Insecticide
organophosphorus



NOMENCLATURE
Common name acephate (BSI, E-ISO, (m) F-ISO, ANSI, ESA, JMAF)
IUPAC name O,S-dimethyl acetylphosphoramidothioate 
Chemical Abstracts name N-[methoxy(methylthio)phosphinoyl]acetamide 
CAS RN [30560-19-1]  EEC no. 250-241-2  Development codes Ortho 12 420 (Chevron)  Official codes ENT 27 822

PHYSICAL CHEMISTRY
Composition Tech. grade is >97% pure.  Mol. wt. 183.2  M.f. C₄H₁₀NO₃PS  Form Colourless crystals; (tech., a colourless solid).  M.p. 88-90 ºC; (tech., 82-89 ºC)  V.p. 0.226 mPa (24 ºC)  K_OW logP = -0.89  S.g./density 1.35  Solubility In water 790 g/l (20 ºC). In acetone 151, ethanol >100, ethyl acetate 35, benzene 16, hexane 0.1 (all in g/l, 20 ºC).  Stability Hydrolysis DT₅₀ 50 d (pH 5-7, 21 °C), photodegradation DT₅₀ (l = 253.7 nm) 55 h.

APPLICATIONS
Biochemistry Cholinesterase inhibitor.  Mode of action Systemic insecticide.  Uses Control of a wide range of chewing and sucking insects, e.g. aphids, thrips, lepidopterous larvae, sawflies, leaf miners, leafhoppers, cutworms, etc., at 0.5-1.0 kg/ha, in fruit (including citrus), vines, hops, olives, cotton, soya beans, peanuts, macadamia nuts, beet, brassicas, celery, beans, potatoes, rice, tobacco, ornamentals, forestry, and other crops. Of moderate persistence, with residual activity lasting c. 10-21 d.  Phytotoxicity Non-phytotoxic to most crops, but marginal leaf burn may occur on Red Delicious apples.  Formulation types AE; CG; GR; SP; WP.

ANALYSIS
Product analysis by glc (J. B. Leary, Anal. Methods Pestic. Plant Growth Regul., 1973, 7, 363). Residues determined by glc (idem, ibid.; Pestic. Anal. Man., 1979, I, 201-H, 201-I; AOAC Methods, 1995, 985.22).

MAMMALIAN TOXICOLOGY
Reviews FAO/WHO 59, 61 (see part 2 of the Bibliography).  Oral Acute oral LD₅₀ for male rats 1447, female rats 1030 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rabbits >10 000 mg/kg. Slightly irritating to skin (rabbits); non-sensitising to skin (guinea pigs).  Inhalation LC₅₀ (4 h) for rats >15 mg/l air.  NOEL (2 y) for dogs 0.75 mg/kg daily; LOEL for rats 0.25 mg/kg daily.  ADI (JMPR) 0.03 mg/kg [1990].  Toxicity class WHO (a.i.) III; EPA (formulation) III  EC hazard Xn; R22 

ECOTOXICOLOGY
Birds Acute oral LD₅₀ for mallard ducks 350, chickens 852, ring-necked pheasants 140 mg/kg.  Fish LC₅₀ (96 h) for bluegill sunfish 2050, rainbow trout >1000, channel catfish 2230, largemouth black bass 1725 mg/l.  Daphnia EC₅₀ (48 h) 67.2 mg/l; NOEC 43 mg/l.  Algae EC₅₀ (72 h) >980 mg/l.  Other aquatic spp. LC₅₀ (96 h) for crayfish 750 ppm.  Bees LD₅₀ (contact) 1.2 mg/bee.  Worms LC₅₀ (14 d) 22 974 mg/kg; NOEC 10 000 mg/kg.

ENVIRONMENTAL FATE
EHC 63 (WHO, 1986; a general review of organophosphorus insecticides).  Animals Metabolised to methamidophos (q.v.).  Plants In plants, residual activity lasts for c. 10-15 d. The major metabolite is methamidophos (q.v.).  Soil/Environment Readily biodegraded and non-persistent; soil DT₅₀ 2 d (aerobic) to 7 d (anaerobic). Aqueous DT₅₀ (anaerobic metabolism) 6.6 d. Methamidophos (q.v.) has been identified as a soil metabolite.