Fenamiphos

Mol. wt. 303.4 M.f. C₁₃H₂₂NO₃PS Form Colourless crystals; (tech., tan, waxy solid). M.p. 49.2 ºC; (tech., 46 ºC) V.p. 0.12 mPa (20 ºC); 4.8 mPa (50 ºC) K_OW logP = 3.30 (20 °C) Henry 9.1 ´ 10^-5 Pa m³ mol^-1 (20 °C) S.g./density 1.191 (23 ºC) Solubility In water 0.4 g/l (20 ºC). In dichloromethane, isopropanol, toluene >200, hexane 10-20 (all in g/l, 20 ºC). Stability Hydrolysis DT₅₀ 1 y (pH 4), 8 y (pH 7), 3 y (pH 9) (22 ºC). F.p. c. 200 °C

COMMERCIALISATION Fenamiphos

History Nematicide reported by J. H. O'Bannon & A. L. Taylor (Plant Dis. Rep., 1967, 51, 995) and B. Homeyer (Pflanzenschutz-Nachr. (Engl. Ed.), 1971, 24, 48). Introduced by Baychem Corp., Chemagro Division. Patents DE 1121882; US 2978479 Manufacturers Bayer

APPLICATIONS Fenamiphos

Biochemistry Cholinesterase inhibitor. Mode of action Systemic nematicide with contact action. Absorbed by the roots, with translocation to the leaves. Against soil populations of ectoparasitic nematodes, fenamiphos is more persistent and more effective than the sulfoxide metabolite; the sulfone metabolite is least effective. Against plant endoparasitic nematodes, the sulfone is more effective than the sulfoxide (T. B. Waggoner & A. M. Khasawinah (Residue Rev., 1974, 53, 79)). Uses Control of ectoparasitic, endoparasitic, free-living, cyst-forming, and root-knot nematodes. Used in bananas, pineapples, citrus fruit, pome fruit, stone fruit, vines, hops, cotton, cocoa, coffee, okra, peanuts, soya beans, cucurbits, tomatoes, potatoes, vegetables, sugar beet, ornamentals, tobacco, and turf. Has secondary activity against sucking insects and spider mites. Phytotoxicity Non-phytotoxic when applied to the soil. Formulation types EC; EW; GR. Compatibility Incompatible with alkaline materials. Selected tradenames: 'Nemacur' (Bayer)

MAMMALIAN TOXICOLOGY Fenamiphos

Reviews FAO/WHO 80, 82 (see part 2 of the Bibliography). Oral Acute oral LD₅₀ for male and female rats c. 6, mice, dogs and cats c. 10 mg/kg. Skin and eye Acute percutaneous LD₅₀ for rats c. 80 mg/kg. Slightly irritant to skin and eyes (rabbits). Inhalation LC₅₀ (4 h) for rats c. 0.12 mg/l air (aerosol). NOEL (2 y) for rats 1, mice 10 mg/kg diet; (12 mo) for dogs 1 mg/kg diet. ADI (JMPR) 0.0008 mg/kg b.w. [1997]. Toxicity class WHO (a.i.) Ib; EPA (formulation) I EC hazard T+; R28| T; R24

ECOTOXICOLOGY Fenamiphos

Birds Acute oral LD₅₀ for bobwhite quail 0.7-1.6, mallard ducks 0.9-1.2 mg/kg. Dietary LC₅₀ (5 d) for mallard ducks 316, bobwhite quail 38 mg/kg diet. Fish LC₅₀ (96 h) for bluegill sunfish 0.0096, rainbow trout 0.0721 mg/l. Daphnia LC₅₀ (48 h) 0.0019 mg/l. Algae E_rC₅₀ for Scenedesmus subspicatus 11 mg/l. Worms LC₅₀ for Eisenia foetida 795 mg/kg dry soil (400 EC).

ENVIRONMENTAL FATE Fenamiphos

EHC 63 (WHO, 1986; a general review of organophosphorus insecticides). Animals In mammals, following oral administration, there is rapid metabolism involving oxidation to the sulfoxide and sulfone analogues, followed by subsequent hydrolysis, conjugation and excretion via the urine; some N-dealkylation also occurs (T. B. Waggoner & A. M. Khasawinah, Residue Rev., 1974, 53, 79). Plants Degradation is by thiooxidation and hydrolysis. The major metabolites are fenamiphos sulfoxide and fenamiphos sulfone (idem, ibid.). Soil/Environment No effect on soil bacteria. Readily degradable in water, degradable on soil surfaces. Duration of activity in soil is c. 4 months. Based on K_oc values and leaching studies, fenamiphos can be classified as a compound with low mobility. Soil DT₅₀ (aerobic and anaerobic) several weeks. The major degradation products are fenamiphos sulfoxide and fenamiphos sulfone and their phenols.

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