LAboratoire de Spectrochimie Infrarouge et Raman – UMR 8516
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Characterization tools of aquatic systems under anthropogenic constrains

3.1 Passive samplers
3.2 Voltammetry
3.3 Development of analytical methods

The development and the validation of analytical tools and methods to better characterize the fate of organic and metallic pollutants (as well as nutrients) in water and sediment is a paramount topic of our research in the group because the existing techniques are not always well adapted to our environmental researches. We are working currently on several projects allowing us to carry out measurements in water bodies (on site or in laboratory) with important sensitivity gain, by taking into account speciation issue, and with a better representativeness of the water bodies studied. Note that a relatively new topic is the on line monitoring of pollutants with approximately one measurement per hour.

These researches are performed with several partners [VUB (Brussels), IRB (Zagreb), NTNU (Trondheim), French Water Agency (Douai), Mines Douai (Douai), IRSTEA (Lyon), ANDRA…], and are carried out with the help of the platform “Analytical Chemistry” belonging to LASIR Laboratory.

3.1 Passive samplers

Participants : L. Lesven (MCF), J. Criquet (MCF), B. Ouddane (Pr), G. Billon (Pr)

Passive sampling is based on the use of devices capable to concentrate, in situ, pollutants in the aquatic compartment, thereby allowing highlighting the presence of compounds sometimes undetectable by conventional analytical and field methods. One of the many advantages and benefits offered by these systems lies in their ability to perform without any energy input, integrated sampling of pollutants present in the water column during several days or even weeks in order to determine average concentrations in dissolved phase over a defined period of time.

The POCIS (Polar Organic Chemical Integrative Samplers) and Chemcatchers® passive sensors are deployed in collaboration with the Regional Water Agency Artois-Picardie in order to study the interest to use these devices for monitoring pesticides in the regional water bodies. In addition, a system to control turbulent conditions (speed > 1m s-1) has been developed and fit one of the monitoring stations of Water Agency.

Developed by Zhang and Davison (1995), the Diffusive Gradients in Thin films (DGT) consists on a three-layer system locked in a plastic device. It contains a resin-impregnated hydrogel layer (chelating resin), a polyacrylamide hydrogel diffusion-layer and a filter membrane in cellulose acetate. This technique allows the accumulation of dissolved labile species having an environmental interest. DGT whose gels are completely synthesized in our laboratory for over 10 years are regularly used in different matrices (water column, sediment, soil) and sampling sites (coastal areas and estuaries, rivers, lakes and ponds) and for various dissolved species (trace metals, sulfides, phosphates, arsenic …) in many research projects performed by LASIR. These last years, new chelating resins have been tested in the laboratory either to reach redox speciation of some compounds or to map, in 2D, concentrations of species involved in diagenetic processes.

Concept of DGT passive sensors

Study cases

Seasonal monitoring of sulfides and trace metals by DGT in the North Sea

Several DGT devices coupled with Chelex resins for trace metals or AgI resins for dissolved sulfides have been exposed monthly in sediments from North Sea in order to follow concentration of species involved in diagenetic processes.

Concentration profiles in dissolved sulfides (in µmol L-1) as a function of the depth (cm) using DGT-AgI devices (A) in the North Sea sediments from February (1) to July 2008 (6); Picture of AgI resins after exposition (B) and average of labile trace metals concentrations in the 10 first centimeters of the same sediments using DGT-Chelex (C).

Following the spring bloom and organic matter degradation that occurs some weeks later, sulfides concentrations have dramatically increased in the first centimeters of pore water, trapping trace metals previously labile. Apart Mn and Cu, other metals are precipitated in metallic sulfides, forms less available for benthic organisms (Louriño-Cabana et al., 2014).

Vertical concentration profiles of Mn, Fe, Co, and Cd (in µg L-1) using DGT-Chelex in February (1), March (3), June (4), July (5) and November (6) 2008 in North Sea sediments. Maps carried out with the Surfer software (v11).

Comparison of sampling for phosphates determination in the Scheldt River

This inter-comparison demonstrates the representativeness of punctual sampling performed in the Scheldt River. The three punctual sampling over a 48h period (0.83 ppm on average) are not representative of the average phosphate concentration recorded by the AEAP monitoring station (0.58 ppm on average). The passive sampling using a DGT-Metsorb device shows, after analysis, an average concentration of 0.56 ppm. This study have shown that DGT method could be a pertinent tool for the French Water Agencies that have to assess, appropriately, the status of water bodies in the context of the WFD.

