Title Participants Abstract "Mercury distribution, mobilization and bioavailability in polluted sediments of Scheldt Estuary and Belgian Coastal Zone" "Tianhui Ma, Vincent Perrot, Willy Baeyens, Guanlei Li, Sybrien Lievens, Huong Thi Thuy Ngo, Thi Thanh Thao Nguyen, Martine Leermakers, Yue Gao" "In this study, the vertical distribution of mercury (Hg) in estuarine and marine sediment porewaters and solid phases was assessed by conventional and passive sampling techniques in the historically polluted Scheldt Estuary and Belgian Coastal Zone (BCZ). The Diffusive Gradients in Thin-films (DGT) measured labile Hg concentrations (HgLA) were mostly lower than the porewater Hg concentrations (HgPW), and they also presented different vertical distribution patterns. Still high Hg concentrations in the sediment solid phases, comparable to the historical ones, were observed. Even though pH, redox potential and dissolved sulfide concentration could influence the Hg biogeochemical behaviour, organic matter (OM) played a key role in governing Hg mobilization from sediment solid phase to porewater and in its partitioning between porewater and solid phase over depth. In the marine sediments, where OM had a marine signature, higher labile Hg concentrations in the porewater and faster resupply from the solid phase were observed. The DGT technique showed significant potential not only for the measurement of bioavailable Hg fractions in porewater, but also for the assessment of kinetic parameters governing the release of labile Hg species from the solid phase with the assistance of the DGT Induced Fluxes in Sediments (DIFS) model." "Phosphorus mobilization in sulfidic sediments in the Baltic Sea" "Chunyang Zhou, Yue Gao, Hao Zhang, Mingyue Luo, Tianhui Ma, Guanlei Li, Delphine Vandeputte, Martine Leermakers, Willy Baeyens" "It is well-known that the geochemical behavior of phosphorus (P) in sediments is closely related to that of Fe and Mn, but their relations remain unclear in long-term sulfidic sediments such as those of the Gotland Basin in the Baltic Sea. Therefore, P mobilization in these sediments at both shallow and deep sites was investigated in relation to that of Fe, Mn, and S. To achieve that aim, classic sediment slicing and subsequent solid phase sequential extraction were combined with in situ DGT (Diffusive Gradients in Thin-films) sampling, DIFS (DGT induced flux in sediments) modelling, and Visual MINTEQ calculations. Correlations between total dissolved and labile dissolved concentrations of P, Mn, and Fe in porewater, and the associations between labile fractions of these elements in the solid phase suggested two kinds of sources for P: The dissolution of P-bearing Fe oxides and/or Mn carbonates was observed in the shallower sites, while P and Mn release from different solid sources was observed in the deepest sites. Although the formation of Fe sulfides leads to extremely low dissolved Fe level in porewater, the simultaneous release of P with Mn/Fe was confirmed by theoretical calculations with Visual MINTEQ. The DIFS model showed that the resupply ability of P from sediment solids is determined by labile pool size. The application of experimental and theoretical methods made it possible to clarify the relationships between P, Fe, Mn and S in sulfidic sediments which may contribute to a better understanding of the P cycle in other sulfidic regions." "A comparison of different approaches for the analysis of 36Cl in graphite samples" "Ines Llopart, Mirela Vasile, Andrew Dobney, Bethany Russell, S. Kolmogorova, Sven Boden, Michel Bruggeman, Martine Leermakers, Jixin Qiao, V. De Souza, A Tarancón, H Bagán, Phil Warwick" "This study compares different approaches for the quantification of the massic activity of 36Cl in graphite samples. All approaches consisted of a combustion step in combination with a trapping solution to collect the volatile elements. Two different resins were used to separate 36Cl from the matrix (CL resin and PS resin). Liquid scintillation counting (LSC), scintillation counting (SC) and tandem inductively coupled plasma mass spectrometry (ICP-MS/MS) were used to quantify 36Cl activity. The chemical yield in all approaches was determined by means of ion chromatography (IC). In addition, the methods were applied to a real activated graphite sample." "Assessment of 226Ra and U colloidal transport in a mining environment" "Marine Reymond, Michaël Descostes, Clémence Besançon, Martine Leermakers, Sophie Billon, Gaël Cherfallot, Marie Muguet, Catherine Beaucaire, Vendula Smolíková, Patricia Patrier" "The colloidal transport of trace (Fe, Al, Ba, Pb, Sr, U) and ultra-trace (226Ra) elements was studied in a mining environment. An original approach combining 0.45 μm filtered water sampling, the Diffusive Gradient in Thin films (DGT) technique, mineralogical characterization, and geochemical modelling was developed and tested at 17 sampling points. DGT was used for the truly dissolved fraction of the elements of interest, while the 0.45 μm filtration includes both colloidal and truly dissolved fractions (together referred to as total dissolved fraction). Results indicated a colloidal fraction for Al (up to 50%), Ba (up to 86%), and Fe (up to 99%) explained by the presence of submicrometric grains of kaolinite, barite, and ferrihydrite, respectively. Furthermore, the total dissolved 226Ra concentration in the water samples reached up to 10–25 Bq/L (1.2–3.0 10−12 mol/L) at 3 sampling points, while the truly dissolved aqueous 226Ra concentrations were in the mBq/L range. Such high total dissolved concentrations are explained by retention on colloidal barite, accounting for 95% of the total dissolved 226Ra concentration. The distribution of 226Ra between the truly dissolved and colloidal fractions was accurately reproduced using a (Rax,Ba1-x)SO4 solid solution, with values of the Guggenheim parameter a0 close to ideality. 