metribuzin 70% WP 70% WDG 60% SC 90% TC

metribuzin 70% WP 70% WDG 60% SC 90% TC

NOMENCLATURE

Common name metribuzin (BSI, E-ISO, WSSA); mribuzine ((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  

CAS RN [21087-64-9]  EEC no. 244-209-7  

PHYSICAL CHEMISTRY

Mol. wt. 214.3  M.f. C8H14N4OS  Form White crystals, with a weak characteristic odour.  M.p. 126.2   B.p. 132 /2 Pa.  V.p. 0.058 mPa (20 )  KOW logP = 1.6 (pH 5.6, 20 )  Henry 1 ?10-5 Pa m3 mol-1 (20 , calc.)  S.g./density 1.13 (20 )  Solubility In water 1.05 g/l (20 ). In dimethylformamide 1780, cyclohexanone 1000, chloroform 850, acetone 820, methanol 450, dichloromethane 333, benzene 220, n-butanol 150, ethanol 190, toluene 87, xylene 90, isopropanol 77, hexane 0.1-1.0 (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.  

COMMERCIALISATION

History Herbicide reported by W. Draber et al. (Naturwissenschaften, 1968, 55, 446) and reviewed by L. Eue (Pflanzenschutz-Nachr. (Engl. Ed.), 1972, 25, 175). Introduced by Bayer AG and E. I. du Pont de Nemours and Co., and first marketed in 1971.  Patents BE 697083, DE 1795784 both to Bayer; US 3905801 to Du Pont  Manufacturers Bayer CropScience; DuPont; Feinchemie Schwebda; Rallis

ANALYSIS

Product analysis by glc with FID (AOAC Methods, 17th Ed., 984.11; CIPAC Handbook, 1988, D, 137) or by i.r. spectrometry (J. W. Betker et al., J. Assoc. Off. Anal. Chem., 1976, 59, 278). Residues determined by glc (C. A. Anderson, Anal. Methods Pestic. Plant Growth Regul., 1976, 8, 453). In drinking water, by glc with NPD (AOAC Methods, 17th Ed., 991.07); metabolites by lc with u.v. detection (ibid., 1995, 992.14). Details available from Bayer CropScience.  

MAMMALIAN TOXICOLOGY

Reviews Toxikologie der Herbizide, Deutsche Forschungsgemeinschaft [Data collection on toxicology of herbicides], 7. Lieferung, Weinheim, 1981.  Oral Acute oral LD50 for male rats 510, female rats 322, mice c. 700, guinea pigs c. 250, cats >500 mg/kg.  Skin and eye Acute percutaneous LD50 for rats >20 000 mg/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 class WHO (a.i.) II; EPA (formulation) III  EC classification Xn; R22| N; R50, R53  

ECOTOXICOLOGY

Birds Acute oral LD50 for bobwhite quail 164, mallard ducks 460-680 mg/kg.  Fish LC50 (96 h) for rainbow trout 74.6, golden orfe 141.6, sheepshead minnow 85 mg/l.  Daphnia LC50 (48 h) 49.6 mg/l.  Algae ErC50 for Scenedesmus subspicatus 0.021 mg/l.  Bees Not toxic to bees; LD50 35 mg/bee.  Worms LC50 for Eisenia foetida 331.8 mg/kg dry soil.  

ENVIRONMENTAL FATE

Animals In mammals, following oral administration, 98% elimination occurs within 96 hours, about equally in the urine and the faeces.  Plants In plants, metribuzin undergoes oxidative deamination and further degradation to water-soluble conjugates.  Soil/Environment Rapidly degraded in soil; microbial breakdown is the major mechanism of loss; losses due to photodecomposition or volatilisation are insignificant; DT50 in soil c. 1-2 months; DT50 in pond water c. 7 d. Degradation involves deamination, followed by further degradation to water-soluble conjugates.