Papers by Stéphane Mounier
Journal of Marine Science and Engineering
Heavy rain events alter the biogeochemical outflows, affects water quality and ecosystem health w... more Heavy rain events alter the biogeochemical outflows, affects water quality and ecosystem health within the coastal waters of small Pacific Islands. We characterized snapshots of the optical fingerprints of dissolved organic matter (DOM) sources together with the select nutrients, biogeochemical and physical variables for 10 stations in December 2017 in Laucala Bay, Fiji Islands. DOM absorption coefficients and fluorescence components were determined via spectrofluorometry and Parallel Factor Analysis identifying four components: Type M, two terrestrial (humic, fulvic) components, and a protein component linked to marine biological activity. Associations of DOM together with climate variables and the other tested variables were determined via principal component, hierarchical cluster, and cross-correlation (Pearson) analysis. All component s (together with most tested variables) displayed higher values (plumes) at the southwest coast consistent with surface currents outflow during th...
Soil organic matter (SOM) plays an important role in maintaining soil productivity and accounting... more Soil organic matter (SOM) plays an important role in maintaining soil productivity and accounting for the promotion of biological diversity. The main components of the SOM are the humic substances which can be fractionated according to its solubility in humic acid (HA), fulvic acids (FA) and humin (HU). The determination of the chemical properties of organic matter as well as its interaction with metallic species is an important tool for understanding the structure of the humic fractions. Fluorescence spectroscopy has been studied as a source of information about what is happening at the molecular level in these compounds. Specially, soils of Amazon region are an important ecosystem of the planet. The aim of this study is to understand the molecular and structural composition of HA samples from Spodosol of Amazonia using the fluorescence Emission-Excitation Matrix (EEM) and Time Resolved Fluorescence Spectroscopy (TRFS). The results showed that the samples of HA showed two fluoresce...
The Mediterranean Sea is one of the most impacted basin in terms of microplastics pollution. Land... more The Mediterranean Sea is one of the most impacted basin in terms of microplastics pollution. Land-based activities are the major sources of plastic litter to the ocean, with harbors probably representing significant hotspots. In the framework of the SPlasH! project (Stop alle Plastiche in H2O, Interreg Marittimo project), microplastics were sampled in three north-western Mediterranean harbors during summer and winter. In this study, the areal concentrations of microplastics ranged from 5,576 to 379,965 items.km-2. A decreasing gradient was observed from the inner to the outer zones of the studied harbors, pointing out these enclosed systems as hotspots regarding microplastic pollution. During the summer, because of an enhancement of port activities, the areal concentrations of microplastics were higher than in winter. The investigation microplastics size classes distribution in the surface waters revealed that microplastic within a size range between 300 µm and 500 µm were depleted....
Analytical Methods, 2021
Total phosphorus (TP) in sediments is an important chemical variable in the study of the extent o... more Total phosphorus (TP) in sediments is an important chemical variable in the study of the extent of eutrophication in water bodies.
Environmental Science and Pollution Research, 2020
Human activity puts pressures on coastal zone altering dissolved organic matter quality. No speci... more Human activity puts pressures on coastal zone altering dissolved organic matter quality. No specific self-differentiating fluorescence signal of the anthropogenic DOM in the coastal zone is found in the literature. Solar irradiation were conducted on mixed samples of River water, sea water, wastewater treatment plant effluent. Excitation Emission Matrices of Fluorescence were used to monitor the fate of wastewater treatment plant effluent. Multilinear regression of CP/PARAFAC components contribution depending on mixing composition were done and was excellent. Kinetics of decreasing contribution versus irradiation time were investigated. Second order Kinetics were found for C1 and C2. Distinction between fluorescence signal of endmembers was undoable. Wastewater treatment plant endmember after photodegradation was highly predominant.
