Diazinon

Composition Tech. is ³95% pure. Mol. wt. 304.3 M.f. C₁₂H₂₁N₂O₃PS Form Clear colourless liquid; (tech., yellow liquid). B.p. 83-84 ºC/0.0002 mmHg; 125 ºC/1 mmHg V.p. 1.2 ´ 10¹ mPa (25 ºC) (OECD 104) K_OW logP = 3.30 (OECD 107) Henry 6.09 ´ 10^-2 Pa m³ mol^-1 (calc.) S.g./density 1.11 (20 ºC) Solubility In water 60 mg/l (20 ºC). Completely miscible with common organic solvents, e.g. ethers, alcohols, benzene, toluene, hexane, cyclohexane, dichloromethane, acetone, petroleum oils. Stability Susceptible to oxidation above 100 ºC. Stable in neutral media, but slowly hydrolysed in alkaline media, and more rapidly in acidic media; DT₅₀ (20 ºC) 11.77 h (pH 3.1), 185 d (pH 7.4), 6.0 d (pH 10.4). Decomposes above 120 ºC. pKa 2.6 (OECD 112) F.p. ³62 °C

APPLICATIONS Diazinon

Biochemistry Cholinesterase inhibitor. Mode of action Non-systemic insecticide and acaricide with contact, stomach, and respiratory action. Uses Control of sucking and chewing insects and mites on a very wide range of crops, including deciduous fruit trees, citrus fruit, vines, olives, bananas, pineapples, vegetables, potatoes, beet, sugar cane, coffee, cocoa, tea, tobacco, maize, sorghum, alfalfa, flax, cotton, rice, ornamentals, glasshouse crops, forestry, etc., at 300-600 g/ha; soil insects (by soil application); phorid and sciarid flies in mushroom cultivation; flies, lice, mites, fleas, cockroaches, bedbugs, ants, and other insect pests in animal houses and household use. Seed treatment for maize, for control of frit flies and also conferring bird-repellent properties. Also used as a veterinary ectoparasiticide. Phytotoxicity Non-phytotoxic when used as directed. Russetting may occur on green and yellow apple varieties. Formulation types CS; EC; DP; DS; FT; GR; KN; SD; WP; Aerosol; Coating agent. Compatibility Incompatible with copper-containing compounds. Selected tradenames: 'Basudin' (Syngenta); 'Neocidol' (veterinary use) (Syngenta); 'Cekuzinon' (Cequisa); 'Dianon' (Nippon Kayaku); 'Dianozyl' (Agriphar); 'Diazol' (Makhteshim-Agan, AgroSan); 'Efdiazon' (Efthymiadis); 'Knox-out' (Cerexagri)

MAMMALIAN TOXICOLOGY Diazinon

Reviews FAO/WHO 68, 70, 92, 94 (see part 2 of the Bibliography). Oral Acute oral LD₅₀ for rats 1250, mice 80-135, guinea pigs 250-355 mg/kg. Skin and eye Acute percutaneous LD₅₀ for rats >2150, rabbits 540-650 mg/kg. Not an irritant (rabbits). Inhalation LC₅₀ (4 h) for rats >2330 mg/m³. NOEL (2 y) for rats 0.06 mg/kg b.w.; (1 y) for dogs 0.015 mg/kg b.w. daily, humans 0.02 mg/kg b.w. ADI (JMPR) 0.002 mg/kg b.w. [1993, 2001]. Toxicity class WHO (a.i.) II; EPA (formulation) II or III EC hazard Xn; R22| N; R50, R53

ECOTOXICOLOGY Diazinon

Birds Acute oral LD₅₀ for mallard ducklings 2.7, young pheasants 4.3 mg/kg. Fish LC₅₀ (96 h) for bluegill sunfish 16, rainbow trout 2.6-3.2, carp 7.6-23.4 mg/l. Daphnia LC₅₀ (48 h) 0.96 mg/l. Algae >1 ppm. Bees Highly toxic to bees. Worms Slightly toxic to earthworms.

ENVIRONMENTAL FATE Diazinon

EHC 198 (WHO 1998), 63 (WHO, 1986; a general review of organophosphorus insecticides). Animals The principal metabolites are diethyl thiophosphate and diethyl phosphate. Plants Studies with ¹⁴C-labelled diazinon show a rapid absorption and translocation in plants. Metabolism proceeds via hydrolysis and subsequent transformation and degradation of the hydroxypyrimidine derivatives to CO₂. Soil/Environment Degradation involves oxidation to the phosphate (diazoxon) and hydrolysis (J. Pardue et al., J. Agric. Food Chem., 1970, 18, 405-408). DT₅₀ c. 11-21 d (laboratory). Diazinon is fairly strongly adsorbed onto soil; K_om 332 mg/g o.m. Mobility is low.

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