| Popis: |
To become “available” to a target organism, organic xenobiotics in subsurface environments have to satisfy at least one of a number of conditions. They have to be able to migrate themselves to the immediate vicinity of the organism. Alternatively, extracellular enzymes or surfactants released by the organism have to reach the xenobiotic molecules, wherever they are located, and the products of their interaction have to migrate back to the organism. In any of these situations, chemical compounds (xenobiotic molecules, exoenzymes, biosurfactants, and reaction products) are moving in the liquid phase within the pores of the subsurface material. During this transport, the molecules in motion are subjected to an array of concurrent physical processes (e.g., dispersion, mass flow of the liquid phase, immiscible displacement), all of which can affect significantly the motion of the molecules, and ultimately how available the xenobiotics will be to the target organism. The present chapter provides an overview of these different physical processes. The focus is purposedly on the physics of the processes rather than on their mathematical description, in an attempt to keep this chapter accessible to scientists who come to the bioavailability debate from the biology side and may therefore not be entirely familiar with the mathematical tools traditionally used in the literature on transport phenomena in natural porous media. |
