Integration of magnetic measurements, chemical and statistical analysis in characterizing agricultural soils (central Portugal)

The agricultural soils near the city of Coimbra (central Portugal) have high levels of potentially toxic trace elements (PTEs). This is a pioneering study that allows the characterization of agricultural soils in central Portugal, using the environmental magnetism techniques and further to establish the main sources of pollution. On completion of magnetic analyses, a scanning electron microscope observation was carried out on magnetic extracts to provide information on the possible origin of particles in general. Chemical studies show a high concentration of some of PTEs in the topsoil. Statistical studies were used for examination of the relationships between the magnetic properties of soil samples and the concentrations of chemical elements. A positive and significant correlation was observed between magnetic measurements and PTEs concentrations. Principal component analysis allowed us to conclude that the main sources of the analysed elements are mostly related to the burning of fossil fuels. The results confirm that (1) simple, rapid and non-destructive magnetic measurements can provide useful information about PTEs enrichment in agricultural soils near the urban centre, (2) the environmental magnetism techniques can be used as a proxy for spatial distribution of pollution in this area and (3) the combination of magnetic methods with chemical and statistical analysis is an efficient tool for the identification of the main pollution sources in poorly industrialized areas and to assess environmental implications.