Malgorzata Grybos

Bio-dissolution of colloidal-size clay minerals entrapped in microporous silica gels.

Four colloidal-size fractions of strongly anisotropic particles of nontronite (NAu-2) having different ratios of basal to edge surfaces were incubated in the presence of heterotrophic soil bacteria to evaluate how changes in mineral surface reactivity influence microbial dissolution rate of minerals. To avoid any particle aggregation, which could change the reactive surface area available for dissolution, NAu-2 particles were immobilized in a biocompatible TEOS-derived silica matrix. The resulting hybrid silica gels support bacterial growth with NAu-2 as the sole source of Fe and Mg. Upon incubation of the hybrid material with bacteria, between 0.3% and 7.5% of the total Fe included in the mineral lattice was released with a concomitant pH decrease. For a given pH value, the amount of released Fe varied between strains and was two to twelve-fold higher than under abiotic conditions. This indicates that complexing agents produced by bacteria play an important role in the dissolution process. However, in contrast with proton-promoted NAu-2 dissolution (abiotic incubations) that was negatively correlated with particle size, bacterial-enhanced dissolution was constant for all size fractions used. We conclude that bio-dissolution of nontronite particles under acidic conditions seems to be controlled by bacterial metabolism rather than by the surface reactivity of mineral.

Dissolution of anisotropic colloidal mineral particles: evidence for basal surface reactivity of nontronite.

Anisotropic textural and crystallographic properties of phyllosilicate particles often influence the mineral weathering rate. The purpose of this study was to investigate how the changes in mineral surfaces (basal vs. edge) as a result of changes in crystal size control the dissolution of the mineral. Different nano-size fractions of Na-exchanged nontronites (NAu2 and NAu1) were immobilized in a silica gel and then incubated under acidic conditions using HNO(3) at 28 degrees C for 5 days. For each sample, the dissolution behavior was analyzed by measuring the amount of iron released from the mineral lattice. The results showed that for a given pH, a decrease in particle size significantly increased NAu2 and NAu1 dissolution. At pH 1.5, 7.2% of the total iron of the highest size sample of NAu2 was released in solution whereas this proportion increased up to 25% for the smallest size fraction. The percentage of total iron extracted from NAu1 at the same pH (1.5) was less important: 3.5% and 6.5% for higher and smaller size fractions, respectively. The observed increase in dissolution was not directly correlated to the increase in the amount of edge faces, suggesting that all mineral surfaces contributed to mineral dissolution. In the present case this may be related to the fact that 8% and 2% of total iron of NAu2 and NAu1, respectively, are located in the tetrahedral sheet. In conclusion, the basal surface of nontronites plays an important role in the weathering process.

Role of microbial reducing activity in antimony and arsenic release from an unpolluted wetland soil: a lab scale study using sodium azide as a microbial inhibiting agent

Environmental context Antimony and arsenic are toxic elements occurring naturally in the environment. We found that arsenic release to water from an unpolluted wetland soil is related to microbial reducing activity only, whereas antimony can still be released when this activity is inhibited, suggesting the involvement of additional processes. The findings show that microbial/non-microbial mechanisms control arsenic and antimony release and can thereby impact water quality at wetland outlets. Abstract In wetland soils, the mobility of geogenic metal(loid)s is usually associated with direct or indirect microbial-induced processes (solubilisation of mineral and organic components, pH induced desorption, competition effects, dissimilatory reduction). To identify the role of microbial reducing activity in As and Sb release, we conducted two series of soil incubations (sodium azide-treated (NaN3-T) and non-treated (NT)) in closed batches for 36 days. During the incubation period, we monitored the evolution of dissolved As, Sb, Mn, FeII, organic carbon (DOC), humic substances (HS) and proteins (PN) with their apparent molecular weight distribution (aMW) as well as pH, reduction potential (Eh) and alkalinity. Results showed that the release of As and Sb occurred when microbially reducing conditions prevailed (NT soil Eh ~0mV and FeII>40mg L–1) and was inhibited for As in the absence of microbial reducing activity (NaN3-T soil; Eh>250mV and Fe<1mg L–1). In contrast, Sb behaved differently since its release was only slowed down when microbially reducing conditions were inhibited. We concluded that soil microbial reducing activity fully controls the release of As and to a lesser extent that of Sb when NaN3 is used as a microbial inhibiting agent. Since Sb release and dissolved organic matter (DOM) solubilisation (NaN3-induced artefact) occurred simultaneously in the absence of microbially reducing conditions, we concluded that organic matter could be one key factor controlling Sb mobilisation in the given conditions, which is not the case for As.

Bioweathering of nontronite colloids in hybrid silica gel: implications for iron mobilization

This study aimed to study biotic iron dissolution using a new hybrid material constituted of well‐dispersed mineral colloids in a silica gel matrix. This permitted to prevent adsorption of colloidal mineral particles on bacteria. Hybrid silica gel (HSG) permitted to study bioweathering mechanisms by diffusing molecules.

