Spatial relations of heavy metals in arable and greenhouse soils of a Mediterranean environment region (Spain)

This study characterises and compares Cr, Ni, Pb, Cu, Zn and Cd (HMs) contents and the main edaphic parameters in arable soils (AS) from western areas of the Andalusian Autonomous Community (SE Spain) with greenhouse soils (GS) from the province of Almeria, one of the most productive agricultural systems in Europe. We explored 199 GS and 142 AS, representing local and regional scales of variation in this important Mediterranean area. The hazardousness of HMs was particularly relevant in GS where agricultural practices, which centre on maximising production, end up with products that finally enter the human food chain directly. Despite their similar edaphic characteristics, the main differences between AS and GS were nutrients and HM contents such as P, K, Cd, Pb and Zn, suggesting the widespread use of agrochemicals in greenhouse farming. Cd concentration in GS tripled that in AS. Here, we conclude that despite anthropogenic HM input, the association patterns of these elements were similar on the two spatial variability scales. Cd, Pb and Zn contents, and partly those of Cu, were related with agricultural practices. On the short spatial scale, grouping these HMs gave very high contents in GS. The associations found with Cr and Ni suggest a lithogenic influence combined with a paedogenic effect on spatial maps; this natural origin input becomes more marked on the long spatial scale represented by AS, where the main Cr and Ni contents were found in the vicinity of Mountain areas not influenced by human activities. (C) 2013 Elsevier B.V. All rights reserved.