In 1993 12 eutrophic waterbodies and four laboratory strains were examined for their content of microcystins. In addition to chemical analysis toxicity was assessed with bioassays: primary rat hepatocytes for testing hepatotoxicity and a CHO-K1 cell line for determining more unspecific cytotoxicity. Altogether nine of twelve waterbodies and two laboratory strains contained up to seven different microcystins and were hepatotoxic. Cytotoxicity was observed in six of 24 field samples and one of four laboratory strains. Pure microcystin-LR has an EC50 of 0.2 μg/ml, microcystin-YR of 0.35 μg/ml and microcystin-RR of 4.5 μg/ml on primary rat hepatocytes but showed no further cytotoxicity. Hepatotoxicity was always significantly higher than can be explained by their content of microcystins. Probably other substances from the algae or their environment cause reactions which are synergistic with or additive to microcystins.

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