Waterlogging and soil reduction affect the amount and apparent molecular weight distribution of dissolved organic matter in wetland soil: a laboratory study

The release of dissolved organic matter (DOM) from wetland soils is an important pathway for the input of organic compounds into adjacent aquatic environments. In the present study we investigated, under controlled laboratory conditions, the quantity and quality of DOM released from a wetland soil subject to waterlogging and reducing conditions. Three soil redox conditions (oxic, moderately reducing and advanced reducing) were distinguished based on nitrate, ferrous ions and sulfate concentrations in soil solution. Under each redox condition, the quantity (dissolved organic carbon (DOC), humic substances and peptides plus proteins (P-PN) and quality (aromaticity; specific ultraviolet absorbance at 254 nm (SUVA254nm)) and apparent molecular weight (aMW) distribution) of DOM were investigated. The results showed that soil redox condition affects the amount and properties of mobilised DOM. The rate of DOM release and SUVA254 values were highest during the transition from oxic to moderately reducing conditions, whereas both stabilised during progression to advanced reducing conditions. In addition, the mobilised DOM is expected to be more reactive because of an increase in polar substituents in aromatic structures between oxic and moderately reducing conditions. During the development of moderately reducing conditions, dissolved humic substances increased significantly, whereas their aMW distribution (between 500 and 6000 ) remained constant for each of the three different redox conditions. In contrast, the quantity of dissolved P-PN remained low and steady under the three redox conditions, whereas the aMW distribution of protein-like and microbial by-product-like compounds decreased during the development of reducing conditions (aMW of compounds between 100 and >100 000).

Key role of the sorption process in alteration of metal and metalloid quantification by fouling development on DGT passive samplers

The DGT technique (diffusive gradients in thin films) is widely used for passive sampling of labile trace metals and metalloids in natural waters. Although development of fouling on the protective membranes is frequently observed, its effect on DGT sampling has been barely investigated. This study evaluates the influence of fouling on sampling of trace cationic metals Cd(II), Cu(II), Ni(II) and Pb(II) and oxyanions As(V), Cr(VI), Sb(V) and Se(VI). Fouling was developed in situ on polycarbonate membranes in four diverse natural freshwater environments and sampling alteration was assessed in controlled laboratory experiments. Accumulation of oxyanions and Ni was unaltered in the presence of fouling whereas significant alteration occurred in sampling of Cd, Cu and Pb (at pH ∼5.4). Characterization of the fouled membranes highlighted the intervention of sorption phenomenon as sampling alteration was systematically observed alongside element sorption onto fouled membrane. A preliminary flowchart for identifying potentially biased quantifications linked to fouling development during in situ DGT deployment in natural waters is proposed.

Weathering of historical copper slags in dynamic experimental system with rhizosphere-like organic acids

This study was undertaken to simulate experimentally the weathering of slags disposed nearby soil rhizosphere. The aim of the research was to differentiate the effect of pH and organics on slags dissolution as well as to indicate weathering sequence of phase components. The studied slags are mainly composed of Fe (34.5 wt%) and Si (17.9 wt%) and contain up to 3761 mg kg-1 of Cu and 3628 mg kg-1 of Zn. The main identified phases are fayalite and glass, whereas sulfides and metallic Cu are volumetrically minor. A 30 days long slag weathering experiment was carried out with artificial root exudates (43.7 mM) and demineralized water at initial pH = 3.5 and pH = 6.7. The highest metal release (up to 10.9% of Zn and 4.6% of Cu) was observed in ARE solution at initial pH 3.5. Dissolution of sulfides and fayalite was mainly driven by pH. Artificial root exudates enhance glass dissolution as compared to demineralized water regardless of initially fixed pH. Based on this study following weathering sequences are delineated: i) under ARE 3.5 conditions: silicates > glass > sulfides, ii) under DW 3.5 conditions: sulfides > silicates > glass, iii) under near-neutral conditions: sulfides > glass > silicates.

Response to the comment on “Copper metallurgical slags - current knowledge and fate: A review”

Anna Potysz, Eric D. van Hullebusch, Jakub Kierczak, Malgorzata Grybos, Piet N.L. Lens, and Gilles Guibaud Universit e Paris-Est, Laboratoire G eomat eriaux et Environnement (EA 4508), UPEM, Marne-la-Vall ee, France; Universit e de Limoges, Groupement de Recherche Eau Sol Environnement (EA 4330), Facult e des Sciences et Techniques, Limoges Cedex, France; UNESCO-IHE Institute for Water Education, DA Delft, The Netherlands; University of Wroclaw, Institute of Geological Sciences, Cybulskiego, Wroc»aw, Poland

QUALITÉ ET POLLUTION DES EAUX D’UN HYDROSYSTÈME LITTORAL TROPICAL : CAS DU SYSTÈME LAGUNAIRE DE LOMÉ, TOGO

The field of Depth of Anaesthesia (DOA) is a very challenging area for neuro-fuzzy control since direct measurements are unavailable. During anaesthesia, the blood pressures (BP), the mean arterial blood pressure (MAP) and the heart rate (HR) are monitored to maintain hemodynamic stability and to assess the level of consciousness. The purpose of this study is to find the best input-output definitions in the Adaptive-Network-based Fuzzy Inference System (ANFIS) to control the Sevoflurane dose to patient under the general anaesthesia with the classical MAP and HR parameters. The best models have been found among many possible input combinations. This study helps to provide an alternate control for the dose of Sevoflurane which is widely used as an anaesthetic agent. The models have been trained and validated by clinical data. The results show that the patients can be modelled by ANFIS if sufficient HR and MAP data are provided. Furthermore, the model performance could be increased if the patients are grouped as adults and children. The performance (up to 0.99) in this study is comparable to recent works in similar subject which detect DOA by Electroencephalograms (EEG).