Degradation and environmental fate of 1-(2,6-difluorobenzoyl)-3-(4-chlorophenyl)urea

Abstract

Radiolabeled preparations of the insect growth regulator PH-6040 were evaluated for degradation in a laboratory model ecosystem and after exposure to sheep microsomes, Pseudomonas, soil, and ultraviolet light. The parent compound was found to be moderately stable but was not highly concentrated through food chains or by direct ab-sorption from water. The degradative pathways were almost entirely through cleavage between the carbonyl and amide groups of the urea bridge to give 2,6-difluorobenzamide and 2,6-difluorobenzoic acid, 4-chlorophenylurea, and 4-chloroaniline.The insect growth regulator l-(2,6-difluorobenzoyl)-3-(4-chlorophenyl)urea (PH-6040, OMS-1804) has novel and highly specific activity against a wide variety of insects (Neal, 1974; Wellinga et al., 1973a,b;Jakob, 1973;Van Daalen et al., 1972). The compound is very effective against mosquito larvae, inhibiting growth and development of fourth instar Culex pipiens quinquefasciatus larvae at concentrations of 0.0001-0.001 ppm. The biochemical lesion is suggested to result from the inhibition of chitin synthesis with a resulting defect in endocuticular deposition (Post and Vincent, 1973). As a result, the insect seems characteristically to be unable to complete development. There appear to be no discernible effects on higher animals, and the mouse oral LD50 is in excess of 3000 mg/kg and the LC50 to the guppy >100 ppm. Thus, PH-6040 is a fourth generation insecticide with many attractive properties of selectivity. As it is likely to have extensive usage, we report here on the degradation and environmental fate of PH-6040 in a laboratory model ecosystem, under photochemical stimulation, and in soil.

Insect detoxifying enzymes: Their importance in pesticide synergism and resistance

“…Hydrolysis has been identified as probably the major route of benzoylphenyl urea detoxification in studies done with diflubenzuron [61][62][63][64]. The major hydrolytic metabolites of diflubenzuron in S. littoralis larvae are 4-chloroaniline and 4-chlorophenylurea [7].…”

Environmental and toxicological aspects of insect growth regulators.

“…Studies on the environmental degradation of TH-6040 by Metcalf et al (27) showed that it is moderately persistent in their laboratory model ecosystem in alga, snail, caterpillar, and mosquito larva. The fish, Gambusia spp., was able to metabolize it very efficiently which demonstrated no bioconcentration.…”

Laboratory and field effects of the insect growth regulator diflubenzuron on the European corn borer

“…Diflubenzuron was not metabolized by the salt marsh caterpillar, Estigmene acrea, (Metcalf et al, 1975), the boll weevil, Anthonomous grandis, (Still and Leopold, 1975) or Pieris brassicae larvae (Verloop and Ferrell, 1977). Diflubenzuron was degraded only to a very limited extent by sheep liver microsomes (Metcalf et al, 1975) but was extensively metabolized after oral administra tion to laboratory rats (Verloop and Ferrell, 1977). Ivie (1978) reported that the major metabolites of diflubenzuron excreted by the cow and sheep resulted from hydroxylation on the difluorobenzoyl and chlorophenyl rings and by the cleavage between the carbonyl and amide groups to give metabolites that were excreted either free or as conjugates.…”

“…A thorough evaluation of the environ mental fate of diflubenzuron is, therefore, of utmost impor tance. Studies by Metcalf et al (1975) showed that difluben zuron was moderately stable in a model ecosystem, but the compound was not highly concentrated through food chains or by absorption from water. Diflubenzuron was not metabolized by the salt marsh caterpillar, Estigmene acrea, (Metcalf et al, 1975), the boll weevil, Anthonomous grandis, (Still and Leopold, 1975) or Pieris brassicae larvae (Verloop and Ferrell, 1977).…”

“…Studies by Metcalf et al (1975) showed that difluben zuron was moderately stable in a model ecosystem, but the compound was not highly concentrated through food chains or by absorption from water. Diflubenzuron was not metabolized by the salt marsh caterpillar, Estigmene acrea, (Metcalf et al, 1975), the boll weevil, Anthonomous grandis, (Still and Leopold, 1975) or Pieris brassicae larvae (Verloop and Ferrell, 1977). Diflubenzuron was degraded only to a very limited extent by sheep liver microsomes (Metcalf et al, 1975) but was extensively metabolized after oral administra tion to laboratory rats (Verloop and Ferrell, 1977).…”