Science of The Total Environment, 2020
Sterilization techniques are largely employed to distinguish biotic and abiotic processes in biog... more Sterilization techniques are largely employed to distinguish biotic and abiotic processes in biogeochemical studies as they inhibit microbial activity. Since one century, chemical sterilizers, supposed to preserve original environmental samples, have taken precedence over physical sterilization techniques considered too destructive. Sodium azide (NaN 3) is nowadays the most commonly used inorganic chemical sterilizer. It is sufficiently purified to study trace metals, as well. Nevertheless, its (in)activity in physico-chemical processes was never ascertained. Through the investigation of sediment resuspension in seawater, the present work unequivocally demonstrated that NaN 3 can impact carbon and balance and pH. Unlike decades of blind practice, NaN 3 should be used with great care to track abiotic processes from organic matter rich and reductive matrices.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019
Numerous studies have shown the impact of inner filter effect (IFE) on the fluorescence signal. I... more Numerous studies have shown the impact of inner filter effect (IFE) on the fluorescence signal. IFE reduces the fluorescence intensity and distorts the fluorescence peak shape and position, through the absorption of the emitted radiation by the sample components. In this study, we aimed to understand the role of a non-fluorescing chromophore in IFE correction and PARAFAC decomposition. Solutions of three fluorophores, tryptophan, fluorescein and quinine sulfate, and an absorbing compound, green ink, have been prepared using the controlled dilution approach (CDA). PARAFAC identified three components associated with quinine sulfate, fluorescein and an IFE artifact, which was caused by a shift in peak position. Results showed that the absorption of the chromophore plays an important role in component determination. We observed that the CDA-PARAFAC was able to correct the quinine sulfate and fluorescein signals, and to suppress the IFE artifact component. However, the method was not effective in removing the IFE impact at high concentrations. The results have significant implications on the analysis of samples that contain complex mixtures of fluorophores and chromophores, such as colored natural organic matter or nutrients, like NO 3 2- .
Chemical Geology, 2018
By assessing U geochemistry as well as U isotopic composition in marine sediments (Toulon Bay, NW... more By assessing U geochemistry as well as U isotopic composition in marine sediments (Toulon Bay, NW Mediterranean Sea), authigenic U accumulation in sediments was found to be tightly linked to that of Mo and V with a slight difference in accumulation rate depending on sediment redox conditions and with a typical U loss in re-oxidized sediments. In sediments collected on a transect along a river plume, the authigenic accumulation of these redoxsensitive elements appears to be linked to the sediment grain size which probably drives the redox status of the sediments. The U isotopic composition in Toulon Bay sediments showed enrichment of the heavy isotope (δ 238 U =-0.12±0.12 ‰ relative to CRM-145 in the surface sediments). However, while U isotopic fractionation reaches half fractionation factor (Δ 238 U = 0.6 ‰) in some sediment cores, similar to typical values observed in the literature, other cores show a full fractionation factor (Δ 238 U = 1.2 ‰). In parallel, the dissolved U profiles do not show a simple and typical depletion trend but rather a depletion in the top 10 cm followed by release below 10 cm that is probably linked to the biotic reoxidation of authigenic U(IV). The released U could be further scavenged by a competition between UP precipitation and biotic reduction which is most likely driven by diagenetic reactions via porewater acidification and release of chelators and phosphorus.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
The front face fluorescence spectroscopy is often used to quantify chemicals in well known matric... more The front face fluorescence spectroscopy is often used to quantify chemicals in well known matrices as it is a rapid and powerful technique, with no sample preparation. However it was not used to investigate extracted organic matter like humic substances. This work aims to fully investigate for the first time front face fluorescence spectroscopy response of a ternary system including boric acid, tryptophan and humic substances, and two binaries system containing quinine sulfate or humic substance in boric acid. Pure chemicals, boric acid, tryptophan, quinine sulfate and humic acid were mixed together in solid pellet at different contents from 0 to 100% in mass. The measurement of excitation emission matrix of fluorescence (3D fluorescence) and laser induced fluorescence were then done in the front face mode. Fluorescence matrices were decomposed using the CP/PARAFAC tools after scattering treatments. Results show that for 3D fluorescence there is no specific component for tryptophan and quinine sulfate, and that humic substances lead to a strong extinction effect for mixture containing quinine sulfate. Laser induced fluorescence gives a very good but non specific related response for both quinine sulfate and tryptophan. No humic substances fluorescence response was found, but extinction effect is observed as for 3D fluorescence. This effect is stronger for quinine sulfate than for tryptophan. These responses were modeled using a simple absorbance versus emission model.
