Toxicity and metabolism of 2,4‐dichlorophenol by the aquatic angiosperm Lemna gibba

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Abstract
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 EC10 and EC50 were 2.5 and 9 2 μM, respectively. Metabolism of 2,4‐dichlorophenol was monitored by incubation of the plants with radiolabeled substrate, and periodic sampling and analysis by reversed‐phase 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‐14C]‐2,4‐DCP. The growth medium was lyophihzed and then mixed with the plants, extracted, and analyzed using reversed‐phase HPLC, followed by scintillation counting of the fractions The major metabolite was isolated and identified as 2,4‐dichlo‐rophenyl‐β‐D‐glucopyranoside by high‐field NMR and MS. The structure of the metabolite was confirmed by synthesis and by enzymatic cleavage of the β‐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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