of the effluent dissolved organic carbon discharged into the Seine River from the
entire conurbation, thus offering highly representative samples. Treatment consisted
of primary settling for suspended solid removal, aerobic activated sludge for carbon
removal and biofilters for nitrogen removal (nitrification and denitrification).
To characterise the spatial evolution of DOM trace metal complexation
parameters in receiving waters throughout the Paris conurbation, three sampling
sites (labelled Downstream and Upstream I and II) were selected (see Sect. 2.2 and
Fig. 1). Five sampling campaigns were carried out at these three sites during both
the high-flow period (November 2010 to January 2011) and low-flow period (March
2011, June 2011 and September 2011).
A standard fulvic acid (Suwannee River Fulvic Acid, SRFA 2S101F), purchased
from the International Humic Substances Society, was used as a “natural organic
matter” reference for follow-up investigations relative to DOM influence on copper
bioavailability and pollutant adsorption onto particles.
3.2.2 Experimental Procedures
Experimental procedures concerning (1) sample treatment; (2) characterisation of
copper-, lead-, zinc- and mercury-binding abilities; and (3) characterisation of DOM
influence on copper bioavailability as well as the methodology used for trace metal
speciation modelling are given in several publications [29, 38, 47–49].
Concerning the influence of the DOM type on pollutant adsorption, experimental
procedures are described elsewhere [57]. Briefly, EfDOM or SRFA (10 mgC L
–1 )
and particles (0–5,000 mg L
À1 of montmorillonite, goethite or quartz) were mixed
for 72 h. Seven metals (Cd, Co, Cu, Ni, Pb, V and Zn) as well as As were then added,
and the whole was left in equilibrium for 72 h. Trace metal concentrations were
around 1 μmol L
À1 except for cadmium (0.1 μmol L
À1 ). Tubes were centrifuged at a
relative centrifugal field of 4,000 Â g for 60 min. Supernatant solutions were filtered
through a 0.45-μm polypropylene filter, and the total dissolved metal concentration
was determined by ICP-AES in order to deduce the proportion of adsorbed metals.
Another aliquot was filtered through a chelating disc (Chelex 100
® ) to distinguish
between labile complexes (mainly mineral) and inert complexes (mainly organic)
[58]. The control was processed without DOM.
Adsorption of six PAHs – pyrene (Pyr), benzo[a]anthracene (B[a]A), chrysene
(Chry), benzo[b]fluoranthene (B[b]F), benzo[k]fluoranthene (B[k]F) and benzo[a]
pyrene (B[a]P) – were studied with the same procedure.
3.3 Characterisation of DOM Trace Metal-Binding Ability
3.3.1 Binding Site Modal Distribution
For the sake of simplicity, in the bimodal distribution of binding site stability
constants, the modal distribution with a lower stability constant was labelled “L 1 ”,
230
G. Varrault et al.
entire conurbation, thus offering highly representative samples. Treatment consisted
of primary settling for suspended solid removal, aerobic activated sludge for carbon
removal and biofilters for nitrogen removal (nitrification and denitrification).
To characterise the spatial evolution of DOM trace metal complexation
parameters in receiving waters throughout the Paris conurbation, three sampling
sites (labelled Downstream and Upstream I and II) were selected (see Sect. 2.2 and
Fig. 1). Five sampling campaigns were carried out at these three sites during both
the high-flow period (November 2010 to January 2011) and low-flow period (March
2011, June 2011 and September 2011).
A standard fulvic acid (Suwannee River Fulvic Acid, SRFA 2S101F), purchased
from the International Humic Substances Society, was used as a “natural organic
matter” reference for follow-up investigations relative to DOM influence on copper
bioavailability and pollutant adsorption onto particles.
3.2.2 Experimental Procedures
Experimental procedures concerning (1) sample treatment; (2) characterisation of
copper-, lead-, zinc- and mercury-binding abilities; and (3) characterisation of DOM
influence on copper bioavailability as well as the methodology used for trace metal
speciation modelling are given in several publications [29, 38, 47–49].
Concerning the influence of the DOM type on pollutant adsorption, experimental
procedures are described elsewhere [57]. Briefly, EfDOM or SRFA (10 mgC L
–1 )
and particles (0–5,000 mg L
À1 of montmorillonite, goethite or quartz) were mixed
for 72 h. Seven metals (Cd, Co, Cu, Ni, Pb, V and Zn) as well as As were then added,
and the whole was left in equilibrium for 72 h. Trace metal concentrations were
around 1 μmol L
À1 except for cadmium (0.1 μmol L
À1 ). Tubes were centrifuged at a
relative centrifugal field of 4,000 Â g for 60 min. Supernatant solutions were filtered
through a 0.45-μm polypropylene filter, and the total dissolved metal concentration
was determined by ICP-AES in order to deduce the proportion of adsorbed metals.
Another aliquot was filtered through a chelating disc (Chelex 100
® ) to distinguish
between labile complexes (mainly mineral) and inert complexes (mainly organic)
[58]. The control was processed without DOM.
Adsorption of six PAHs – pyrene (Pyr), benzo[a]anthracene (B[a]A), chrysene
(Chry), benzo[b]fluoranthene (B[b]F), benzo[k]fluoranthene (B[k]F) and benzo[a]
pyrene (B[a]P) – were studied with the same procedure.
3.3 Characterisation of DOM Trace Metal-Binding Ability
3.3.1 Binding Site Modal Distribution
For the sake of simplicity, in the bimodal distribution of binding site stability
constants, the modal distribution with a lower stability constant was labelled “L 1 ”,
230
G. Varrault et al.