Colloidal mobilization from soil and transport of uranium in (sub)-surface waters.

An analytical methodology was developed to characterize the colloidal distribution of trace elements of interest in environmental waters sampled in a same site and enables the different colloidal distributions from waters to be compared. The purpose was to provide consistent information related to the origin and nature of colloids responsible for the transport of trace element(s). The work was motivated by the observed enhanced mobility of uranium in soil. The colloidal size continuum was investigated by a multi-technique approach involving asymmetric flow field-flow fractionation (AF4) coupled with ultraviolet spectroscopy (UV), multi angle light scattering (MALS), and atomic mass spectrometry (ICPMS). To take into consideration the size and shape variability specific to each sample, the size distributions were established from the gyration radii measured from MALS, also considering the size information from standard nanospheres fractionated by AF4. A new parameter called "shape index" was proposed. It expresses the difference in hydrodynamic behavior between analytes and spherical particles taken as reference. Under AF4 diffusion conditions, it can be considered as an evaluator of the deviation from the sphericity of the fractionated analytes. AF4-UV-MALS-ICPMS enabled the dimensional and chemical characteristics of the colloidal size continuum to be obtained. As a "proof of concept", the developed methodology was applied at a field scale, in a reference study site. In order to have a "dynamic understanding", the investigation was based on the joint characterization of colloids from surface waters and soil leachates from static and dynamic processes. In the water samples of the study site, the continuum of gyration radius ranged from a few nanometers up to 200 nm. Colloids containing iron, aluminum, and organic carbon were involved in the uranium transport in the soil column and surface waters. The colloidal uranium concentration in the surface water increased from the upstream location (approximately 13 ng (U) L-1) to the downstream location (approximately 60 ng (U) L-1).

Distribution and speciation of ambient selenium in contrasted soils, from mineral to organic rich.

Selenium adsorption onto oxy-hydroxides mainly controls its mobility in volcanic soils, red earths and soils poor in organic matter (OM) while the influence of OM was emphasized in podzol and peat soils. This work aims at deciphering how those solid phases influence ambient Se mobility and speciation under less contrasted conditions in 26 soils spanning extensive ranges of OM (1-32%), Fe/Al oxy-hydroxides (0.3-6.1%) contents and pH (4.0-8.3). The soil collection included agriculture, meadow and forest soils to assess the influence of OM quality as well. Trace concentrations of six ambient Se species (Se(IV), Se(VI) and 4 organo-Se compounds) were analyzed by HPLC-ICP-MS in three extractants (ultrapure water, phosphate and sodium hydroxide) targeting Se associated to different soil phases. The Kd values determined from ultrapure water extraction were higher than those reported in commonly used short-term experiments after Se-spiking. Correlations of ambient Se content and distribution with soil parameters explained this difference by an involvement of slow processes in Se retention in soils. The 26 Kd values determined here for a wide variety of soils thus represent a relevant database for long-term prediction of Se mobility. For soils containing less than 20% OM, ambient Se solubility is primarily controlled by its adsorption onto crystalline oxy-hydroxides. However, OM plays an important role in Se mobility by forming organo-mineral associations that may protect adsorbed Se from leaching and/or create anoxic zones (aggregates) where Se is immobilized after its reduction. Although for the first time, inorganic Se(IV), Se(VI) and organo-Se compounds were simultaneously investigated in a large soil collection, high Se proportions remain unidentified in each soil extract, most probably due to Se incorporation and/or binding to colloidal-sized OM. Variations of environmental factors regulating the extent of OM-mineral associations/aggregation may thus lead to changes in Se mobility and bio-availability.

Optimization of flow field-flow fractionation for the characterization of natural colloids.

