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  • 1
    Language: English
    In: Vadose Zone Journal, 2004, Vol.3(2), p.352
    Description: Mobile organic sorbents (MOS) such as dissolved and colloidal phase organic matter control flow of water and transport of solutes in soils. We studied the effect of MOS on contaminant fate by systematic numerical case studies. The scenarios considered were (i) enhanced mobility, (ii) reduced mobility due to cosorption, and (iii) reduced mobility due to cumulative sorption. The enhanced mobility and cosorption scenario require contaminant sorption to the MOS. The cosorption and cumulative sorption scenario require sorption of MOS to the immobile sorbent. Simulations were run for physicochemically different fractions of dissolved organic matter and two model contaminants. Mobile organic sorbents mobility is characterized by a wide range of retardation parameters. Continued import of MOS to subsoil material high in MOS-specific sorption sites will increase the solid phase organic matter content. Enhanced mobility was observed for soils without MOS-specific sorption sites or for situations where MOS are in sorptive equilibrium with the immobile sorbent. Cosorption resulted in reduced contaminant mobility. The extent to which reduced mobility was observed depended on the ratio of the affinities of the free contaminant and the MOS-bound contaminant. As the sorption of the MOS-bound contaminants is controlled by the properties of the MOS, the characterization of these properties is a crucial step for the estimation of the effect of MOS on contaminant mobility. Cumulative sorption resulted in reduced contaminant mobility as well. However, this result is the consequence of the increase of the sorption capacity due to the sorption of MOS, a long-term process that may last for years to decades. ; In the special section: Colloids and colloid-facilitated transport of contaminants in soil and sediments. Paper presented at an international workshop held September 19-20, 2002, Tjele, Denmark. Includes references
    Keywords: Soil Transport Processes ; Sorption ; Vadose Zone ; Porous Media ; Dissolved Organic Matter ; Pollutants ; Soil Pollution ; Mathematical Models ; Soil Colloids ; Simulation Models ; Colloid-Facilitated Transport ; Mobile Organic Sorbents ; Cosorption ; Contaminants;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 2
    Language: English
    In: Vadose Zone Journal, 2007, Vol.6(2), p.233
    Description: Mobile colloidal and suspended matter is likely to affect the mobility of polycyclic aromatic hydrocarbons (PAHs) in the unsaturated soil zone at contaminated sites. We studied the release of mobile particles and dissolved organic matter as a function of variable climatic boundary conditions, and their effect on the export of PAHs at a coal tar-contaminated site using zero-tension lysimeters. Seepage water samples were analyzed for dissolved organic carbon (DOC), pH, electrical conductivity, turbidity, and particles larger than 0.7 mu m. The 16 Environmental Protection Agency PAHs were analyzed in the filtrate 〈0.7 mu m and in the particle fraction. Our results show that extended no-flow periods that are followed by high-intensity rain events, such as thunderstorms, promote the mobilization of particles in the size 0.7 to 200 mu m. Mobilization is enforced by extended drying during summer. High particle concentrations are also associated with freezing and thawing cycles followed by either rain or snowmelt events. The export of PAHs is strongly connected to the release of particles in the 0.7- to 200-mu m size fraction. During the 2-yr monitoring period, up to 0.418 mu g kg (super -1) PAHs were mobilized in the filtrate (〈0.7 mu m) while the eightfold mass, 3.36 mu g kg (super -1) , was exported with the retentate (0.7-200 mu m). Equilibrium dissolution of PAHs and transport in the dissolved phase seem to be of minor importance for the materials studied. Extreme singular-release events occurred in January 2003 and January 2004, when up to 55 mu g L (super -1) PAHs per one single seepage event were observed within the retentate. Freezing and thawing cycles affect the PAH source materials, that is, the remnants of the nonaqueous phase liquid (NAPL). High mechanical strain during freezing results in the formation of particles. At the onset of the thawing and following rain or snowmelt events, PAHs associated with these particles are then exported from the lysimeter.
    Keywords: Environmental Geology ; Aromatic Hydrocarbons ; Bavaria Germany ; Carbon ; Central Europe ; Climate ; Coal Tar ; Colloidal Materials ; Europe ; Germany ; Hydrocarbons ; Lysimeters ; Munich Germany ; Nonaqueous Phase Liquids ; Organic Carbon ; Organic Compounds ; Petroleum Products ; Pollution ; Polycyclic Aromatic Hydrocarbons ; Soil Pollution ; Soils ; Solutes ; Suspended Materials ; Unsaturated Zone ; Upper Bavaria Germany;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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  • 3
    Language: English
    In: Vadose Zone Journal, 2006, Vol.5(1), p.469
    Description: The fate of polycyclic aromatic hydrocarbons (PAH) is known to depend on the release and redistribution of dissolved organic carbon (DOC) and particles. We studied the release of PAH, DOC, and particles up to a size of 200 microns with column outflow experiments using gravelly soil material. The material was collected at an abandoned industrial tar-oil contaminated site. To detect rate-limited release, the experiments were performed at two different mean pore water velocities, while multiple flow-interrupts were imposed. Effluent was analyzed for DOC, pH, electrical conductivity, turbidity, and particles larger than 〈0.7 microns after filtration. The 16 Environmental Protection Agency PAHs were analyzed in the filtrate and in the particle fraction. Upon onset of flow large initial effluent concentrations were found for DOC, particles, turbidity, and particle-associated PAHs. This so-called first-flush export levelled off after a few pore volumes had been exchanged. The release of DOC and PAH in the filtrate was strongly rate limited. Measured PAH concentrations differed markedly from those calculated by Raoult's law. Equilibrium dissolution seems to be of minor importance for the studied materials. Particle release as well as the release of particle-associated PAHs was dependent on the flow velocity. However, effluent concentrations decreased significantly during no-flow conditions due to sedimentation of larger particles. At the lower flow velocity, 33% of the total PAHs were found in the retentate (66% in the filtrate), while at the higher flow velocity the amount of particle-associated PAH increased to 42%. The comparison of the PAH pattern in the filtrate and the retentate suggests that PAH transport takes place predominantly in the form of small NAPL droplets or fragments. The strong correlation of DOC with the PAH in the filtrate implies a marked influence of DOC on PAH transport. From these findings we conclude that PAH release and transport at contaminated sites is affected by three processes, i.e., (i) first-flush export, (ii) detachment of particle-associated PAHs due to hydraulic mobilization and (iii) the rate-limited release of particles and particle/colloid-associated PAHs. ; Includes references ; p. 469-479.
    Keywords: Soil Transport Processes ; Industrial Wastes ; Nonaqueous Phase Liquids ; Dissolved Organic Carbon ; Gravelly Soils ; Soil Pollution ; Polycyclic Aromatic Hydrocarbons;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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