in the WWTP effluents would be necessary to validate or improve the quantification
of the flux discharged to the Seine River. This investigation would even be crucial at
the Seine River basin scale because small-capacity WWTPs vary greatly in efficiency. A similar consideration can be made for most of the urban fluxes because
various inconsistencies appeared in the mass balance at the Seine River basin scale
due to the lack of representative databases for such an extended area. Consequently,
research is still required to precisely quantify the PAH flux in the urban parts of
the basin other than the Paris conurbation. In particular, fluxes related to the sewer
system and the WWTP are poorly known in less densely populated areas. This
difficulty was highlighted by the road runoff estimation. To properly quantify this
flux, one should investigate the relationship between the PAH concentrations in
the runoff water, the runoff volume and the daily vehicle traffic.
In addition, certain fluxes could not be estimated based on the compiled databases, especially the environmental degradation fluxes. However, according to our
PAH budgets, only degradation within the atmosphere would be significant. Indeed,
the long-term contaminations of the soils which constituted the main PAH reservoir
suggest that no significant degradation occurs in this compartment. This result could
be reinforced by long-term monitoring of soils. Similarly, PAH volatilisation from
soils was not quantified. More generally, the gaseous exchanges at the ground-plantatmosphere interface required further investigation.
Finally, there is a serious need to investigate the enrichment process to refine the
PAH flux related to soil erosion at the Seine River basin scale. Indeed, this parameter
plays a crucial role in determining if the Seine River basin is currently balanced in
terms of PAH input and outputs or if it is currently undergoing a decontamination
phase. Contaminated sediment stored in the river bed and in reservoirs is likely to be
remobilised during massive flood events such as the one that occurred in June 2016
[69]. A long-term survey of the Seine River would be required to precisely quantify
the average annual fluxes in the Seine system. In particular, closer monitoring of
flood events would drastically improve the accuracy of the estimation of the PAH
flux being carried by the Seine River downstream of Paris (F21).
Acknowledgements This work was conducted in the framework of the PIREN-Seine research
programme (www.piren-seine.fr), a component of the Zone Atelier Seine within the international
Long Term Socio-Ecological Research (LTSER) network.
References
1. Meybeck M, Lestel L, Bonté P et al (2007) Historical perspective of heavy metals contamination (Cd, Cr, Cu, Hg, Pb, Zn) in the Seine River basin (France) following a DPSIR approach
(1950–2005). Sci Total Environ 375:204–231
2. Thévenot DR, Moilleron R, Lestel L et al (2007) Critical budget of metal sources and pathways
in the Seine River basin (1994–2003) for Cd, Cr, Cu, Hg, Ni, Pb and Zn. Sci Total Environ
375:180–203
Mass Balance of PAHs at the Scale of the Seine River Basin
183
of the flux discharged to the Seine River. This investigation would even be crucial at
the Seine River basin scale because small-capacity WWTPs vary greatly in efficiency. A similar consideration can be made for most of the urban fluxes because
various inconsistencies appeared in the mass balance at the Seine River basin scale
due to the lack of representative databases for such an extended area. Consequently,
research is still required to precisely quantify the PAH flux in the urban parts of
the basin other than the Paris conurbation. In particular, fluxes related to the sewer
system and the WWTP are poorly known in less densely populated areas. This
difficulty was highlighted by the road runoff estimation. To properly quantify this
flux, one should investigate the relationship between the PAH concentrations in
the runoff water, the runoff volume and the daily vehicle traffic.
In addition, certain fluxes could not be estimated based on the compiled databases, especially the environmental degradation fluxes. However, according to our
PAH budgets, only degradation within the atmosphere would be significant. Indeed,
the long-term contaminations of the soils which constituted the main PAH reservoir
suggest that no significant degradation occurs in this compartment. This result could
be reinforced by long-term monitoring of soils. Similarly, PAH volatilisation from
soils was not quantified. More generally, the gaseous exchanges at the ground-plantatmosphere interface required further investigation.
Finally, there is a serious need to investigate the enrichment process to refine the
PAH flux related to soil erosion at the Seine River basin scale. Indeed, this parameter
plays a crucial role in determining if the Seine River basin is currently balanced in
terms of PAH input and outputs or if it is currently undergoing a decontamination
phase. Contaminated sediment stored in the river bed and in reservoirs is likely to be
remobilised during massive flood events such as the one that occurred in June 2016
[69]. A long-term survey of the Seine River would be required to precisely quantify
the average annual fluxes in the Seine system. In particular, closer monitoring of
flood events would drastically improve the accuracy of the estimation of the PAH
flux being carried by the Seine River downstream of Paris (F21).
Acknowledgements This work was conducted in the framework of the PIREN-Seine research
programme (www.piren-seine.fr), a component of the Zone Atelier Seine within the international
Long Term Socio-Ecological Research (LTSER) network.
References
1. Meybeck M, Lestel L, Bonté P et al (2007) Historical perspective of heavy metals contamination (Cd, Cr, Cu, Hg, Pb, Zn) in the Seine River basin (France) following a DPSIR approach
(1950–2005). Sci Total Environ 375:204–231
2. Thévenot DR, Moilleron R, Lestel L et al (2007) Critical budget of metal sources and pathways
in the Seine River basin (1994–2003) for Cd, Cr, Cu, Hg, Ni, Pb and Zn. Sci Total Environ
375:180–203
Mass Balance of PAHs at the Scale of the Seine River Basin
183