Cátia Prazeres

Source and pathway analysis of lead and polycyclic aromatic hydrocarbons in Lisbon urban soils.

One hundred soil samples were collected from urban spaces, in Lisbon, Portugal, in two surveys that were carried out in consecutive years, to assess the potential adverse human health effects following exposure to potentially toxic elements and organic compounds in the urban soils. The study hereby described follows on from the earlier work of the authors and aims at performing a source-pathway-fate analysis of lead (Pb) and polycyclic aromatic hydrocarbons (PAHs) in the urban soils in order to increase current knowledge on factors influencing exposure of the population. Various techniques were combined to achieve the proposed goal. Geogenic and anthropogenic sources were apportioned by means of Pb isotope mixing models. Isotope data was further coupled with geographic information system mapping to assess local mixed sources of Pb and PAHs. Unleaded vehicle exhaust and cement production show the largest relative contribution to the total soil-Pb, but their respective importance depends on factors such as location and urban landscape. The primary sources of PAHs to the urban soils are probably air and land traffic. Multivariate analysis was used to investigate which soil properties could influence mobility and fate of the contaminants. Whilst principal components analysis indicates carbonates and other calcium phases as probable factors controlling the dispersion of Pb in the urban soils, the linear models obtained from stepwise multiple regression analysis show that soil phosphorous (P) and manganese (Mn) are good predictors of the total soil Pb content. No robust model was obtained for the PAHs, impeding identifying environmental factors most likely to influence their dispersion in the urban soils. The solid-phase distribution study provided critical information to untangle the, at a first glance, contradictory results obtained by the multivariate analysis. Carbonates and other calcium phases, having these a probable anthropogenic origin, are soil components containing major fractions of Pb, P, and Mn.

Uranium distribution and mobility in the weathering zone of the Nisa deposit, Portugal

The Nisa deposit is the largest known uranium reserve in the country, and is hosted by metasediments of the Beiras Group, in the Alto Alentejo region, central Portugal. After almost two decades without significant studies, the current trend to seek improved knowledge of raw materials motivated the application of different surface geophysical and geochemical characterization methods, which proved to be a valuable exploration approach for this type of deposit. Detailed mapping in the experimental open pit showed the structural aspects controlling the mineralization. A radiometric survey of the deposit was carried out, providing a map of the main sites of mineralization. The U mineralization is of secondary origin, formed exclusively by uranyl phosphates that were formed during the development of a weathering profile. The mineralization occurs along schistosity planes, quartz veinlets and alteration zones, along a general trend N60°–80°W (approximately the same as S0) in association with iron oxyhydroxides, as demonstrated by both petrographic and geochemical data. These hydroxides, in addition to the geochemical characteristics of the host rocks, were key factors in the precipitation and trapping of dissolved uranyl ions.ResumenEl depósito de Nisa es la mayor reserva de uranio conocida en el país, y está hospedada por metasedimientos del Grupo das Beiras, en la región del Alto Alentejo, centro de Portugal. Después de casi dos décadas sin estudios significativos, la actual tendencia de aumentar el nível de conocimiento de las materias primas ha motivado la aplicación de diferentes métodos geofísicos e geoquímicos de superficie, lo que se ha demostrado ser un abordaje valioso para este tipo de depósito. La cartografía de detalle en la corta experimental ha evidenciado los aspectos estructurales que controlan la mineralización. Se ha efectuado un levantamiento radiométrico del depósito que ha proporcionado un mapa de los pricipales sitios mineralizados. La mineralización de uranio es de origen secundaria, compuesta exclusivamente por fosfatos de uranilo que se han formado durante el desarollo de un perfil de meteorización. La mineralización ocurre a lo largo de los planos de esquistosidad, venas de cuarzo y zonas de alteración, según una tendencia general N60º–80ºW (aproximadamente igual a S0) en asociación con oxidróxidos de hierro, como ha sido demostrado sea por los datos petrograficos como geoquímicos. Estos hidróxidos, junto con las características geoquímicas de la roca huésped, han sido factores clave en la precipitación y retención de los iones de uranilo disueltos.