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Top-down and bottom-up effects in a diclofenac contaminated model ecosystem
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International audience. Pharmaceuticals are widely used in human and veterinary health care products. Their occurrence in the aquatic environment is nowadays a well established issue and has become a matter of both scientific and public concern. As these substances are biologically active and might be persistent, toxic effects on organisms are suspected at low concentrations and have been demonstrated mainly for steroidal hormones. Diclofenac is a non-steroidal anti-inflammatory drug, which is found at concentrations ranging between 10- 100 ug/L in European freshwater ecosystems. As chronic ecotoxicity data as well as information on the current distribution patterns in environmental compartments are scarce, an integrated hazard assessment strategy was proposed based on low tier (standardized tests, biomarkers studies) and high tier studies (lotic mesocosms). The results of the lotic mesocosm experiment are described in this communication. The study was carried out, in twelve 20 meter long channels, under continuous, environmentally realistic concentrations of diclofenac (0.1, 1 and 10 ug L-1 in triplicats). The mesocosms were set up with artificial sediments, macrophytes, periphyton, benthic and pelagic invertebrates, decomposers and one fish species (Gasterosteus aculeatus). After three months of ecosystem stabilization, treatment lasted 6 months. Periphyton biomass, macrophyte biovolume, zooplankton and invertebrate abundance and diversity and fish individual physiological responses along with population dynamics were the measured biological endpoints. Diclofenac concentration in water was monitored each month by chemical analysis. In order to account for the observed effects, degradation products and major metabolites were also measured in the sediment, watercress and fish. Effects on water quality parameters, macrophytes and fish were observed at the highest tested concentration. Top-down and bottom-up effects seem to drive and structure the responses of the other populations and communities. A conceptual model presenting the overall response is proposed.
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