Search

Mercury (Hg) distribution was achieved in a pristine Amazonian forested area during a rainfall event along a basin thalweg. Hg concentrations were measured in both surface runoff and underground waters and soils. Total Hg concentrations in the particulate and dissolved phase were related to the main hydrological processes in order to trace the fate of mercury during the flood event. Rainfall waters were also collected to assess the amount of Hg from atmospheric deposition and foliage leaching. Total Hg concentrations were found relatively homogenous over thé basin and were typical of remote area (9 ng l-1). In addition, air samples collected at the same site, at the ground level and at different heights (1-40m), which allowed us to determine temporal and spatial variability of total gaseous atmospheric Hg. Finally, dynamic flux chambers experiments were carried out to directly determine the exchanges of gaseous Hg at the soil/atmosphere interface, in order to better understand the role of the atmospheric compartment within the forest ecosystem.

Although the contamination of number of estuarine environments in the European Atlantic Coast has largely been studied [1-2], the Adour urban estuary watershed (southwestern, France) is poorly known. The estuarine part is characterized by an important anthropogenic pressure close to its mouth with large urban and industrial activities of Bayonne city.
An environmental assessment program was funded to evatuate and quantify the anthropogenic pressure on the ecosystem. A preliminary sampling strategy approach was adopted to identify 25 specific sources of contaminants, monitored more extensively under four campaigns. Data treatment allows to trace effluent source and origin resulting in a specific classification. Trace metal concentrations were determined (filtrate (<0,45 μm) and particulate fractions) for each effluent and combined with discharge flow measurements to establish anthropogenic net fluxes. Industrial effluents presents the highest concentrations observed, followed by waste landfield drainage and sewage effluents. The large variability in terms of effluent characteristics and concentrations observed, can be explained by strong relationship between trace elements and both organic matter level (TOC) and flow rate.
This study point out the dominance of upstream inputs compared to downstream localized sources, but their influence into the estuarine ecosystem during low discharge conditions (summer) lead to a maximum metal impact

Abstract. Foams produced from surfactant solutions containing micelles of the anionic surfactant sodium polyoxyethylene-2 sulfate and counterions of different valence (aluminium, calcium or sodium) are investigated. For this purpose an experimental setup consisting of a glass column and units for detection of pressure, flow and frequency is constructed. Blowing gas bubbles in the surfactant solution at a constant gas pressure produces the foam. Simultaneous monitoring of the bubble volume and frequency relates the foam growth rate to the dynamic surface tension of the surfactant solution. The foam growth rate plotted versus the gas flow rate exhibits a break point at about 80 mL/min, attributed to the transition from regime of bubbles (at lower flow rates - monodisperse foam) to jet regime (at higher flow rates - polydisperse foam). Due to the high surfactant concentration, the foam is stable and its height is linearly increasing with the time. Two types of experiments are carried out. (i) At a constant counterion concentration and variable surfactant concentration, the rate of foam growth increases initially with increasing of the surfactant concentration reaching a plateau at higher concentrations. The foams of pure surfactant grow always slower than the foams with added aluminium ions. (ii) At a constant surfactant concentration and variable counterion concentration, the rate of foam growth exhibits a maximum. It corresponds to number of aggregated surfactant monomers nearly equal to the number of charges provided by the counterions, for example when one aluminium ion binds three surfactant monomers in a micelle. The point of maximum coincides with the transition from small spherical micelles to large cylindrical ones. This transition affects also the micelle lifetime, which is related to the ability of releasing monomers by a micelle in order to supply the bubble surface with surfactant. In support to this hypothesis, the maximum foam growth is found corresponding to lower dynamic surface tension allowing the generation of a large number smaller in size bubbles. The results for the foam growth agree in some extent with the data from independent measurements on the liquid drainage from wet foams.

A synthesis method for the micro‐scale laboratory preparation of isotopically enriched monomethylmercury (MMHg) has been successfully established. This compound is an important standard for species‐specific isotope dilution analysis. The isotopically enriched MMHg has been synthesized from commercially available mercury oxide (201HgO) using methylcobalamin co‐enzyme as methylating agent. The time required is less than 2 h and the final yield is about 90%. The proposed method is faster than those previously reported in the literature. It allows work on a micro scale to control the use of expensive enriched isotope standard. It also allows control of unintentional formation of dimethylmercury. The enriched mercury‐containing reaction products were analyzed by capillary gas chromatography coupled to an inductively coupled plasma mass spectrometer after derivatization with sodium tetraethylborate. The isotopic composition, concentration, purity and stability of the synthesized, enriched MMHg have been investigated in order to establish standard protocols for MMHg isotope dilution analysis or isotope labeling incubation experiments. Copyright © 2002 John Wiley & Sons, Ltd.

The suggested new ballistic method of obtaining a hysteresis curve for materials with a small permeability has a number of advantages as copared with the conventional ballistic method. Magnetization by means of current pulses provides a current density in the magnetizing winding of the sample 400 to 500 times higher than normal and greatly simplifies the conditions of magnetization and measurement. Moreover, the sample does not heat up during measuring, which often occurs in the conventional ballistic method.