title: Quantifying the impact of immobile water regions on the fate of nitroaromatic compounds in dual-porosity media.
abstract: Nitroaromatic compounds (NACs) are reduced by structural or surface bound Fe (II) species under anaerobic conditions in the subsurface. This reaction preferentially occurs on clay minerals which are mainly present in areas with low hydraulic conductivity containing nearly immobile water. Diffusion is the dominating transport process in these zones. Due to the complexity in such heterogeneous systems, the mathematical prediction of reactive solute transport taking into account diffusive mass exchange into immobile water regions still remains challenging. Therefore, the influence of immobile water regions on the fate of 4-Cl-Nitrobenzene (4-Cl-Nb) was quantified in dual-porosity column experiments at three different mean transit times under saturated anaerobic conditions in the presence of soluble Fe (II). A multi-tracer approach and a Single Fissure Dispersion Model (SFDM) were used to estimate input parameter to further model the transport of 4-Cl-Nb. Reactive solute transport of 4-Cl-Nb was quantified considering instantaneous sorption on to the clay matrix and a reduction within the immobile water region following first-order kinetics. The experimental results indicated that sorption onto the clay matrix enhanced the mass exchange of 4-Cl-Nb into immobile water region compared to nonreactive solutes. At the same time the abiotic reduction of 4-Cl-Nb limited the process of back diffusion to mobile water regions. Fitted retardation factors (Rim=4.62±0.68) and decay rates (k=1.51±0.08h(-1)) were independent on tested flow velocities. Findings of this study can advance the understanding on the fate of NACs in the subsurface which is essential for prediction of reactive solute transport at field scale.
authors.affiliation: Institute of Groundwater Ecology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany.
authors.forename: Bastian
authors.initials: B
authors.lastname: Knorr
authors.affiliation: Institute of Groundwater Ecology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany; AGH University of Science and Technology, Department of Hydrogeology and Engineering Geology, Al. Mickiewicza 30, 30-059 Kraków, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Maloszewski
authors.affiliation: Institute of Groundwater Ecology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Ingolstaedter Landstr. 1, 85764 Neuherberg, Germany. Electronic address: christine.stumpp@helmholtz-muenchen.de.
authors.forename: Christine
authors.initials: C
authors.lastname: Stumpp
mesh_terms: D000538:Aluminum Silicates; D000077215:Clay; D004058:Diffusion; D062070:Hydrology / Q000379:methods; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D008962:Models, Theoretical; D009574:Nitro Compounds / Q000737:chemistry; D009578:Nitrobenzenes / Q000737:chemistry*; D016062:Porosity; D014867:Water / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D009574:Nitro Compounds; D009578:Nitrobenzenes; D014874:Water Pollutants, Chemical; D014867:Water; C010407:4-chloronitrobenzene; D007501:Iron; D000077215:Clay
keywords: Abiotic reduction; Analytical modeling; Column experiment; Diffusion; Nitroaromatic compounds; Reactive solute transport