STABILITY OF MICROCYSTINS FROM CYANOBACTERIA .2. EFFECT OF UV-LIGHT ON DECOMPOSITION AND ISOMERIZATION

Microcystins are very potent hepatotoxins and strong liver tumor promo ters produced by cyanobacteria, and their occurrence has been reported all over the world, They could threaten human health when toxic Micro cystis occurs in water supply reservoirs. In this study, we examined t he stability of microcystins during photolysis with UV light, The toxi ns were easily decomposed by UV light at wavelengths around the absorp tion maxima of the toxins and the decomposition depended on the intens ity of the light. The half-life of microcystin LR by 147 mu W/cm(2) UV irradiation was 10 min, and the toxin was completely decomposed by 25 50 mu W/cm(2) UV after 10 min. When the toxins were irradiated with we aker UV light, isomerization was also observed by a different mechanis m from that during photolysis by sunlight and pigment, and several pro ducts including three geometrical isomers of the conjugated diene of A dda were detected. Microcystin RR showed almost the same behavior as t hat of microcystin LR under the same conditions, Since no noxious prod ucts were formed in the present study, a water treatment including UV irradiation is very possible for removing microcystins from raw water.