Kinetic processes of copper and lead remobilization during sediment resuspension of marine polluted sediments.

Contaminated sediments could act as a source of contamination to the surrounding environments by several processes (e.g., diffusive flux, sediment resuspension). This study aimed at highlighting the mechanisms of copper and lead mobilization from resuspended particles to the aqueous phase using laboratory experiments and a kinetic model. Three sediments, differed by their compositions and metal partition from Toulon Bay (SE France) were used. In addition, three solid/liquid ratios (0.1, 1 and 10 g L-1) allowed simulating at best natural and anthropogenic scenarios (e.g., storm, nautical traffic, dredging). We monitored metal concentrations, physicochemical parameters (pH, Eh, [O2]) and organic matter concentration along with their optical properties. Experimental results showed successive reactions over short and long terms (hour and day scale, respectively) that controlled Cu and Pb exchanges between particles and the aqueous phase over 4 weeks. The quick Cu removal was attributed to the implications of newly formed oxides while the long-term Cu release in the dissolved fraction from the more refractory solid pool is more likely related to organic complexation. In fact, we observed a transformation of the dissolved organic matter: an increase in molecular weight and in humic fluorescence properties. However, the Pb removal toward the end of the experiment could be explained by a migration toward the exchangeable sites of higher energy, which could correspond to the particulate organic matter or a combination with organic-coating carrier phases. Both kinetic rate and system response times (τi) were coherent despite the variability of parameters intrinsic to sediments (e.g., sediment composition and initial metal repartition) but also extrinsic parameters (solid/liquid ratios). Such a coherence would imply the universality of the obtained constants to be used in a more predictive approach to assess the potential of metal mobility using metal repartition in contaminated sediments when combined with hydrological and sedimentological models.

Spatio-temporal variability of fluorescent dissolved organic matter in the Rhône River delta and the Fos-Marseille marine area (NW Mediterranean Sea, France).

The spatio-temporal variability of fluorescent dissolved organic matter (FDOM) and its relationships with physical (temperature, salinity) and chemical (nutrients, chlorophyll a, dissolved and particulate organic carbon, nitrogen and phosphorus) parameters were investigated in inland waters of the Rhône River delta and the Fos-Marseille marine area (northwestern Mediterranean, France). Samples were taken approximately twice per month in two inland sites and three marine sites from February 2011 to January 2012. FDOM was analysed using fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC). In inland waters, humic-like components C1 (λEx/λEm: 250 (330)/394 nm) and C3 (λEx/λEm: 250 (350)/454 nm) dominated over one tryptophan-like component C2 (λEx/λEm: 230 (280)/340 nm), reflecting a background contribution of terrigenous material (~67% of total fluorescence intensity, in quinine sulphate unit (QSU)) throughout the year. In marine waters, protein-like material, with tyrosine-like C4 (λEx/λEm: <220 (275)/<300 nm) and tryptophan-like C5 (λEx/λEm: 230 (280)/342 nm), dominated (~71% of total fluorescence intensity, in QSU) over a single humic-like component C6 (λEx/λEm: 245 (300)/450 nm). In inland waters of the Rhône River delta, humic-like components C1 and C3 were more abundant in autumn-winter, very likely due to inputs of terrestrial organic matter from rainfalls, runoffs and wind-induced sediment resuspension. In marine sites, intrusions of the Berre Lagoon and Rhône River waters had a significant impact on the local biogeochemistry, leading to higher fluorescence intensities of humic- and protein-like components in spring-summer. On average, the fluorescence intensities of FDOM components C4, C5 and C6 increased by 33-81% under lower salinity. This work highlights the complex dynamics of FDOM in coastal waters and confirms the link between marine FDOM and the Rhône River freshwater intrusions on larger spatial and temporal scales in the Fos-Marseille marine area.

Identification and quantification of known polycyclic aromatic hydrocarbons and pesticides in complex mixtures using fluorescence excitation-emission matrices and parallel factor analysis.

Polycyclic aromatic hydrocarbons (PAHs) and pesticides are among the most widespread organic contaminants in aquatic environments. Because of their aromatic structure, PAHs and pesticides have intrinsic fluorescence properties in the ultraviolet/blue spectral range. In this study, excitation-emission matrix (EEM) fluorescence spectroscopy and parallel factor (PARAFAC) analysis were used to characterise and discriminate fluorescence signatures of nine PAHs and three pesticides at the µg L(-1) level in the presence of humic substances (0.1-10 mgCL(-1)). These contaminants displayed a diversity of fluorescence signatures regarding spectral position (λEx: 220-335 nm, λEm: 310-414 nm), Stokes shift (39-169 nm) and number of peaks (1-8), with detection limits ranging from 0.02 to 1.29µgL(-1). The EEM/PARAFAC method applied to mixtures of PAHs with humic substances validated a seven-component model that included one humic-like fluorophore and six PAH-like fluorophores. The EEM/PARAFAC method applied to mixtures of pesticides with humic substances validated a six-component model that included one humic-like fluorophore and three pesticide-like fluorophores. The EEM/PARAFAC method adequately quantified most of the contaminants for humic substance concentrations not exceeding 2.5 mg CL(-1). The application of this method to natural (marine) samples was demonstrated through (1) the match between the Ex and Em spectra of PARAFAC components and the Ex and Em spectra of standard PAHs, and (2) the good linear correlations between the fluorescence intensities of PARAFAC components and the PAH concentrations determined by GC-MS.

Spatial and seasonal variabilities of dissolved hydrocarbons in surface waters from the Northwestern Mediterranean Sea: results from one year intensive sampling.

Dissolved aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) were analysed from surface water collected in continental, harbour and off-shore marine sites from Marseilles coastal area (Northwestern Mediterranean Sea) from February 2011 to February 2012. AH and PAH concentrations were in the range of 0.04-0.53 µgl(-1) and 8.1-405 ngl(-1), respectively. They both displayed seasonal and spatial variations in their concentrations and molecular composition. The lowest AH concentrations were found in summer and the highest PAH concentrations in winter. Both natural and anthropogenic (pyrogenic and petrogenic) hydrocarbon sources were identified. In winter, concentrations and composition patterns highlighted an increase in the signature of unburned and combusted fossil fuels, while they suggested an enhancement of weathering processes in summer months. Hydrocarbon inputs to the dissolved phase seemed to originate mainly from the atmosphere and the Rhône River. Hydrocarbon additional sources were identified only at the harbour site, emphasising the intense shipping traffic and industrial activities occurring in one of the most important Mediterranean harbours. This study underscores the strong dynamics of dissolved hydrocarbons and the uncoupling of the sources, transport and removing processes affecting AHs and PAHs. It also demonstrates the pertinence of taking this dynamics into account for the budget assessments of organic pollutants in coastal environments.