IDENTIFICATION
Common name:Benomyl
Other name:benomyl (BSI,E-ISO,(m) F-ISO,ANSI,JMAF)
Iupac name:methyl 1-(butylcarbamoyl)benzimidazol-2-ylcarbamate
Chemical abstracts name:methyl [1-[(butylamino)carbonyl]-1H-benzimidazol-2 yl]carbamate
Type:Fungicide
CAS RN: [17804-35-2]
M.F.: C14H18N4O3
Mol Wt: 290.3
PHYSICAL CHEMISTRY
Form (appearance): Coloudess crystals.
M.P.:140℃(decomp.)
V.P.: <5.0 ×10 -3 mPa (25℃)
S.G.: Bulk density 0.38
Solubility. In water 3.6 (pH 5), 2.9 (pH 7), 1.9 (pH 9) (all in μg/l, room temperature). In chloroform 94, dimethylformamide 53, acetone 18, xylene 10, ethanol 4, heptane 0.4 (all in g/kg, 25℃). Stability Hydrolysis DT50 3.5 h (pH 5), 1.5 h (pH 7), <1 h (pH 9) (all 25℃). In some solvents, dissociates to form carbendazim and butyl isocyanate (M. Chiba & E. A. Cherniak, J. Agric. Food Chem., 1978, 26, 573).
Stability: in water and stability at various pH values investigated by R. R Singh & M. Chiba (ibid., 1985, 33, 63). Stable to light. Decomposed on storage in contact with water and under moist conditions in soil. Mechanism of the acid-catalysed decomposition in aqueous media, J. P. Caiman & D. R. Sayag (`ibid., 1976, 24, 314, 317).
Henry: <4.0×10-4 (pH 5); <5.0 × 10-4 (pH 7); <7.7 × 10-4 (pH 9) (all in Pa m3 mol-1 calc.)
KowlogP: l.37
APPLICATION
Formulation types: WP
Mode of action: Systemic fungicide with protective and curative action. Absorbed through the leaves and roots, with translocation principally acropetally.
Uses: Effective against a wide range of Ascomycetes, and Fungi Imperfecti and some Basidiomycetes in cereals, grapes, pome and stone fruit, rice and vegetables. It is also effective against mites, primarily as an ovicide. Also used as pre harvest sprays or dips for the control of storage rots of fruit and vegetables. Typical rates are: on field and vegetable crops, 140-550 g a.i./ha; on tree crops 550-1100 g/ha; for post harvest uses 25-200 g/hi
Phytotoxicity: Non-phytotoxic if used as directed. Russetting is possible with Golden Delicious apples.
Compatibility: Incompatible with alkaline materials.
MAMMALIAN TOXICOLOGY
Reviews: FAO/WHO 74, 76 (see part 2 of the Bibliography).
Oral: Acute oral LD50 for rats >5000 mg a.i./kg.
Skin and eye: Acute percutaneous LD50 for rabbits >5000 mg/kg; negligible irritant to skin, temporary to eyes (rabbits).
Inhalation: LC50 (4 h) for rat >2 mg/I air.
Noel:(2 y) for rats >2500 mg/kg diet (maximum rate tested), no evidence of histopathological changes; for dogs 500 mg/kg diet.
ADI:(JMPR) 0.1 mg/kg b.w. [1995]; residues should be compared against the ADI for carbendazim; environmental assessment also performed.
Toxicity:WHO (a.i.) III (Table 5); EPA (formulation) IV
EC hazard:R40
ECOTOXICOLOGY
Birds: Eight-day dietary LCs0 for mallard ducks and bobwhite quail >10000 mg/kg diet (using 50% formulation)
Fish: LC50 (96 h) for rainbow trout 0.27, goldfish 4.2 mg/l. LC50 (48 h) for guppy 3.4 mg/l.
Daphnia: LC50 (48 h) 640 μg/l.
Algae: EbC50 (72 h) 2.0 mg/l, (120 h) 3.1 mg/l.
Worms: LC50 (14 d) 10.5 mg/kg.
Bees: Not toxic to bees. LD50 (contact) >50 μg/bee.
ENVIRONMENTAL FATE
Plant: EHC 148 (WHO, 1993). EHC 148 concludes that, although highly toxic to aquatic organisms, this effect is unlikely to be seen in the field due to the low bioavailability of sediment-bound residues. Earthworm populations may take more than two years to recover following field application
In plants, the butylcarbamoyl group is removed to give the relatively stable carbendazim, followed by slow degradation to non-toxic 2-aminobenzimidazole. Further degradation involves cleavage of the benzimidazole nucleus. Benomyl per se is stable on the surface of banana skins (j. Cox et al., Pestic. Sci., 1974, 5, 135; J. Cox & J. A. Pinegar, ibid., 1976, 7, 193)
Animals: In animals, the butylcarbamoyl group is removed to give the relatively stable carbendazim, followed by slow degradation to non toxic 2 aminobenzimidazole. Hydroxylation also occurs, and the principal metabolite 5 hydroxybenzimidazole carbamate is converted to the O- and N-conjugates; other possible metabolites include 4-hydroxy-2-benzimidazolemethylcarbamate. Benomyl and its metabolites are excreted in the urine and faeces within a few days, with no accumulation in animal tissue.
Soil/Environment: Benomyl is rapidly converted to carbendazim in the environment, DT50 2 and 19 h in water and in soil, respectively. Data from studies on both benomyl and carbendazim are therefore relevant for the evaluation of environmental effects. Koc 1900.
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