Common name: Methomyl

Other name: methomyl (BSI, E-ISO, (m) F-ISO, ANSI, ESA, JMAF)

Iupac name: S-methyl N-(methylcarbamoyloxy)thioacetimidate

Chemical abstracts name:     methyl N-[[(methylamino)carbonyl]oxy]ethanimidothioate

Type: Insecticide for Agriculture

CAS RN: [16752-77-5]

M.F.: C₅H₁₀N₂O₂S

Mol Wt: 162.2

 

Form (appearance): Colourless crystals, with a slight sulfurous odour

Composition:: Methomyl is a mixture of (Z)- and (E)- isomers, the former predominating
M.P.: 78-79℃

V.P.: 0.72 mPa (25℃)

S.G.: 1.2946 (25℃)

Solubility.: In water 57.9 g/l (25 ℃). In methanol 1000, acetone 730, ethanol 420, isopropanol 220, toluene 30 (all in g/kg, 25℃). Sparingly soluble in hydrocarbons

Stability: Stable in water for 30 d (pH 5 and 7); DT₅₀ c. 30 d (pH 9). Stable up to 140℃. Stable to sunlight when exposed for 120 d

Henry: 2.13 × 10^-6 Pa m³ mol^-1

K_owlogP: 0.093

 

Formulation types: SL; SP; WR

Biochemistry: Cholinesterase inhibitor

Mode of action: Systemic insecticide and acaricide with contact and stomach action

Uses: Control of a wide range of insects (particularly Lepidoptera, Hemiptera, Homoptera, Diptera and Coleoptera) and spider mites in fruit, vines, olives, hops, vegetables, ornamentals, field crops, cucurbits, flax, cotton, tobacco, soya beans, etc. Also used for control of flies in animal and poultry houses and dairies

Phytotoxicity: Non-phytotoxic when used as recommended, except to some varieties of apple.

 

Reviews: CAG (see part 2 of Bibliography).

Oral: Acute oral LD₅₀ for male rats 34, female rats 30 mg/kg.

Skin and eye: Acute percutaneous LD₅₀ for male and female rabbits >2000 mg/kg. Mild eye irritant (rabbits); not a skin irritant (guinea pigs).

Inhalation: LC₅₀ (4 h) for rats 0.3 mg/l air (aerosol).

Noel: (2 y) for rats 100, mice 50, dogs 100 mg/kg diet.

ADI: (JMPR) 0.03 mg/kg b.w. [1994].

Toxicity: WHO (a.i.) lb: EPA (formulation) I, IV

EC hazard: T+; R28|N; RS0, R53

 

Birds: Acute oral LD₅₀ for mallard ducks 15.9. pheasants 15.4 mg/kg. Dietary LC₅₀ (8 d) for Pekin ducks 1890, bobwhite quail 3680 mg/kg diet.

Fish: LC₅₀ (96 h) for rainbow trout 3.4, bluegill sunfish 0.9 mg/l.

Daphnia: LC₅₀ (48 h) 31.7 μg/l.

Algae: EC₅₀ (72 h) 60 mg/l.

Worms: LC₅₀ (14 d) 23 mg/kg dry soil.
Bees Toxic to bees, contact LD₅₀ 0.1 μg/bee, but not hazardous when the spray has dried.

 

Plant: EHC 178 (WHO, 1996). Methomyl Health & Safety Guide: 97 (WHO 1995).
DT₅₀ following leaf application c. 3-5 d. Rapidly degraded to CO₂ and acetonitrile, with incorporation into natural plant components (J. Harvey & R. W. Reiser, Agric. Food Chem., 1973, 21,775).

Animals: In rats, methomyl was rapidly converted to methomyl methylol, oxime, sulfoxide and sulfoxide oxime; these unstable intermediates were converted to acetonitrile and CO₂, which were eliminated primarily via respiration and in the urine. Metabolism of carbamate insecticides is reviewed (M. Cool & C. K. Jankowski in "Insecticides").

Soil/Environment: Rapidly degraded in soil. DT₅₀ in groundwater samples <0.2 d (J. H. Smelt, Pestic. Sci., 1983, 14, 173-181). K_oc 72.