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

 

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.)

K_owlogP: 1.6 (pH 5,6, 20℃)

 

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.

 

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

 

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: E_rC₅₀0 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.