Hepatotoxic microcystin diversity in cyanobacterial blooms collected in portuguese freshwaters

Twelve toxic cyanobacterial bloom samples collected in natural lakes, reservoirs and rivers of Portugal were analysed. Toxicity was evaluated by mouse LD50 bioassay of the lyophilised samples. The main bloom species present in the samples were Microcystis aeruginosa, Microcystis wesenbergii, Anabaena flos-aquae and Nostoc sp. Toxins were extracted, isolated by reverse phase HPLC and characterised by HPLC amino acid analysis and fast atom bombardment mass spectrometry. Two to seven microcystins were purified from each sample, and a total of seven different toxins were isolated and their structure assigned. MCYST-LR was the most common and its proportion in each sample ranged from 45.5% to 99.8% of the total microcystin contents. MCYST-RR, MCYST-YR and [D-Asp3]MCYST-LR were also identified in the samples. Three less common microcystins, MCYST-HilR, [L-MeSer7]MCYST-LR and [Dha7]MCYST-LR, were found in only one sample. Total MCYST concentration varied from 1.0 to 7.1 μg/mg dry weight of cyanobacteria. Significant relationships between LD50-MCYST-LR-total MCYST content were found. The need for monitoring cyanobacteria and their toxins in eutrophic waters that are used for drinking and recreation purposes is discussed.