Assessment of Physical Leaching Processes of Some Elements in Soil upon Ingestion by Continuous Leaching and Modeling

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• 作者：Michael P. Beeston ; Andrej Pohar ; Johannes T. van Elteren ; Igor Plazl ; Zdenka lejkovec ; Marjan Veber ; Hylke J. Glass
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：August 15, 2010
• 年：2010
• 卷：44
• 期：16
• 页码：6242-6248
• 全文大小：301K
• 年卷期：v.44,no.16(August 15, 2010)
• ISSN：1520-5851

文摘

The physical processes controlling the desorption of some elements (B, Cd, Co, Mn, Ni, and Sr) from soils in a continuous leaching system representing the human stomach are investigated here by fitting experimental leaching data to a mathematical particle diffusion model.

Soil samples (50 mg) from Cornwall, UK, contained in a flow-through extraction chamber (ca. 6.5 mL) were intimately contacted with artificial gastric solution at various flow rates (0.42−1.42 mL min⁻¹) for up to ca. 4 h, followed by analysis of the fractions collected with inductively coupled plasma mass spectrometry (ICP-MS). The leaching profiles of the various elements were fitted to a mathematical model incorporating two mass transfer processes (liquid film diffusion and apparent solid phase diffusion) to determine the effective external mass transfer coefficient (β) and the apparent intraparticle soil diffusion coefficient (D_a). A system of partial differential equations was solved numerically with a finite difference discretization of the computational domain allowing the rate limiting physical desorption process(es) for each element to be determined.

The (thermodynamic) driving force of the leaching process is defined by the distribution coefficient (K_d0) between soil and leachant. Although the K_d0 values investigated are very similar (ca. 6−15 L kg⁻¹) for the elements studied with the exception of B (ca. 2.7 L kg⁻¹), the leaching profiles are very different due to diffusion-limited processes. The elements may be classified as limited by β (B, Sr, and Cd), by D_a (Co, and Mn) or by β and D_a (Ni). This results in quantifiable parameters for the liability of elements in soil upon ingestion which may be implemented in future risk assessment protocols.