Persistence of soil-bound chemicals in soils may be attributed to either their recalcitrance (i.e., soil microorganisms lack the enzymatic machinery required to facilitate transformation of the chemical) or their limited bioavailability (i.e., the chemicals are not present in a phase that is directly accessible by degrading microorganisms). Bioavailability limitations may include (1) concentration-limited bioavailability (i.e., where low solubility of the chemical prevents its rapid transformation), (2) mass transfer-limited bioavailability (i.e., where desorption or dissolution rates from a soil or nonaqueous phase to the aqueous phase are slower than biotransformation rates from the aqueous phase), and (3) mass transport-limited bioavailability (i.e., where the heterogeneity of the soil environment is significant enough to require transport of a chemical molecule across a significant spatial dimension in order to reach the vicinity of a microcolony of degrading organisms). Finally, the relationship between microbiology and soil physico-chemistry will be shown by illustrating some of the novel strategies employed by bacteria to modify the bioavailability of soil-bound chemicals.

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Confinement and Remediation of Environmental Hazards

1999-2000 Reactive Flow and Transport Phenomena