isolated (USEPA, 1986). The enzymes necessary for PCP

degradation appeared to be inducible. Steiert et al.

(1987) demonstrated that a suspension of cells grown in the

presence of 2,4,6-trichlorophenol or 2,3,5,6-tetrachloro-

phenol did not show a lag period for degradation of 2,4,6-

trichlorophenol, 2,3,5,6-tetrachlorophenol or PCP,

indicating that one enzyme system can be induced for the

biodegradation of multiple compounds. Chu and Kirsch (1973)

and Karns et al. (1983) also reported similar observations.


3.3.6 Pentachlorophenol Degradation Mechanisms


 Pentachlorophenol is very resistant to biodegradation

and may produce less chlorinated phenols as the degradation

products, therefore, its degradation pathway deserves more

study. Three significant mechanisms appear to account for

the biological degradation of PCP in soils: (1) reductive

dechlorination; (2) oxidative dechlorination; (3)

methylation. Conceivably an aggregate of microorganisms

should be more efficient in mineralizing phenolic compounds

(to CO2) than any of the pure cultures. The structural

formulas of those involved compounds are presented in Figure

3-1.


 Reductive dechlorination. Bacteria such as

Flavobacterium sp. can utilize PCP as a sole source of

carbon and energy. Thus reductive dechlorination under

anaerobic conditions forms less chlorinated phenolic