Use of lake water in testing copper toxicity to desmid species

The toxicity of copper to Staurastrum chaetoceras (Schr.) G. M. Smith and Staurastrum manfeldtii Delp. has been evaluated using lake water and synthetic media. It appeared that the EC50 values of growth inhibition in synthetic medium with chelators were overestimated, compared to natural water. The omission of chelators in the synthetic medium led to EC50 values distinctly lower than in lake water cultures. The species Staurastrum manfeldtii isolated from an oligomesotrophic environment proved to be significantly more sensitive to copper than Staurastrum chaetoceras originating from a eutrophic environment; this difference was observed in all media tested. It is concluded that the use of synthetic media is likely to give distorted information on metal toxicity so that the use of lake water is to be recommended for ecologically relevant tests.