Geoscience Reference
In-Depth Information
The upper part of the subsurface is characterized by enhanced biological
activity. Therefore, contaminant transformation in this zone proceeds mainly by
microbial processes, which are often faster than chemical ones. In the deeper
subsurface, biological activity often is reduced and, therefore, degradation
proceeds abiotically, at a much slower rate. It should be emphasized, however,
that contaminant transformation is related mainly to the formation of metabolites
with properties different from those of the parent material (sometimes more polar,
more soluble in water, and even more toxic), which may reach the groundwater.
Although abiotic and biologically mediated contaminant transformation may occur
simultaneously in the subsurface aqueous solution and in the solid-liquid interface,
they are discussed separately for didactic purposes.
Environmental conditions cause changes in the initial properties of organic and
inorganic contaminants and affect their persistence in the subsurface. Relevant
external factors include temperature and solar radiation, while the principal
subsurface properties include water chemistry, the surface properties of the solid
phase, and bioactivity. In Part V, we focus on research findings that illustrate
abiotic and biologically mediated degradation of individual contaminants occur-
ring in the liquid phase and at the solid-liquid interface, as well as examples of
multiple-component contaminant transformation.
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