L.C. Alves

Stratum corneum is an effective barrier to TiO2 and ZnO nanoparticle percutaneous absorption.

Background: There is increasing concern over the local and systemic side effects of TiO2 and ZnO coated nanoparticles widely used in sun blockers. Objective: To determine the localization and possible skin penetration of TiO2 and ZnO nanoparticles, dispersed in 3 sunscreen formulations, under realistic in vivo conditions in normal and altered skin. Methods: Nuclear microscopy techniques provided spatially resolved quantitative analysis of Ti and Zn nanoparticle distributions in transversal cryosections of skin obtained by biopsy with no further treatment. A test hydrophobic formulation containing coated 20-nm TiO2 nanoparticles and 2 commercial sunscreen formulations containing TiO2 alone or in combination with ZnO were tried, taking into account realistic use conditions by consumers and compared with the recommended standard condition for the sun protection factor test. The protocols consisted of an open test. Results: Following a 2-hour exposure period of normal human skin to TiO2- and ZnO-containing sunscreens, detectable amounts of these physical blockers were only present at the skin surface and in the uppermost stratum corneum regions. Layers deeper than the stratum corneum were devoid of TiO2 or exogenous ZnO, even after 48 h of exposure to the sunscreen, under occlusion. Deposition of TiO2 and ZnO nanoparticles in the openings of the pilosebaceous follicles was also observed, suggesting a preferential fixation area. Penetration of nanoparticles into viable skin tissue could not be detected. Conclusions: TiO2 or ZnO nanoparticles are absent or their levels are too low to be tested under the stratum corneum in human viable epidermal layers. Therefore, significant penetration towards the underlying keratinocytes is unlikely.

Distribution in Portugal of some pollutants in the lichen Parmelia sulcata

During the months of July and August 1993 a lichen (Parmelia sulcata Taylor) collection campaign was held in Portugal where samples were obtained from olive tree bark at 228 sites, following a grid of 10 x 10 km along the Atlantic coast and 50 x 50 km in the interior of the country. The samples were analysed by instrumental neutron activation analysis and proton induced X-ray emission techniques. Concentration data patterns for the pollutants As, Cr, Hg, Ni, Pb, S, Sb, Se, and V were obtained for the whole country surface by making use of an extinction rule of 1/r(3), preventing any cut-off distance from being artificially introduced. Some pollution sources were identified: (1) oil-powered plants on the Lisbon-Setúbal axis (V, Ni), (2) coal-power plants in Porto and Sines (S, Se), (3) traffic in the northern area and the Lisbon-Setúbal axis (Pb), (4) a chemical industry south of Porto (Hg, As), and (5) soil influence (Cr, Sb). Arsenic and chromium results largely exceed, in a few areas, the concentrations acceptable to plants, and in a few spots also Hg, Ni, and Pb data.

DATTPIXE, a computer package for TTPIXE data analysis

Abstract Thick target PIXE (TTPIXE) data analysis requires the calculation of an integral (which we call penetration integral) which accounts for the various effects that take place during proton stopping in the target and lead to X-ray emission. This is done by numerical integration and in most TTPIXE work target homogeneity both along the surface and in depth is necessary. This reduces the applicability of the technique in cases as ion implanted, film coated, or other kinds of samples which are by their own nature nonhomogeneous in depth while preserving their surface homogeneity (we call them layered targets). The DATTPIXE main program, which enables the conversion of spectra peak area data into sample concentration values, is being developed so as to be able to face these kinds of problems. Secondary X-ray fluorescence is accounted for and the correction is calculated for each of the layers into which the target is divided for numerical integration. The program was tested by applying it to the analysis of three metal alloy certified reference materials from the British Chemical Standards. The need for secondary X-ray fluorescence corrections and the correctness of the method used are shown.

Micron-scale analysis of SiC/SiCf composites using the new Lisbon nuclear microprobe

Abstract A new nuclear microprobe has now been commissioned at ITN, Lisbon. This paper first describes the layout and modes of operation of the new microprobe, which is located on a 3.1 MV single-ended Van de Graaff accelerator. Within two days of first commissioning the microprobe, a spatial resolution of ∼1.5 μm was achieved for backscattering analysis, and a resolution of ∼1.0 μm for transmission work. The steps taken to produce this resolution, and the remaining factors, which further limit it are discussed. The first results from this microprobe for the spatially resolved analysis of SiC/SiCf ceramic composites are presented here. These materials have applications in fusion technology and structural changes were investigated after exposure to lithium orthosilicate and lithium titanate breeder materials in fusion relevant conditions. Ti and Cr rich precipitates could be found in the samples that were exposed to lithium titanate.

