Polycyclic aromatic hydrocarbons and polychlorobiphenyls in wastewaters and sewage sludges from the Paris area (France)

Polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) were investigated during 1999-2000 in the sewerage system to the Seine Aval treatment plant which drains the Paris area (France). Contamination of sludges from storage chambers indicated a local origin typical of motor car traffic with PAH concentrations (Σ16) ranging from 14 to 31 mg kg-1 of dry weight, pyrene/fluoranthene ratios ranging between 1.12 and 1.48 and PCB concentrations (Σ7) ranging from 0.07 to 0.65 mg kg-1 of dry weight. In the same way, sludges from sand removal tanks displayed PAH values related to the importance of traffic whereas PCBs were rather characteristic of a diffuse origin. Among the five sewers entering the Seine Aval treatment plant, Clichy Argenteuil, which drains a large industrial area, was the most polluted one (PAHs as Σ3, 10 kg year-1; PCBs as Σ7, 3.5 kg year-1). Seasonal variations were observed for PAHs with higher levels in winter in relation with the occurrence of combustion processes. Ninety-eight percent of the PAHs and 76% of the PCBs were extracted during the treatment plant processes, the primary clarifier of which retained 50% of the pollutants. Fluoranthene and PCB concentrations in the final dehydrated sludge (mean values) were 1.07 and 0.623 mg kg-1 of dry weight, respectively. For PCBs, a significant correlation was found (r=0.668, P<0.001) between wastewater and dehydrated sludge concentrations. Yearly measured amounts of PAHs (Σ3) were twice higher in sludges (76.3 kg) than in precipitations (37.7 kg) whereas those of PCBs (Σ7) brought by total atmospheric fallout (17.6 kg) and sludges (21.1 kg) did not differ significantly