Water Research, 1999
ÐCross-¯ow ultra-®ltration from the Rio Negro basin (Amazon) samples was undertaken with tangenti... more ÐCross-¯ow ultra-®ltration from the Rio Negro basin (Amazon) samples was undertaken with tangential¯ow equipment producing concentrated fractions on which UV-¯uorescence produced information about the individual characteristics of the organic matter in dierent size fractions. The major novelty is that conductance (ionic strength) and¯uorescence were both linearly (r>0.95) correlated with total organic carbon (TOC) determined at each individual station. The physico-chemical characteristics (¯uorescent sensitivity and electro-mobility) of the organic carbon seem to be constant within each size fraction (particulate, colloidal and dissolved). The complexing capacity of copper was found to be elevated, with as consequence that more than 80% of the metal transport occurred in the dissolved phase. By comparing these various results, we have deduced that the functional groups responsible for complexation are not the same as those responsible for¯uorescence and conductance.
Marine Environmental Research, 2009
A two-step protocol (nano-filtration and reverse osmosis) was applied for natural organic matter ... more A two-step protocol (nano-filtration and reverse osmosis) was applied for natural organic matter (NOM) preconcentration of a seawater sample. Complexing affinities of the so concentrated marine dissolved NOM (DNOM) towards major and trace cations were studied by potentiometric and voltammetric titration techniques. The potentiometric titration experiments fitted by models describing and characterising the DNOM-cation interactions, revealed four distinct classes of acidic sites (pKa of 3.6, 4.8, 8.6 and 12). A total acidic sites density of 445 meq/mol C was estimated, with a majority (60%) of carboxylic-like sites. Pseudopolarographic measurements revealed two distinct groups of copper complexes: labile, reducible at about À0.2 V; and inert, directly reducible at about À1.4 V. Simultaneous competition between copper, calcium and proton highlighted the presence of two classes of binding sites (density of 1.72 and 10.25 meq mol À1 C , respectively, corresponding to 3% of total acidic sites). The first class was more specific to copper (log K CuL 9.9, log K CaL 2.5, pKa 8.6), whereas stronger competition between copper and calcium occurred for the second class (log K CuL 6.9, log K CaL 5.5, pKa 8.2). The binding sites characterisation was validated by the very good matching of the non-concentrated seawater sample titration data with the simulated curves obtained using the binding parameters from the concentrated sample. Furthermore, this comparison also validated the applied preconcentration protocol, highlighting its negligible influence on organic matter properties when considering copper complexation.
Marine Chemistry, 2009
An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of... more An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K i equ), total ligands concentration (L iT) and association/dissociation rate constants (k i 1 ,k i-1). A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater-seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K 1 equ : 11.2-13.0, log K 2 equ :8.8-10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter. Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by atequilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k 1 1 :6.1-20 × 10 3 (M s) − 1 , k 2 1 : 1.3-6.3 × 10 3 (M s) − 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h. It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM C , i.e. 1 mg C L − 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).
La mobilite et la biodisponibilite des metaux traces dans l'environnement sont influencees pa... more La mobilite et la biodisponibilite des metaux traces dans l'environnement sont influencees par la presence de matiere organique naturelle dissoute (MON) [1]. Les associations metaux- MON, souvent fortes (ex. le FeIII est associe a plus de 99% par des ligands organiques dans les eaux de mer de surface), sont specifiques de la MON et du metal, et dependent des conditions physico-chimiques: force ionique, pH, presence d'autres cations majeurs et traces [2]. De part les faibles teneurs en carbone organique dissout (0.1-1 mgC.L-1), la complexite de la MON, et des concentrations totales en metaux depassant rarement la nanomole, l'etude des interactions entre MON et metaux dans des eaux de mer non polluees reste un challenge. Parmi les techniques utilisees pour l'etude de la MON, les techniques voltametriques sont bien adaptees car elles sont suffisamment sensibles, non perturbees par la presence de sels et permettent d'etudier la speciation des metaux sans separation physique ou chimique prealable. Realisee dans le cadre du GDR MONALISA (coordonnee par l'IFREMER), cette etude a consiste a coupler differents outils d'analyse et de modelisation afin de mieux caracteriser les proprietes de complexation de MON marine vis-a-vis du cuivre. Parmi les techniques utilisees, la pseudopolarographie, basee sur la repetition de mesures par Anodic stripping Voltametry (ASV) en modifiant le potentiel de depot, permet de quantifier les differentes fractions du metal comme presente fig. 1 : libre/labile, complexes electrolabiles, complexes inertes, et par consequent de mieux caracteriser la fraction complexee par la MON [3]. L'association de cette technique a des mesures de potentiometrie, de capacites complexantes et de competition entre Cu2+/Ca2+/H+ nous renseigne sur la nature et la force des sites complexants specifiques de la MON. Les donnees ainsi obtenues sont ensuite modelisees par une distribution discrete a l'aide du logiciel PROSECE [4] afin d'obtenir des parametres de complexation realistes et relatifs a la MON etudiee. Ces parametres de complexation seront par la suite utilises dans le code de speciation MOCO, developpe par l'IFREMER, afin de mieux apprehender le role de la MON sur la speciation du Cu en milieu marin.
