FIRST REPORT ON THE IDENTIFICATION OF MICROCYSTIN IN A WATER BLOOM COLLECTED IN BELGIUM

A toxic cyanobacterial bloom dominated by Microcystis aeruginosa occur red in 1995 in three adjacent ponds near Liege (Belgium) where at the same time conspicuous bird deaths were observed. The toxicity assay us ing primary rat hepatocytes indicated a high hepatotoxicity. A 4 h inc ubation yielded a LD50 of 0.23 mg bloom material (dry weight)/ml cell culture medium. Toxicity was due to hepatotoxins of the microcystin cl ass, microcystin-LR and -RR being the major microcystins present as de termined by RP-HPLC absorption spectra, H-1 NMR, and ESMS spectra. Add itionally, the bloom sample contained small amounts of microcystin-YR. The microcystin content of the dry bloom biomass was 870 mu g/g ton t he basis of the hepatotoxicity assay) and 556 mu g/g ton the basis of the RP-HPLC peak area). A higher yield of microcystins was obtained by acetic acid extraction instead of methanol extraction, whereas differ ent extraction temperatures (20 degrees C, 40 degrees C) had no effect on the yield.