Impact of different redox conditions on thallium (im)mobilization in soil (Serbia)
2015
Antić-Mladenović, Svetlana (Faculty of Agriculture, Belgrade-Zemun (Serbia)) | Kresović, Mirjana (Faculty of Agriculture, Belgrade-Zemun (Serbia)) | Rinklebe, Jörg (School of Architecture and Civil Engineering, Wuppertal (Germany). Institute of Foundation Engineering, Water- and Waste-Management, Soil- and Groundwater-Management) | Frohne, Tina (School of Architecture and Civil Engineering, Wuppertal (Germany). Institute of Foundation Engineering, Water- and Waste-Management, Soil- and Groundwater-Management) | Stärk, Hans-Joachim (UFZ - Helmholtz Centre for Environmental Research, Leipzig (Germany). Department of Analytical Chemistry) | Ličina, Vlado (Faculty of Agriculture, Belgrade-Zemun (Serbia))
Thallium (Tl) is a highly toxic element, even in small concentrations, to a range of organisms and in different environments. Therefore, our aim was to study (i) Tl geochemical fractionation by the means of the modified BCR sequential extraction procedure and (ii) the impact of redox potential (EH) alteration and principal factors such as iron (Fe), manganese (Mn), dissolved organic carbon (DOC), chlorides (Cl-) and sulfates (SO4 2-) on Tl (im)mobilization in periodically flooded arable soil (Serbia). Flooding was simulated using an automated biogeochemical microcosm system that allows systematical control of pre-defined redox-windows. Afterwards, EH was increased stepwise for approximately 100 mV from reducing (-205 mV) to oxidizing (530 mV) conditions. EH was automatically monitored at 10 minutes intervals. Total duration of the experiment was 914 hours. The sequential extraction revealed majority of pseudo-total soil Tl (0.15 mg kg−1) in the residual fraction (85.5 %), following by reducible (10.2 %), oxidable (3.8 %) and acid soluble (exchangeable) (0.5 %) fraction. The soluble Tl concentrations (0.024–0.116 μg l−1) were significantly affected by EH, having an increase with EH increase (r=0.75, p<0.01, n=30). Concentrations of soluble Fe, Mn, and DOC showed significant negative correlations with soluble Tl (r=-0.78, r=-0.73 and r=-0.91, respectively, p<0.01, n=30), whereas Tl correlated significant positive with SO4 2- and Cl- (r=0.89, r=0.81, respectively, p<0.01, n=30). Thallium mobilization was attributed to several simultaneous processes, involving the reductive dissolution of Fe-Mn oxides and gradual oxidation of Tl-bearing metallic sulfides. Our results imply that soluble Tl concentrations might increase when soil redox status evolves from reducing to oxidizing conditions. Due to high Tl toxicity at low doses, and increasing flooding events, our findings suggest that Tl should be included in future monitoring of plants and groundwater on the site or on similar sites.
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