As mentioned, aromatic hydrocarbons have a six-member ring structure in which single and double carbon bonds alternate. This ring structure tends to be stable, so chemical reactions tend to result in the substitution of hydrogen atoms for another atom or functional group. Five of these compounds are hydrocarbons (benzene, ethylbenzene, toluene, phenol, and 2,4-dimethyl phenol) and the rest are halogenated or nitrogenated derivatives of benzene, toluene, and phenol. Moore and Ramamoorthy110 reviewed the behavior of monocyclic aromatics and phenols in natural waters.
Adsorption may be important for most of the compounds in this group, whereas hydrolysis may not be a significant process except for pentachlorophenol. Tabak and colleagues111 found that significant degradation with rapid or gradual adaptation occurred for 15 of a listed 23 compounds. Anaerobic degradation has been reported for five compounds in this group (benzene, ethylbenzene, phenol, 2-chlorophenol, and 2,4-dichlorophenol). Chapman113 discusses in some detail the reaction sequence used for the bacterial degradation of phenolic compounds; Gibson and Subramanian114 provide a general review of microbial degradation of aromatic hydrocarbons; and Reinke115 reviews microbial degradation of halogenated aromatics.
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