ENEX Environmental Fate

(a message field)

The ENEX field is displayed in records but is not searchable and contains the following text:

ENVIRONMENTAL FATE (USE CODE ZENE).

Its purpose is to act as a record section delimiter. The Environmental Fate superfield (ZENE) is associated with this message field.

Degradation data are used to assess the persistence of a chemical substance in the environment, in water, soil and air. If the substance does not persist, information on the degradation products is also desirable. Intermediates may be either harmless or toxic substances which may themselves persist. Degradation occurs via two major routes, microbial degradation utilising micro-organisms from a variety of habitats and decomposition by chemical methods.

Microbial degradation is associated with the production of elemental carbon, nitrogen and sulfur from complex molecules. Standard biodegradation tests estimate the importance of microbial biodegradation as a persistence factor. Most tests use relatively dense microbial populations adapted to the compound being studied. Rapid degradation results in these tests imply that the compound will degrade under most environmental conditions, although specialised environments where degradation would not occur can exist. Compounds which are not readily degradable are likely to persist over a wide range of environmental situations. Biodegradation in the environment is difficult to assess because the natural environment is highly variable and almost impossible to reproduce under laboratory conditions. This should be given due consideration when assessing the data in DOSE.

Chemical degradation processes include photolysis, hydrolysis, oxidation and removal by reversible/irreversible binding to sediment. Factors which influence degradation rates: duration of exposure; temperature; pH; salinity; concentrations of test substance, microbial populations, and other nutrients; must also be taken into account.

Due care must also be given when metabolism results in the production of substances that are more toxic than their parents.