[Transformation of xenobiotics by soil microorganisms and their potential distribution]

Xenobiotics, i.e., unnaturally occurring organic substances, become transformed in soils, waters and ground water aquifers primarily by co-metabolism or by physico-chemical processes. The persistence of both xenobiotics and natural substances, i.e., time required for a 95% disappearance of the original compounds, is dependent on the chemical and physical characteristics of a compound itself (its molecular recalcitrance), on soil properties and conditions, and on the relationships of these factors. Among the specific factors which influence the persistence of individual compounds belong both natural and anthropogenic "non-physiological" characteristics and structures. Naturally occurring compounds become transformed metabolically, those with a xenobiotic character mainly co-metabolically. The degradation kinetics for both types of compounds have an exponential character, and according to a semi-logarithmic figure, it is a first order function (i.e., mineralization or transformation have a linear character). The co-metabolic processes depend closely on the concentration of the given compound in soil solution as well as on the general microbial activity. Metabolically utilizable compounds may serve microorganisms as sources of C, N, and eventually also of P and energy, after the necessary enzymes have become induced and synthetized. Co-metabolical compounds may not have these functions or microorganisms may require a long period to become adapted to them. In general, all means which support the microbial activity, may also support the co-metabolical transformations in the soil. This is especially true for aeration and manuring of soil both of which stimulate unspecifically the proliferation and activity of microorganisms, and indirectly also a co-metabolism of xenobiotics.