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Vadose Zone Journal
Vol. 3, No. xx, 2004; Pages: 352–367

Mobile Organic Sorbent Affected Contaminant Transport in Soil: Numerical Case Studies for Enhanced and Reduced Mobility

Kai Uwe Totsche* and Ingrid Kogel-Knabner

Department fur Okologie, Wissenschaftszentrum Weihenstephan,Technisce Univerdsitat Munchen, D85350 Freising Weihenstephan.


Mobile organic sorbents (MOS) such as dissolved and colloidalphase organic matter control flow of water and transport of solutes insoils. We studied the effect of MOS on contaminant fate by systematicnumerical case studies. The scenarios considered were (i) enhancedmobility, (ii) reduced mobility due to cosorption, and (iii) reducedmobility due to cumulative sorption. The enhanced mobility and cosorption scenario require contaminant sorption to the MOS. Thecosorption and cumulative sorption scenario require sorption of MOSto the immobile sorbent. Simulations were run for physicochemicallydifferent fractions of dissolved organic matter and twomodel contaminants. Mobile organic sorbents mobility is characterized by a widerange of retardation parameters. Continued import of MOS to subsoilmaterial high in MOS-specific sorption sites will increase the solidphase organic matter content. Enhanced mobility was observed forsoils without MOS-specific sorption sites or for situations where MOSare in sorptive equilibrium with the immobile sorbent. Cosorptionresulted in reduced contaminant mobility. The extent to which reducedmobility was observed depended on the ratio of the affinities of thefree contaminant and the MOS-bound contaminant. As the sorptionof the MOS-bound contaminants is controlled by the properties ofthe MOS, the characterization of these properties is a crucial stepfor the estimation of the effect of MOS on contaminant mobility.Cumulative sorption resulted in reduced contaminant mobility as wellHowever, this result is the consequence of the increase of the sorptioncapacity due to the sorption of MOS, a long-term process that maylast for years to decades.

Keywords:Mobileorganicsorbents;cosorption;cumulativesorption;heavymetals;retardationparameters;polycyclic aromatic hydrocarbons;radionuclides.

Corresponding author:

E-mail: totsche@wzw.tum.de


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