Evaluation of the level of contamination in sediments from watercourses of the Caveira Mining System (Grândola)

Abstract

The following work is inserted in the GeoMatRe Project, in which the conditions of the most updated physical and chemical parameters of an Acid Mine Drainage are analysed. This study shows that the mining area of Caveira, in Grândola, Portugal, which was abandoned since the 60’s, presents a critical situation of contamination, with high levels of Potentially Toxic Elements (PTE) present in the whole mining area and its surroundings. It is intended, within the scope of the project, and through geochemical analysis, to observe the conditions of contamination by PTE in native sediments from the mine tailing, which occur either in mobile phases, dissolved in the interstitial water of the sediments, or in more immobile phases. With that in mind, preparation of methodologies for geochemical studies were carried out, namely Fusion for further analysis of the element’s total forms, and Partial Digestion with Aqua Regia for quantification of the most easily extratable forms, which represent the most contaminating fraction. Ultimately, Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) was used to analyse and quantify the previously prepared samples. It is herein presented a general characterization of the mining system, through analysis and understanding of the Geo-accumulation Index (IGEO) and the Enrichment Factor (EF), tools that improve the visualization of the previously obtained data on the ICP-OES, demonstrating the content and chemical nature of the contaminating elements (As, Cu, Zn, Pb and Hg) as main PTE’s in the region, presenting values, in some cases, thousands of times higher than those stipulated by Nacional standards.