Evaluate Long-Term Fate of Metal Contamination after Mine Spill; Assessing Contaminant Changes in Soil The Guadiamar Case Study; Southern Spain

57 páginas.-- 12 figuras.-- 10 tablas.-- 99 referencias.-- 2 Appendices.-- Master Program: International Land and Water Management.-- Chair Group: Soil Physics and Land Management

The mine spill accident (1998), inundating 4500ha of fertile agricultural land along the Guadiamar river with toxic sludge and releasing metals into the environment, is considered as one of the biggest environmental catastrophes in the recent Spanish history. Immediate actions have been taken directly after the mine spill, including mechanical removal of the toxic sludge from the soil surface, application of soil amendments and re-vegetation, giving priority to immobilize the metals. RECARE, a European wide project started in 2013 focusing on different soil threats is stimulating further soil research by involving local stakeholders. In this study, the Guadiamar Green Corridor (South Spain) is assessed, aiming to obtain new knowledge and soil data on soil metal contamination. Since no harmonized soil database was available for the Guadiamar case study, a compilation of physiochemical soil data of Guadiamar is the first objective of this study and base for the RECARE project. A subsequent spatial analysis using ArcGIS is carried out dividing the study site into land units based on geomorphology, lithology and the land use before the mine spill facilitates. Based on this the sampling area for the present study were determined. The current situation (2014) of a selected area within the Guadiamar Green Corridor is assessed by analysing the most important soil properties, pH, soil organic carbon and soil texture, related to total and available Cd, Pb, Cu and Zn. Soil sampling, laboratory and statistical analysis have been applied in this study to assess the current situation, while data from the past 15 years is derived from literature. Huge data variability of pseudo-total and bioavailable (EDTA extracted) metal concentrations is evident, due to natural variability and irregular distribution and inaccurate cleaning of the toxic sludge along the Guadiamar river. Since the sludge has been removed mechanically, 15 years ago, the variability of soil metal concentrations (pseudo- total and EDTA extracted) did not change. Threshold values for pseudo-total metal concentrations do still exceed the values proposed by the European Directive, and this is not expected to change fast since metals are not biodegradable. With a neutral soil pH, soil organic carbon contents around 3g 100 g-1 and clayey soils the current situation of a selected area is supporting metal absorption and immobilization. Due to these soil conditions and the natural protection of the Green Corridor, which is ensuring permanent vegetation cover, environmental risks are minimized. Nevertheless, the huge amount of currently immobilized metals present in the soils of Guadiamar, form a huge stock and potential risk to the environment. Probably, the highest risk is a potential decrease of soil pH with a subsequent increase of bioavailable metals. Therefore, environmental monitoring or even repeated applications of soil amendments is essential, especially in high risk areas where soil pH is naturally low.

Peer reviewed