Metabolic Fate of Monuron and Diuron in Isolated Leaf Discs

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Abstract
Leaf discs of cotton (Gossypium hirsutum L.), broadleaf plantain (Plantago major L.), soybeans (Glycine max Merrill), and corn (Zea mays L.) were incubated 1 hr in aqueous solutions of methyl- or ring-labeled 3-(p-chlorophenyl)-l,l-dimethylurea-14C (monuron) or carbonyl-labeled 3-(3,4-dichlorophenyl)-l,l-dimethyl-urea-14C (diuron). The loss of herbicide and formation of metabolites were determined at approximately 1-hr intervals up to 7 hr. Cotton leaf discs actively metabolized monuron to l-(p-chlorophenyl)-3-methylurea (monomethylmonuron), l-(p-chlorophenyl)urea (p-chlorophenylurea), and p-chloroaniline. Plantain leaf discs strongly metabolized diuron to l-(3-,4-dichlorophenyl)-3-methylurea (monomethyldiuron) and l-(3,4-dichlorophenyl)urea (3,4-dichlorophenylurea). Plantain degraded monuron less actively than diuron and cotton degraded diuron less rapidly than monuron. In soybean leaf discs, metabolism did not progress beyond the first demethylation, and corn leaf discs were unable to metabolize the herbicides in short-term studies.