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Background values and distribution trends of Cu and Zn in soils of humid Mediterranean environment

Soil is the foundation of the entire biosphere. Knowledge of its heavy metal content and regional variability is essential to assess the environmental quality of soil and the extent of any contamination. In this study, 250 soil samples (within 125 soil profiles) were collected in undisturbed soils of the La Rioja region (an ideal place of the humid Mediterranean environment of Spain). The ‘total and bioavailable’ contents of copper (Cu) and zinc (Zn) were measured and their spatial variability assessed. The results indicate that Zn and Cu values were found to be very close to national and global averages. The spatial distribution of those elements was related to the nature of the bedrock and, to a lesser extent, was of anthropogenic origin. The variation of vertical distributions can be related, firstly, to natural sources – mainly the bedrock – and, secondly, to soil processes. From an ecological perspective, the ecosystem has not been affected by pollution.