Action of sediments in the River Seine (Paris area) on the short term development of cultures of the micro-alga Selenastrum capricornutum Printz
A bioevaluation of the state of health of soft bottoms depends on the experimental conditions in which samples of sediment are treated to obtain the water phase to be subjected to chemical and toxicological analyses. In the course of this preliminary study we have considered the action of these principal conditions. We have noted that the inhibiting effect of a sediment on the short-term growth of a microalga Selenastrum capricornutum is not easy to eliminate, whether by a series of washes of the sediment, by a finer filtration of the water extracted from this sediment or by e previous autoclavage of this sediment. This study quickly revealed which sediments in the River Seine (Paris area) inhibited most the test micro-alga Selenastrum capricornutum (Chlorophyceae); the cause of these inhibitions was then sought. There is no correlation between the often high content of heavy metals in the sediment water (Pb 70, Cu 100, Cr 150, Cd 9, Ni 280, Zn 400 μg.L-1) and the development of the algae; the metal pollutants are probably masked by the chelating capacity of these biotopes rich in organic substances. The experimental conditions under which the sediment samples are treated to obtain the water phase used for the chemical and toxicological analyses are also important. One conclusion drawn is that a chemical analysis alone of the sediments is of limited interest. The most reliable data from the ecological point of view are those provided by the bio-assays.