Diflubenzuron degradation

Diflubenzuron (Dimilin , TH-6040) is an IGR which inhibits the normal deposition of chitin. The metabolic fate of diflubenzuron has been studied in sheep U, 2), cattle (1 ), rats (1, 3), house flies (4, 5), stable flies (5), chickens (6), swine (6), boll weevils (7), plants (8 9), and soil (2, 8, 10). Since good reviews of diflubenzuron metabolism have been given by Ivie (11) and Verloop and Ferrell (9), we will present only a tabular summary of the degradation of diflubenzuron in nonaguatic systems for comparative purposes (Table I). The remaining discussion will focus on diflubenzuron degradation in the aquatic environment. 

Soil. The half-life in soil is <1 wk (Hartley and Kidd, 1987). Diflubenzuron degrades more rapidly in neutral or basic conditions but more slowly under acidic conditions (pH <6) (Ivie et al., 1980). 

Selected properties of diflubenzuron are listed in Table 13.1. Diflubenzuron degradative pathways are almost entirely through cleavage between the carbonyl and amide groups of the urea bridge. Ultimately, the end products are either conjugated into predominantly water-soluble products or are acy-lated and ethylated biologically. Hydrolysis,... 

Diflubenzuron breakdown by hydrolysis, soil degradation, or plant and animal metabolism initially yields 2,6-difluorobenzoic acid and 4-chlorophenylurea. Ultimately, the end products are... 

Figure 17.1 Generalized degradation pattern for diflubenzuron. Diflubenzuron (A) degrades initially to 2,6-difluorobenzoic acid (B) and 4-chlorophenylurea (C). 2,6-Difluorobenzoic acid (B) degrades to 2,6-difluorobenzamide (D) and 4-chlorophenylurea (C) degrades to 4-chloroaniline (E).

Cunningham, P.A. 1986. A review of toxicity testing and degradation studies used to predict the effects of diflubenzuron (dimilin) on estuarine crustaceans. Environ. Pollut. 40A 63-86. 

Gattavecchia, E., A.M. Di Pietra, D. Tonelli, and A. Borgatti. 1981. Effect of diflubenzuron and its major degradation products on the growth of Euglena gracilis Z. and incorporation of glycine-U-14C in protein. Jour. Environ. Sci. Health B16 159-166. 

Schaefer, C.H., A.E. Colwell, and E.F. Dupras, Jr. 1980. The occurrence of p-chlorophenylurea from the degradation of diflubenzuron in water and fish. Proc. Califor. Mosquito Contr. Assoc. 48 84-89. 

Hydrolysis. Schaefer and Dupras (12) investigated the hydrolytic stability of diflubenzuron as a 0.1 ppm aqueous solution. At pH 7.7 diflubenzuron is stable at 10-24°, but gradually decomposes at 38°. At pH 10 it is stable at 10°, but degrades slowly at temperatures greater than 24°. 

Photodegradation. The photochemical degradation products of diflubenzuron in strictly aqueous solution are unreported, perhaps because of the compound s refractory solubility. Exposure of thin films on glass or a 0.1 ppm aqueous solution to sunlight... 

Microorganisms. Diflubenzuron was stable to degradation by uncharacterized microorganisms from a sewage lagoon (12). Pseudomonas putida (soil microbe) also was unable to metabolize ... 

Plectonema boryanum, were voracious degraders of diflubenzuron (Table III). Just 5 mg of algae cells could metabolize almost 80% of the applied diflubenzuron in just 1 hr. Curiously, this pace was not sustained since 45 mg of algae could degrade only 95% of the applied dose after four days. 

Table IV. Degradation of Diflubenzuron in the Metcalf et al. (2) Model Ecosystem.

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