Magnetic parameters as indicators of major elements and lead contamination in urban soils from Aburrá valley, Colombia

Abstract

We report an environmental magnetism study aimed to determine the relationship between heavy metals and magnetic parameters in urban soils of the Metropolitan Area of Aburrá Valey, Colombia, in order to establish magnetic indicators which in turn may allow the identification of high pollution areas. The study was carried out on 83 urban soil samples, which were subjected to a magnetic analysis, the concentration of the major elements (Al₂O₃, Fe₂O₃ and MnO) and Pb concentration determined by means of X-ray fluorescence. A significant variation is observed in the distribution of the magnetic material in the urban soil, which contains a mixture of relatively low coercivity magnetite minerals of both natural and anthropogenic origin. Superparamagnetic size particles were detected in medium and low concentrations in soils with low anthropic activity, suggesting a natural origin. On the other hand, by combining the magnetic parameters and thermomagnetic curves, soils with a high concentration of anthropic magnetic mineral were revealed. Al₂O₃ and Fe₂O₃ concentrations are high in most urban soils compared to MnO content. The areas characterized with low anthropic activity showed low content of Pb.

The soils with low anthropic activity was used to determine the reference value for each element and magnetic parameter. Statistical analysis showed that soils have a directly proportional relationship between the magnetic material and the Pb content and inversely proportional to the Al₂O₃, Fe₂O₃ and MnO contents. It was demonstrated that the mathematical model that predicts the concentration of elements from magnetic parameters has an efficiency of 62 %. The area characterized with high values of magnetic parameters and Pb content represents 25 % (46 km²) of the total studied urban area.