Mineralogy and Distribution of Cd, Ni, Cr, and Pb in Biosolids-Amended Soils From Castellon Province (NE, Spain)

Heavy metals can be transferred from soils to other portions of the ecosystem, with effects at both the ecosystem level and on human health from transmission through the web chain. For several years, this environmental issue has concerned scientists. In this context, heavy metal concentrations were studied in agricultural soils devoted to vegetable crops in the province of Castellon (NE Spain), in areas of intensive agriculture. Currently, the use of biosolids to improve the nutrient contents of the soil is a common practice. Contamination of soils by potentially toxic elements (e.g., Cd, Ni, Cr, Pb) from amendments of biosolids is subject to strict controls in relationship to total permissible metal concentrations, soil properties, and intended use within the European Community. This study is aimed at determining the chemical partitioning of Cd, Ni, Cr, and Pb in agricultural soils repeatedly amended with sludge. The distribution of chemical forms of Cd, Ni, Cr, and Pb in five biosolids-amended soils was Studied using a sequential extraction procedure that fractionated the metal into soluble-exchangeable, specifically sorbed-carbonate bound, oxidizable, reducible, and residual forms. The biosolids incorporation has modified the soil composition, leading to the increment of heavy metals. The residual, reducible, and carbonate-sorbed forms were dominant. The mineralogical association of the clay fraction was illite, kaolinite, and chlorite.