Bio-monitoring of trace-element air pollution in Portugal: Qualitative survey

During the months of July and August 1993 a lichen collection campaign was held in Portugal where about 250 samples were collected and analysed by thick target TIPIXE and INAA. Results for 44 different elements were obtained and a data base was built and subjected to Monte Carlo Aided Target Transform Factor Analysis (MCATTFA), a method developed at IRI (Delft). 10×10 km2 coast and 50×50 km2 far from coast sampling grids were used for collection. In this work we will present the results which were obtained based on a reduced data set of 36 elements measured by INAA. The results for 22 elements obtained by TTPIXE were published elsewhere. In this work we will also present the conclusions considering all the 44 elements determined by both techniques.

Lichens (Parmelia sulcata) time response model to environmental elemental availability

Parmelia sulcata transplants, collected in a non-polluted area, were exposed to new atmospheric conditions at six stations, of which five were located near power plants and one at an unpolluted area. Data were collected for a 1-year period, on rainfall, airborne particulates, elemental deposition and on lichen elemental composition. The study was carried out to quantify the relationships between elemental availability and elemental accumulation in lichens. A mathematical model was developed, involving a simple representation of the lichen, and a memory loss function which describes the time relations for the lichens progressive representation of its new ambient conditions. The collected data set was used to test the model. The results indicate that the environmental data on Na, Al and Pb could be reproduced and predicted by the model, including the variability patterns. Half-memory times were calculated for Na, Al and Pb as 200, 500 and 600 days, respectively, based on using all station data. However, further improvements are still needed, including the clarification of differences in model outcomes between stations. Copyright (C) 1998 Elsevier Science B.V.

Matrix effects correction for quantitative TTPIXE analysis

Abstract The use of thick targets in PIXE analysis has many advantages, namely the smaller probability of significative contamination, easy target handling and preparation. Also in some applications as archaeometry, materials sciences and many others, the use of thick targets is imperative. A correct calculation of the thick target yield is then needed in order to obtain good results. In this work, corrections for the enhancement effects due to secondary X-ray fluorescence in metal alloys and due to radiation damage in biological samples are proposed. Numerical integration problems in critical matrix absorption situations are also presented.

Imaging of charge transport in polycrystalline diamond using ion-beam-induced charge microscopy

Studies have been made using a 1 μm spatial resolution ion-beam-induced charge (IBIC) technique of the charge transport distribution in polycrystalline diamond produced by chemical vapor deposition. The devices tested used a coplanar electrode structure fabricated only on the growth side of the diamond film, and were predominantly sensitive to charge transport close to the growth surface of the diamond film where the diamond crystallites are largest. Irradiation with 5.48 MeV alpha particles gave a pulse height spectrum with a broad full energy peak and a mean charge collection efficiency of 15%. IBIC images obtained using microfocus proton and alpha particle beams showed spatially resolved regions of high charge collection efficiency correlating to individual diamond crystallites with a typical width of 20 μm, as observed by secondary electron microscopy.

Main atmospheric heavy metal sources in Portugal by biomonitor analysis

Abstract During the months of July and August of 1993 a lichen collection campaign was held in Portugal where about 250 samples were collected and analysed by thick target PIXE and INAA. Results for 43 different elements were obtained and a data base was built and subjected to Monte Carlo aided target transform factor analysis (MCATTFA), method developed at IRI TU Delft. 10 × 10 km coast and 50 × 50 km far from coast sampling grids were used for collection, concentration data as well as factor patterns were extrapolated to the whole country making use of an extinction rule of 1/r 3 . In this work we present the results that were obtained based on a reduced data set of 22 elements measured by TTPIXE. The results for INAA data subset and the total data set are presented elsewhere.

InStory: a system for mobile information access, storytelling and gaming activities in physical spaces

This paper describes the work carried out in the InStory project. InStory has the goal of defining and implementing a platform for mobile storytelling, information access, and gaming activities. The platform has a flexible computational architecture that integrates heterogeneous devices, different media formats and computational support for different narrative modes and gaming activities. The system is driven and validated by a set of story threads and narratives that are centered on the exploration of physical spaces. This exploration is combined with the perspective of sharing information between users and providing historic context. The project also wants to explore the social aspect of shared narratives and activities, with the idea that the technology can provide new innovative approaches to social participation in different types of events.