from open water. It means that indirect photolysis may lead to products which microorganisms can rapidly decompose and utilize the energy content.
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