TOXIC CYANOBACTERIA (BLUE-GREEN-ALGAE) IN PORTUGUESE FRESH-WATERS

A survey on the distribution of toxic fresh water cyranobacteria on 36 lakes, reservoirs and large rivers of Portugal was made during 1989-9 2. Eighteen of thirty waterbloom samples were found to be. toxic by in traperitoneal mouse bioassay. Only hepatotoxic waterblooms were found with Microcystis aeruginosa occurring in all waterblooms and being dom inant in 22 of them. LD50 of these blooms varied from 20 mg/kg to 700 mg/kg but over 60 % of them had an LD50 < 100 mg/kg. Toxicity was foun d to vary a lot along time within a same lake. LD50 of Microcystis spp . isolated strains varied from 15 mg/kg to 75 mg/kg. The results revea led a high incidence of toxic waterblooms in Portuguese water supplies including many drinking water reservoirs. Toxicity is due to the pres ence of potent hepatotoxic tumor promoting peptide toxins called micro cystins. It is recommended that a monitoring programme be established in order to detect the presence of cyanobacteria toxins in these water bodies.