The methodological approach used to robustly optimize the characterization of the polydisperse colloidal phase of drain water samples is presented. The approach is based on asymmetric flow field-flow fractionation coupled to online ultraviolet/visible spectrophotometry, multi-angle light scattering, and inductively coupled plasma mass spectrometry. Operating factors such as the amount of sample injected and the ratio between main-flow and cross-flow rates were considered. The evaluation of the injection and fractionation steps was performed considering the polydispersity index and the contribution to the polydispersity of the plate height, the recovery, the retention ratio and the size range of the fractionated colloids. This approach allows the polydispersity of natural colloid samples to be taken into consideration to achieve the most efficient and representative fractionation. In addition to the size characterization, elemental analysis was also evaluated using the recovery, precision, and limits of detection and quantification relative to a trace element of interest (copper) in drain water. To complete this investigation, the potential application of the methodology was assessed using several independent drain water samples from different soils. The contribution of the polydispersity to the plate height ranges from 4.8 to 8.9 cm with a mean precision of 6%. The mean colloidal recovery was 81 ± 3 %, and the mean retention ratio was 0.043-0.062. The limits of detection and quantification for copper were 0.6 and 1.8 µg L(-1), respectively.

Asymmetric flow-field flow fractionation-multidetection coupling for assessing colloidal copper in drain waters from a Bordeaux wine-growing area.

The objective of this study was to show that on-line asymmetric flow-field flow fractionation (AFFFF)-multidetection coupling is useful for studying environmental colloids in a qualitative and quantitative way. The utility of the technique was illustrated by assessing the colloidal fraction of the copper that was extracted from the soil, transferred to an aqueous phase and then transported by drain waters in a wine-growing area. To determine the size and composition of the colloids, AFFFF was coupled to UV, multi-angle light scattering and inductively coupled plasma mass spectrometry detectors. Colloidal copper represents between 20 and 60% of the total copper in the sub 450 nm of drain waters. Copper is mainly associated with organic-rich colloids with a size below 10 nm. It is also found in organo-mineral populations (as clay or (oxy)hydroxides), with sizes ranging between 10 and 450 nm.

A new methodology involving stable isotope tracer to compare simultaneously short- and long-term selenium mobility in soils.

A better understanding of Se fate in soils is required for different environmental issues, such as radioactive waste management or soil fertilization procedures. In these contexts, the mobility and speciation of Se have to be studied at both short and long terms after Se inputs. Here, we present a new methodology to monitor simultaneously the reactivity of added (isotopic enriched tracers) and ambient Se at trace level in soils by high-performance liquid chromatography inductively coupled plasma mass spectrometry (ICP-MS) following specific extractions. To do so, the collision/reaction cell of the ICP-MS instrument and the interference corrections were optimized to measure reliably the four major Se isotopes. To exemplify the method capabilities, the behaviors of added (77)Se(IV) and ambient Se were followed up in two soils submitted to an ageing process during 3 months. The solid/liquid distribution of added Se reached a steady state after 1 month while its speciation and distribution among soil solid phases were still changing after 3 months. The results clearly demonstrate that slow processes are involved in Se retention and transformation in soils. The usual short-term experiments (<1 month) performed after Se addition are thus not suitable for long-term risk assessment. Interestingly, the behavior of added Se tended to that of ambient Se, suggesting that ambient Se would be useful to infer the fate of Se input over long time scales.

Assessment of diffuse contamination of agricultural soil by copper in Aquitaine region by using French national databases.

A long-term application of copper-based fungicides to fight against downy mildew has led to soil contamination by copper particularly in Aquitaine region where viticulture is important. This work aims to statistically validate the origin of diffuse contamination of Aquitaine agricultural soils and show that contamination is closely related to wine-growing in this region. For this purpose, several national databases have been used. From the French National Soil Monitoring Network (Réseau de Mesures de la Qualité des sols RMQS) data, an Exploratory Data Analysis (EDA) was performed to bring out the copper contamination. The French test soil database (Base de Données des Analyses de Terre BDAT) and the national census of agriculture (Recensement Général Agricole RGA) have been crossed. A statistical approach has been used to determine the relationship between the median concentration of copper extracted by Ethylene Diamine Tetra-acetic Acid (EDTA) referred to as CuEDTA in cultivated topsoils of the Aquitaine region and the ratio between winegrowing area (Svine) and the Used Agricultural Area (UAA) expressed as the form Svine/UAA. The results revealed a strongly significant exponential correlation between these two variables. They allow concluding that at cantonal scale, when vines cover more than 80% of the UAA, an overexposure of soils to the diffuse contamination by copper can occur.

