A systematic study of the aerobic and anaerobic biodegradation of 18 chlorophenols and 3 cresols

Aerobic and anaerobic biodegradation processes for 18 chlorophenols and 3 cresols were systematically evaluated under a controlled laboratory system, using an acclimatized mixed culture of pentachlorophenol-degrading bacteria. The biodegradation processes were characterized based on the lag time (time in hours required to observe 10% degradation of the added test chemical against the control), t90 (time in hours required to degrade 90% of the added test chemical). The results indicate that nonspecific generalizations such as the degree of a chemical's chlorination cannot be reliably used to predict the persistence of chemicals in the environment. On the other hand, a systematic analysis of the molecular structure of analogues and related chemicals, in particular the positions of chlorine substitution on the phenolic ring, appears to be the logical approach to provide useful information for predicting the environmental fate of existing and new chemicals. The substitution effect in dictating a chlorophenol's biodegradability appears to follow in the descending order of 2,4 > 4 > 3,5 > 2,6 > 3, or 5, or 2. Microbial acclimation was found to be a distinct feature associated with the biodegradation of toxic substances and thus having the potential to be utilized in characterizing the biodegradation process of such chemicals. Ignorance of this acclimation period in kinetics study could nullify the usefulness of using mathematical models in predicting the environmental fate of chemical compounds.