duced structural alteration in the organic chemical. Ultimate biodegradation refers to the degradation of the organic chemical into carbon dioxide, oxygen, water, and other inorganic products.

Primary biodegradation of an organic chemical can generate a variety of degradation products that can contaminate groundwater. For example, the degradation of trichloroethylene (TCE) can lead to dichloroethylenes (DCEs), dichloroethanes (DCAs), vinyl chloride, and chloroethane (Dragun 1988b; Alexander 1981; Goring and Hamaker 1972). The degradation of cyclic hydrocarbons can lead to aliphatic hydrocarbons, and aliphatic hydrocarbons can be converted in successive reactions into alcohols, aldehydes, and then aliphatic acids (Tabak et al. 1981).

The biodegradation of many organic chemicals is generally first-order with respect to the organic chemical's concentration (Scow 1982). As a result, the biodegradation rate constant can be calculated with use of the following first-order equation as in hydrolysis:

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