Sequential Fractionation of Copper, Lead, Cadmium and Zinc in Soils from or near Doñana National Park

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Abstract
A knowledge of the total amount of trace metals is not enough to assess the environmental impact of polluted soils. For this reason, the determination of metal species in solution is important to evaluate their behavior in the environment and their mobilization capacity. Soils contaminated by Cu, Pb, Cd, and Zn found at Doñana National Park (Spain) were examined for total content. Sequential extraction schemes were used to determine the degree of pollution and to partition the trace elements in soils. The three areas studied (marshes, stabilized sand, and mine) have different contamination levels. The northern‐most marshes of Doñana National Park have the highest total levels of the four metals due to the influence of a mine located 40 km away. The stabilized sand was not polluted by the metals studied. The bioavailable fraction of Cd represents more than 50% of the total Cd found in soils, and this percentage is much greater than that of the other elements examined. Most of the Cu was present in the organic fraction, with only small amounts being associated with the crystalline Fe‐oxide fraction. Lead and Zn were associated mainly with the crystalline Fe‐oxide fraction, but the amount of Zn associated with the carbonates and amorphous Fe‐oxide fractions was also significant. The total amount of Cu, Pb, Cd, and Zn in the soils and their distribution in the five fractions depended on total metal contents, soil type, and soil properties (i.e., pH and percentage of sand, clay, organic matter, and carbonates). Mobility of soil metals were Cd > Zn > Pb > Cu.

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