Uptake and Metabolism of Dichlobenil by Emersed Aquatic Plants

[¹⁴C]Nitrile-labeled 2,6-dichlorobenzonitrile (dichlobenil) was readily absorbed by the roots of the emersed aquatic plants, alligator weed (Alternant hera philoxeroides) and parrot feather (Myriophyllum brasiliense) and was translocated to the shoots. The concentration of the ¹⁴C was greater in parrot feather than in alligator weed 24 hr after treatment. The roots of the alligator weed contained a considerably greater amount of ¹⁴C than the shoots, whereas in parrot feather, a major portion of the absorbed ¹⁴C was present in the shoot. [¹⁴C]Dichlobenil leaked from the roots of alligator weed but not from those of parrot feather. Alligator weed was not able to metabolize dichlobenil; on the contrary, parrot feather transformed the herbicide into several metabolites. The major metabolite resulting from the transformation was 3-hydroxy-2,6-dichlorobenzonitrile; small amounts of 2,6-dichlorobenzamide and 2,6-dichlorobenzoic acid were also present. A significant amount of radioactivity (14-18% of 14C in the shoot) was present as highly polar, unknown metabolites. The tolerance of parrot feather to dichlobenil appears to be related to its ability to metabolize the herbicide.