Mobility and transformation of CdSe/ZnS quantum dots in soil: Role of the capping ligands and ageing effect.

The increasing application of Quantum Dots (QDs) is cause of concern for the potential negative effects for the ecosystem, especially in soils that may act as a sink. In this study, soil leaching experiments were performed in quartz sand packed columns to investigate the behavior of core-shell CdSe/ZnS QDs coated with either small ligands (TGA-QDs) or more complex polymers (POAMA-QDs). Fluorescence emission was compared to mass spectrometric measurements to assess the nanoparticles (NPs) state in both the leachate (transported species) and porous media (deposited amounts). Although both QDs were strongly retained in the column, large differences were observed depending on their capping ligand stability. Specifically, for TGA-QDs elution was negligible and the retained fraction accumulated in the top-columns. Furthermore, 74% of the NPs were degraded and 38% of the Se was found in the leachate in non-NPs state. Conversely, POAMA-QDs were recovered to a larger extent (78.1%), and displayed a higher transport along the soil profile. Further experiments with altered NPs showed that homo-aggregation of the QDs prior injection determined a reduced mobility but no significant changes in their stability. Eventually, ageing of the NPs in the column (15 days) caused the disruption of up to 92% of the original QDs and the immobilization of NPs and metals. These results indicate that QDs will accumulate in top-soils, where transformations phenomena will determine the overall transport, persistency and degradation of these chemicals. Once accumulated, they may act as a source for potentially toxic Cd and Se metal species displaying enhanced mobility.

Development of a new passive sampler based on diffusive milligel beads for copper analysis in water.

A new passive sampler was designed and characterized for the determination of free copper ion (Cu(2+)) concentration in aqueous solution. Each sampling device was composed of a set of about 30 diffusive milligel (DMG) beads. Milligel beads with incorporated cation exchange resin (Chelex) particles were synthetized using an adapted droplet-based millifluidic process. Beads were assumed to be prolate spheroids, with a diameter of 1.6 mm and an anisotropic factor of 1.4. The milligel was controlled in chemical composition of hydrogel (monomer, cross-linker, initiator and Chelex concentration) and characterized in pore size. Two types of sampling devices were developed containing 7.5% and 15% of Chelex, respectively, and 6 nm pore size. The kinetic curves obtained demonstrated the accumulation of copper in the DMG according to the process described in the literature as absorption (and/or adsorption) and release following the Fick's first law of diffusion. For their use in water monitoring, the typical physico-chemical characteristics of the samplers, i.e. the mass-transfer coefficient (k0) and the sampler-water partition coefficient (Ksw), were determined based on a static exposure design. In order to determine the copper concentration in the samplers after their exposure, a method using DMG bead digestion combined to Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES) analysis was developed and optimized. The DMG devices proved to be capable to absorb free copper ions from an aqueous solution, which could be accurately quantified with a mean recovery of 99% and a repeatability of 7% (mean relative uncertainty).

Isotopic investigation of the colloidal mobility of depleted uranium in a podzolic soil.

The mobility and colloidal migration of uranium were investigated in a soil where limited amounts of anthropogenic uranium (depleted in the 235U isotope) were deposited, adding to the naturally occurring uranium. The colloidal fraction was assumed to correspond to the operational fraction between 10 kDa and 1.2 µm after (ultra)filtration. Experimental leaching tests indicate that approximately 8-15% of uranium is desorbed from the soil. Significant enrichment of the leachate in the depleted uranium (DU) content indicates that uranium from recent anthropogenic DU deposit is weakly bound to soil aggregates and more mobile than geologically occurring natural uranium (NU). Moreover, 80% of uranium in leachates was located in the colloidal fractions. Nevertheless, the percentage of DU in the colloidal and dissolved fractions suggests that NU is mainly associated with the non-mobile coarser fractions of the soil. A field investigation revealed that the calculated percentages of DU in soil and groundwater samples result in the enhanced mobility of uranium downstream from the deposit area. Colloidal uranium represents between 10% and 32% of uranium in surface water and between 68% and 90% of uranium in groundwater where physicochemical parameters are similar to those of the leachates. Finally, as observed in batch leaching tests, the colloidal fractions of groundwater contain slightly less DU than the dissolved fraction, indicating that DU is primarily associated with macromolecules in dissolved fraction.

