Statistical Approach to Discriminate Background and Anthropogenic Input of Trace Elements in Soils of Catalonia,Spain

A study was conducted in Catalonia (NE Spain) to determine the baseline levels and the polluted contents of Ba, Cd, Cr, Cu, Ni, Pb, V and Zn (aqua regia-extractable) in soils of an agroindustrial area near Barcelona. The samples analyzed proceeded from two soil surveys. 268 samples belonged to 67 representative, and slightly disturbed, soil profiles sampled during a previous soil survey, and 95 superficial samples were taken near a composting plant (heavily disturbed and presumably polluted). Probability plots were used to establish the reference (or background) levels and a literature comparison was made to check the validity of the background ranges established. The raw data sets and the uncontaminated resulting populations were studied by means of frequency histograms and of statistical tests in order to verify the general assumption, which states that trace element distributions in soils follow the log-normal law. The results showed that the studied elements were distributed in these soils following the log-normal law and that the established reference values were in agreement with those reported in the literature.