CAS 60-51-5 Dimethoate 40% EC Nematode Pesticide Environment
Composition Tech. grade is 95% pure. Mol. wt. 229.3 M.f. C5H12NO3PS2 Form Colourless crystals; (tech., white solid pellets). M.p. 50.0-51.5 °C (purity 99.5%) B.p. 117 ºC/0.1 mmHg V.p. 0.25 mPa (25 °C) KOW logP = 0.704 Henry 1.42 ´ 10-6 Pa m3 mol-1 S.g./density 1.31 (20 °C, 99.1% pure) Solubility In water 23.3 (pH 5), 23.3 (pH 7), 25.0 (pH 9) (all in g/l, 25 ºC).
Readily soluble in most organic solvents, e.g. in alcohols,
ketones, benzene, toluene, chloroform, dichloromethane >300,
carbon tetrachloride, saturated hydrocarbons, n-octanol >50 (all in g/kg, 20 ºC). Stability Relatively stable in aqueous media at pH 2-7. Hydrolysed in
alkaline solutions; DT50 4.4 d (pH 9). Photostability DT50 >175 d (pH 5). Decomposes on heating, forming the O,S-dimethyl analogue. pKa 2.0 (20 °C) Other properties Surface tension 47.8 mN/m.
Biochemistry Cholinesterase inhibitor. Mode of action Systemic insecticide and acaricide with contact and stomach action. Uses Control of a wide range of Acari, Aphididae, Aleyrodidae, Coccidae,
Coleoptera, Collembola, Diptera, Lepidoptera, Pseudococcidae and
Thysanoptera in cereals, citrus, coffee, cotton, fruit, grapes,
olives, pastures, beetroot, potatoes, pulses, tea, tobacco,
ornamentals, ornamental shrubs, and vegetables. Also used for
control of flies in animal houses. Typical application rates for
cereals 340-680, citrus 2100, olives 720, beetroot 84-600,
vegetables 330 -600 (all in g/ha per application). Phytotoxicity Non-phytotoxic when used as directed, except to some varieties of
lemon, peach, fig, olive, walnut, hop, tomato, bean, cotton, and
pine. Russetting is possible with Red Delicious and Golden
Delicious apples, and with some ornamentals. Phytotoxicity is
dependent on crop variety and climate.
Product analysis by glc with FID or by hplc (CIPAC Handbook, 1998, H, 153; ibid., 1992, E, 69). Residues determined by glc (Analyst (London), 1977, 102, 858; 1980, 105, 515; 1985, 110, 765; J. E. Boyd, Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 357; Man. Pestic. Residue Anal., 1987, I, 3, 6, S8, S13, S17, S19; Anal. Methods Residues Pestic., 1988, Part I, M5, M12); J. Chromatogr., 1996, A, 750, 369.
Reviews FAO/WHO 77, 79 (see part 2 of the Bibliography). Oral Acute oral LD50 for rats 387, mice 160, rabbits 300, guinea pigs 350 mg/kg b.w. Skin and eye Acute dermal LD50 for rats >2000 mg/kg. Non-irritating to skin and eyes (rabbits).
Not a skin sensitiser. Inhalation LC50 (4 h) for rats >1.6 mg/l air (highest attainable concentration). NOEL (2 y) for rats 0.23 mg/kg b.w. daily; (1 y) for dogs 0.2 mg/kg b.w.
daily; (39 d) human volunteer 0.2 mg/kg b.w. daily. ADI (JMPR, PSD) 0.002 mg/kg b.w. (sum of dimethoate and omethoate,
expressed as dimethoate) [1996, 2001]. Toxicity class WHO (a.i.) II; EPA (formulation) II EC classification (Xn; R21/22| R48/22)
Birds Acute oral LD50 for mallard ducks 42, bobwhite quail 10.5, Japanese quail 84,
ring-necked pheasants 14.1 mg/kg b.w. LC50 for mallard ducks 1011, bobwhite quail 154, Japanese quail 346,
ring-necked pheasants 396 ppm. Fish LC50 (96 h) for rainbow trout 24.5, bluegill sunfish 17.6 mg/l. Daphnia EC50 (48 h) 2 mg/l; NOEC (24 h) 1 mg/l. Algae EbC50 (72 h) for Selenastrum capricornutum 90.4 mg/l; ErC50 (72 h) for Selenastrum capricornutum 282.3 mg/l; NOEC (72 h) 30.5 mg/l. Bees Toxic to bees; LD50 (oral) 0.15 mg/bee; (contact) 0.12 mg/bee. Worms LC50 31 mg/kg dry soil. Other beneficial spp. LR50 (7 d) for Typhlodromus pyri 2.24 g/ha; LR50 (48 h) for Aphidius rhopalosiphi 0.024 g/ha.
EHC 90 (WHO, 1989), 63 (WHO, 1986; a general review of organophosphorus
insecticides). Dimethoate degrades with short half-life in soil,
water and plants. When used correctly, exposure of the population
through air, food or water is negligible. Animals In mammals, metabolism follows the same pattern as in plants. Plants In plants, the following metabolite transformations occur:
oxidation to yield omethoate (q.v.), O-demethylation and N-demethylation of omethoate to yield O-desmethyl N-desmethyl omethoate, hydrolysis of amide bond to give dimethoate
carboxylic acid and subsequent degradation to give O,O-dimethyl dithiophosphoric acid, demethylation and rearrangement to
yield O-desmethyl dimethoate or O-desmethyl isodimethoate, demethylation of omethoate to give O-desmethyl omethoate and subsequent hydrolysis of the amide bond to
give O-desmethyl omethoate carboxylic acid. Omethoate is classified as
toxic and a strong cholinesterase inhibitor, and appears to show
similar rapid degradation in environmental compartments as
dimethoate. Soil/Environment Adsorption and desorption constants have been shown to be a linear
function of soil silt content. Koc ranges from 16.25 (sandy loam) to 51.88 (sand/loamy sand). Aerobic
DT50 2-4.1 d. Photolytic DT50 on soil surface 7-16 d. Low potential for leaching to groundwater
because of rapid degradation in soil.