Saponins: a renewable and biodegradable surfactant from its microwave-assisted extraction to the synthesis of monodisperse lattices.

Synthetic surfactants are widely used in emulsion polymerization, but it is increasingly desirable to replace them with naturally derived molecules with a reduced environmental burden. This study demonstrates the use of saponins as biodegradable and renewable surfactants for emulsion polymerization. This chemical has been extracted from soapnuts by microwave assisted extraction and characterized in terms of surfactant properties prior to emulsion polymerization. The results in terms of particle size distribution and morphology control have been compared to those obtained with classical nonionic (NP40) or anionic (SDS) industrial surfactants. Microwave-extracted saponins were able to lead to latexes as stable as standard PS latex, as shown by the CMC and CCC measurements. The saponin-stabilized PS particles have been characterized in terms of particle size and distribution by Dynamic Light Scattering and Asymmetrical Flow Field Flow Fractionation. Monomodal and monodispersed particles ranging from 250 to 480 nm in terms of diameter with a particle size distribution below 1.03 have been synthesized.

On-line and off-line quantification of trace elements associated to colloids by As-Fl-FFF and ICP-MS.

A quantification procedure of trace elements during colloid size fractionation was developed and validated. This procedure is based on the hyphenation between Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) and Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The optimisation of the procedure was performed on a soil leachate spiked with six trace elements selected for their environmental and health impact (As, Cd, Sb, Se, Sn and Pb). The elements in the spiked sample were on-line monitored during the fractionation. The validation was carried out by comparison with a second off-line quantification procedure based on fraction collection and total element analysis by ICP-MS. This off-line one was previously validated using reference materials. Finally, the analytical performances of the two procedures were compared.

Optimisation of asymmetrical flow field flow fractionation for environmental nanoparticles separation.

The fractionation of natural nanoparticles by Asymmetrical Flow Field Flow Fractionation (As-Fl-FFF) was optimised by considering the following operating conditions: ionic strength, surfactant concentration and crossflow rate. The method performances such as fractionation recovery and fractionation efficiency were evaluated on a stable solution of colloidal-size natural inorganic particles. The online multi-detection by ultraviolet/visible spectrophotometer (UV) and multi-angle laser light scattering (MALLS) provided the monitoring of the sample during the separation and the evaluation of the fractionation efficiency. The lowest ionic strength and surfactant concentrations (i.e. 10(-3) mol L(-1) NH4NO3 and 3 x 10(-4) mol L(-1) SDS) allowed to obtain the highest sample recovery and lowest loss of the largest particles. The crossflow rate was investigated in order to avoid significant membrane-sample interaction. The applicability of the fractionation in optimised conditions was evaluated on a natural soil leachate, which was filtrated with different filter cut-offs. Filtration efficiency was stressed by the decrease of the large unfractionated particle influence in the void volume. For the first time, robust operating conditions were proposed to well size-fractionate and characterize soil nanoparticles within a single multi-detection analysis.

Organotin speciation in Bizerte lagoon (Tunisia).

For the first time, organotins have been assessed in samples collected from Bizerte lagoon, in Tunisia, during two seasons (summer and winter). The organotin distribution was studied in marine sediments and mussels tissues of this lagoon. Butyl-, phenyl- and octyltins were determined using a rapid speciation analytical method based on one-step ethylation/extraction with sodium tetraethylborate in aqueous phase. Simultaneously to the ethylation, the extraction was performed by either liquid/liquid extraction (LLE) or head-space solid phase microextraction (HS-SPME). Gas chromatography with pulsed flame photometric detection (GC-PFPD) was used to perform quantitative determination. The technique has been validated using biological and sediment reference materials. The different samples from Bizerte lagoon were found to be moderately contaminated, especially by butyltins. This pollution was attributed to industrial activities, which are very important in this area. Organotins appeared accumulated in both sediments and mussels, while significant degradations of triorganotins to monosubstituted ones was observed in water.

