EGU2020-2399, updated on 11 Jan 2022
https://doi.org/10.5194/egusphere-egu2020-2399
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Stable thallium isotope fractionation in soils as affected by pedogenesis

Ales Vanek1, Andreas Voegelin2, Martin Mihaljevic3, Vojtech Ettler3, Jakub Trubac3, Petr Drahota3, Maria Vankova3, Vendula Oborna1, Vit Penizek1, Lenka Pavlu1, Ondrej Drabek1, Petra Vokurkova1, Tereza Zadorova1, and Ondrej Holubik1
Ales Vanek et al.
  • 1Czech University of Life Sciences Prague, Faculty of Agrobiology, Food, and Natural Resources, Praha 6, Czech Republic (vaneka@af.czu.cz)
  • 2EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
  • 3Charles University, Faculty of Science, Albertov 6, 128 00 Praha 2, Czech Republic

In this study, we investigated if variations in the stable Tl isotope ratios in soil samples from different profiles can be linked to data on the extractability and speciation of soil Tl and whether the isotopic data allow drawing conclusions on the geochemical processes linked with soil formation/rock weathering. We observed a significant accumulation of the heavy 205Tl isotope in the B horizons, with ε205Tl values that were up to 7 higher than in the underlying bedrock. This 205Tl enrichment, however, was neither reflected in the speciation of Tl nor its chemical fractionation. Furthermore, exchangeable soil Tl in the B horizons was found to be much isotopically lighter than the bulk soil Tl. Our findings suggest that the observed isotopic shift may be linked to cyclic Tl mobilization and immobilization processes over the period of rock weathering and soil formation. Oxidative Tl uptake by Mn-oxides associated with a 205Tl enrichment, continuous weathering of the Tl(III)-containing phases, followed by a Tl(I) remobilization (leading to enrichment in 205Tl) are suggested to be responsible for the binding of the heavy Tl isotope fraction into other phases, mainly illite (a dominant Tl host), which is not normally expected. We therefore conclude that the use of the Tl isotopic data for phase or sorption mechanism identification in a dynamic multi-phase (soil) system can be very complicated, but, in contrast, suggesting their efficient use as a proxy for redox-controlled processes.

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