Dans les ecosystemes aquatiques, la matiere organique dissoute (MOD) joue un role majeur sur le c... more Dans les ecosystemes aquatiques, la matiere organique dissoute (MOD) joue un role majeur sur le comportement des elements traces (inorganiques et organiques) et leur biodisponibilite vis-a-vis des micro-organismes, de part ses proprietes de complexation. Bien que la MOD marine represente le principal reservoir organique dans les oceans, la caracterisation de ses proprietes reste difficile de part les faibles teneurs en MOD (INF a ppm) associees a des contaminants a l'etat de traces (quelques nM). Cette etude presente un protocole experimental adapte a des concentrations ultratraces de MOD et de metaux, telles que celles rencontrees dans les eaux oligotrophes de l'estuaire de la Krka (Croatie) et de la Mer Ligure (nord-ouest de la mediterranee). Les echantillons obtenus ont ete caracterises par leur teneur en carbone organique dissous (COD), les proprietes de fluorescence de la MOD, ainsi que sa reactivite vis-a-vis du Cu etudiee par voltametrie. Dans l'estuaire de la Krka, caracterise par une stratification verticale tres marquee, les concentrations en COD et en Cu totales et la fluorescence 3D de la MOD ne sont pas conservatives, impliquant des processus de desorption des metaux ainsi qu'une activite biologique plus importante a l'interface eau douce/eau de mer. Les proprietes de complexation de la MOD ont ete determinees par deux approches complementaires: "a l'equilibre" et "cinetique". Les parametres de complexation obtenus montrent que la MOD d'origine marine s'associe plus fortement avec le cuivre que la MOD terrigene. Bien que la concentration en ligands complexant soit plus importante dans la couche de melange, elle ne suffit pas a tamponner completement l'augmentation de la teneur en Cu totale. En consequence, les concentrations de Cu libre dans cette zone depassent le seuil de toxicite (10 pM) defini par Sunda et al. (1987, Marine Biology) pour les micro-organismes estuariens. De plus, la cinetique d'association/dissociation est considerablement ralentie, indiquant que la speciation des metaux dans de tels milieux, soumis a des variations hydrodynamiques frequentes, n'est probablement pas a l'equilibre. En utilisant les parametres de complexation determines, il a ete montre qu'une augmentation de la teneur en Cu totale de la couche de surface jusqu'a atteindre 12 nM (valeur observee en ete a cause des activites nautiques) conduit a des teneurs en Cu libres depassant systematiquement le seuil de toxicite. En mer Ligure, des profils verticaux ont ete realises chaque mois durant l'annee 2008, a 12 profondeurs jusqu'a 2200 m (site DYFAMED, nord-ouest de la mediterranee). Les profils de COD presentent un maximum en surface (1 ppm) puis decroissent jusqu'a 0.5 ppm en dessous de 200 m. La spectroscopie de fluorescence, associee a un traitement statistique (PARAFAC) des matrices d'excitation/emission de fluorescence, a permis de determiner la distribution des composantes proteiniques et humiques de la MOD. Sur deux profils verticaux (ete/automne), les proprietes de complexation de la MOD vis-a-vis du Cu ont ete modelises a l'aide de parametres utilisables dans les codes de speciation (ex. MINEQL, CHESS). Ces parametres permettent de calculer la distribution verticale du Cu libre (6.5-1.0 pM) en comparaison au Cu total (2.2-1.4 nM).