Organotin survey in the Adour-Garonne basin.

Organotin monitoring was performed in waters of 11 rivers of the southwest of France during a 9 months period, between February and October 2001. Surface sediments were studied during the summer. Eighteen sampling points were chosen as representative of specific industrial or agricultural activities. In most samples, organotins were detected and butyltins are the most frequently present, with concentrations ranging over 0.2-30 ng(Sn)/L. Phenyltins were detected especially in spring and at the end of summer, which corresponds to likely diffusion from agricultural sources. Some high butyl- and phenyltin concentrations up to 700 ng(Sn)/L occurred during the spring where pesticides for agricultural activities were largely used. Octyltins were present in water frequently as well, with lower concentrations, probably originating from continuous leaching of plastics. Sediments appeared contaminated by the same species, with higher monobutyltin concentrations of about 30-40 microg(Sn)/kg which shows the importance of biological degradations occurring in surface sediments. This non-pesticidal organotin compounds can also be introduced from leaching of organotin-stabilized PVC by water. Using the different organotin concentrations obtained and other physico-chemical parameters measured, such as temperature or water flow rate, a statistical study was performed by principal component analysis. The results obtained allow the main sources of organotin diffusion to be identified and the hydrological cycle of these compounds better understand.

Optimisation of the storage of natural freshwaters before organotin speciation.

The speciation of organotin compounds is essential due to the species-dependent toxicity, especially in natural waters. Precautions have to be taken during sampling and storage of waters in order to prevent degradations and losses. Experimental design methodology has been used to study the conditions of stability of organotins after water sampling in rivers. The modelling of results allows the determination of optimal conditions of preservation. After acidification at pH = 4 with nitric acid, the storage in polyethylene containers at 4 degrees C in the dark is suitable to preserve the most degradable trisubstituted (butyl- and phenyl-) species over 1 month. These conditions of sampling and storage are applied to two different freshwaters. The rate of species decomposition appears to be only dependent on the water nature, whatever the organotin concentrations in the sample. Speciation could be so preserved between 1 and 3 months.

Improved routine speciation of organotin compounds in environmental samples by pulsed flame photometric detection.

The high toxicity of the organotin species requires sensitive analytical methods in order to understand the origins of pollution and perform monitoring programs in the water cycle. The optimisation of a new detection method, pulsed flame photometric detection (PFPD), is reported for the simultaneous determination of butyl-, phenyl- and octyltins. The methodology of the experimental designs at two levels was used. It allows the evaluation of the influence of the three gas flow-rates on the peak heights and resolution between the closest peaks obtained using two different wavelengths of detection (390 and 611 nm). The modelling of these two responses, according to second-order polynomials, leads to the precise adjustment of the operating conditions. PFPD has shown two significant improvements over conventional flame photometric detection: increased sensitivity (absolute detection limits: 0.07 to 2 pg as Sn) and greater selectivity, whatever the wavelength used. This new analytical process was validated by the analysis of certified reference material and spiked river water. It was used in routine analysis of environmental samples (wastewater, sludge, sand and oyster).

Determination of butyl- and phenyltin compounds in sediments by GC-FPD after NaBEt(4) ethylation.

A reliable and rapid speciation method for the simultaneous determination of butyl- and phenyltin species in sediment samples has been developed. Two extraction procedures are compared: methanolic hydrochloric acid (at four different concentrations) and ethanoic acid leaching. Derivatization is carried out by the one-step ethylation/extraction procedure using the sodium tetraethylborate reagent directly in aqueous phase in the presence of an isooctane layer. Analysis is performed by capillary gas chromatography hyphenated to flame photometric detection (GC-FPD). Detection limits range from 0.5 to 1.5 ng(Sn) g(-1)(dry weight). Analysis of environmental samples and certified reference materials demonstrate the accuracy of the analytical method.