Pollution potential of copper mine spoil used for road making

Abstract

Copper mine spoil from Touro (A Coruña, Spain) has been used in the construction of rural roads and unasphalted tracks. Here the pollution potential of the spoil for water and soil is investigated which is derived fundamentally from the high copper content of the spoil. On the basis of a visual survey of affected roads, five sites were chosen because they seemed to be especially susceptible to pollution by runoff or sediment. Triplicate surface soil samples were taken at various distances along roads and their copper content was compared to that of triplicate pollution free control samples. Samples of sediment were taken from roadside drainage ditches at 14 locations. Six samples of water were taken from representative first order water courses receiving the runoff from the road. Extracts for determination of total Cu (Cu t) were obtained by treating subsamples in a microwave oven with HNO 3, HCl and HF. To estimate the copper fraction susceptible to uptake by plants (Cu e), the samples were extracted with a NH 4OAc/EDTA solution. The copper content of extracts was determined by atomic absorption spectrometry. Copper contents in filtered water samples were determined by inductively coupled plasma atomic emission spectroscopy. Total Cu (Cu t) values in soils of 249.2 mg kg −1 at site 5, and 180.0 and 156.7 mg kg −1 at site 4 were the only ones which exceeded the phytotoxically excessive level of 100 mg kg −1 of Cu t. Furthermore, analysis of variance shows that it is only at sites 4 and 5 that Cu t depended significantly on sampling distance and that Cu t values differed significantly from those of the controls, making it evident that Cu pollution is derived from the spoil. Nevertheless, even at these sites, the copper fraction susceptible to uptake by plants remains low, as all mean Cu e values were <13 mg kg −1 except the three associated with high Cu t samples, which ranged from 65.3 to 80.3 mg kg −1. At no site did visual inspection show any signs of phytotoxicity. Total copper concentration in the <2 mm fraction of sediment samples ranged from 71 to 652 mg kg −1. In most of sediment samples, the Cu e/Cu t ratio was <0.2. Copper concentration in primary water course samples was in no case >8 μg l −1, well below the threshold values established by the EC legislation on the quality of water for human consumption and for supporting fish life.