Alcides Pereira

On the influence of faulting on small-scale soil-gas radon variability: a case study in the Iberian Uranium Province

In order to evaluate the influence of faulting on the variability of geogenic radon at detailed scale (1:2000), data on gamma ray fluxes, U and Th concentrations in rocks, radon in soil-gas and radon in groundwater were collected in three target areas on the Oliveira do Hospital region (Central Portugal). This region stands on the Iberian Uranium Province, and is dominantly composed of Hercynian granites and metasedimentary rocks of pre-Ordovician age, crosscut by faults with dominant strike N35 degrees E, N55 degrees E and N75 degrees E. Radiometric anomalies are frequent, associated with faults of the referred systems and metasedimentary enclaves; the analytical data confirms that these anomalies are produced by local high uranium contents in rocks and fault-filling materials (n=34, range 13-724 ppm), while other radiogenic elements are relatively constant (e.g. Th 4-30 ppm). Radon concentration in soil can be extremely high, up to 12,850 kBq m(-3) (n=215), with a large proportion of results above 100 kBq m(-3). Unsurprisingly, groundwater also shows high radon concentrations, with observed values in the range 150-4850 Bq.L(-1) (n=17). From the results it is concluded that metasedimentary enclaves, as well as faults, can accumulate uranium from circulating fluids, and as a consequence, strongly locally enhance geogenic radon potential. Due to this fact, for the purpose of land use planning in such uranium-enriched regions, very detailed geological mapping is needed to precisely recognize radon high risk areas. A correlation between radon concentration in soil or in groundwater and gamma ray fluxes was established pointing to the possible use of these fluxes as a first step in assessing geogenic radon potential, at least to geological setting similar to the study area.

Aerobic uranium immobilization by Rhodanobacter A2-61 through formation of intracellular uranium-phosphate complexes.

Severe environmental problems arise from old uranium mines, which continue to discharge uranium (U) via acid mine drainage water, resulting in soil, subsoil and groundwater contamination. Bioremediation of U contaminated environments has been attempted, but most of the conceptual models propose U removal by cell suspensions of anaerobic bacteria. In this study, strain Rhodanobacter A2-61, isolated from Urgeiriça Mine, Portugal, was shown to resist up to 2 mM of U(vi). The conditions used (low nutrient content and pH 5) potentiated the interaction of the toxic uranyl ion with the tested strain. The strain was able to remove approximately 120 μM of U(vi) when grown aerobically in the presence of 500 μM U. Under these conditions, this strain was also able to lower the phosphate concentration in the medium and increased its capacity to take up inorganic phosphate, accumulating up to 0.52 μmol phosphate per optical density unit of the medium at 600 nm, after 24 hours, corresponding approximately to the late log phase of the bacterial culture. Microscopically dense intracellular structures with nanometer size were visible. The extent of U inside the cells was quantified by LS counting. EDS analysis of heated cells showed the presence of complexes composed of phosphate and uranium, suggesting the simultaneous precipitation of U and phosphate within the cells. XRD analysis of the cells containing the U-phosphate complexes suggested the presence of a meta-autunite-like mineral structure. SEM identified, in pyrolyzed cells, crystalline nanoparticles with shape in the tetragonal system characteristic of the meta-autunite-like mineral structures. U removal has been reported previously but mainly by cell suspensions and through release of phosphate. The innovative Rhodanobacter A2-61 can actively grow aerobically, in the presence of U, and can efficiently remove U(vi) from the environment, accumulating it in a structural form consistent with that of the mineral meta-autunite inside the cell, corresponding to effective metal immobilization. This work supports previous findings that U bioremediation could be achieved via the biomineralization of U(vi) in phosphate minerals.

Indoor radon periodicities and their physical constraints: a study in the Coimbra region (Central Portugal)

Indoor radon activities were measured during a period of 6 months, as well as several physical environmental variables (temperature, pressure, humidity and rainfall). The location was a small room at an administrative building of the University of Coimbra, usually undisturbed by human activities and situated over bedrock of low-uranium Triassic red sandstones. A low average activity of radon was observed (36 Bq m(-3)), however showing a very well marked daily periodicity (10+/-5 Bq m(-3)), with maximum values occurring more frequently between 9 and 10 a.m. Daily variations are shown to have no relation with earth tides, and their amplitudes exhibit a significant correlation with outdoor temperature; no dependence on barometric pressure was found. Rainfall disturbs the observed daily radon cycles through a strong reduction of their amplitude, but has no effect on the long-term variability of the gas concentration.

