Reductive Dechlorination of the Pesticides 2,4-D, 2,4,5-T, and Pentachlorophenol in Anaerobic Sludges
1985
Mikesell, Mark D. | Boyd, Stephen A.
The degradation of seven chlorinated aromatic compounds in anaerobic sewage sludge from three Michigan communities was examined. The compounds tested were 2,4-D (2,4-dichlorophenoxy acetic acid), 2,4,5-T (2,4,5-trichlorophenoxy acetic acid), PCP (pentachlorophenol), 2,4,6-trichlorophenol, and 2-, 3-, and 4-chlorophenol. All of the compounds tested were degraded in one or more of the sludges during a 70-d incubation period. Overall, 4-chlorophenol was the most persistent compound tested followed by 3-chlorophenol. The most rapid degradative reactions were cleavage of the ether linkage of the phenoxy acetic acid herbicides 2,4-D and 2,4,5-T, and the removal of Cl atoms ortho to the phenolic OH group of the chlorophenols. The initial products of 2,4-D and 2,4,5-T degradation were 4-chlorophenol and 2,4,5-trichlorophenol. Reductive dechlorination of 2,4,5-trichlorophenol (produced from 2,4,5-T) gave 3,4-dichlorophenol and 4-chlorophenol which were the final products of 2,4,5-T degradation. Dechlorination of PCP gave 3,4,5-trichlorophenol as the initial transformation product, and further dechlorination gave 3,5-dichlorophenol as the final product of PCP degradation. The Jackson sludge had the greatest capacity to degrade the compounds tested. With the exception of 3- and 4-chlorophenol, all other compounds tested were completely degraded in 7 to 14 d in the Jackson sludge. Mason and Adrian sludges were similar in their degradative pathways overall, but significantly less active than the Jackson sludge.
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