Lessons from a large scale deployment of DGT in the Seine basin

Diffusive Gradient in Thin film (DGT) is a speciation technique now commonly used in the scientific literature to assess metallic contamination in water. However applications usually take place in a same watercourse or in neighbouring sites. We propose here to present the first results of a large scale deployment of DGTs. The main objective of the project, which is supported by the French water agency of the Seine-Normandie basin, is to evaluate the potential of passive samplers as monitoring tools. DGT devices were deployed in 45 sites, on 30 locations in the entire Seine river basin. The sampling area was 500 km long and 200 km wide around Paris. The total sampling period lasted over the whole 2009 year. Restricted gels of 0.78 were used to measure labile Cd, Cr, Co, Cu, Mn, Ni, Pb and Zn. In parallel, raw and filtered water samples were collected to measure total and dissolved metals. General physico-chemical parameters were also measured. The whole set of measurements constitute a rich dataset including large and small rivers, and reference as well as impacted sites. The results first allow us to draw a map of total, dissolved and labile metal concentrations, representing the spatial variability of metal contamination in the Seine basin. Moreover, considering the temporal variability, different behaviours, depending on the metal, can be identified. The large scale deployment of DGT in the Seine river basin was successful: all the samples have been interpreted and are exploitable, whereas the dissolved metal samples are sometimes under the detection limit. We have then built a representative data set on the water contamination in labile metal of an urban impacted basin. The results are also interpreted as labile percentage, showing the operationally possible values of lability in contrasted environmental conditions. A first approach of the factors influencing the lability highlights the significance of the nature of the organic matter to interpret the lability of the metals

Polymeric membrane as passive sampler : a new simple calibration protocol

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What does Semi-Permeable membrane device (SPMD) sampling mean? an insight on the "time-weight integrative" and "SPMD-availability" hypothesis

International audienceSPMDs are commonly used integrative passive samplers for hydrophobic organic compounds [1]. Because of steric hindrance in the polyethylene membrane, only a fraction of dissolved organic compounds in water may be accumulated. It is usually assumed that only truly dissolved compounds are available to SPMD. From the accumulated amount of a substance in SPMD, and dissipation of Performance Reference Compounds, the exchange rate constant and the concentration of SPMD-available substance in water can be estimated. It is usually assumed that the SPMD-available concentration estimated from accumulation in SPMD corresponds to the time-weight average (TWA) concentration. Moreover, provided that the half-time is higher than the exposure duration, the sampling is supposed to be fully integrative. In this study, we investigate the significance of the "time-weight" integrative sampling: factors such as deployment duration, exchange rate constants, but also water concentration variations are examined. The chemical form of SPMD-available compounds is also investigated: compiling several field studies, SPMDavailable concentrations are compared to total dissolved concentrations of Polycyclic Aromatic Hydrocarbons (PAHs). Assuming that PAHs that are bond to dissolved organic matter cannot enter the membrane of SPMD, in situ partitioning coefficients KDOC are computed and compared to lab data

What does Semipermeable Membrane Device (SPMD) sampling mean? accuracy of time-weighted average concentration estimations of truly dissolved compounds

International audienceSPMDs1 are commonly used integrative passive samplers for hydrophobic organic compounds in water. Two major assumptions drive the interpretation of accumulated amounts of contaminants: Because of steric hindrance in the polyethylene membrane, only a fraction of dissolved organic compounds in water may be accumulated. - 1st assumption : only truly dissolved compounds are SPMD-available From the accumulated amount of a substance in SPMD, and dissipation of Performance Reference Compounds, the concentration of SPMD-available substance in water can be estimated. - 2nd assumption : the estimated SPMD-available concentration is a time-weighted average (TWA) concentration. Compiling field studies (sampling campaigns in rivers2 and wastewater treatment plants3) and using numerical simulations, we investigated the validity of these two assumption

Leçons d'une campagne de déploiement de DGT à grande échelle dans le bassin de la Seine