Investigation of uranium-colloid interactions in soil by dual field-flow fractionation/capillary electrophoresis hyphenated with inductively coupled plasma-mass spectrometry.

This paper deals with the study of uranium-colloid interactions in a carbonated soil. The work is focused on the immediately available fraction obtained after a leaching process, according to a normalized batch method. In order to characterize the different colloidal carriers, Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) coupled to different detectors (UV, Multi Angle Laser Light Scattering (MALLS) and Inductively coupled Plasma-Mass Spectrometry (ICP-MS)) was used. The colloidal carriers are mainly inorganic particles (carbonated particles and clays) mixed with organic substances. Furthermore, dissolved and colloidal uranium species in the leaching solutions were monitored by Capillary Electrophoresis (CE) coupled to ICP-MS, in order to investigate the uranium/colloids interactions. According to the first results, uranium fate in this specific soil is controlled by sorption/desorption phenomena, strongly pH dependent.

Selenium speciation analysis at trace level in soils.

This paper describes the development of an analytical methodology to determine speciation of selenium present in soils at trace level (µg kg(-1)). The methodology was based on parallel single extractions and high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICPMS). Two complementary chromatographic separations were used to confirm Se species identity. Different extractants, selected on the basis of sequential extraction schemes, were compared. Ultrapure water, 0.1 molL(-1) phosphate buffer (KH(2)PO(4)/K(2)HPO(4)) at pH 7 and 0.1 molL(-1) sodium hydroxide extractants were finally chosen owing to their efficiency in extracting Se and compatibility with Se species stability. These extractants allow also assessing respectively water-soluble Se (i.e. the most mobile Se fraction), exchangeable Se (i.e. sorbed onto soil component surface) and Se bound to soil organic matter. This methodology gives thus information on Se mobility related to its distribution in soil with preservation of original Se speciation. Detection limits range from 3 to 29ng(Se)L(-1) and from 0.1 to 10 µg(Se)kg(-1), allowing determination of Se species concentrations in extracts from soils containing native Se at trace level. The methodology was applied to three soils with total Se concentrations between 210 and 1560 µg(Se)kg(-1).

Single walled carbon nanotube length determination by asymmetrical-flow field-flow fractionation hyphenated to multi-angle laser-light scattering.

Asymmetrical flow field-flow fractionation (AFlFFF) hyphenated to multi-angle laser-light scattering (MALS) was evaluated in order to determine single walled carbon nanotube (SWCNT) length distribution. Fractionation conditions were investigated by examining mobile phase ionic strength and pH, channel components and cross-flow rate. Ammonium nitrate-based mobile phase with 10(-5)molL(-1) ionic strength and pH 6 allows the highest sample recovery (89±3%) to be obtained and the lowest loss of the longest SWCNT. A cross-flow rate of 0.9mLmin(-1) leads to avoid any significant membrane-sample interaction. Length was evaluated from gyration radius measured by MALS by comparing SWCNT to prolate ellipsoid. In order to validate the fractionation and the length determination obtained by AFlFFF-MALS, different SWCNT aliquots were collected after fractionation and measured by dynamic light scattering (DLS). AFlFFF is confirmed to operate in normal mode over 100-2000nm length. MALS length determination after fractionation is found to be accurate with 5% RSD. Additionally, a shape analysis was performed by combining gyration and hydrodynamic radii.

Selenate bioaccumulation and toxicity in Chlamydomonas reinhardtii: Influence of ambient sulphate ion concentration.

