Fate of the herbicides mecoprop, dichlorprop, and 2,4-D in aerobic and anaerobic sewage sludge as determined by laboratory batch studies and enantiomer-specific analysis

Aerobic degradation experiments with the racemic mixtures of mecoprop and d ichlorprop revealed that activated sludge collected from the aeration tank of a municipal waste water treatment plant degraded both enantiomers of mec oprop and dichlorprop within 7 days, albeit in an enantioselective manner; the (S) enantiomers were preferentially degraded. Mecoprop, dichlorprop, an d 2,4-D were completely metabolized under aerobic conditions, as shown by t he 86-98% elimination of dissolved organic carbon. Under anaerobic conditio ns, the concentration of 2,4-D decreased exponentially with a first-order r eaction rate constant of 0.24 per day and without a lag-phase. After an inc ubation time of 17 days, 2,4-D was completely removed. 2,4-Dichlorophenol w as the main metabolite of anaerobic 2,4-D degradation; only traces of 4-chl orophenol were detected. In contrast, the chiral phenoxypropionic acid herb icides mecoprop and dichlorprop persisted under anaerobic conditions during 49 days of incubation.