Microcystins (hepatotoxic heptapeptides) in german fresh water bodies

In 1995 and 1996 a total of 55 German water bodies with different trophic states were investigated for the presence of potentially microcystin-producing cyanobacteria. The seston biomass of over 500 samples was analyzed by HPLC to assess microcystin content. The highest microcystin content per dry weight was found when Planktothrix rubescens was dominant, followed by Planktothrix agardhii and Microcystis spp. The microcystin to chlorophyll-a ratio mostly varied between 0.1 and 0.5, with maxima of 1–2. In over 70% of the samples from pelagic water, particulate microcystin concentrations were below 10 μg L−1. By contrast, spatial and temporal concentrations varied by 4 orders of magnitude (2–25,000 μg L−1) at bathing sites in 1997 during a mass development of Microcystis spp. The seasonal peak of development of Microcystis spp. occurred from June to September and of Planktothrix agardhii from September to November. Planktothrix rubescens, however, was almost perennial. The seasonal levels of these cyanobacteria were clearly reflected by microcystin concentrations in the water bodies.