Establishment of the PCBs contamination by the trophic pathway of a freshwater planktonic rotifer species, Brachionus calyciflorus

ngestion and assimilation rates of the rotifer species Brachionus Calyciflorus were established in order to determine the PCB contamination of zooplankton by ingestion of contaminated food (i.e. by the indirect pathway) in the river Meuse (Belgium). Ingestion and assimilation rates of the rotifers were measured using 14C-labelled algae (Dictyosphaerium ehrenbergianum). Besides, the concentration of PCBs of the phytoplankton and the zooplankton living in the river Meuse were determined. The ingestion rate of Brachionus calyciflorus ranged from 1.62 to 17ngC/ind.h. when the concentration of algae present in the culture medium varied from 14 to 300 algal cells/1 (that is 0.14 to 3 mg C/1) at a temperature of 23 ± 1°C. The assimilation rate measured in a culture medium containing 300 algal cells/l was about 50% of the ingestion rate measured in a culture medium containing 300 algal cells/1 was about 50% of the ingestion rate. The PC B contamination level measured in the phytoplankton of the river Meuse was about 3µ PCBs/g D. W. and the PCBs concentration of the zooplankton varied from 0.6 to 1µg PCBs/g D. W. On the basis of these data, the concentration of PCBs accumulated by the zooplankton of this river by ingestion of contaminated food was calculated. The minimal value found was 1.7 µg PCBs/g D.W. So these experiments show that the PC B contamination of zooplankton by the indirect pathway is sufficient to justify the concentration of PCBs measured in the zooplankton of the river. (C. J.-J. acknowledges a IRSIA grant).