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This paper contributes to increase the knowledge of the contents and sources of heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) to agricultural soils in Castellón province (Spain), a representative area of the European Mediterranean region. The surface horizons of 77 agricultural soils under vegetable crops were sampled and heavy metals were analysed by atomic absorption spectroscopy (AAS) after microwave extraction using the USEPA 3051A method. Mean heavy metal contents were similar to those obtained in other areas of this region. However, heavy metal contents (e.g. Cr, Pb) in some soils were above the maximum limit set in the 86/278/CEE Directive. Multivariate analysis (correlation analysis and principal component analysis -PCA) was performed so as to identify the sources of heavy metals to soils. Co, Fe and Ni were highly correlated amongst them (r>0.800; p<0.01), whereas Cr and Mn were less correlated with Co, Fe and Ni (r>0.500; p<0.01). Other relationships among heavy metals (i.e. Cu, Pb and Zn) were also identified, although correlation coefficients were not so high as those among Co, Fe and Ni (r<0.500; p<0.01).Contents of Co, Fe, Mn and Ni were interpreted to be mainly associated with parent rocks corresponding to the first principal component (PC1). On the other hand, Cd, Cu, Pb and Zn were interpreted to be mainly related to anthropogenic activities and comprised the second (Pb and Zn) and the third (Cd and Cu) principal components (PC2 and PC3, respectively), designated as anthropogenic components. Remarkably, Cr appears to be related in the study area to both the lithogenic and the anthropogenic components. Lithogenic elements were highly correlated with soil properties. Positive relationships with CEC (r>0.200; p<0.05) and clay (r>0.400; p<0.01), and negative relationships with carbonates (r > −0.400; p < 0.01) and sand (r>−0.300; p<0.01) were observed. Anthropogenic elements were less correlated with soils properties, since these elements are generally more mobile because they form more soluble chemical species associated to anthropogenic sources. Particularly, no correlation was found between Cd and Zn and soil properties. These findings extend results achieved in other parts of the region, highlighting the need to set soil quality standards in order to declare soils affected by anthropogenic pollution, particularly in the case of anthropogenic metals such as Cd, Cu and Pb, and also Cr and Zn in some areas. Further knowledge from other areas in this region would improve the basis for proposing such standards at regional level, which is a priority objective in Europe according to the European Thematic Strategy for Soil Protection.

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Assessment of the content and sources of heavy metals in soils is required to identify agricultural areas affected by contamination on a regional level, according to the European Thematic Strategy for Soil Protection. The total content of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn of 29 agricultural soils used to grow vegetable crops such as artichoke, broccoli, and potato, in the Segura River Valley, Alicante, Spain, as a representative area of the semiarid Mediterranean region, was determined to assess the current state of heavy metal contamination of agricultural soils.The mean values (mg kg -1 ) were: Cd, 0.38; Co, 7.9; Cr, 28.3; Cu, 21.6; Fe, 15,274; Mn, 320; Ni, 23.7; Pb, 19.6; and Zn, 57.8. These values followed the sequence: Fe > Mn > Zn > Cr > Ni > Cu > Pb > Co > Cd. Despite intensive production, the soil heavy metal concentrations were equal to, or lower than concentrations determined by others working on Spanish agricultural soils. Nevertheless, some plots had high Cd and Pb concentrations. Based on these results and others from the Spanish Mediterranean region, further studies under semiarid conditions are required to obtain a better knowledge of the pollution levels, especially in the case of anthropogenic metals such as Cd and Pb. This is critical to safeguard the environmental and production functions of these soils and, therefore, their quality. Further, given the importance of vegetables in the Mediterranean diet, it is important to extend the work to other areas of the European Mediterranean region.Additional key words: agriculture, Alicante province, contamination, vegetable crops. ResumenContenido de metales pesados en suelos agrícolas de un área del Mediterráneo semiárido: el valle del río Segura (Alicante, España)

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.

Different digestion methods can be applied for analyzing trace elements in soils. Selection of the most useful and convenient method is critical for the adequate determination of their concentrations in each type of soil to appropriately detect potential environmental pollution. Open-vessel digestion using a digester block (method 1) and microwave-assisted digestion (method 2) were compared using a certified reference material (CRM) with similar properties and characteristics to calcareous Mediterranean soils. Both methods were contrasted in terms of accuracy by calculating the recovery of cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the CRM and precision of replicate analysis through the relative standard deviation (RSD). Recoveries from the digester block method were slightly higher than recoveries from microwave digestion because the use of perchloric acid (HClO 4 ), whereas RSD values for microwave digestion were generally lower but with higher measured precision than values obtained by open-vessel digestion. The digestion methods were compared for analyzing trace elements in calcareous agricultural soils devoted to vegetable crops in the Alicante province (southeast Spain), as a representative area of the European Mediterranean region. Results of the paired-sample t-test showed significant differences between both methods for Co, Cr, Cu, and Pb in calcareous Mediterranean soils, whereas regression analysis indicated a good correlation between both methods for Cu, Ni, Pb, and Zn. Consequently, the choice of the digestion method is more relevant for minor elements such as Co and Cr. Microwave-assisted digestion seems to be the best option to determine most of the 890 trace elements in calcareous Mediterranean soils, because closed-vessel digestion exhibited lower variability according to the RSD values obtained in the study area, particularly for Co and Cr. Trace element concentrations were in agreement with background levels, except for Cu and Pb in some soils, which seem to be related to anthropic activities.