The aim of the present study was to investigate selenate toxicity in the unicellular green algae Chlamydomonas reinhardtii as a function of sulphate ion concentration and the relationship with intracellular bioaccumulation. The toxicity of selenate was evaluated by measuring the effect of different selenate concentrations on algal growth during a 96h exposure period. A non-linear regression according to the Hill model was used to describe the dose-effect relationship and estimate the effect concentrations (EC) of selenate. EC(50) values of 0.40[0.24-0.52]micromolL(-1) and of 3.10[1.65-4.86]micromolL(-1) of ambient selenate were obtained, at 8 and 80micromolL(-1) of sulphate ions in the medium, respectively. For non-toxic and low-level ambient selenate concentrations, bioaccumulation in presence of 80micromolL(-1) was one tenth that of 8micromolL(-1) of sulphate ions. When expressed as intracellular selenium burden, EC(50) values determined at 8 and 80micromolL(-1) of sulphate ions were not significantly different (126 and 67nmolSe.10(9)cells(-1), respectively). In conclusion, toxicity appeared to be correlated to selenate bioaccumulation which suggests that toxicity must be linked to intracellular selenium accumulation that is directly dependent on ambient sulphate ions that may compete with selenate for transport sites.

Colloidal transport of uranium in soil: Size fractionation and characterization by field-flow fractionation-multi-detection.

The aim of this study was to characterize colloids associated with uranium by using an on-line fractionation/multi-detection technique based on asymmetrical flow field-flow fractionation (As-Fl-FFF) hyphenated with UV detector, multi angle laser light scattering (MALLS) and inductively coupling plasma-mass spectrometry (ICP-MS). Moreover, thanks to the As-Fl-FFF, the different colloidal fractions were collected and characterized by a total organic carbon analyzer (TOC). Thus it is possible to determine the nature (organic or inorganic colloids), molar mass, size (gyration and hydrodynamic radii) and quantitative uranium distribution over the whole colloidal phase. In the case of the site studied, two populations are highlighted. The first population corresponds to humic-like substances with a molar mass of (1500+/-300)gmol(-1) and a hydrodynamic diameter of (2.0+/-0.2)nm. The second one has been identified as a mix of carbonated nanoparticles or clays with organic particles (aggregates and/or coating of the inorganic particles) with a size range hydrodynamic diameter between 30 and 450nm. Each population is implied in the colloidal transport of uranium: maximum 1% of the uranium content in soil leachate is transported by the colloids in the site studied, according to the depth in the soil. Indeed, humic substances are the main responsible of this transport in sub-surface conditions whereas nanoparticles drive the phenomenon in depth conditions.

Determination of the correlation between physical measurements of roughness, optical properties, and perception of frosted glass surfaces.

Chemical frosting is used as a surface decorating method by many glass package producers. After immersion in an acid frosting bath, glass items present the desired frosted effect. The perception of this particular effect is due to the formation of a microscopic crystalline pattern on the glass surface, which scatters light passing through the glass surface. The chemical composition of the frosting bath influences these properties by modifying the surface roughness, the depth, and the average slopes of the crystalline pattern. Perception of the final aspect can be modified according to the chemical composition of the frosting bath. Different correlations between all these parameters exist and have been quantified.

Comprehensive study of the parameters influencing the detection of organotin compounds by a pulsed flame photometric detector in sewage sludge.

An investigation of the operating conditions of a pulsed flame photometric detection (PFPD) system for the determination of organotin compounds (OTCs) in sewage sludge is reported. During the analyses, some spectral interferences were observed. For their elimination detector parameters such as gate delay and gate width were investigated. In addition, the applicability of three different internal standards was evaluated. Under optimised analytical conditions (gate delay 3 ms, gate width 2 ms, tripropyltin as internal standard) limits of detection (LOD) were determined. The LOD for butyltins ranged between 8 and 16 ng Sn g(-1), for phenyltins around 8 ng Sn g(-1) and for octyltins between 5 and 10 ng Sn g(-1). Since there is no certified reference material (CRM) available for sewage sludge, the accuracy of the analytical procedure was checked by the analysis of CRM PACS-2 (marine sediment) and a spiked sludge sample. Good agreement between determined and certified values was obtained. Sewage sludge from a local wastewater treatment plant was analysed and the results compared with data from the literature.

Advantages of hydride generation interface for selenium speciation in waters by high performance liquid chromatography-inductively coupled plasma mass spectrometry coupling.

