Reductive Dechlorination of the Pesticides 2,4‐D, 2,4,5‐T, and Pentachlorophenol in Anaerobic Sludges

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.