Distribution of naturally occurring radionuclides (U, Th) in Timahdit black shale (Morocco).

Attention has been focused recently on the use of Moroccan black oil shale as the raw material for production of a new type of adsorbent and its application to U and Th removal from contaminated wastewaters. The purpose of the present work is to provide a better understanding of the composition and structure of this shale and to determine its natural content in uranium and thorium. A black shale collected from Timahdit (Morocco) was analyzed by powder X-ray diffraction and SEM techniques. It was found that calcite, dolomite, quartz and clays constitute the main composition of the inorganic matrix. Pyrite crystals are also present. A selective leaching procedure, followed by radiochemical purification and alpha-counting, was performed to assess the distribution of naturally occurring radionuclides. Leaching results indicate that 238U, 235U, 234U, 232Th, 230Th and 228Th have multiple modes of occurrence in the shale. U is interpreted to have been concentrated under anaerobic conditions. An integrated isotopic approach showed the preferential mobilization of uranium carried by humic acids to carbonate and apatite phases. Th is partitioned between silicate minerals and pyrite.

An improved radiochemical separation of uranium and thorium in environmental samples involving peroxide fusion.

A radiochemical procedure for the accurate determination of uranium and thorium using peroxide fusion followed by ion exchange and extraction chromatography is described. The method of extraction of the element from solid samples is the most important factor in the investigation. It is demonstrated, by measuring a number of reference materials, that fusion with Na(2)O(2) ensures a complete destruction of the mineral lattice and greatly improves the determination of the true activity of actinides.

Application of vesicles to rat skin in vivo: a confocal laser scanning microscopy study.

A major problem in (trans)dermal drug delivery is the low penetration rate of most substances through the barrier of the skin, the stratum corneum. One of the methods to increase the penetration rate across the skin is encapsulation of a (model) drug in lipid vesicles. In this study fluorescently labelled liposomes were applied on rat skin, in vivo. Bilayer labelled gel-state and liquid-state liposomes (conventional or with flexible bilayers) were non-occlusively applied on the dorsal area in the neck of the rat for 1, 3 or 6 h. Micelles were used as a control formulation. The penetration pathway and penetration depth of the lipophilic fluorescent label into the skin was visualised by confocal laser scanning microscopy (CLSM). During the first 3 h of application almost no differences in penetration depth were observed, when the label was applied in the various formulations. After 6 h application, it was clear that the label applied in micelles and gel-state liposomes did not penetrate as deep into the skin as the label applied in liquid-state vesicles. Among the liquid-state vesicles, the suspension with the most flexible bilayers showed the highest fluorescence intensity in the viable epidermis and dermis, 6 h post-application. Thus the vesicular form and the thermodynamic state of the bilayer and to a smaller extent the flexibility of the bilayer influence the penetration depth of the label into the skin at longer application periods. These results are in good agreement with CLSM results obtained from in vitro experiments with human skin.