The toxicity and metabolism of 2,4-dichlorophenol, with regard to the aquatic macrophyte Lemna gibba (duckweed), have been studied Toxicity is described in terms of the effect of 2,4-dichlorophenol(2,4-DCP) on the vegetative reproduction of duckweed over a 10-d growth period, the EClO and EC5O were 2.5 and 9 2 pM, respectively. Metabolism of 2,4-dichlorophenol was monitored by incubation of the plants with radiolabeled substrate, and periodic sampling and analysis by reversedphase HPLC of the plant growth medium Depending on the growth conditions, up to 95% of the 2,4-DCP was metabolized over a 6-d growth period. To analyze the metabolites, the plants were grown in the presence of sublethal concentrations of [U-I4C]-2,4-DCP. The growth medium was lyophilized and then mixed with the plants, extracted, and analyzed using reversedphase HPLC, followed by scintillation counting of the fractions The major metabolite was isolated and identified as 2,4-dichlorophenyl-~-~-glucopyranoside by high-field NMR and MS. The structure of the metabolite was confirmed by synthesis and by enzymatic cleavage of the P-glucosidic linkage to afford 2,4-DCP. An important consequence of conjugate formation IS the masking of the presence of 2,4-DCP to the usual analytical techniques used for its detection and quantitation. This finding is probably applicable to other contaminants and organisms.

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Abstract-The toxicity of a series of chlorinated phenols, from phenol to pentachlorophenol, was determined using frond reproduction in aseptically grown Lemna gibba. The toxicities of the phenols tended to increase as the number of chlorine substituents on the phenol ring increased. The plants metabolized each of the phenols in the same manner producing metabolites that were more polar than their parent compounds. The metabolite for 2,4,5-trichlorophenol was isolated and identified by nuclear magnetic resonance spectroscopy and chemical ionization mass spectroscopy. The structural identity was confirmed by comparison with synthetic material as 2,4,5-trichlorophenyl-␤-D-glucopyranoside. These results, together with previously published results, suggest that conjugation with D-glucose is a stereotypic response of duckweed to challenge by phenol and chlorinated phenols.

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 β-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.Phenol and the 19 chlorinated phenols are used extensively as pesticides, herbicides, fungicides, bactericides, etc. In addition, significant amounts of chlorophenols are generated as a result of the bleaching process in paper mills (/), the chlorination of drinking water and the incineration of waste materials (2). The magnitude of the problem 3