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Background information

Hazards caused by cyanobacteria

Cyanobacteria have often been observed to be toxic: numerous fatalities of wild and domestic animals after ingestion of cyanobacteria from drinking cyanobacteria-contaminated water are documented. Also a number of cases of human illness have been attributed to cyanobacteria.

Cyanobacteria contain a multitude of secondary metabolites, some of which are toxic. These cyanotoxins can be classified according to their mode of action as hepatotoxins, cytotoxins, neurotoxins and inflammatory substances. Moreover, some of the substances are suspected carcinogens or promote the growth of tumors. In addition, unspecific symptoms include irritation or allergic reactions of the skin, intestinal tract, the respiratory system, ears and mucous membranes of the eyes, which are, however, rarely attributable to a particular toxin or substance.

Humans can be affected by cyanobacteria and/or their toxins through use of water bodies contaminated with cyanobacteria, especially through recreational use with intensive body contact or if drinking water contains cyanotoxins exceeding guideline values. Further, food can be contaminated with cyanotoxins (e.g. fish or dietary supplements from cyanobacteria).

Acute intoxications of animals have often been caused by neurotoxins, but also for hepatotoxins (microcystins, cylindospermopsins) acute intoxications are observed when high amounts of toxic cyanobacteria have been swallowed. However, the major health hazard of hepatotoxins is by chronic exposure with small amounts. The World Health Organization thus recommends a provisional guideline value of 1 µg/l for one of the most toxic microcystin variants Microcystin-LR, and for cylindrospermopsin, a guideline value of 1 µg/l has been suggested. For neurotoxins, no guideline values can be derived as sufficient toxicological data on chronic exposure are lacking.

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