A comprehensive analysis of groundwater resources using GIS and multicriteria tools (Caldas da Cavaca, Central Portugal): environmental issues

Hard-rock watersheds are essentially confined to fractured and weathered horizons, but they are a source of valuable water resources at a regional level, namely for domestic, industrial and agricultural purposes, and public supply. They commonly exhibit complex geological bedrock and morphological features as well as distinctive gradients in rainfall and temperature. Hydromineral and geothermal resources have relevant economic value both for the bottled water/thermal spas industry and for energy supply. A comprehensive evaluation and integrated groundwater resources study has been carried out for the Caldas da Cavaca hydromineral system in Central Portugal, using hydrogeomorphology and GIS mapping techniques. Thematic maps were organised from a geodatabase comprising several layers, namely lithology, tectonic lineaments density, slope, drainage density, rainfall, net groundwater recharge and water quality. Normalised weights were assigned to all these categories according to their relative importance to groundwater potential, based on their effectiveness factors. Hydrogeochemistry, natural radioactivity and intrinsic vulnerability assessment (GOD-S, DRASTIC-Fm, SINTACS, SI indexes) issues were also cross-checked. Based on all the compiled information, a hydrogeomorphological map was produced. This multidisciplinary approach highlights the importance of hydrogeomorphological mapping as a tool to support hydrological conceptualisation, contributing to groundwater decision-making process in different stages, like water resources management and territory planning, and thus, to environmental sustainability.

Evidence for the Unroofing History of Hercynian Granitoids in Central Portugal Derived from Late Palaeozoic and Mesozoic Sedimentary Zircons

The Lusitanian Basin on the western Iberian margin comprises Mesozoic and Cenozoic sediments derived from the surrounding Precambrian to Lower Palaeozoic and Hercynian basement. Apatite fission-track data from Hercynian granitoids to the east of the basin show that the intrusives were being actively eroded throughout the Jurassic and Cretaceous; however, exactly when these rocks first became exposed and eroded is not clear. In this study we have attempted to reconstruct the erosional history of the granitoids of Central Portugal by examining the detrital zircon fission-track signatures contained within post-granite emplacement sediments.

Pullulanibacillus uraniitolerans sp. nov., an acidophilic, U(VI)-resistant species isolated from an acid uranium mill tailing effluent and emended description of the genus Pullulanibacillus.

Two Gram-positive-staining, rod-shaped, endospore-forming isolates (UG-2(T) and UG-3), with an optimum growth temperature of around 37 °C and an optimum pH for growth of about 4, were recovered from an acidic effluent of the uranium mill tailing at Urgeiriça in Central Portugal. On the basis of 16S rRNA gene sequence similarity, the strains belonged to the family Sporolactobacillaceae and were closely related to Pullulanibacillus naganoensis ATCC 53909(T) (97.9 %). Unlike P. naganoensis, strains UG-2(T) and UG-3 grew in medium containing up to 5000 p.p.m. U(VI) but did not hydrolyse pullulan. Chemotaxonomic data also supported the affiliation of strains UG-2(T) and UG-3 to the genus Pullulanibacillus. Physiological and biochemical tests along with fatty acid composition allowed differentiation of strains UG-2(T) and UG-3 from P. naganoensis. It is suggested that strains UG-2(T) and UG-3 represent a novel species, for which the name Pullulanibacillus uraniitolerans is proposed; the type strain is UG-2(T) (=DSM 19429(T) = LMG 24205(T)). An emended description of the genus Pullulanibacillus is also proposed.

