Degradation of organic contaminants in soils

1 Specific microbes or enzymes required for degradation may not be present in the soil. 

2 Unusual or complex substitutions in a molecule (e.g. chlorine (Cl), bromine (Br) or fluorine (F)), or unusual bonds or bond sequences, may confuse microorganisms that would otherwise recognize the molecule as a substrate (Box 4.16). 

3 A high degree of aromaticity (see Section 2.7), i.e. strongly bonded structures based on a number of fused benzene rings, results in molecules that are difficult to break down. 

4 Large, complex and heavy molecules tend to be less water soluble, and therefore are physically unavailable to microorganisms that use intracellular degradation processes. 

Biodegradation of organic contaminants can be carried out by a single microbial species in pure cultures, but in nature the efforts of a mixture of microbes (a consortium) are usually required. The degradation process ranges from only minor structural changes to the parent molecule, known as primary degradation, to complete conversion to mineral constituents, for example C02 or H20, and termed mineralization  

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