Cyanobacterial extracts and microcystin-LR are inactive in the micronucleus assay in vivo and in vitro

Cyanobacteria are sometimes widespread in lakes and can produce potent toxins, which can be dangerous for animals that drink the water, e.g. cattle and dogs. If the toxins are taken up by fish and other organisms in the food chain, or occur in drinking-water, they may pose a problem also for humans.Microcystin-LR, a hepatotoxic cyclic peptide, is one of the most frequently found cyanobacterial toxins. Data on the genotoxic potential of microcystin-LR and other cyanobacterial toxins are contradictory. Here we report results of the micronucleus assay carried out in vivo and in vitro with these toxins. To increase the sensitivity, we used the flow cytometry-based micronucleus assay in the mouse.In this study both pure microcystin-LR and cyanobacterial extracts originating from four different lakes in Sweden were analysed. Although doses up to near lethality were used and an average of 200,000 young erythrocytes, polychromatic erythrocytes, were analysed from each animal, no genotoxic effect was observed, nor could any effect be shown in the in vitro micronucleus study, using human lymphocytes.These results show that the low concentration of microcystins that now and then occur in drinking-water does not increase the cancer risk through chromosome breaks or mal-distribution of chromosomes.