Cyanobacterial blooms in fresh water lakes have become an increasing problem in temperate zones due to eutrophication of the water. In some fresh water lakes in Bavaria cyanobacteria developed to one of the dominant plankonic organisms. Cyanobacteria are able to produce toxins, such as microcystins (MCYSTs), anatoxin, cylindrospermopsin or saxitoxin. MCYSTs are hepatotoxic, cyclic heptapeptides. Illness after recreation in lakes exhibiting cyanobacterial bloom has been observed. A graduated scheme of visual inspection and chemical analysis was applied to monitor the Bavarian recreational water. When algae bloom occurred and/or water transparency decreased to one metre or less a water sample was taken for analysis of total MCYSTs content by ELISA. If total MCYSTs content exceeded 10μg/l, verification by HPLC analysis was performed. Since 2003 164 samples have been analyzed originating from 66 Bavarian lakes. In 49 lakes no MCYSTs were detected. However, 10-100μg/l total MCYSTs were detected in five lakes, 100-1000μg/l in five lakes and more than 1000μg/l in four lakes. The main MCYSTs detected were MCYST-RR, -LR and YR in changing concentrations. In two out of three lakes MCYSTs content correlated linear with chlorophyll a content. However, no correlation between phosphate content and MCYSTs content was observed. Even at phosphate concentrations as low as 0.02 mg/l up to 2600 μg/l MCYST were formed.

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