Inter-comparison exercise for the determination of phosphate concetrations in the Scheldt River in May 2013. Phosphates measurements by the AEAP monitoring station (over a 48h period, each 10 min) and after punctual and integrative sampling (DGT-Metsorb). In the three cases, phosphates have been analyzed by UV-Visible spectrometry.

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3.2 Voltammetry

Participants : G. Billon (Pr), L. Lesven (MCF), P.J. Superville (MCF)

Electrochemistry is an interesting technique for the quantification of trace elements in the aquatic environment and for their speciation determination (e.g. with pseudo-polarography). For a few year, in collaboration with European partners [IRB (Croatia), NTNU (Norway) and Liverpool University (England)], an automated voltammetric system was developed for the on line monitoring of trace metals as well as reduced sulphur species. Implemented in the field, e.g. in the French Water Agency monitoring station, it helps to understand the dynamic behaviour of metals at the daily scale.

Trace metal automatic monitoring system using voltammetric analysis developed in the laboratory.

The French Water Agency and the LASIR work in close collaboration on topics such as the measurement quality and representativeness. On this photography, an inter-calibration between the mobile monitoring stations of the Agency on the Scarpe canal in Douai can be seen. Analytical devices from our team are often installed within these stations for on-line or integrative measurements (voltammetry or passive sampler).

The voltammetric monitoring station has also been used for a reduced sulphur species on-line characterisation, using pseudopolarography along with copper additions. (Superville et al., 2014)

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3.3 Development of analytical methods

Participants : B. Ouddane (Pr), G. Billon (Pr), L. Lesven (MCF), S. Net-David (MCF), J. Criquet (MCF), A. Le Person (MCF), D. Dumoulin (IR)

One of the paramount steps in environmental chemistry is the determination of pollution levels in the different compartments (water, sediment, aerosols, organism…). To achieve this goal, the development and the validation of new analytical methods to characterize and quantify organic and metallic substances in the environment is a key issue because these substances have direct and indirect impacts on the environment, human health and climate (e.g.; the emission of organic aerosols).

Organic contaminants

Organic contaminants such as PAHs, PCBs, phthalates, pesticides, drug residues are ubiquitous in the environment. However, they are present generally at trace or ultra-trace levels which ranging from pg to µg/L in water and from ng to mg/kg in sediments or soils. Their quantification requires specific techniques of separation and analysis. A wide variety of extraction methods such as liquid-liquid extraction (LLE) and solid phase extraction (SPE) or SPME (solid-phase microextraction) for dissolved phases, as well as extraction by Soxhlet, ultrasonic or under pressurized fluid (ASE) for solid matrices can be used with good efficiencies. There are large varieties of organic pollutants in the environment. For compounds such as PAHs, PCBs, phthalates and certain thermally stable and volatile pesticides, the detection by GC-MS may be preferred. For other compounds, namely drugs and bisphenols (less thermally stable), LC-MS analysis should be considered. However, chemical modification of their functions (alcohol, carboxylic acid or amine) using a derivatization agent (BSTFA, PFPH, PFBHA …) allows to possible quantification with GC-MS. This technique is also useful to identify byproducts from the (photo)oxidation which are often highly functionalized. It allows identifying the secondary or tertiary reaction products and thus identifying a comprehensive scheme of degradation process.

On the left, the figure presents the simplified scheme with a picture of the ASE extractor. Each compound has specific physicochemical properties and to extract them with good accuracy, the extraction conditions should be optimized. Using the experimental design approach can be an effective and appropriate method. This mathematical model allows not only to reduce the number of experiments but also to facilitate the data treatment. On the right is an example of surface response curve obtained from the mathematical model MODDE for extractions of PAHs with ASE. The studied parameters were pressure, temperature, extraction time and solvent nature. (Net et al., 2014)

Arsenic

Arsenic is present at trace levels in aquatic systems under several oxidation states, and eventually can be methylated as a function of micro-organisms activity (such as phytoplankton, bacteria and/or fungi) (Gorny et al., 2015). As its toxicity and its fate are closely dependent on its chemical speciation, it is necessary to characterize each species. This work requires specific and sensitive techniques to separate and detect As species, as the High Performance Ionic Chromatography (HPIC) coupled to ICP-MS. HPIC-ICP-MS assembly has been developed in the laboratory to determine the speciation of dissolved As [As(III), As(V), MMAAV, DMAAV]. An environmental application has been performed in the Marque River in which only inorganic species have been detected. In the sediment pore waters, this powerful tool has also evidenced other species, attributed to thio-arsenical species.

Operating principle of HPIC-ICP-MS for determining the As speciation in water samples.

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