SREL Reprint #2661




Geochemical and Hydrological Reactivity of Heavy Metals in Soils

John C. Seaman, M. Guerin, B. P. Jackson, P. M. Bertsch, and J. F. Ranville

Surface chemical reactions play a major role in controlling contaminant fate and transport in the environment. To better understand such processes, one often resorts to well-defined laboratory studies using mineral and organic standards or synthetic analogs as surrogates for the more complicated natural systems, either focusing on homogeneous systems or assuming the additivity of the major system components. In reality, such mixtures may display changes in particle size, surface area, and reactivity that differ from the individual surrogate components or the natural diagenetic environment that the investigator wishes to emulate. For example, natural colloids observed in the electron microscope often appear irregularly eroded or coated with other mineral or organic phases and rarely resemble synthetic or pure mineral particies. Complex mixtures and the presence of "surface coatings" or surface heterogeneities, often representing only a small fraction of the total suspension or matrix composition, can alter the reactivity of the more abundant components in ways that are difficult to quantify or predict based on the idealized systems. Even common lab practices, such as homogenization and air-drying of soil materials can alter surface reactivity more than generally recognized.
In recent years the study of mobile soil and groundwater colloids has received considerable attention because of concerns that such a vector may enhance the mobility of strongly sorbing contaminants, a process that is often referred to as "facilitated transport." However, our ability to predict colloid movement and deposition is often confounded by the complexities of surface interactions in such dynamic, unstable systems. The lack of universally accepted analytical techniques and failure to realize instrumental limitations have made it difficult to compare and critically evaluate the results of different studies. Artifacts associated with groundwater sampling, filtration, and storage, and the dilute nature of most soil and groundwater suspensions further hamper characterization efforts. . . .

SREL Reprint #2661

Seaman, J. C., M. Guerin, B. P. Jackson, P. M. Bertsch, and J. F. Ranville. 2003. Analytical techniques for characterizing complex mineral assemblages: mobile soil and groundwater colloids. pp. 271-309 In: H. M.Selim and W. L. Kingery (Eds.). Geochemical and Hydrological Reactivity of Heavy Metals in Soils. Lewis Publishers, Boca Raton, FL.

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