ISOLATION OF MICROCYSTIN-LR FROM A MICROCYSTIS (CYANOBACTERIA) WATERBLOOM COLLECTED IN THE DRINKING-WATER RESERVOIR FOR PORTO, PORTUGAL

Plankton tows collected over the water intake towers on Crestuma reservoir, which is the drinking water supply for about 2,000,000 persons in the Porto, Vila Nova de Gaia, and Gondomar regions near the city of Porto, were found to be hepatotoxic using the mouse intraperitoneal bioassay. Phytoplankton in these samples was dominated by the cyanobacteria Microcystis aeruginosa (95%). The lethal dose for 50% of the animals tested of lyophilized bloom material was approximately 30 mg/kg (dry cell weight/animal weight). Using HPLC separation, a single fraction was obtained. Isolation and purification of this fraction resulted in a toxin that was shown to be microcystin-LR by amino acid and MS analyses. Since microcystin-LR is a potent hepatotoxin and liver tumor promoter, and since high cell densities of Microcystis aeruginosa producing microcystin-LR were found near the water intake lines, it shows that a regular monitoring of microcystin(s) should be developed in water used for human consumption to prevent any health hazard. The eutrophication of the Douro River due to agricultural runoff, domestic effluents, and effluents from large Spanish towns leads us to conclude that M. aeruginosa toxic waterblooms will continue to occur and possibly increase during periods of low rainfall and warm weather. This creates the distinct possibility that human and animal intoxications will occur. We recommend that regulations concerning the control of microcystins in waters be developed in countries where this problem occurs. A national program in Portugal to inform the public about the possibility of cyanobacteria intoxication is also recommended.