Biodegradation of pentachlorophenol and its commercial formulation

Abstract

Biodegradation processes for pentachlorophenol (PCP) and a commercial PCP formulation were evaluated to delineate factors limiting the rate of PCP degradation in the aquatic environment. Analyses of the data on PCP disappearance and chloride ion release, as well as gas chromatography and UV-VIS (ultra-violet and visible spectroscopy) spectra of the fermentor broth strongly indicate that the bacterial culture acted on PCP by completely stripping off all the chloride ions from a molecule of PCP, rather than following the normal pattern of removing only one chloride ion at a time. The haloaromatic ring structure of PCP was completely broken down, and not channeled into the unproductive meta-cleavage pathway. Despite repeated transfers of the bacterial culture, an initial lag phase in PCP biodegradation was apparent in all experiments and was followed by a steady state, nearly linear rate of PCP degradation. Thus in the aquatic environment the biodegradation rate of a persistent contaminant is more likely to be regulated by whether or not this compartment has been previously subjected to a long or continuous exposure to a particular chemical. First-order kinetics alone cannot be used to predict accurately the fate of a persistent chemical in the environment, because of the inability of such a simple equation to accommodate the effects of rate-limiting factors such as the length of adaptation period on the overall biodegradation rate of a contaminant. For this reason, factors that may influence a chemical's biodegradability in the natural environment must be considered in the design of laboratory biodegradation experiments.