This paper focuses on the analytical performance improvement of the coupled technique HPLC-ICPMS using on-line collision/reaction cell technology for selenium elemental and speciation analyses at the ng (Se) l(-1) level in aquatic environment. Collision/reaction cell operating parameters were optimised, resulting in selected conditions of 5.5 ml min(-1) H(2) and 0.5 ml min(-1) He mixture. The detection limits obtained were around 5 ng (Se) l(-1) for total analysis, and between 7 and 15 ng (Se) l(-1) depending on the species for speciation analysis. The capability of UV irradiation-hydride generation interfacing to increase detector sensitivity was also evaluated for speciation analysis. The detection limits obtained were in the range 2-8 ng (Se) l(-1) depending on the species. Moreover, such interface allowed to prevent bromine introduction to the ICPMS which is particularly convenient for selenium trace analysis in natural waters as (80)Se is preserved free from BrH interferences. The developed method was validated using certified water with low selenium content (TM Rain 95, NWRI, Canada) and applied to the analysis of different waters.

Evaluation of a combined fractionation and speciation approach for study of size-based distribution of organotin species on environmental colloids.

Results relating to the first original application of an analytical approach combining asymmetric flow field-flow fractionation (As-Fl-FFF) with multi-detection and chemical speciation for determination of organotins in a landfill leachate sample are presented. The speciation analysis involved off-line head-space solid-phase microextraction (HS-SPME)-gas chromatography with pulsed-flame photometric detection (GC-PFPD) performed after three consecutive collections of five different fractions of interest from the As-Fl-FFF system and cross-flow part (assumed to be representative of the <10 kDa phase). After 0.45 microm filtration and without preconcentration before fractionation and speciation analysis, limits of detection (LOD) were 4-45 ng (Sn) L(-1) in the sample, with relative standard deviations (RSD) of 3-23%. The As-Fl-FFF fractionation of this sample enables characterization of two distinct populations-organic-rich and inorganic colloids with gyration radius up to 120 nm. Total Sn and mono and dibutyltins (MBT and DBT) appear to be distributed over the whole colloidal phase. Tributyl, monomethyl, monooctyl, and diphenyltins (TBT, MMT, MOcT, and DPhT) were also detected. Quantitative speciation analysis performed on the two colloidal populations and in the <10 kDa phase revealed concentrations from 130 +/- 10 (MMT) to 560 +/- 50 ng (Sn) L(-1) (DPhT).

Organotin speciation in French brandies and wines by solid-phase microextraction and gas chromatography--pulsed flame photometric detection.

An analytical method devoted to organotin compounds (OTC) determination in brandy and wine was developed. It is based on solid-phase microextraction (SPME) of ethylated organotins. The following operating factors were examined: SPME mode/nature of fibre coating, sample volume/dilution, and sampling time. The optimisation work led to dilute the sample in an aqueous buffer (1/11, v/v ratio) in order to satisfactorily decrease the matrix effects due to competitive sorption of non-OTC species onto/into fibre coating. The optimised operating conditions consist of polydimethylsiloxane (PDMS) coated fibre used in headspace mode for 30 min. In wines, the limits of detection (LOD) and quantification (LOQ) ranged from 1 to 40 and 3 to 80 ng(Sn)L(-1) respectively, according to the species. The analytical validation was made by evaluating the accuracy of OTC determination in spiked samples with various concentrations over the whole calibration range, i.e. from LOQ to 1000 ng(Sn)L(-1). Recovery was around 80-110% and precision (relative standard deviation, RSD) was between 12% and 25%. Despite the presence of two chromatographic peaks corresponding to sulphur compounds during brandy analysis, the selectivity of the method is adequate. The analysis confirmed the analytical performances and applicability of the method to wine and brandy samples. The obtained results emphasise the contamination of brandy and wine by organotins, the storage in plastic container seeming to be confirmed as the main OTC source.

Speciation analysis of arsenic in landfill leachate.

