Rhizodegradation, which is also variously described as phytostimulation or enhanced rhizospheric biodegradation, refers to the biodegradation of contaminants in the soil by edaphic microbes enhanced by the inherent character of the rhizosphere itself. This region generally supports high microbial biomass and consequently a high level of microbiological activity, which tends to increase the speed and efficiency of the biodegradation of organic substances within the rhizosphere compared with other soil regions and microfloral communities. Part of the reason for this is the tendency for plant roots to increase the soil oxygenation in their vicinity and exude metabolites into the rhizosphere. It has been estimated that the release of sugars, amino acids and other exudates from the plant and the net root oxygen contribution can account for up to 20% of plant photosynthetic activity per year (Foth 1990), of which denitrifying bacteria, Pseudomonas spp., and general heterotrophs are the principal beneficiaries.In addition, mycorrhizae fungi associated with the roots also play a part in metabolising organic contaminants. This is an important aspect, since they have unique enzymatic pathways that enable the biodegradation of organic substances that could not be otherwise transformed solely by bacterial action. In principle, rhizodegradation is intrinsic remediation enhanced by entirely natural means, since enzymes which are active within 1 mm of the root itself, transform the organic pollutants, in a way which, clearly, would not occur in the absence of the plant. Nevertheless, this is generally a much slower process than the previously described phytodegradation.