Biodegradation is a very important property for toxic chemicals, because if the biodegradation rate is high, the concentration and thereby the toxic effect will be reduced rapidly, while very persistent chemicals will maintain their toxic effect for a very long time.
The range of biodegradation rates is very wide -from readily biodegraded compounds as for instance monomer carbohydrates, low molecular alcohols, and acids to very refractory compounds that have a biological half-life of several years as for instance DDT and dioxins.
In principle, biodegradation is carried out by many organisms, but in most cases we consider microbiological biodegradation for the most important from an environmental point of view. The biodegradation rates in water and in soil by microorganisms are of particularly interest. It is, however, not a characteristic value that can be used as a constant for a compound, because the biodegradation is strongly dependent on the conditions for the microorganisms in the water and in the soil. The biodegradation is furthermore dependent on the presence or absence of oxygen; it means aerobic or anaerobic conditions. Environmental degradation rates can, however, be found in the literature and in environmental handbooks, but they are always indicated as ranges. The biodegradation rate of the same compound in water or soil may vary orders of magnitudes from one type of aquatic or terrestrial ecosystem to the next. The half-life of methyl methacrylate in soil, to mention a typical example, is in the literature indicated as 168-672 h.
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