Dynamics of Cu and Pb during sediment remobilization and associated risk for coastal water quality
Résumé
Laboratory resuspension experiments were performed using three sediments and seawater, contrasted in terms of metals concentration/contents, metals partitioning in sediments as well as physical-chemical characteristics of both sediment and seawater. The aim of the study was to examine if the variability in metals content and metals distribution onto carrier phases are influencing the dynamics of metal transfers from and to sediment. Since Cu and Pb are classical contaminants found in coastal areas, their dissolved concentrations were monitored (up to 360 h) to assess their release or removal by particles, with a particle concentration of 2.5 g L−1 (wet weight). The dynamics of Cu and Pb transfers were similar between experiments while the amplitude of transfers was specific to each sediment. The results of the study clearly demonstrated that while Cu first undergoes an adsorption onto particles (after few minutes of mixing), Pb first undergoes a desorption from particles (after few hours of mixing). Then Cu was desorbed from particles (from 48 to 360 h), while Pb remained adsorbed onto particles (from few 24 to 360 h). The impact of the quantity of resuspended particles was evaluated after 24 h (Pb) and 360 h (Cu) of mixing with different sediment:water ratio. The increase of resuspended particles leads to a non-linear release of dissolved Cu with Cu concentration overpassing the trigger values to protect 80 % (La Spezia), 90 % (Toulon) and 95 % (Olbia) marine species as defined by the ANZECC (Australian and New Zealand Environment and Conservation Council). On the contrary, the increase of resuspended particles leads to a bell-shaped curve for dissolved Pb pointing out Pb affinity for particles.