Environmental Impact Assessment in the Former Mining Area of Regoufe (Arouca, Portugal): Contributions to Future Remediation Measures.

Nuno Durães,Sara Sousa,Eduardo Ferreira Da Silva,Luís Portela,Carla Patinha

doi:10.3390/ijerph18031180

Abstract

The W-Sn Regoufe mine, closed since the 1970s, was once intensively exploited for tungsten concentrates. Throughout its activity, considerable amounts of arsenopyrite-rich mine wastes were produced and, to this day, are still exposed to weathering conditions. Thus, this work aims at assessing soil contamination, using a combination of chemical, physicochemical and mineralogical analyses and sequential selective chemical extraction of the main potentially toxic elements (PTEs) in topsoils. Results show that Regoufe soils are enriched in most of the PTEs associated with the ore assemblage, but As and Cd contents far outstrip both international and national guidelines. The estimated contamination factor reveals that 67% of soil samples are classified as highly to ultra-highly contaminated. Similar distribution patterns, with the main focus around the unsealed mine adits, are observed when spatially projecting the modified degree of contamination (mCd) and arsenic contents. Fe-oxyhydroxides and organic matter demonstrate to have a preponderant role in the retention of Cd and As. In fact, despite the high PTE contents in soils, local surface waters are characterised by low metal(loid) contents and nearly neutral pH, with PTE concentrations below national thresholds for irrigation waters.

Highlights

Metal(loid)s are the most toxic inorganic pollutants, the reason why they are often referred to as potentially toxic elements (PTEs)
A typical case is mining activity, where high amounts of metal(loid)-hosting minerals are exposed to the oxidising and weathering conditions of the surface, causing the dispersion of metal(loid)s that can reach several environmental compartments and cause their contamination [4]. These processes are more relevant in abandoned mines, where the lack of environmental mining regulations and the uncontrolled disposal of mine tailings with low cohesion facilitate the dispersion and mobility of contaminants to the surrounding areas [5,6,7,8]. Since these contamination effects may persist for long decades, or even centuries [9,10], the study of these processes at such areas continues to be of high relevance, to help solve several current problems, and to prevent new cases of environmental contamination caused by mines
The geochemical data allows one to verify that soils from the Regoufe region are enriched in some PTEs in relation to the geochemical background of Portuguese soils and to uncontaminated world typical values

Summary

Introduction

Metal(loid)s are the most toxic inorganic pollutants, the reason why they are often referred to as potentially toxic elements (PTEs). A typical case is mining activity, where high amounts of metal(loid)-hosting minerals are exposed to the oxidising and weathering conditions of the surface, causing the dispersion of metal(loid)s that can reach several environmental compartments and cause their contamination [4] These processes are more relevant in abandoned mines, where the lack of environmental mining regulations and the uncontrolled disposal of mine tailings with low cohesion facilitate the dispersion and mobility of contaminants to the surrounding areas [5,6,7,8]. This scenario may be accompanied by an increase in severe contamination cases, as the economically viable exploitation of low-grade ore deposits requires greater refinement than the ore-rich ones

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Conclusion