Geochemical position of thallium in soils from a smelter-impacted area

The study complements our previous research, focused on metal contamination of soils in the area historically affected by Zn smelting near Olkusz (Silesia–Krakow region, southern Poland) and provides complex data on the geochemistry of anthropogenic Tl in soils with contrasting land use. Significant differences in Tl concentrations and chemical fractionation were observed between forest and grassland soil profiles, indicating the effect of land use on Tl behavior. Our findings proved the ability of forest soils to concentrate high amounts of Tl, particularly within the organic layers. A comparison of Tl concentrations in the upper (O or A) and the bottom horizons (C) of forest and grassland soils clearly demonstrates vertical mobility of Tl. The results of the sequential extraction procedure indicated the important role of soil organic matter in Tl mobilization, probably as a result of long-term alteration/dissolution of smelter-derived particles followed with Tl release; up to ~ 20% of total Tl amount was associated with the exchangeable/acid-extractable fraction in forest soils. The Tl concentrations detected in grassland soils were up to an order of magnitude lower than in forest soils. Taking into account the dominant bonding of Tl to the residual fraction, Tl present in grassland soils poses lower environmental hazard with respect to the potential mobilization or uptake by plants. Nevertheless, further research on Tl dynamics with emphasis to the environmental stability of Tl-bearing phases is essential for precise understanding of Tl behavior in such polluted (agro)systems.

► Tl concentration and fractionation differed between forest and grassland soils.
► Forest soils accumulate high amounts of Tl.
► Soil organic matter plays an important role in Tl mobilization.