Common name: chlorpyrifos; chlorpyriphos; chlorpyriphos-éthyl
IUPAC name: O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate
Chemical Abstracts name: O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate
CAS RN: [2921-88-2]
PHYSICAL CHEMISTRY
Mol. wt.: 350.6; M.f.: C9H11Cl3NO3PS; Form: Colourless crystals, with a mild mercaptan odour. M.p.: 42-43.5 ºC; V.p.: 2.7 mPa (25 ºC); KOW: logP = 4.7; Henry: 6.76x10-1 Pa m3 mol-1 (calc.) S.g./density: 1.44 (20 °C) Solubility: In water c. 1.4 mg/l (25 ºC). In benzene 7900, acetone 6500, chloroform 6300, carbon disulfide 5900, diethyl ether 5100, xylene 5000, iso-octanol 790, methanol 450 (all in g/kg, 25 ºC). Stability: Rate of hydrolysis increases with pH, and in the presence of copper and possibly of other metals that can form chelates; DT50 1.5 d (water, pH 8, 25 ºC) to 100 d (phosphate buffer, pH 7, 15 ºC).
APPLICATIONS
Biochemistry: Cholinesterase inhibitor.
Mode of action: Non-systemic insecticide with contact, stomach, and respiratory action.
Uses: Control of Coleoptera, Diptera, Homoptera and Lepidoptera in soil or on foliage in over 100 crops, including pome fruit, stone fruit, citrus fruit, nut crops, strawberries, figs, bananas, vines, vegetables, potatoes, beet, tobacco, soya beans, sunflowers, sweet potatoes, peanuts, rice, cotton, alfalfa, cereals, maize, sorghum, asparagus, glasshouse and outdoor ornamentals, turf, and in forestry. Also used for control of household pests (Blattellidae, Muscidae, Isoptera), mosquitoes (larvae and adults) and in animal houses.
Phytotoxicity: Non-phytotoxic to most plant species when used as recommended. Poinsettias, azaleas, camellias, and roses may be injured.
Formulation types: DP; EC; GR; UL; WG; WP; Microcapsule.
Compatibility: Incompatible with alkaline materials.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for rats 135-163, guinea pigs 504, rabbits 1000-2000 mg/kg.
Skin and eye: Acute percutaneous LD50 for rabbits >5000 mg/kg; (tech.) for rats >2000 mg/kg.
Inhalation: LC50 (4-6 h) for rats >0.2 mg/l (14 ppb).
NOEL: (2 y) for rats 1 mg/kg b.w. daily; (18 mo) for mice 0.7 mg/kg b.w. daily; (2 y) for dogs 1 mg/kg b.w. daily.
ADI: 0.01 mg/kg b.w.
Other: Non-teratogenic.
Toxicity class: WHO (a.i.) II; EPA (formulation) II
EC hazard: T; R24/25| N; R50, R53
ECOTOXICOLOGY
Birds: Acute oral LD50 for mallard ducks 490, house sparrows (Passer domesticus) 122, chickens 32-102 mg/kg. Dietary LC50 (8 d) for bobwhite quail 423 ppm.
Fish: LC50 (96 h) for bluegill sunfish 0.002-0.010, rainbow trout 0.007-0.051, roach 0.25, fathead minnow 0.12-0.54 mg/l.
Daphnia: LC50 (48 h) 1.7g/l.
Algae: NOEC for Selenastrum capricornutum >0.4 mg/l.
Other aquatic spp.: LC50 for Korean shrimp (Palaemon macrodactylus) 0.05g/l.
Bees: Toxic to bees. LD50 (oral) 360 ng/bee; (contact) 70 ng/bee.
Worms: LC50 (14 d) for Eisenia foetida 210 mg/kg soil.
Other beneficial spp.: Toxic to Collembola.
ENVIRONMENTAL FATE
Animals: In rats, dogs, and other mammals, following oral administration, rapid metabolism occurs, the principal metabolite being 3,5,6-trichloropyridin-2-ol. Excretion is principally in the urine.
Plants: Non-systemic in plants, not absorbed from soil via the roots. Residues taken up by plant tissues are metabolised to 3,5,6-trichloropyridin-2-ol which is conjugated and sequestered.
Soil/Environment: In soil, chlorpyrifos is degraded at a moderate rate; DT50 (lab.) 10-120 d (25 °C); field DT50 for soil-incorporated applications 33-56 d, for soil-surface applications 7-15 d. Primary route of degradation is transformation to 3,5,6-trichloropyridin-2-ol, which is subsequently degraded to organochlorine compounds and CO2. Koc 1250-12600.
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