226Ra sorption on ferrihydrite and kaolinite, other minerals well known for their retention properties, could not explain the measured colloidal fractions despite their predominance. This illustrates the key role of barite in such environments. The measured concentrations of total dissolved U were very low at all the sampling points (" "Insights into the release of triclosan from microplastics in aquatic environment assessed with diffusive gradient in thin-films" "Yuwei Jia, Yue Gao" "Organic chemicals associated with microplastics (MPs) can be released and thus pose potential risks during weathering processes. However, the thermodynamics and kinetics of their release processes still need to be better understood. Herein, the adsorption and desorption kinetics of triclosan on polystyrene (PS) and polyvinyl chloride (PVC) were investigated by using both batch experiments and diffusive gradients in thin-films (DGT) technique. The pseudo-second-order model fitted the data best, implying that both intraparticle diffusion and external liquid film diffusion influence the adsorption and desorption processes. DGT continuously accumulated triclosan from MP suspensions but slower than theoretical values, indicating some restrictions to desorption. The DGT-induced fluxes in Soils/Sediment (DIFS) model, employed to interpret DGT data, gave distribution coefficients for labile species (Kdl) of 5000 mL g−1 (PS) and 1000 mL g−1 (PVC) and the corresponding response times (Tc) were 10 s and 1000 s, respectively. Higher Kdl but smaller Tc for PS than PVC showed that more triclosan adsorbed on PS could be rapidly released, while there were some kinetic limitations for triclosan on PVC. A novel finding was that pH and ionic strength individually and interactively affected the supply of triclosan to DGT. This is the first study to quantify interactions of organics with MPs by using DGT, aiding our understanding of MPs' adsorption/desorption behavior in the aquatic environment." "Diffusive Gradients in Thin films as a tool for arsenic speciation in the estuarine environments" "Vendula Smolíková, Tianhui Ma, Yue Gao, Martine Leermakers" "Although we are able to routinely monitor concentrations of trace elements in the environment, this information generally serves as a poor predictor of their potential bioavailability and toxicity. To thoroughly evaluate the ecotoxicological status of any environment, we have to focus on the determination of the labile fraction of trace elements in addition to conventional analysis. This especially applies to arsenic (As) – redox-sensitive element that occurs in the environment in a form of various species whose bioavailability and impact on living organisms may be diametrically different. The Diffusive Gradients in Thin Films (DGT) in-situ passive sampling technique which directly discriminates free ions and weak complexes has been shown to be a suitable tool for the evaluation of trace elements’ labile fraction in the aquatic environment (Gontijo et al., 2016; Rodríguez et al., 2021). To evaluate the speciation of labile As in the natural waters, the DGT samplers with various sorbents for total As (organic + inorganic fraction), AsIII, or AsV were deployed in the Scheldt estuary along the salinity gradient and in the coastal zone (Zeebrugge harbour). Water samples were taken at both stations and were processed by filtration (on 0.45 μm) in order to describe As distribution between particulate, dissolved as well as labile (DGT-determined) fractions in the water column. The results will be presented at the conference." "Investigation of a new approach for 36Cl determination in solid samples using plastic scintillators" "Ines Llopart, Mirela Vasile, A Tarancón, H Bagán, Andrew Dobney, Sven Boden, Marianne Bruggeman, Martine Leermakers, Jixin Qiao, Phil Warwick" "This work reports a new approach for the determination of 36Cl in radioactive waste samples from nuclear decommissioning, wherein novel plastic scintillator (PS) materials were used for the concentration of 36Cl prior to the detection with scintillation counting. Different plastic scintillator (PS) materials were tested for their selective absorption and detection of 36Cl activity in solid samples. PS microspheres (PSm), cross-linked PSm (CPSm) and PS resin have been investigated. PS resin was identified as the most suitable material for 36Cl analysis. Pyrolysis and subsequent trapping of the volatile elements in a bubbler was used. The trapping solution was finally loaded onto a cartridge of the PS resin. Scintillation