International audienceDiffusive Gradient in Thin film (DGT) is a speciation technique now commonly used in the scientific literature to assess metallic contamination in water. However, applications usually take place in a same watercourse or in neighbouring sites. The study presented here shows the first results of a large scale deployment in the Seine basin, around Paris in France. The data set acquired allows us to draw several lessons from it about the level of contamination of the basin and the behaviour of the labile fraction defined by DGT

Polycyclic aromatic hydrocarbon sampling in wastewaters using semipermeable membrane devices: Accuracy of time-weighted average concentration estimations of truly dissolved compounds

International audienceSemipermeable membrane devices (SPMDs) previously spiked with performance reference compounds were exposed in wastewater. After 6 days of exposure, 13 polycyclic aromatic hydrocarbons (PAHs) were quantified in SPMDs. Exchange rate constants and time-weighted average (TWA) concentrations of SPMD-available PAHs in water were calculated. The bias of using SPMDs to estimate an actual TWA concentration if the concentration in water fluctuates, as can be expected in wastewater, was studied with numerical simulations. The bias increased with the exchange rate constant. However, most exchange rate constants evaluated in SPMDs exposed in wastewater were small enough for SPMDs to estimate a TWA concentration of PAHs even when the water concentration varied. TWA-SPMD-available concentrations were always below total dissolved (operationally defined as 0.7 lm) concentrations, indicating that part of the dissolved PAHs was not available for sampling. In situ partitioning coefficients KDOC were computed and found to be slightly higher than data from the literature. This confirms that only truly dissolved PAHs should be sampled by SPMDs in wastewater

Evaluation de la relation entre pression anthropique et concentrations en HAP dans les eaux de surface du bassin de la Seine par utilisation de méthodes multivariées

International audienceUnderstanding the relation between polycyclic aromatic hydrocarbons (PAHs) in freshwater and anthropogenic pressure is fundamental to finding a solution to reduce the presence of PAHs in water, and thus their potential impact on aquatic life. In this paper we propose to gain greater insight into the ariability, sources and partitioning of PAHs in labile (or freely dissolved= not associated to the organic matter), dissolved and particulate phases in freshwater. This study was conducted using land use data as a marker of anthropogenic pressure and coupling it with chemical measurements. This study was conducted on 30 sites in the Seine River basin, which is subjected to a strong human impact and exhibits awide range of land uses. Half of the siteswere studied twice. Labile PAHs were measured by semi-permeable membrane devices (SPMDs), and dissolved and particulate phases by grab samples. Partial least squares regressions were performed between chemical measurements and data of anthropogenic pressure. The results indicate different sources for the dissolved phase and particles. Dissolved and labile phases were more related to the population density of the watershed, while particles were more related to a local pressure. Season and land use data are necessary information to correctly interpret and compare PAH concentrations from different sites. Furthermore, the whole data set of the 45 field deployments comprising labile, dissolved, total and particulate PAH concentrations as well as the physico-chemical parameters is available in the supplementary information

Labile, dissolved and particulate PAHs and trace metals in wastewater: passive sampling, occurrence, partitioning in treatment plants

International audienceThe occurrence and the partitioning of polycyclic aromatic hydrocarbons (PAHs) and seven metals (Al, Cd, Cr, Cu, Ni, Pb and Zn) were investigated in activated sludge wastewater treatment plants by means of passive and active sampling. Concentrations total dissolved and particulate contaminants were determined in wastewater at several points across the treatment system by means of grab sampling. Truly dissolved PAHs were sampled by means of semipermeable membrane devices. Labile (inorganic and weakly complexed) dissolved metals were also sampled using the diffusive gradient in thin film technique. This study confirms the robustness and the validity of these two passive sampling techniques in wastewater. All contaminant concentrations decreased in wastewater along the treatment, although dissolved and labile concentrations sometimes increased for substances with less affinity with organic matter. Solidliquid and dissolved organic matter/water partitioning constants were estimated. The high variability of both partitioning constants for a simple substance and the poor relation between KD and KOW shows that the binding capacities of particles and organic matter are not uniform within the treatment and that other process than equilibrium sorption affect contaminant repartition and fate in wastewater