Chemical Partitioning of Fe, Mn, Zn and Cr in Mountain Soils of the Iberian and Pyrenean Ranges (NE Spain)

Abstract

Listen

Translate article

The bioavailability of heavy metals, and thus their possible harmful impact on ecosystems and humans, depends on metal partitioning. This study describes the chemical partitioning of iron, manganese, zinc and chromium, because the potential effect of soil contamination is better assessed through the knowledge of the forms in which a given metal is present rather than the use of its total concentration. In four soil types representative of mountain soils in the Iberian and Pyrenean ranges in Aragón, a total of 16 selected sites have been sampled and five subsamples were taken in each site to create a composite sample. The 4 heavy metals have been extracted by the sequential extraction procedure of Tessier et al. (1979) and analyzed by emission atomic spectrometry of solid state (ICP OES). Little Fe, Mn and Zn (< 1, 2.4–35.9, < 1–24.5 mg/kg, respectively) were retrieved from the exchangeable phase, a readily available phase for biogeochemistry cycles in the ecosystems. Chromium was not detected in the potentially bioavailable forms. The largest contents of Fe, Zn and Cr were retrieved from the residual phase with mean values of 21100, 72 and 60 mg/kg, and maximum values of 35700, 279 and 271 mg/kg, respectively. Mn was mainly bound to oxide phases with mean and maximum values of 236 and 887 mg/kg, respectively. For all metals, the highest contents are found in Leptosols on igneous rocks due to the rich and diverse mineral composition of their parent materials. The knowledge of the chemical partitioning of Fe, Mn, Zn and Cr provides information to identify the soils in which their mobile forms may be transferred to the soil-water-plant system. This information is of interest for the management of fragile mountain soils to avoid the environmental risk of cycling these metals in the environment.