LEVELS OF MICROCYSTINS IN JAPANESE LAKES

Microcystins LR and RR in two lakes were identified and their concentr ations were determined. Water blooms containing Microcystis aeruginosa , M. viridis and M. weisenvergii covered the surface of both lakes. M. aeruginosa was the most prevalent toxic cyanobacterium detected. Micr ocystin was identified by the mass spectra of the oxidation product, 2 -methyl-3-methoxy-4 phenyl butyric acid. Microcystin RR was detected a t a concentration of 8.8 mug/l of lake A water collected in June, 1992 , whereas that of microcystin LR was 1.5 mug/l. Microcystin RR in lake A water was detected during the October (the warm season) but microcy stin LR was not detected in the period from July to October. The conce ntration of microcystin RR is associated with that of chlorophyll-a in water blooms.