Preliminary study on the kinetics of oxytetracycline in shellfish exposed to an effluent of a land-based fish farm: Experimental approach

In many ancient saltmarshes marine fish farms are now being developed. These farms, during their production cycles, use many chemical and veterinary products to prevent or fight disease. Since effluents from the farms are discharged directly into shellfish rearing areas, it is necessary to be aware of how shellfish accumulate such substances. An experimental apparatus allowed the creation of a fish farm effluent containing oxytetracycline (OTC) for a seven day treatment period. This effluent was poured into three test tanks, into which individuals of three edible species of bivalves, Crassostrea gigas, Ruditapes philippinarum and Scrobicularia plana, had previously been placed. The highest concentrations were observed in C. gigas (average 1.42 μg.g−1 wet weight). After treatment, the OTC concentration decrease was gradual and slow in C. gigas, reaching 0.68 μg.g−1 wet weight 14 d after the end of medication. Concentrations were stable in R. philippinarum and S. plana until the end of the experiment. Differences observed in the kinetics and maximal OTC concentration values may be related to the filtering rate of the species and their feeding behaviour. These findings illustrated the long persistence of OTC in shellfish. This may be related to the availability of OTC from sediment, the formation of complexes between OTC and some mineral or organic components of the bivalves, and their low xenobiotic metabolism. Considering the dilution processes of the coastal ecosystem, one might surmise that the influence of such contamination is only restricted to the vicinity of the farms. Nevertheless, special care should be taken in the utilization of such substances, especially in integrated aquaculture systems.