urbanisation or humic substances (HS), as isolated from natural waters. HS represent
the hydrophobic acid fraction of DOM [41] and typically constitute 40–60% of DOC
in most natural surface waters [42–44]. However, in rivers under strong urban
pressure such as the Seine River in the Paris conurbation, the proportion of the
HPO fraction of DOM decreases as a result of various urban discharges, and the HPI
fraction can increase to 50% of DOC, as was shown in the previous section.
At the beginning of this study, very little information focusing specifically on
trace metal binding by HPI DOM in freshwater was available in the literature, most
likely due to the difficulty of its isolation and purification. The aim of this study was
to determine trace metal-binding parameters of EfDOM from WWTPs, most particularly its HPI fraction, in order to improve the knowledge of metal speciation and
bioavailability within aquatic systems under strong urban pressure.
The study of metal complexation by EfDOM and by DOM from receiving water
under high urban pressure was conducted in two phases. In the first phase, DOM was
fractionated according to its polarity into HPO, TPI and HPI fractions [45, 46].
In this first phase, lead, mercury and zinc [47–49] complexation by the different
DOM fractions was studied. Unfortunately, this very time-consuming method can
only be applied to a small number of samples, which makes it difficult to characterise
DOM spatio-temporal variability in receiving waters.
For this reason, in the second phase, we decided to no longer fractionate DOM so
that the complexing properties of the urban DOM could be investigated for a larger
number of samples and then the DOM spatio-temporal variability taken into account.
Only copper complexation was studied [29, 38] in this second phase, focusing on the
role of EfDOM from WWTPs in copper speciation and bioavailability in receiving
waters across the Paris conurbation.
Furthermore, DOM can play an important role in the sorption/desorption of
pollutants on suspended solids in aquatic environments. Indeed, there may be
(1) competition between DOM and pollutants for adsorption on the particle surface
[50], (2) DOM can also clog the particles pores and thus limit pollutant adsorption
[51–53], (3) by adsorbing on particles, DOM can modulate their pollutant binding
ability [54] and (4) DOM can also bind pollutants and therefore maintain them in
solution or, on the other hand, make it easier for them to adsorb as they are associated
with DOM [55, 56]. These interactions may depend on the quality of the DOM.
EfDOM and DOM of terrigenous origin could therefore have a different effect on
the pollutant sorption onto particles. In this study [57], the effect of EfDOM or fulvic
acid onto adsorption of PAHs and trace metals was studied.
3.2 Material and Methods
3.2.1 Sampling Points
To collect EfDOM, seven campaigns were conducted at the Seine-Aval WWTP
(see Fig. 1), which collected, in 2012, over 70% of dry weather flows from the Paris
conurbation (six million inhabitants). These effluents accounted for more than 80%
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
229
the hydrophobic acid fraction of DOM [41] and typically constitute 40–60% of DOC
in most natural surface waters [42–44]. However, in rivers under strong urban
pressure such as the Seine River in the Paris conurbation, the proportion of the
HPO fraction of DOM decreases as a result of various urban discharges, and the HPI
fraction can increase to 50% of DOC, as was shown in the previous section.
At the beginning of this study, very little information focusing specifically on
trace metal binding by HPI DOM in freshwater was available in the literature, most
likely due to the difficulty of its isolation and purification. The aim of this study was
to determine trace metal-binding parameters of EfDOM from WWTPs, most particularly its HPI fraction, in order to improve the knowledge of metal speciation and
bioavailability within aquatic systems under strong urban pressure.
The study of metal complexation by EfDOM and by DOM from receiving water
under high urban pressure was conducted in two phases. In the first phase, DOM was
fractionated according to its polarity into HPO, TPI and HPI fractions [45, 46].
In this first phase, lead, mercury and zinc [47–49] complexation by the different
DOM fractions was studied. Unfortunately, this very time-consuming method can
only be applied to a small number of samples, which makes it difficult to characterise
DOM spatio-temporal variability in receiving waters.
For this reason, in the second phase, we decided to no longer fractionate DOM so
that the complexing properties of the urban DOM could be investigated for a larger
number of samples and then the DOM spatio-temporal variability taken into account.
Only copper complexation was studied [29, 38] in this second phase, focusing on the
role of EfDOM from WWTPs in copper speciation and bioavailability in receiving
waters across the Paris conurbation.
Furthermore, DOM can play an important role in the sorption/desorption of
pollutants on suspended solids in aquatic environments. Indeed, there may be
(1) competition between DOM and pollutants for adsorption on the particle surface
[50], (2) DOM can also clog the particles pores and thus limit pollutant adsorption
[51–53], (3) by adsorbing on particles, DOM can modulate their pollutant binding
ability [54] and (4) DOM can also bind pollutants and therefore maintain them in
solution or, on the other hand, make it easier for them to adsorb as they are associated
with DOM [55, 56]. These interactions may depend on the quality of the DOM.
EfDOM and DOM of terrigenous origin could therefore have a different effect on
the pollutant sorption onto particles. In this study [57], the effect of EfDOM or fulvic
acid onto adsorption of PAHs and trace metals was studied.
3.2 Material and Methods
3.2.1 Sampling Points
To collect EfDOM, seven campaigns were conducted at the Seine-Aval WWTP
(see Fig. 1), which collected, in 2012, over 70% of dry weather flows from the Paris
conurbation (six million inhabitants). These effluents accounted for more than 80%
Aquatic Organic Matter in the Seine Basin: Sources, Spatio-Temporal. . .
229