OCCURRENCE OF TOXIC WATER BLOOMS CONTAINING MICROCYSTINS IN A GERMAN LAKE OVER A 3 YEAR PERIOD

Toxic cyanobacterial blooms occurred in the pears of 1992, 1993 and 19 94 in a recreational lake in Germany (Leipzig). Each year, the bloom w as dominated by Microcystis sp. and heaviest in September/October. Sam ples were collected from the surface as a scum and the toxicity was de termined by the mouse bioassay (LD(50) Of the bloom sample 1992: 80 mg dry wt/kg body weight). Toxicity was primarily due to hepatotoxins of the microcystin class; microcystin-LR and microcystin-RR were found t o be the major microcystins present in the samples of 1992, 1993, and 1994. Additionally, the bloom sample of 1993 contained microcystin-YR as a major hepatotoxin. Other microcystins were detected only in small er amounts. The microcystins were identified applying common methods a nd included purification by a combination of Sephadex LH-20 gel filtra tion and anion exchange chromatography. The latter method proved to be applicable for the rapid separation of microcystin-RR from the other microcystins. Microcystin-YR revealed a UV absorbance maximum at 232 n m in contrast to the other microcystins found.