Heavy metal fractionation in sediments from the Jarama River (central Spain)

Concentrations of certain heavy metals are analyzed in sediments from the Jarama River, in the autonomous region of Madrid (Spain) as well as their variation along the river course. In addition, the distribution of heavy metals among the solid phases present in the samples is studied in accordance with the sequential extraction procedure of the European Union described in the Standard Material and Testing (SM&T) Program. Our results show that the upper course of the Jarama River carries low levels of pollution, the middle course has moderate levels of heavy metals, due to pollution from urban areas and some agricultural industries, and the lower course carries pollution from urban areas and some industrial areas. Major metals, such as Fe and Mn, showed low mobility (less than 23 % of total metal). The other metals presented mobilities of between 44 and 52 % of the total metal content. Cd and Zn were extracted mainly in the acid-soluble fraction, whereas Cu, Ni and Pb were mainly bound to amorphous iron and manganese hydroxides (reducible fraction). Correlation studies between some of the variables under analysis showed an association between the metal extracted in the third step of the SM&T sequential extraction procedure and organically bound metal. Multivariate principal components characterized the structures from the samples, which were grouped into samples in three zones according to their level of metal pollution and their physicochemical and mineralogical characteristics. The first sample group was sampled at points on the upper river; the second in the middle course of the river; and the third group, containing the most contaminated sediments, were samples from the lower course of the river.