Transport state of PCBs in the river Seine (France)
The evolution of pollution by PCBs and their transport state in rivers was studied in the River Seine in Paris, in relation to the yearly hydrological cycle. Sampling took place just upstream of main waste waters (output) in the Paris area, and downstream from the junction of the Marne and the Seine, in order to establish the mean quality of water pumped upstream of these two rivers for drinking water production. Micropollutant concentrations were measured on 500 ml of raw water and 500 ml of water centrifuged at 6 000 G. Three extractions were carried out on these samples with a solvent mixture (85 % hexane, 15 % dichloromethane). In some cases extracts were purified on unactivated Florisil. After concentration down to 1 ml, extracts were measured through GC (falling needle injector; fused silica capillry column I.D. 0.25 mm, stationary phase SPB5; E.C.D. ni 63; vector gas He, make up Ar + 10 % CH4). Identification and quantification were carried out using an integrator and commercial Aroclor : 1242, 1254 and 1268 standards. In natural samples, the isomer composition is generally close to that of Aroclor 1254. Analytical data show that pollution linked to PCBs is higher than that due to other organochlorinated products, in spite of the official PCBs use limitation for closed systems since 1975. Except for a pollution peak of 990 ng.l-1, concentrations in raw water are irregular and vary from 25 to 250 ng.l-1. For 88 % of analyzed samples, dissolved PCB concentrations are higher than the concentrations of PCBs adsorbed onto suspended matter and reach 170 ng.1-1. The main transport (73 %) of the total flux is by solution, in contradiction with commonly accepted views based on the low solubility of PCBs. The study of adsorption capacity of solid particles demonstrates that its evolution is negatively correlated with the water flux and the solid load, which explains the prevalence of PCBs transport through solution, whatever the suspended matter concentration. Thereafter, it appears that high values of the partition coefficient are not linked to the concentration of suspended matter. For about half of them, values are low, between 2.102 and 12.101 l.kg-1.