[en] To determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used 14 C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ingestion and assimilation rates in the rotifer species Brachionus calyciflorus . When the concentration of algae in the culture medium varied from 20 103 to 200 103 algal cells ml -1 (0.12 to 1 .18 mg C 1 - '), the Brachionus calyciflorus ingestion rate varied from 0 .25 ± 0 .12 to 1 .52 ± 0 .43 ng C ind -1 h-1 at 15 °C and from 0 .74 ± 0 .17 to 5 .93 ± 0.61 ng Cind-' h-1 at 20 °C . The assimilation efficiency (ratio of the assimilation rate to the ingestion rate) measured in a culture medium containing 200 103 algal cells ml`' was 55 .7 ± 5.8%. Since the PCB concentration measured in the phytoplankton of the river Meuse is about 3 pg PCBs g -1 D.W., the estimated PCB contamination of zooplankton ascribable to the trophic pathway ranges from 0 .22 ± 0 .17 to 1 .31 ± 0.77 jag PCBs g -1 D.W. at 15 °C and from 0.64 ± 0 .34 to 5 .10 ± 2 .10 pg PCBs g -1 D. W. at 20'C . The lower figure based on measurements effected at 20 ° C is comparable to the actual level measured in zooplankton samples collected in the river Meuse (0 .69 ± 0.20 pg PCBs g`' D.W.) . The applicability of the formula used in our estimate was checked in a 48-hour in vitro experiment in which the rotifers were fed contaminated algae . The PCB accumulation measured in the rotifers was found to coincide with the calculated PCB contamination . Additional experiments were carried out to determine the contribution of the direct pathway to PCB contamination of zooplankton living in the river Meuse (0.02 pg PCBs 1-1 of water; average dissolved organic matter : 3 mg C 1 -1 ). The PCB concentration in zooplankton resulting from direct uptake of PCBs from the water was estimated at 0 .19 ± 0.05 jug PCBs g -1 D.W. These results show that in zooplankton living in polluted ecosystems, PCBs are likely to accumulate via the trophic pathway to concentrations up to 30 times higher than by direct contamination . Furthermore, our estimates of PCB contamination via the trophic pathway coincide quite well with actual concentrations measured in situ .