HEPATOTOXIC MICROCYSTIN DIVERSITY IN CYANOBACTERIAL BLOOMS COLLECTED IN PORTUGUESE FRESH-WATERS

Twelve toxic cyanobacterial bloom samples collected in natural lakes, reservoirs and rivers of Portugal were analysed. Toxicity was evaluate d by mouse LD(50) bioassay of the lyophilised samples. The main bloom species present in the samples were Microcystis aeruginosa, Microcysti s wesenbergii, Anabaena flos-aquae and Nostoc sp. Toxins were extracte d, isolated by reverse phase HPLC and characterised by HPLC amino acid analysis and fast atom bombardment mass spectrometry. Two to seven mi crocystins were purified from each sample, and a total of seven differ ent toxins were isolated and their structure assigned. MCYST-LR was th e most common and its proportion in each sample ranged from 45.5% to 9 9.8% of the total microcystin contents. MCYST-RR, MCYST-YR and [D-Asp( 3)]MCYST-LR were also identified in the samples. Three less common mic rocystins, MCYST-HilR, [L-MeSer(7)]MCYST-LR and [Dha(7)]MCYST-LR, were found in only one sample. Total MCYST concentration varied from 1.0 t o 7.1 mu g/mg dry weight of cyanobacteria. Significant relationships b etween LD(50)-MCYST-LR-total MCYST content were found. The need for mo nitoring cyanobacteria and their toxins in eutrophic waters that are u sed for drinking and recreation purposes is discussed. Copyright (C) 1 996 Elsevier Science Ltd