Persistent toxic substance inputs to the river Seine basin (France) via atmospheric deposition and urban sludge application

Paris constitutes a major direct and indirect source of persistent toxic substances (PTS) to the river Seine, its tributaries and its basin, by atmospheric depositions and sewage sludge land-filling. The contaminant cycle and transfer pathways were investigated from 1999 to 2003 at local and inter regional scales in order to determine the respective importance of the main input and diffusion processes (wastewater, rainwater and runoff) from urban to rural areas. Paris constitutes an atmospheric emission hot spot for PAHs and PCBs. For example, for 2002, atmospheric concentrations ranged from 0.5 to 3 ng m−3 for PAHs (Σ 6 WHO) and from 0.06 to 0.69 ng m−3 for PCBs (Σ 7, EEC) and concentrations in bulk deposition ranged from 6.6 to 647 ng L−1 for PAHs (Σ 14) and from 0.6 to 8.1 ng L−1 for PCBs. At Paris, annual atmospheric deposition inputs of PAHs (Σ 6) and PCBs (Σ 7) reached 104 g km−2 and 35 g km−2, respectively. PAHs followed a marked seasonal cycle in relation with winter domestic heating and bulk deposition concentrations were 5 to 15 times lower in remote areas. No seasonal cycle was observed for PCBs which varied little according to the area considered. PCB deposition fluxes were ruled by the rainfall amount, while for PAHs, the fluxes depended on local anthropogenic characteristics. At the scale of the Seine-Aval treatment plant comparison of annual inputs of PTS in wet period indicated that PCBs essentially come from atmospheric sources whereas PAHs are derived from both atmospheric and urban runoff sources. At the scale of the sub-basin, atmospheric inputs to the soil (Σ 3 PAHs: 14–25 g km−2, Σ 7 PCBs: 5.6–25 g km−2) represent the prevailing source for PAHs and PCBs, as compared to that from the disposal of urban sludge on agricultural plots (Σ 3 PAHs: 3–8 g km−2, Σ 7 PCBs: 0.5–2 g km−2).