counting and ion chromatography were used to determine the activity concentration and the chemical recovery, respectively." "A multimethodological evaluation of arsenic in the Zenne River, Belgium: Sources, distribution, geochemistry, and bioavailability" "Vendula Smolíková, Natacha Brion, Tianhui Ma, Vincent Perrot, Yue Gao, Pavlina Pelcova, Andrea Ridoskova, Martine Leermakers" "The distribution and geochemistry of arsenic (As) in water and sediments of the Zenne River, a small urban river flowing through Brussels (Belgium), were assessed based on the results of 18 sampling campaigns performed between 2010 and 2021. In general, concentrations of As sharply increase between Vilvoorde and Eppegem and are up to 6–8 times higher in the section downstream of Eppegem in comparison to the upstream part of the Zenne. The monitoring surveys in which the grab water samples were taken at a 1-hour sampling frequency revealed that the large temporal variability in As concentrations found in the downstream part of the river is driven by the tidal cycle. The diffusive gradients in thin films (DGT) technique was used to assess the DGT labile As species in surface water and sediment porewater. Three DGT sorbents (Metsorb, Lewatit FO 36, and ZrO2) for the determination of total As were applied to compare their performance, and the 3-mercaptopropyl-functionalized silica (3-MFS) was used for the speciation of As(III) in porewater. Arsenic species are fully labile in surface waters as the DGT time-integrated concentrations of As were in good agreement with the average concentrations calculated from the grab samplings. In sediment porewaters, As is predominantly present as non-DGT labile species (66–93 %), and the DGT labile As fraction is dominated by As(III). Flux calculations evaluating the relative importance of different As sources to the Zenne River revealed the presence of a point source on the tributary Tangebeek, which contributes to 87 % of the As load carried by the Zenne River." "Investigating the 36Cl memory effect in pyrolysis of solid samples from nuclear decommissioning activities" "Ines Llopart, Mirela Vasile, Andrew Dobney, Sven Boden, Marianne Bruggeman, Martine Leermakers, Jixin Qiao, Phil Warwick" "During the optimization of 36Cl determination in solid wastes from nuclear decommissioning, a residual 36Cl signal was observed in procedural blanks measured after processing active samples. To uncover the possible causes, we investigated the interaction of chlorine with the components of a Pyrolyser-6 Trio™, as well as the chemicals used during the procedure. Different treatments for identifying the source of chlorine carryover were thoroughly investigated, demonstrating that the 36Cl memory effect arises from the interaction with pyrolyser components and that it occurs almost every time when the analysis procedure is performed. Therefore, results obtained using this analysis procedure need to be corrected for this memory effect by measuring procedural blank samples before and after measuring 36Cl-containing samples." "Anthropogenic activities influence the mobilization of trace metals and oxyanions in coastal sediment porewaters" "Mingyue Luo, Chunyang Zhou, Wei Guo, Tianhui Ma, Lawrence Percival, Willy Baeyens, Yue Gao" "The biogeochemical cycle of trace metals and oxyanions in marine sediments is mainly controlled by early diagenesis of organic material, but anthropogenic activities such as dumping of dredged sludge or shipyard activities can strongly perturb these natural processes. Therefore, the impact of dumping of dredged sludge, shipyard activities such as blasting of boat hulls and the mixing of polluted Scheldt estuary water with less polluted coastal water on the mobilization of trace metals and oxyanions in the sediments was studied in the pre- and post-bloom period (March and October) in Belgian Coastal Zone (BCZ). Vertical profiles of total and labile dissolved trace element concentrations, dissolved sulfide, pH and redox potential were assessed in sediment porewaters. Generally, total and labile dissolved element profiles in the porewaters are well correlated, showing higher concentrations in March when the redox potential is lower and sulfide concentrations higher. Low pH levels were documented together with high amounts of Fe and associated elements in March at the dumping station. At the coastal station in the vicinity of the shipyards, sediment porewaters are enriched in dissolved Zn while at the mouth of the Scheldt estuary the highest dissolved Cu levels were found. Theoretical calculations with Visual MINTEQ confirm the increased Fe and associated element concentrations in March (lower pH) and the lower metal concentrations in October (lower Eh). R values, ratio of labile dissolved to total dissolved concentrations, reflect the potential of the solid sediment phase to supply labile elements to the porewater. They were lowest for Cu and highest for V. This study showed that anthropogenic activities in the BCZ such as dumping of dredged sludge and blasting of boat hulls have a serious impact on the levels, distribution and bioavailability of contaminants in the sediments, which may form a real threat to the benthic ecosystem."