Levels and pedogeochemical mapping of lead and chromium in soils of Barcelona province (NE Spain)

In this paper an analysis of the spatial distribution of Cr and Pb in topsoils in Barcelona province using 319 samples (approximately in a regular 5 km spaced grid) is presented. Ordinary kriging (OK) maps are obtained after examining and modelling observational variograms. A verification using cross-validation methods has been applied to evaluate the performance of the resulting maps for both Cr and Pb OK maps, which have also been compared to inverse distance weighting (IDW) interpolated maps, used as an additional benchmark. Both Cr and Pb OK maps have been obtained with better cross-validation scores in terms of median residuals and correlations between estimates and sampled values. Interpolated maps have been used to calculate the area of the province above a soil target threshold (Cr: 100 mg kg−1 and Pb: 85 mg kg−1)—higher intervention values were not observed. Target values corresponded to the 99.8 percentile for the Cr (9 km2, 0.2% of the area of Barcelona province) and 92.7% percentile for the Pb (567 km2, i.e. 7.2% of the province).

Research Highlights
► 319 topsoil samples of Cr and Pb in Barcelona province (NE Spain) studied.
► Ordinary kriging and inverse distance weighted maps obtained and validated.
► Maps compared with threshold target values (Cr:100 mg kg-1; Pb:85 mg kg-1).
► Barcelona province area above threshold target values were: Cr 0.2% and Pb 7.2%.