No 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.

From polluted river sediment, two bacterial species were isolated which utilized p‐cresol as the sole source of carbon when grown in coculture under nitrate‐reducing conditions. One species, PC‐07, metabolized p‐cresol (pCr) anaerobically to p‐hydroxybenzoate (pOHB), which in turn was further metabolized by the second isolate, PB‐04. The PC‐07 isolate was unable to degrade and utilize pOHB, and PB‐04 was unable to utilize pCr, thereby demonstrating a syntrophic relationship for pCr utilization under anaerobic conditions. Nitrate served as external electron acceptor for both microorganisms under anaerobic conditions and was reduced via NO2− and N2O to N2. pCr, therefore, appears to be metabolized to ring fission products via the formation of pOHB under nitrate reducing conditions, with the metabolism being mediated by a 2‐member microbiol food chain.