As environmental impacts of landfill last from beginning of cell filling to many years after, there is an increasing interest in monitoring landfill leachate composition especially with regards to metals and metalloids. High-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the speciation of arsenic in landfill leachates. The difficulty is related to the complexity and heterogeneity of leachate matrices. A soft sample preparation protocol with water dilution and filtration of leachates has proved to be sufficient for the achievement of identification and quantification of arsenic species without matrix effect. The cationic-exchange separation method developed has enabled the detection of six arsenic species (AsIII, MMA, AsV, DMA, AsB, TMAO) in different landfill leachates. The wide range of concentrations of arsenic species (from 0.2 to 250 microg As L(-1)) and their repartition illustrate the high variability of these effluents depending on the nature of the wastes, the landfill management, the climatic conditions and the degradation phase, to list a few. These results provide new information about the chemical composition of these effluents which is useful to better adapt their treatment and to achieve the risk assessment of landfill management.

Optimisation of ICPMS collision/reaction cell conditions for the simultaneous removal of argon based interferences of arsenic and selenium in water samples.

The optimisation of ICPMS collision/reaction cell conditions for the simultaneous analysis of arsenic and selenium is described. A mixture of 3.8mL min(-1) of H(2) and 0.5mL min(-1) of He was found to be suitable for the removal of both ArAr(+) and ArCl(+) interferences. Detection limits down to 30ng (element) L(-1) in total analysis, and between 81 and 230ng (element) L(-1) in speciation analysis were achieved in chloride matrix (1gL(-1) NaCl). After validation, the method was applied to commercially available mineral waters.

Speciation analysis of antimony in marine biota by HPLC-(UV)-HG-AFS: Extraction procedures and stability of antimony species.

Speciation analysis of antimony in marine biota is not well documented, and no specific extraction procedure of antimony species from algae and mollusk samples can be found in the literature. This work presents a suitable methodology for the speciation of antimony in marine biota (algae and mollusk samples). The extraction efficiency of total antimony and the stability of Sb(III), Sb(V) and trimethylantimony(V) in different extraction media (water at 25 and 90 degrees C, methanol, EDTA and citric acid) were evaluated by analyzing the algae Macrosystis integrifolia (0.55+/-0.04mugSbg(-1)) and the mollusk Mytilus edulis (0.23+/-0.01mugSbg(-1)). The speciation analysis was performed by anion exchange liquid chromatography (post-column photo-oxidation) and hydride generation atomic fluorescence spectrometry as detection system (HPLC-(UV)-HG-AFS). Results demonstrated that, based on the extraction yield and the stability, EDTA proved to be the best extracting solution for the speciation analysis of antimony in these matrices. The selected procedure was applied to antimony speciation in different algae samples collected from the Chilean coast. Only the inorganic Sb(V) and Sb(III) species were detected in the extracts. In all analyzed algae the sum of total antimony extracted (determined in the extracts after digestion) and the antimony present in the residue was in good agreement with the total antimony concentration determined by HG-AFS. However, in some extracts the sum of antimony species detected was lower than the total extracted, revealing the presence of unknown antimony species, possibly retained on the column or not detected by HPLC-(UV)-HG-AFS. Further work must be carried out to elucidate the identity of these unknown species of antimony.

Evaluation of porous graphitic carbon stationary phase for simultaneous preconcentration and separation of organic and inorganic selenium species in "clean" water systems.

A high performance liquid chromatography procedure, based on porous graphitic carbon stationary phase, was evaluated for simultaneous on-line preconcentration and separation of organic and inorganic selenium species. Detection was achieved by inductively coupled plasma mass spectrometry with collision/reaction cell (ICP-CRC-MS). Different concentrations of formic acid were tested as mobile phase. A 240 mmol L(-1) concentration with pH adjusted to 2.6, allowed the separation of five species, i.e. selenite, selenate, selenomethionine, selenocystine and selenoethionine. On-line preconcentration of these five species was achieved when heptafluorobutyric acid was used as injection medium, inducing an enrichment of solutes at the top of the column which allowed large volumes (up to 1 mL) to be injected. Combining these injection conditions and 80Se monitoring with ICP-CRC-MS, detection limits between 2 and 8 ng (Se)L(-1), depending on the species, were obtained. Because of the extremely low detection limits obtained, the method was successfully applied to mineral waters.