Contamination d'une chaine trophique experimentale par le methylmercure: Importance du systeme ‘producteur-consommateur primaire’

Abstract

Within the framework of methylmercury bioaccumulation and bioamplification along an experimental food chain with four links, the contamination procedure of the first two trophic levels, Chlorella vulgaris and Daphnia magna is accurately defined. After developing the chosen methodology and the constraints inherent in each link, the main results showing the primary producer are presented from the toxicological point of view (inhibition rate of Chlorella growth). A sublethal concentration is defined for each species in our model (1 μg litre −1 in the environment) and the dynamics of mercury fixation for Chlorella vulgaris and Daphnia magna are quantified at three temperatures (10, 18 and 26°C) over contamination periods of 24 and 96 h, respectively. The study enabled us to show the great fixation capacity of algae for mercury. Therefore, the first consumer level is essentially contaminated trophically. The results obtained underline the temperature factor effect on Daphnia magna accumulation processes; moulting, in relation to temperature, partly explaining the differences observed. The high values of the pollutant concentration factors relative to the ‘water- Chlorella-Daphnia’ system confirm the importance of the inclusion of an autotrophic link at the base of an experimental trophic chain. On the other hand, the accuracy of the measurement shows the high level of reliability and reproducibility of the procedure chosen.