Parámetros magnéticos de los suelos de la periferia de Coimbra (Portugal)

Resumo

The main goal of this study is to investigate the magnetic properties of topsoils in an area of about16 Km2 near Coimbra. Also, the possible linkages between contents on heavy metals and magnetic parameters were investigated. 104 surface samples were taken over a square grid with a cell size ot500 m, and at various distances from the main roads. Laboratory measurements of high- and low-field susceptibilities were performed using Bartington MS2 dual-frequency meter. Direct magneticfields up to 3T were used to acquire isothermal remanent magnetization using MM PM 9 magnetizer,measured with a Molspin Minispin magnetometer. A subset of these soil samples (N=39) were analyzed for Pb, Zn, Co, Cu, Cr and Ni by using atomic absorption spectroscopy (Perkin-Elmer 2380). Susceptibility values are in the range 6 to 325x1 O'5SI and MRI1T values in the range 0.25 to 18.174 A/m.High correlation coefficients between these two parameters were found (r=0.8). Higher values ofboth parameters were reported near roads and rivers. S-ratios (IRM WOm/SIRM and lRM 300m/S!RM)and IRM acquisition curves indicated the presence of ferrimagnetic minerals. Concentrations of Pb(=115 mg/Kg), Ni (=48mg/Kg), Zn (=387 mg/Kg) and Cu (=78mg/Kg) were higher than the mean background values for the world soils; urban pollution and emission from vehicles seem to be the mainreason for these values; for the agricultural soils, chemical products (e.g. fertilizers) are the responsible for the high concentrations in those elements. Positive correlation was found between Pb andIRM, and also between Cu and IRM (0.4 and 0.5 respectively).