Sorption kinetics of isotopically labelled divalent mercury (196Hg2+) in soil. (April 2019)

• Record Type: Journal Article
• Authors: Shetaya, Waleed H.; Huang, Jen-How; Osterwalder, Stefan; Mestrot, Adrien; Bigalke, Moritz; Alewell, Christine
• Is Part Of: Chemosphere. Volume 221(2019)
• Page Start: 193
• Page End: 202
• Publication Date: 2019-04
• Subjects: Environmental pollution -- Heavy metals -- Stable isotopes -- Kinetic modelling; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.01.034
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Understanding the sorption kinetics of Hg 2+ is the key to predicting its reactivity in soils which is indispensable for environmental risk assessment. The temporal change in the solubility of 196 Hg 2+ spikes (6 mg kg −1 ) added to a range of soils with different properties was investigated and modelled. The sorption of 196 Hg 2+ displayed a biphasic pattern with a rapid initial (short-term) phase followed by a slower (time-dependent) one. The overall reaction rate constants ranged from 0.003 to 4.9 h −1 and were significantly correlated (r = 0.94) to soil organic carbon (SOC). Elovich and Spherical Diffusion expressions compellingly fitted the observed 196 Hg 2+ sorption kinetics highlighting their flexibility to describe reactions occurring over multiple phases and wide timeframes. A parameterized Elovich model from soil variables indicated that the short-term sorption is solely controlled by SOC while the time-dependent sorption appeared independent of SOC and decreased at higher pH values and Al(OH)3 and MnO2 concentrations. This is consistent with a rapid chemical reaction of Hg 2+ with soil organic matter (SOM) which is followed by a noticeably slower phase likely occurring through physical pathways e.g. pore diffusion of Hg 2+ into spherical soil aggregates and progressive incorporation of soluble organic-Hg into solid phase. The model lines predicted that in soils with >4% SOC, Hg 2+ is removed from soil solution over seconds to minutes; however, in soils with <2% SOC and higher pH values, Hg 2+ may remain soluble for months and beyond with a considerable associated risk of re-emission or migration to the surrounding environments. Graphical abstract: Image 1 Highlights: Sorption of 196 Hg 2+ in soil occurred over two distinct phases. Elovich and spherical diffusion models best fitted the experimental data. Sorption of Hg 2+ can be predicted from soil variables by an optimized Elovich expression. Instantaneous sorption of Hg 2+ is controlled by soil organic carbon. Hg 2+ may remain soluble for months in alkaline soils.