Metabolism of chlorinated phenols by Lemna gibba, duckweed

The toxicity and metabolism of phenol and a series of chlorinated phenols, 4-chlorophenol to pentachlorophenol, in axenically grown Lemna gibba were studied. It was found that the toxicities of the phenols tended to increase with increasing number of chlorine substituents on the phenol ring. Over relatively short incubation periods (< 7 days), the plants metabolized each of the phenols in the same manner, producing compounds that were more polar than the corresponding phenol from which they were derived. The plant-produced metabolites of phenol, 2,4-dichlorophenol and 2,4,5-trichlorophenol were isolated, purified and their structures were identified by high field NMR and chemical ionization MS to be beta-glucoside conjugates. It was further shown, by GC/MS, that over longer incubation periods (ca 20 days), the plants were able to progressively dechlorinate the phenols. While conversion of the chlorinated phenols to their corresponding phenyl glucosides results in compounds that are more water-soluble and less toxic to the plants than were the parent phenols, the potential for regeneration of the original phenols, as a result of low pH or enzymatic cleavage of the glucoside, remains. In contrast, reductive dechlorination represents a real detoxification since the toxicity of the chlorinated phenols decreases with decreasing number of chlorine substituents. It is possible therefore, that the ability of duckweed to perform reductive dechlorination can be exploited as part of a remediation technology.