Analytica Chimica Acta, 2004
A set of simulated experiments was analysed in order to compare the influence of the titration ty... more A set of simulated experiments was analysed in order to compare the influence of the titration type and of data treatment methods on the accuracy of metal complexing parameters determination for one-and two-ligand systems. The simulated data corresponded to those obtained by anodic stripping voltammetry and were chosen to represent experiments in linear, logarithmic and decade titration modes. The values of preset complexing parameters for one-and two-ligand systems were chosen to fit into the expected experimental range. Random noise was added to the data prior to the treatment. Five different data treatments were applied: Chau-Buffle, Ružić-van den Berg and Scatchard linearisations, and non-linear fitting and PROSECE optimisations. The investigation has shown that even in the case of a one-ligand system, logarithmic and decade titrations are much better compared to the linear ones. Linearisation methods are in many cases inferior to those using optimisation algorithms. Random noise has a significant influence on the results of linearisation methods as well. For linearisation methods, in the case of a one-ligand system, high correlation has been found for the confidence interval of the calculated parameters and the difference between the preset and the calculated values. This correlation is proposed to be used as an estimation for the results quality in real experiments. PROSECE is by far superior to other methods in most of the cases due to its flexible and powerful mathematical background. It is highly recommended as a tool for data treatment. Construction of "contour-graphs" enables error prediction of the calculated complexing parameters. PROSECE is proposed as an orientation and valorisation tool in real samples analyses.
Analytica Chimica Acta, 2010
Different procedures of voltammetric peak intensities determination, as well as various experimen... more Different procedures of voltammetric peak intensities determination, as well as various experimental setups were systematically tested on simulated and real experimental data in order to identify critical points in the determination of copper complexation parameters (ligand concentration and conditional stability constant) by anodic stripping voltammetry (ASV). Varieties of titration data sets (Cu measured vs. Cu total) were fitted by models encompassing discrete sites distribution of one-class and two-class of binding ligands (by PROSECE software). Examination of different procedures for peak intensities determination applied on voltammograms with known preset values revealed that tangent fit (TF) routine should be avoided, as for both simulated and experimental titration data it produced an additional class of strong ligand (actually not present). Peak intensities determination by fitting of the whole voltammogram was found to be the most appropriate, as it provided most reliable complexation parameters. Tests performed on real seawater samples under different experimental conditions revealed that in addition to importance of proper peak intensities determination, an accumulation time (control of the sensitivity) and an equilibration time needed for complete complexation of added copper during titration (control of complexation kinetics) are the keypoints to obtain reliable results free of artefacts. The consequence of overestimation and underestimation of complexing parameters is supported and illustrated by the example of free copper concentrations (the most bioavailable/toxic specie) calculated for all studied cases. Errors up to 80% of underestimation of free copper concentration and almost two orders of magnitude overestimation of conditional stability constant were registered for the simulated case with two ligands.
Analytica Chimica Acta, 2008
The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater... more The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater sample was characterised by pseudopolarography. Measurements performed at increased concentrations of copper(II) ions showed successive saturation of active DOM sites which indicate possible partition of copper between (i) free or labile complexes, (ii) reduced and released within the potential window of the method, and (iii) electroinactive copper complexes. Pseudopolarograms measured at pH 4 indicate a release of copper which was bound to the active sites of DOM that formed non-labile complexes. Variation of the peak position and half-peak width along the scanned deposition potentials and with the increasing concentration of copper bear the information about the complex electrochemical processes at the electrode surface and in the bulk of the solution. Pseudopolarograms of zinc showed a strong dependence of the peak current and the peak position along the scanned deposition potentials on pH values, indicating preferentially complexation of zinc with carboxylic-like active sites of DOM in the measured sample. Pseudopolarography is a valuable method in the trace metal complexation and speciation studies, serving as a fingerprint of the analysed sample.
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Papers by Stéphane Mounier