An integrative assessment of environmental degradation of Caveira abandoned mine area (Southern Portugal)

Abstract

Since the end of the 1990s the Portuguese Iberian Pyrite Belt (IPB) is a typical European post-mining region with significant problems related to acid mine drainage (AMD), metal dispersion, mine waste management and unsafe mining infra-structures. The Portuguese government is providing particular attention on the sulphide abandoned mines and doing considerable investments on the mining recovery all over the country. The former Caveira mine was closed in the 1980s. It is considered an extremely impacted site due to the dimension of the areas affected by mining activities. Tailings, mine addicts and associated waste rock dumps, resulting from 129 years of pyrite and Cu exploitation, are spread along the Grândola stream. Despite the semi-arid climatic conditions of the area, the tailings are considerably eroded by the surficial waters, particularly during rainfall events. The past mining and smelting activities have resulted in severe contamination of the Grândola stream and its tributary by AMD (pH b 2) as well as degradation of surrounding stream sediments, soils and vegetation. In order to evaluate possible environmental risks, a sediment and surface water survey was carried out downstream the Caveira mine. The acidic effluent and mixed stream water show high Al, As, Ca, Cd, Cu, Fe, Hg, Mg, Mn, Ni, Pb and SO 4 concentrations, with several of these contaminants exceeding local and/or surface water quality standards. The data show a strong seasonal variation of surface water quality with poorer water quality during the dry and rainy seasons caused by evaporation and efflorescent salt dissolution, respectively. The variable flow regime at the local streams causes dilution of AMD rich in trace metals reaching background within 14 km downstream. The potential toxicity of stream metal concentrations was determined using cumulative criterion unit (CCU) scores and the modified AMD index (MAMDI), which highlighted As, Cd, Cu, Pb and Zn as the major sources of potential chronic stream toxicity, with emphasis on winter season. Although the threshold of the likely harm to aquatic life is exceeded at all sites, the two indexes highlight differences relating to the extension of contamination effects. The Average Index of Toxicity (AIT) showed that sediment contamination is very high even when the distance to mine promoted a decreasing in water metal concentrations, which are being precipitated in the sediments due to pH increase.

Partitioning of potentially toxic elements among two colloidal fractions and relevance for their mobility in different water types

“…The waters have a pH range of 1.80 (CE1, in the AMD stream in the Caveira, Aljustrel-Lousal sector) to 8.57 (SD A water reservoir in the S. Domingos area). These two samples have also the maximum (19500 m/cm) and minimum (300 m/cm) ECs, the first expressing the leaching of the Caveira mine sulphide wastes, as already reported by [8]. Like pH, the filtered metal contents (<0.45 and <0.20 m) at the several sampling locations are very distinct, reflecting the heterogeneity of the waters.…”

Trace element contamination in the mine-affected stream sediments of Oued Rarai in north-western Tunisia: a river basin scale assessment

“…The high Ag contamination, mainly in correspondence with the drainage basin of the Oued Maaden mining site and Oued Rarai plain. Following numerous previous studies, high Ag concentrations can be related to former mining activities at Oued Maaden, which was responsible for the release of several millions of tons of tailings in the drainage basin (Ferreira da Silva et al, 2015;Oyarzun et al, 2011). Silver concentrations (range from 0.05 to 9.40 mg kg -1 ), however, were 10-100 times lower than those observed in mining sites worldwide (Cortada et al, 2018;Ferreira da Silva et al, 2015;Oyarzun et al, 2011).…”

The Tolerance of Eucalyptus globulus to Soil Contamination with Arsenic

“…The contamination by metals and metalloids due to different anthropogenic activities is a reality worldwide [1,2] and in Portugal and a reason of concern of several scholars and public environmental agencies [3][4][5][6]. The mining activity was an important contribute to the Portuguese economy until the first half of the 20th century when the majority of the mines were closed [7]. In this context, huge tailings were formed with high concentrations of heavy metals and/or metalloids-arsenic (As), copper (Cu), lead (Pb), and zinc (Zn), with the consequent dispersion of contaminants mainly due to acid mine drainage [8,9].…”