3.2.7 Flux Transported by the Seine River
To investigate the PAH flux within the Seine River, calculations were based on
concentrations measured independently in the particulate and the aqueous phases.
The databases for the particulate and the dissolved fluxes of PAHs contained
15 samples from two studies [9, 60] and 11 samples from two studies [8, 60]. The
annual PAH flux was estimated by attributing random values of the PAHs drawn
from the databases to the monthly aqueous and solid fluxes. Finally, the total PAH
flux reached F21 ¼ 2,700 Æ 550 kg year
À1 (Σ15), the largest part (77%) of it being in
the particulate phase. This result was consistent with a previous publication that
reported an estimation of the PAH inputs to the Seine River mouth ranging from
2000 to 2,535 kg year
À1 over the 2009–2013 period [61]. However, the limited
number of samples did not allow for a correct investigation of the relationships
between the PAH contents and the hydrological parameters, especially SS concentrations. Due to sampling difficulties, few data were available to quantify PAHs in
the dissolved and particulate phases for the flood period downstream of the Paris
conurbation. Contamination data measured during the low-flow period were therefore used for the flood period. Yet, previous studies have reported an increase in
PAH contents in river water during floods [62] by a factor 2 for upstream sampling
sites. This flux might therefore have been underestimated by about 30%. Considering the low number of samples, this flux estimation was awarded a grade of 1.
3.2.8 Estimation of Urban Fluxes at the Basin Scale
PAH atmospheric emissions (Fig. 4) were quantified based on source spatial inventory established by INERIS, as previously described. The emissions from domestic
and industrial sources were estimated at approximately E5 # ¼ 122 tons year
À1 and
E6 # ¼ 220 kg year
À1 , respectively. The atmospheric deposition over urban areas was
estimated considering the whole urban surface (4,020 km
2 ) and by integrating
complementary data collected at other urban areas [11] into the bulk deposition
database (n ¼ 115). No significant change was measured in the concentrations
between the four sampling sites (Kruskal-Wallis test, p ¼ 0.27). The total fallout
over urban areas totalled F12 # ¼ 680 Æ 153 kg year
À1 (Σ15).
Scarce data were available to quantify other urban fluxes at the basin scale. In
particular, only a few studies investigated the PAH concentrations in the sewer
systems outside of the Paris conurbation [12, 63]. However, the concentrations
measured in the Paris conurbation were consistent with data reported elsewhere in
France and Europe [32]. Since these fluxes were estimated based on the average
wastewater produced per capita, it was assumed that the calculations made at the
Paris conurbation scale could be used to estimate the urban fluxes at the entire basin
scale by taking into account the population considered at the different spatial scales.
This approach was reasonable for most urban fluxes, except for the runoff contribution because changes in the population density led to a lower runoff coefficient but
Mass Balance of PAHs at the Scale of the Seine River Basin
179
To investigate the PAH flux within the Seine River, calculations were based on
concentrations measured independently in the particulate and the aqueous phases.
The databases for the particulate and the dissolved fluxes of PAHs contained
15 samples from two studies [9, 60] and 11 samples from two studies [8, 60]. The
annual PAH flux was estimated by attributing random values of the PAHs drawn
from the databases to the monthly aqueous and solid fluxes. Finally, the total PAH
flux reached F21 ¼ 2,700 Æ 550 kg year
À1 (Σ15), the largest part (77%) of it being in
the particulate phase. This result was consistent with a previous publication that
reported an estimation of the PAH inputs to the Seine River mouth ranging from
2000 to 2,535 kg year
À1 over the 2009–2013 period [61]. However, the limited
number of samples did not allow for a correct investigation of the relationships
between the PAH contents and the hydrological parameters, especially SS concentrations. Due to sampling difficulties, few data were available to quantify PAHs in
the dissolved and particulate phases for the flood period downstream of the Paris
conurbation. Contamination data measured during the low-flow period were therefore used for the flood period. Yet, previous studies have reported an increase in
PAH contents in river water during floods [62] by a factor 2 for upstream sampling
sites. This flux might therefore have been underestimated by about 30%. Considering the low number of samples, this flux estimation was awarded a grade of 1.
3.2.8 Estimation of Urban Fluxes at the Basin Scale
PAH atmospheric emissions (Fig. 4) were quantified based on source spatial inventory established by INERIS, as previously described. The emissions from domestic
and industrial sources were estimated at approximately E5 # ¼ 122 tons year
À1 and
E6 # ¼ 220 kg year
À1 , respectively. The atmospheric deposition over urban areas was
estimated considering the whole urban surface (4,020 km
2 ) and by integrating
complementary data collected at other urban areas [11] into the bulk deposition
database (n ¼ 115). No significant change was measured in the concentrations
between the four sampling sites (Kruskal-Wallis test, p ¼ 0.27). The total fallout
over urban areas totalled F12 # ¼ 680 Æ 153 kg year
À1 (Σ15).
Scarce data were available to quantify other urban fluxes at the basin scale. In
particular, only a few studies investigated the PAH concentrations in the sewer
systems outside of the Paris conurbation [12, 63]. However, the concentrations
measured in the Paris conurbation were consistent with data reported elsewhere in
France and Europe [32]. Since these fluxes were estimated based on the average
wastewater produced per capita, it was assumed that the calculations made at the
Paris conurbation scale could be used to estimate the urban fluxes at the entire basin
scale by taking into account the population considered at the different spatial scales.
This approach was reasonable for most urban fluxes, except for the runoff contribution because changes in the population density led to a lower runoff coefficient but
Mass Balance of PAHs at the Scale of the Seine River Basin
179