The Influence of Vertical Sorbed Phase Transport on the Fate of Organic Chemicals in Surface Soils

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• 作者：Michael S. McLachlan ; Gertje Czub ; and Frank Wania
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：November 15, 2002
• 年：2002
• 卷：36
• 期：22
• 页码：4860 - 4867
• 全文大小：358K
• 年卷期：v.36,no.22(November 15, 2002)
• ISSN：1520-5851

文摘

Gaseous exchange between surface soil and theatmosphere is an important process in the environmentalfate of many chemicals. It was hypothesized that thisprocess is influenced by vertical transport of chemicalssorbed to soil particles. Vertical sorbed phase transport insurface soils occurs by many processes such asbioturbation, cryoturbation, and erosion into cracksformed by soil drying. The solution of the advection/diffusion equation proposed by Jury et al. to describeorganic chemical fate in a uniformly contaminated surfacesoil was modified to include vertical sorbed phasetransport. This process was modeled using a sorbedphase diffusion coefficient, the value of which was derivedfrom soil carbon mass balances in the literature. Theeffective diffusivity of the chemical in a typical soil wasgreater in the modified model than in the model withoutsorbed phase transport for compounds with log K_OW > 2 andlog K_OA > 6. Within this chemical partitioning space, therate of volatilization from the surface soil was larger in themodified model than in the original model by up to afactor of 65. The volatilization rate was insensitive to thevalue of the sorbed phase diffusion coefficient throughoutmuch of this chemical partitioning space, indicating thatthe surface soil layer was essentially well-mixed and thatthe mass transfer coefficient was determined by diffusionthrough the atmospheric boundary layer only. When thisprocess was included in a non-steady-state regionalmultimedia chemical fate model running with a genericemissions scenario to air, the predicted soil concentrationsincreased by up to a factor of 25, while the air concentrationsdecreased by as much as a factor of ~3. Verticalsorbed phase transport in the soil thus has a majorimpact on predicted air and soil concentrations, the stateof equilibrium, and the direction and magnitude of thechemical flux between air and soil. It is a key processinfluencing the environmental fate of persistent organicpollutants (POPs).