Discrimination of Lithogenic and Anthropogenic Metals in Calcareous Agricultural Soils: A Case Study of the Lower Vinalopó Region (SE Spain)

Abstract

Analysis of heavy metal concentrations in soils and their sources is required to identify agricultural areas affected by contamination on a regional level, according to the European Thematic Strategy for Soil Protection. Pseudo-total and EDTA-extractable concentrations of nine elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in eighteen agricultural soils with vegetable crops in the Lower Vinalopó region (southeast Spain) were determined. The main aim was to assess the present state of the agricultural soils in relation to contamination processes by heavy metals for a representative area of the Mediterranean region under semiarid conditions. The pseudo-total concentrations for heavy metals analyzed in the study area were higher than those reported in the literature for Cd, Pb and Zn, although differences were not statistically significant. Levels for each element in the EDTA-extractable form, as a percentage of pseudo-total concentration, arranged in the following order: Cd > Pb > Cu > Zn > Mn > Co > Ni > Cr > Fe. The higher percentage of extractable fraction in relation to pseudo-total concentration, the higher bioavailability to other components such as crops, as seems likely for Cd, Cu and Pb. Moreover, soil properties were determined to characterize the agricultural soils and to analyze relationships with heavy metal concentrations. Multivariate analysis (correlation analysis and cluster analysis) was performed to identify the relationships among variables and classify them into groups. Pseudo-total and EDTA-extractable concentrations of Cd, Cu, Pb and Zn were mainly recognized as anthropogenic metals and showed a weaker relationship with soil properties as a consequence of their external sources. Co, Cr, Fe, Mn and Ni were mostly associated with parent rocks and corresponded to lithogenic metals. Findings achieved in this work contribute to the knowledge of the content and the origin of heavy metals in agricultural soils within the Mediterranean region, which is relevant for soil quality policy-making at regional level.