Geochemical characterisation of mercury mining spoil heaps in the area of Mieres (Asturias, northern Spain)

Asturias has important and abundant mercury deposits, and the legacy of the historical mining activities remains in the form of old and abandoned industrial installations. Tn areas where years of mercury mining has occurred, large amounts of wastes with high contents of Hg and As were disposed on the surface, without any preventive measures to avoid ore leaching and the dispersion of toxic elements into the environment. In proximity to Mieres village, three spoil heaps (EI Terronal, El Rucio, and Los Rueldos) were selected to undertake a multielemental geochemical study of soils, water and plants. In soils, systematic sampling was carried out at the site of the old mining and metallurgical works in El Terronal. Spoil heaps were also systematically sampled at the sites of EI Terronal, El Rucio and Los Rueldos. Tn the area of El Terronal, different types of plants have been sampled, including grass, fruit trees, edible crops and thickets. The soluble fraction resulting from a strong acid attack of the sample was analysed by FAA and ICP. Superficial water was sampled monthly, upstream and downstream of mining works; data obtained from filtered samples include pH, E-h, and arsenic and mercury concentrations. Soil samples from the mined areas show mercury concentrations between 1.7 and 472.1 mg/kg, and arsenic concentrations between 6 and 7287 mg/kg. Arsenic content in samples of spoil heaps is in the range 4746-62,196 mg/kg (Los Rueldos), and 192-2057 mg/kg (El Rucio); mercury content is in the range 14-2224 mg/kg (Los Rueldos), and 21-1984 mg/kg (El Rucio). Arsenic content of superficial water upstream and downstream of the mining works is lower than 0.005 mg/l (analytical detection limit), and 0.9-5.6 mg/l, respectively; mercury concentrations upstream and downstream of mining works are always lower than 0.001 mg/l (analytical detection limit). Leachates collected at the bottom of the Los Rueldos spoil heap show acidic pH (between 2.43 and 2.50), E-h around 550 mV, arsenic concentrations between 5.3 and 8.3 mg/l, and mercury concentrations always lower than 0.001 mg/l (analytical detection limit). Maximum values of As and Hg content in grass in the mined area are 53 mg/kg and 4.84 mg/kg, respectively (C) 1999 Elsevier Science B.V. All rights reserved.