The use of oxygen evolution to assess the short-term effects of toxicants on algal photosynthetic rates

O-2-production using either Selenastrum capricornutum or Chlorella vulgaris as indicator organisms to assess the presence or not of toxic compounds, was measured in a small volume oxygen chamber. These measurements were done at predetermined I-k irradiancies. At EC50 and EC90 levels, the response of S. capricornutum and C. vulgaris to atrazine toxicity was opposite to the response as determined at the EC10 level. Chlorella vulgaris is more sensitive than S. Capricornutum to high atrazine concentrations, but S. capricornutum is more sensitive than C. vulgaris at the EC10 level. It was shown that the heavy metals Hg, Cd and Cu and the herbicide, atrazine, influenced the photosynthetic rates but the organophosphate, gusathion, had no effect. The oxygen evolution assay may be useful as a rapid prelimiary screening method for the presence or absence of toxic substances.