SENSITIVITY OF PLANKTONIC PHOTOSYNTHESIS TO VARIOUS TOXICANTS IN THE RIVER RHINE

Natural populations of phytoplankton from the lower River Rhine were exposed to selected pollutants in order to estimate their sensitivity to chemical pollution. The photosynthesis, measured as C-14 incorporation, was inhibited by 50% when circa 100 mug.L-1 copper or atrazine was added. Potassium dichromate (K2Cr2O7) and an anionic detergent (tetrapropylbenzenesulphonate) affected the photosynthesis of Rhine phytoplankton only at concentrations of about 3 and 40 mg L-1, respectively. A tenfold concentrate of the organic compounds from river water, harvested on XAD resin, inhibited the photosynthesis by 50%. Comparison of the results of this study with literature data indicate that the algal populations in the River Rhine are as sensitive and not more tolerant than several algae from less polluted habitats. These observations on the Rhine plankton also indicate that the pollution level in the River Rhine is likely to affect the photosynthesis of phytoplankton. This supports the request for a further reduction in toxicant input in the River Rhine.