Influence of alternative electron acceptors on the anaerobic biodegradability of chlorinated phenols and benzoic acids

Abstract

Nitrate, sulfate, and carbonate were used as electron acceptors to examine the anaerobic biodegradability of chlorinated aromatic compounds in estuarine and freshwater sediments. The respective denitrifying, sulfidogenic, and methanogenic enrichment cultures were established on each of the monochlorinated phenol and monochlorinated benzoic acid isomers, using sediment from the upper (freshwater) and lower (estuarine) Hudson River and the East River (estuarine) as source materials. Utilization of each chlorophenol and chlorobenzoate isomer was observed under at least one reducing condition; however, no single reducing condition permitted the metabolism of all six compounds tested. The anaerobic biodegradation of the chlorophenols and chlorobenzoates depended on the electron acceptor available and on the position of the chlorine substituent. In general, similar activities were observed under the different reducing conditions in both the freshwater and estuarine sediments. Under denitrifying conditions, degradation of 3and 4-chlorobenzoate was accompanied by nitrate loss corresponding reasonably to the stoichiometric values expected for complete oxidation of the chlorobenzoate to CO2. Under sulfidogenic conditions, 3and 4-chlorobenzoate, but not 2-chlorobenzoate, and all three monochlorophenol isomers were utilized, while under methanogenic conditions all compounds except 4-chlorobenzoate were metabolized. Given that the pattern of activity appears different for these chlorinated compounds under each reducing condition, their biodegradability appears to be more a function of the presence of competent microbial populations than one of inherent molecular structure.

Biotransformation of 3,5‐dibromo‐4‐hydroxybenzonitrile under denitrifying, Fe(III)‐reducing, sulfidogenic, and methanogenic conditions

“…In contrast, 3,5-dibromo-4-hydroxybenzoate, the aerobic metabolite of bromoxynil, was degraded under all four anaerobic conditions tested. This is consistent with previous studies with halogenated benzoic acids, specifically their utilization under denitrifying conditions [15,[27][28][29]. No intermediates were detected, and thus the biotransformation pathway of 3,5-dibromo-4-hydroxybenzoate was not elucidated.…”

“…Very little is known about transformation of bromoxynil under anaerobic conditions and how biodegradability is affected by different redox conditions. Previous studies have shown that many halogenated aromatic compounds can be degraded under nitrate-reducing, Fe(III)-reducing, sulfidogenic, selenate-reducing, and methanogenic conditions [13][14][15][16][17]. For example, transformation of the herbicide 2,4-dichlorophenoxyacetic acid has been demonstrated under anaerobic conditions both in the presence and absence of sulfate [13].…”

Anaerobic mineralization of pentachlorophenol (PCP) by combining PCP‐dechlorinating and phenol‐degrading cultures

“…For this reason, it is desirable to completely mineralize PCP and chlorophenols under anaerobic conditions. In the past two decades, the anaerobic oxidation of phenol and monochlorinated phenols (possible PCP anaerobic reductive dechlorination products) has been described under denitrifying, sulfate-reducing, iron-reducing, or methanogenic conditions (Bae et al, 2002;Evans and Fuchs, 1988;Häggblom and Young, 1993;Kazumi et al, 1995). A number of pure phenol-degrading cultures that use nitrate or sulfate as electron acceptors have been isolated (Bak and Widdel, 1986;Boopathy, 1995;Tschech and Fuchs, 1987).…”

Biodegradation of resorcinol and catechol by denitrifying enrichment cultures

“…Denitrifying enrichment cultures were established under strictly anaerobic conditions according to the method of Häggblom et al [15] using an inoculum from the Arthur Kill tidal strait in New Jersey, USA. This site is heavily impacted by petroleum hydrocarbons and other anthropogenic contaminants.…”