SEASONAL CYCLE OF POLYCHLORINATED-BIPHENYLS IN THE WATERS OF THE CATCHMENT BASIN OF THE RIVER SEINE (FRANCE)

In an attempt to explain the origin of Polychlorinated biphenyl (PCB) pollution peaks exceeding 1000 ng L-1 in the River Seine, their concentrations have been studied in relation to the flow rate and the solid load. Longitudinal profiles of the River Seine and two of its tributaries, the Marne and the Orge, show that the PCB concentration in these rivers follows a seasonal rhythm, depending on how much leaching occurs. Indeed leaching is the main cause of the concentrations above 200 ng L-1 observed at high water, both in rural and urban zones. When investigating floods in the sewerage network and the rivers, the PCB concentrations are usually seen to follow the flow rate. PCB and suspended matter concentrations vary in the same way during flood time, though when comparing the distribution of PCBs in the aqueous phase and the solid load, scarcely any connection is seen between PCB transport and the solid load. Thus during flood time in the Seine at Paris, PCB transport remains under the control of the soluble phase (75%). We have been unable to establish a link between the hydric conditions and the PCB spectrum in the river waters.