HUMAN EXPOSURE TO INDOOR RADON: A SURVEY IN THE REGION OF GUARDA, PORTUGAL

Radon ((222)Rn) is a radioactive gas, abundant in granitic areas, such as the city of Guarda at the northeast of Portugal. This gas is recognised as a carcinogenic agent, being appointed by the World Health Organization as the second leading cause of lung cancer after tobacco smoke. Therefore, the knowledge of radon concentrations inside the houses (where people stay longer) is important from the point of view of radiological protection. The main goal of this study was to assess the radon concentration in an area previously identified with a potentially high level of residential radon. The radon concentration was measured using CR-39 detectors, exposed for a period of 2 months in 185 dwellings in the Guarda region. The radon concentration in studied dwellings, ranged between 75 and 7640 Bq m(-3), with a geometric mean of 640 Bq m(-3) and an arithmetic mean of 1078 Bq m(-3). Based on a local winter-summer radon concentration variation model, these values would correspond to an annual average concentration of 860 Bq m(-3). Several factors contribute to this large dispersion, the main one being the exact location of housing construction in relation to the geochemical nature of the soil and others the predominant building material and ventilation. Based on the obtained results an average annual effective dose of 15 mSv y(-1) is estimated, well above the average previously estimated for Portugal.

Advances in the Stratigraphy and Geochemistry of the Organic-Rich Lower Jurassic Series of the Lusitanian Basin (Portugal)

Here we present the main results of a study of the high-resolution stratigraphy of the Lower Jurassic organic-rich marine series in the Lusitanian Basin, Portugal. In this basin, the Lower Jurassic consists mainly of an alternating marl–limestone succession (upper Sinemurian–Toarcian), with some intervals enriched in organic matter (upper Sinemurian and Pliensbachian). These Lower Jurassic carbonate units correspond to the Coimbra, Agua de Madeiros, Vale das Fontes, Lemede, and S. Giao/Cabo Carvoeiro formations. In the last few years, these units have been the subject of a multidisciplinary and integrated stratigraphic analysis, based on the study of a range of biotic and abiotic parameters. In our study, high-resolution analysis of these units in the main reference sections of the basin have allowed seven main themes to be developed, involving sedimentological and sequential analysis, ammonite biostratigraphy, macroinvertebrate palaeontology and palaeoecology, ostracod analysis, chemostratigraphy, organic and petrographic geochemistry, and gamma-ray analysis. Besides the novel results obtained in each scientific domain, the integration of all the collected data has improved our knowledge of not only the stratigraphy and sedimentary knowledge of the Lower Jurassic carbonates but also the hydrocarbon generation potential of the different Sinemurian and Pliensbachian units.

Mapping of salt structures and related fault lineaments based on remote-sensing and gravimetric data: The case of the Monte Real salt wall (onshore west-central Portugal)

The Monte Real (MR) salt wall (MR structure) is a salt structure located in the Monte Real–Pombal Subbasin (onshore west-central Portugal). The MR structure was emplaced during post–Triassic–Mesozoic extensional and Tertiary compressional tectonics and is now partially buried under Miocene to Pliocene–Pleistocene sediments. The region is dominated by NS 20, N45 10E, N30 10W, and N70 10W trending main tectonic systems. Remote-sensing data constrained by gravimetric data allowed the recognition of the two-dimensional surface geometry of this salt structure and its associated structural features. The use of remote-sensing images (optical and microwave data) allow mapping the MR structure based on the heat radiated from rocks and soils, changes in vegetation cover, and texture analysis of synthetic aperture radar imagery. In addition, remote-sensing data, combined with modeled topographic data, also allowed recognition of a lineament pattern consistent with the fracture pattern of the region, probably related to the implantation and deformation of this salt body. The crosscut behavior of the identified structural lineaments can justify the north-northwestern elongated arcuate shape of the MR structure and the corresponding gravimetric anomaly. This work shows that remote-sensing techniques are a powerful tool to study buried salt domes even in the absence of detailed geophysical data.

Recognizing salt-structures on the basis of geophysical and remote sensing data: the case of monte real salt-structure (onshore west-central portugal)

Remote sensing data from Monte Real sub-basin (onshore West-Central Portugal), collected by the LANDSAT 7 ETM+, JERS-1 (SAR) and Envisat (ASAR) satellites, are used with the purpose to give new insights relatively to the Monte Real salt-structure. The recognized pattern of the diapir and of the structural lineaments is in agreement with the geophysical and geological data.