Azamethiphos

NOMENCLATURE
Common name: azamethiphos
IUPAC name: S-6-chloro-2,3-dihydro-2-oxo-1,3-oxazolo[4,5-b]pyridin-3-ylmethyl O,O-dimethyl

phosphorothioate; 6-chloro-3-dimethoxyphosphinoylthiomethyl-1,3-oxazolo[4,5-b]pyridin-2

(3H)-one
Chemical Abstracts name: S-[(6-chloro-2-oxooxazolo[4,5-b]pyridin-3(2H)-yl)methyl] O,O-

dimethyl phosphorothioate
CAS RN: [35575-96-3]
EEC no.: 252-626-0

PHYSICAL CHEMISTRY
Composition: Tech. is >95%. Mol. wt.: 324.7; M.f.: C₉H₁₀ClN₂O₅PS; Form: Colourless

crystals; (tech. is a beige to grey powder). M.p.: 89 ^oC. V.p.: 0.0049 mPa (20 ^oC). KOW:

logP = 1.05; Henry: 1.45x10^-6 Pa m³ mol^-1 (calc.) S.g./density: 1.60 (20 ^oC). Solubility:

In water 1.1 g/l (pH 7, 20 ^oC). In dichloromethane 610, benzene 130, methanol 100, n-

octanol 5.8 (all in g/kg, 20 ^oC). Stability: Unstable in acids and alkalis; DT50 (20 ^oC)

(calc.): 800 h (pH 5), 260 h (pH 7), 4.3 h (pH 9). F.p.: >150 ^oC (Marcusson, without

stirring).

APPLICATIONS
Biochemistry: Cholinesterase inhibitor.
Mode of action: Insecticide with contact and stomach action. Gives rapid knockdown, and has

good residual activity.
Uses: Control of flies and other insect pests in animal houses. Control of mosquitoes,

tsetse flies, cockroaches, and other public hygiene pests.
Formulation types: AE; WP.

MAMMALIAN TOXICOLOGY
Oral: Acute oral LD₅₀ for rats 1180 mg/kg.
Skin and eye: Acute percutaneous LD₅₀ for rats >2150 mg/kg. Mild eye irritant; non-

irritating to skin (rabbits).
Inhalation: LC₅₀ (4 h) for rats >560 mg/m3 air.
NOEL: (90 d) for rats 20 mg/kg diet (2 mg/kg daily), for dogs 10 mg/kg diet (0.3 mg/kg

daily).
ADI: 0.025 mg/kg.
Toxicity class: WHO (a.i.) III; EPA (formulation) III

ECOTOXICOLOGY
Birds: Acute oral LD₅₀ for bobwhite quail 30.2, mallard ducks 48.4 mg/kg. Dietary LC₅₀ (8

d) for bobwhite quail 860, Japanese quail >1000, mallard ducks 700 ppm. Based on the

results of acute laboratory trials, azamethiphos is classified as highly toxic to birds.

However, sublethal doses have a repellent effect on birds, so the risk for birds is

significantly reduced.
Fish: LC₅₀ (96 h) for channel catfish 3, crucian carp 6, guppy 8, rainbow trout 0.115-0.2,

sheepshead minnow 2.22 mg/l. Based on the test with the most sensitive species, rainbow

trout, azamethiphos is classified as highly toxic to fish. All other test species were less

sensitive to this compound.
Daphnia: LC₅₀ (48 h) 0.67 ug/l.
Bees: Toxic to bees; LD₅₀ (24 h) (oral) <0.1 ug/bee; (contact) 10 ug/bee.

ENVIRONMENTAL FATE
Animals: In rats and goats, the glucuronic acid conjugate of 2-amino-3-hydroxy-5-

chloropyridine represents the major metabolite, accounting for 27-48% of the dose, followed

by the corresponding sulfuric acid conjugate accounting for 3-20% of the dose.
Soil/Environment: In loamy sand (aerobic), DT₅₀ c. 6 h.