DOM, which acts as a good proxy for DOM aromaticity, or between EC50 tot and the
DOM aromaticity percentage [29, 49]. The highest EC50 tot values, however, were
observed for EfDOM with very low aromaticity and a low UV absorbance. Compared to DOM from Upstream I and II, EfDOM and Downstream DOM presented
higher densities of high-affinity binding sites (L 2 ) and even very high-affinity
binding sites (L 3 ) for EfDOM, which may be responsible for the greater protective
role played by these DOM samples.
Logically, given the strong affinity of EfDOM for copper, these results prove
that EfDOM has a considerable influence on copper toxicity on Daphnia magna
with a slightly greater protecting effect than both SRFA and DOM from upstream
of Paris.
3.7 Effect of EfDOM on Trace Metal Sorption by Mineral
Particles in Aquatic Systems Subjected to Strong Urban
Pressure
The results obtained showed that in many cases trace metal adsorption onto montmorillonite (MMT) and goethite was strongly modified by DOM compared to the
control without DOM [57]. In the case of adsorption onto MMT, there was no
influence of the DOM type on copper adsorption, with a 65% decrease with both
EfDOM and SRFA. The adsorption decrease for Zn was 17% with SRFA and
reached 60% with EfDOM. Given the very large increase of inert complexes in
the dissolved fraction (+200%) with EfDOM compared to SRFA, it would appear
that the substantial Zn adsorption decrease with EfDOM is due to maintaining Zn in
solution by complexation with EfDOM. As for Zn, Cd was weakly adsorbed on
MMT in the presence of EfDOM due to its retention in solution as inert complexes
with EfDOM.
In the case of adsorption onto goethite, the Cd adsorption with SFRA was higher
compared to the control (+162%), while it was lower in the presence of EfDOM
(À20%). Zn showed a similar behaviour, while for As, adsorption was lower with
DOM, especially with EfDOM (À65%). For Cu and Ni, adsorption with SRFA was
similar to that of the control, while it decreased by 54% and 77%, respectively, with
EfDOM. For Cd, Ni and Zn, the sorption decrease is probably due to maintaining
in solution by complexation with EfDOM.
3.8 Effect of EfDOM on PAH Adsorption by Mineral
Particles in Aquatic Systems Subjected to Strong Urban
Pressure
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]
236
G. Varrault et al.
DOM aromaticity percentage [29, 49]. The highest EC50 tot values, however, were
observed for EfDOM with very low aromaticity and a low UV absorbance. Compared to DOM from Upstream I and II, EfDOM and Downstream DOM presented
higher densities of high-affinity binding sites (L 2 ) and even very high-affinity
binding sites (L 3 ) for EfDOM, which may be responsible for the greater protective
role played by these DOM samples.
Logically, given the strong affinity of EfDOM for copper, these results prove
that EfDOM has a considerable influence on copper toxicity on Daphnia magna
with a slightly greater protecting effect than both SRFA and DOM from upstream
of Paris.
3.7 Effect of EfDOM on Trace Metal Sorption by Mineral
Particles in Aquatic Systems Subjected to Strong Urban
Pressure
The results obtained showed that in many cases trace metal adsorption onto montmorillonite (MMT) and goethite was strongly modified by DOM compared to the
control without DOM [57]. In the case of adsorption onto MMT, there was no
influence of the DOM type on copper adsorption, with a 65% decrease with both
EfDOM and SRFA. The adsorption decrease for Zn was 17% with SRFA and
reached 60% with EfDOM. Given the very large increase of inert complexes in
the dissolved fraction (+200%) with EfDOM compared to SRFA, it would appear
that the substantial Zn adsorption decrease with EfDOM is due to maintaining Zn in
solution by complexation with EfDOM. As for Zn, Cd was weakly adsorbed on
MMT in the presence of EfDOM due to its retention in solution as inert complexes
with EfDOM.
In the case of adsorption onto goethite, the Cd adsorption with SFRA was higher
compared to the control (+162%), while it was lower in the presence of EfDOM
(À20%). Zn showed a similar behaviour, while for As, adsorption was lower with
DOM, especially with EfDOM (À65%). For Cu and Ni, adsorption with SRFA was
similar to that of the control, while it decreased by 54% and 77%, respectively, with
EfDOM. For Cd, Ni and Zn, the sorption decrease is probably due to maintaining
in solution by complexation with EfDOM.
3.8 Effect of EfDOM on PAH Adsorption by Mineral
Particles in Aquatic Systems Subjected to Strong Urban
Pressure
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]
236
G. Varrault et al.