Heavy metals in the dump of an abandoned mine in Galicia (NW Spain) and in the spontaneously occurring vegetation

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The concentrations of different forms of heavy metals (Fe, Mn, Zn, Cu, Cr, Ni, Cd and Pb) were determined in a mine dump material rich in chalcopyrite. The concentrations were compared with those of the natural vegetation colonising the dump. Samples taken from the dump are acid (pH H 2O between 3.0 and 5.0), have carbon contents lower than 0.5%, N lower than 0.2%, effective cation exchange capacity between 0.74 and 4.96 cmol(+) kg −1 and percent Al saturation in the exchange complex higher than 20% in 85% of the samples. Iron was the most abundant heavy metal, in both total and bioavailable forms, and the relative abundance of metals was: Fe>Cu>Mn>Zn>Cr. The total Fe concentrations ranged between 4315 and 31 578 mg kg −1, the total Cu between 273 and 5241 mg kg −1, the total Mn between 294 and 2105 mg kg −1, the total Zn between 73 and 894 mg kg −1 and total Cr between 0.01 and 30 mg kg −1. Ni, Cd and Pb were below the analytical detection limits. The concentration of bioavailable Fe ranged between 40 and 1550 mg kg −1; Zn was the least abundant metal in this fraction (between 2 and 100 mg kg −1). Copper was the most abundant heavy metal in the exchange complex and in the aqueous extracts, followed by Zn, Mn and Fe. Exchangeable Cu ranged between 17.7 and 1866 mg kg −1, whereas the maximum concentrations of exchangeable Zn, Mn and Fe did not exceed 140 mg kg −1. The Cu concentration in the aqueous extracts varied between 0.1 and 8.3 mg l −1 and the concentration of Fe was always less than 0.52 mg l −1. The heavy metal contents in the spontaneously occurring vegetation in the dump ranged between: 150 and 900 mg Fe kg −1, 84 and 2069 mg Mn kg −1, 20.5 and 106 mg Cu kg −1 and between 35 and 717 mg Zn kg −1, when considering all the plant samples analysed. Festuca sp. accumulated Fe, Salix atrocinerea accumulated Zn and Mn, and Frangula alnus and Quercus robur accumulated Mn. These native plant species may contribute to decrease the heavy metal contents in the dump material.