IDENTIFICATION
Common name: Metribuzin
Other name: metribuzin (BSI, E-ISO, WSSA): metribuzine ((f) F-ISO)
Iupac name: 4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one; 4-amino-6- tert- butyl-3-methylthio-1,2,4-triazin-5(4H)-one
Chemical abstracts name: 4-amino-6-(1,1-dimethylethyl)-3- (methylthio)-1,2,4-triazin-5(4H)-one
Type: Herbicide
CAS RN: [21087-64-9]
M.F.: C8H14N4OS
Mol Wt: 214.3
PHYSICAL CHEMISTRY
Form (appearance): White crystals, with a weak characteristic odour.
M.P.: 126.2℃
B.P.: 132℃/2 Pa.
V.P.: 0.058 mPa (20℃)
S.G.: 1.28 (20℃)
Solubility.: In water 1.05 g/l (20℃). in dimethylformamide 1780, cyclohexanone 1000, chloroform 850, acetone 820, methanol 450, dichloromethane 340, benzene 220, n- butanol 150, ethanol 190, toluene 87, xylene 90, isopropanol 77, hexane 1.0 (all in g/l, 20℃).
Stability: Relatively stable to u.v. irradiation. At 20℃, stable to dilute acids and alkalis: DT50 (37℃) 6.7 h (pH 1.2); DT50 (70℃) 569 h (pH 4), 47 d (pH 7), 191 h (pH 9), Photodecomposition in water is very rapid (DT50 <1 d). On soil surfaces under natural light conditions, DT50 14-25 d.
Henry: 1 × 10-5 Pa m3 mol-1 (20℃, talc.)
KowlogP: 1.6 (pH 5,6, 20℃)
APPLICATION
Formulation types: SC: WG: WP
Biochemistry: Photosynthetic electron transport inhibitor at the photosystem Ⅱreceptor site. Selectivity is due to metabolism (mostly conjugation) within the plant (C. Fedtke, Proc. Br. Crop Prot. Conf. Weeds, 1993, l, 221).
Mode of action: Selective systemic herbicide, absorbed predominantly by the roots, but also by the leaves, with translocation acropetally in the xylem.
Uses: Pre- and post-emergence control of many grasses and broad leaved weeds in soya beans, potatoes, tomatoes, sugar cane, alfalfa, asparagus, maize and cereals, at 0.07-1.05 kg a.i./ha.
Phytotoxicity: Phytotoxic to many crops, including crucifers, cucurbits, lettuce, onions, sugar beet, sunflowers, flax, strawberries, sweet potatoes, and tobacco.
Compatibility: Compatible with most other herbicides, except in highly concentrated mixtures.
MAMMALIAN TOXICOLOGY
Reviews: Toxikologie der Herbizide, Deutsche Forschungsgemeinschaft [Data collection on toxicology of herbicides], 7. Lieferung, Weinheim, 1981.
Oral: Acute oral LD50 for rats c. 2000, mice c. 700, guinea pigs c. 250, cats >500 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats >20000 rog/kg. Not irritating to skin and eyes (rabbits).
Inhalation: LC50 (4 h) for rats >0.65 mg/l air (dust).
Noel: (2 y) for rats and dogs 100, mice c, 800 mg/kg diet.
ADI: 0.013 mg/kg b.w.
Toxicity: WHO (a.i.) lit (Table 5); EPA (formulation) Ⅲ
EC hazard: Xn; R22| N; R50, R53
ECOTOXICOLOGY
Birds: Acute oral LD50 for bobwhite quail 168, mallard ducks 460-680 mg/kg. Dietary LC50 (5 d) for bobwhite quail and mallard ducks >4000 mg/kg diet.
Fish: LC50 (96 h) for bluegill sunfish 80, rainbow trout 76, goldfish >10, catfish >10 ppm.
Daphnia: LC50 (48 h) 4.5-35 mg/l.
Algae: ErC500 for Scenedesmus subspicatus 0.021 mg/l.
Worms: C50 for Eisenia foetida 331.8 mg/kg dry soil.
Bees: Not toxic to bees; LD50 35 μg/bee.
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