Establishment of the background levels of some trace elements in soils of NE Spain with probability plots

The total content of Ba, Cr, Cu, Ni, Pb, V and Zn, determined by means of X-ray fluorescence was studied in soils of an agro-industrial area near Barcelona (NE Spain) in order to establish their background levels. A total of 363 samples were analysed, of which 268 belonged to 67 slightly disturbed and representative soil profiles. The remainder were taken at the soil surface (0-5 cm) in a polluted area located near a composting plant. The background ranges were established with probability plots and the upper limits of the resulting ranges were compared with those reported in the literature. In order to study the statistical distribution of the trace elements in the soils of the area, the Kolmogorov-Smirnov test of distribution fitting was applied. The upper limits of the established background ranges were: Ba, 1762 mg/kg; Cr, 275 mg/kg; Cu, 145 mg/kg; Ni, 83 mg/kg; Pb, 91 mg/kg; V, 183 mg/kg; and Zn, 326 mg/kg. It was concluded that probability plots seemed to be a reliable statistical method for establishing the background contents of these elements in the soils of the area studied. The trace elements investigated were distributed in these soils following the log-normal law. (C) 1997 Elsevier Science B.V.