Common name: fenthion

IUPAC name: O,O-dimethyl O-4-methylthio-m-tolyl phosphorothioate

Chemical Abstracts name: O,O-dimethyl O-[3-methyl-4-(methylthio)phenyl] phosphorothioate

CAS RN: [55-38-9]

EEC no.: 200-231-9

 

Mol. wt.: 278.3; M.f.: C10H15O3PS2; Form: Colourless, oily liquid; (tech., brown, oily liquid, with a mercaptan-like odour). M.p.: No solidification point down to -80 °C. B.p.: 90 °C/1 Pa (calc.), 117 °C/10 Pa (calc.), 284 °C (calc.) V.p.: 0.74 mPa (20 ºC); 1.4 mPa (25 ºC). KOW: logP = 4.84; Henry: 5x10-2 Pa m3 mol-1 (20 °C). S.g./density: 1.25 (20 ºC). Solubility: In water 4.2 mg/l (20 ºC). In dichloromethane, toluene, isopropanol >250, hexane 100 (all in g/l, 20 ºC). Stability: Stable to ligh,t and up to 210 ºC. Relatively stable in acidic conditions, and moderately stable in alkaline conditions; DT50 (22 ºC) 223 d (pH 4), 200 d (pH 7), 151 d (pH 9). F.p.: 170 ºC (tech.)

 

Biochemistry: Cholinesterase inhibitor.

Mode of action: Insecticide with contact, stomach, and respiratory action.

Uses: Control of fruit flies, leafhoppers, leaf miners, leaf-eating larvae, stem borers, cereal bugs, and other insect pests in fruit (including citrus), vines, olives, vegetables, cotton, tea, sugar cane, rice, beet, tobacco, ornamentals, etc. For agricultural uses, application rates vary from 60 to 1200 g/ha, depending on crop, pest, pest stage and application method. Control of insect pests (flies, mosquitoes, cockroaches, fleas, ants, ticks, lice, etc.) in public health situations and animal houses, and control of animal ectoparasites.

Phytotoxicity: Non-phytotoxic when used as recommended. Some varieties of apples and cotton may be injured.

Formulation types: DP; EC; GR; HN; PO; UL; WP.

Compatibility: Incompatible with insecticides and fungicides which are highly alkaline.

 

Oral: Acute oral LD50 for male and female rats c. 250 mg/kg.

Skin and eye: Acute percutaneous LD50 (24 h) for male rats 586, female rats 800 mg/kg; not irritating to skin and eyes (rabbits).

Inhalation: LC50 (4 h) for male and female rats c. 0.5 mg/l air (aerosol).

NOEL: (2 y) for rats <5, mice 0.1 mg/kg diet; (1 y) for dogs 2 mg/kg diet.

ADI: 0.007 mg/kg b.w.

Toxicity class: WHO (a.i.) II; EPA (formulation) II

EC hazard: R40| T; R23, R48/25| Xn; R21/22| N; R50, R53

 

Birds: Acute oral LD50 for bobwhite quail 7.2 mg/kg. Dietary LC50 (5 d) for bobwhite quail 60, mallard ducks 1259 mg/kg.

Fish: LC50 (96 h) for bluegill sunfish 1.7, rainbow trout 0.8-1.0, golden orfe 2.7 mg/l.

Daphnia: LC50 (48 h) 0.0057 mg/l.

Algae: ErC50 for Scenedesmus subspicatus 1.79 mg/l.

Bees: Toxic to bees.

Worms: LC50 for Eisenia foetida 375 mg/kg dry soil.

 

Animals: In mammals, following oral administration, elimination is mainly in the form of hydrolysis products in the urine. Major metabolites are fenthion sulfoxide, fenthion sulfone and their oxygen analogues. These metabolites are hydrolysed in further degradation, forming the corresponding phenols.

Plants: In plants, fenthion is oxidised to the sulfoxide and sulfone, both of which possess insecticidal properties, and to the monodesmethyl compound of fenthion sulfoxide. Further degradation occurs to the sulfone phosphate, which undergoes hydrolysis.

Soil/Environment: Koc 1500. In sediment/water system with and without plants, DT50 is c. 1.5 d. The degradation of fenthion occurs rapidly under aerobic conditions, forming the metabolites fenthion sulfoxide, fenthion sulfone, followed by the analogous phenol compounds.