Pedro Valério

Geochemical tracers of northern Portuguese estuarine sediments on the shelf

The northern Portuguese coastal zone is drained by large Iberian rivers, along which there is intensive industrial, agricultural and urban activity. Offshore of the two main river basins of the Douro and Minho, two fine-grained sedimentary formations can be characterised. A geochemical study of this sediment cover has been performed focussing in particular on the fine deposits and the adjacent estuaries. The chemical composition of superficial sediments collected from the northern Portuguese shelf and from the river basins of the Minho and Douro rivers was determined for major, minor and trace elements; the rare earth elements (REE) composition was also determined in selected samples. Statistical analyses of these data for the shelf sediments allow us to identify elements with similar behaviours and the different sediment types along the shelf, and to evaluate of their origins. Downcore profiles of the chemical composition of the fine sediments reveal no evidence for changes induced by recent human activities. To assess the influence of the rivers on the fine sedimentary formations, the elemental distribution patterns of selected sediments have been compared with the estuarine sediments. Lithogenic elements composition normalised to Al and the shale normalised REE distributions showed there are similarities between the Douro River sediments and the sediment composition of the Douro and Galicia mud patches. However, the Galicia mud field showed no relationship in its chemical composition to sediments derived from the Minho River. Nor was any evidence for heavy metal contamination originating from the Douro estuary detected in anthropogenic element/Al ratios in the shelf sediments. This may be because of processes associated with resuspension, complexation and bioturbation that occur during sediment transport and deposition. Nevertheless, the Douro River seems to be the main continental source of fine sediments being deposited on the northern Portuguese shelf.

Heavy metal assessment in sediments of the Ave River Basin (Portugal) by energy-dispersive X-ray fluorescence spectrometry

Anthropogenic activities have contaminated stream sediments around the world with toxic metals. In Portugal, the Ave river basin, draining to the northwestern Portnguese shelf, is heavily contaminated. The Ave river course and its tributaries are located in one of the most populated regions of the country with intensive agricultural and industrial activities, which effluents have been discharged directly into the local stream. This paper reports results obtained in the analysis of superficial sediments collected at the Ave estuary and along the river course within a distance of about 50 km during February 1993. In order to account for seasonal variabilities occurring in the estuary, stations located in this region were also sampled in August 1993. A total of 16 sediment samples were analysed as pressed pellets by energy-dispersive X-ray fluorescence spectrometry for 15 elements. The trend of the elemental contamination was evaluated as a function of the location, taking into account external factors that may influence that distribution (tributaries, industries, etc.) and anthropogenic contributions were identified. Comparison of our data with published values considered as the background for non-polluted sediments (average shale) were carried out by calculating enrichment factors. The latter proved that sediment contamination by Zn and Pb exists all over the river basin and also by Cr and Cu in two regions of the area studied. A general depletion in Ni was measured. No significant seasonal variabilities were detected.

Elemental composition in sediments and water in the Trancão river basin. A preliminary study

Abstract The Trancao river basin, located in the Lisbon area shows preoccupying pollution levels, that constitute a threat to public health and the ecological system. This work reports on the results obtained in the analysis of surface sediments (EDXRF) and water (PIXE) collected in the wet and dry season during 1996. In general, bulk sediments and water show high concentration levels for some heavy metals like Cr, Cu, Zn and Pb. The elemental contents variation of samples collected at the different sites of the river basin were large, owing apparently to pollution sources, seasonal variabilities and grain size distribution (sediments). In the dry season, effluents (industrial and domestic) showed a stronger influence on the sediment composition. High levels of As and Br were found in the water that can be attributed to extended sources like sewage sludge and fertilizers. In some locations, the metals, Ca and organic matter enrichment could be associated with a paper mill and metal processing industry (high levels of Cr). At the estuary, the decrease of metal content determined in the sampled water indicates the flocculation of dissolved organic and inorganic materials. However, no effects were found for the surface sediment metal content, probably due to a dilution with materials from the Tagus inner estuary (the largest in Portugal).

Microstructural Signatures of Bronze Archaeological Artifacts from the Southwestern Iberian Peninsula

This study concerns the elemental and microstructural characterization of proto-historic bronze rings from the southwestern Iberian Peninsula. Micro-EDXRF analyses demonstrate that the artifacts are binary bronze alloys (8–13% Sn) with arsenic and lead as the major impurities. Optical microscopy and SEM-EDS allowed the identification of common inclusions (e.g. copper sulphides) and alteration processes (redeposited copper, intergranular and intragranular corrosion). Microstructures consisting of fine dendrites, coarse and/or equiaxial grains were also identified, as well as the presence of (+) eutectoid, deformed inclusions, twinned grains and/or slip bands. The combination of these characteristics allowed establishing the metallurgical procedures (casting, forging and annealing) used in the production of the bronze rings. The identification of different thermomechanical operational sequences indicates that the metallurgical knowledge was well established in the southwestern Iberian Peninsula during those ancient times.

Pollution assessment in the Trancão river basin (Portugal) by PIXE, EDXRF and isotopic analysis

Abstract This paper reports on the inorganic contamination assessment of a river basin and local water resources in order to establish quality standards. PIXE was applied to the elemental determination of the freeze-dried water dry residue and EDXRF was used for the evaluation of elemental content of sediments. To infer the water provenance the electrical conductivity was measured as well as the isotopic composition of surface waters using the 18 O/ 16 O ratio. The combined isotopic and elemental composition information enables to establish dominant contamination contributions from the several tributaries. Moreover, the variability observed for certain parameters, associates them with specific basin regions as for instance, dry residue mass, conductivity and Br, or S, Cl and As or Cr, Ni, Zn and Pb which permit to establish both pollution characterisation and their origin (agriculture, industrial, etc.). At certain locations, enhanced concentrations of elements as Cr, Cu, Zn and Pb are observed both in sediments and in the surface water. The elemental particular associations also permit to characterise pollution sources.

Manufacture of copper weapons and tools from the chalcolithic settlement of São Pedro (Portugal)

ABSTRACT A collection of 30 copper-based artefacts recovered during archeological excavations at the São Pedro settlement (Redondo, Portugal) was characterized by optical microscopy and Vickers microhardness testing. The radiocarbon dating of bone samples and the existence of Bell Beaker ceramics establish a chronology of c. 2700–2000 BC for tools and weapons made of copper with varying arsenic contents. The manufacture included one or more cycles of forging and annealing, while final work hardening was uncommon. The collection shows a wide range of hardness (52–142 HV0.2) without any correlation with typology or arsenic content, suggesting unawareness of the hardening potential of this alloying element. Technological features of São Pedro artefacts were compared with those of coeval metallurgies from neighboring regions (Portuguese Estremadura and Southern Andalusia) revealing common and distinctive characteristics that help to understand the use of arsenical copper alloys among communities of the third millennium BC.