Metsulfuron-Methyl 95%TC and 75%WDG/DF
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Various professional pesticide packing
FAO Standards
Herbicide
NOMENCLATURE
metsulfuron-methyl
Chemical Abstracts name methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoate
CAS RN [74223-64-6] Development codes DPX-T6376 (Du Pont)
metsulfuron
Common name metsulfuron (BSI, WSSA, ANSI, draft E-ISO, (m) draft F-ISO)
IUPAC name 2-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)benzoic acid
Chemical Abstracts name 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid
CAS RN [79510-48-8]
PHYSICAL CHEMISTRY
metsulfuron-methyl
Mol. wt. 381.4 M.f. C14H15N5O6S Form Colourless crystals; (tech., off-white solid, with a faint ester-like odour). M.p. 158 ºC V.p. 3.3 ´ 10-7 mPa (25 ºC) KOW logP = -1.74 (pH 7) Henry 2.3 ´ 10-10 Pa m3 mol-1 (calc.) S.g./density 1.47 Solubility In water 0.55 (pH 5), 2.79 (pH 7), 213 (pH 9) (all in g/l, 25 ºC). In hexane 0.00079, xylene 0.58, ethanol 2.3, methanol 7.3, acetone 36, dichloromethane 121 (all in g/l, 20 ºC). Stability Stable in air up to c. 140 ºC. Hydrolysis DT50 (25 °C), 22 d (pH 5), stable (pH 7 and 9). pKa 3.3
metsulfuron
Mol. wt. 367.3 M.f. C13H13N5O6S Form Solid.
APPLICATIONS
metsulfuron-methyl
Biochemistry Branched chain amino acid synthesis (ALS or AHAS) inhibitor. Acts by inhibiting biosynthesis of the essential amino acids valine and isoleucine, hence stopping cell division and plant growth. Selectivity derives from rapid metabolism in the crop. Metabolic basis of selectivity in sulfonylureas reviewed (M. K. Koeppe & H. M. Brown, Agro-Food-Industry, 6, 9-14 (1995)). Mode of action Selective systemic herbicide absorbed through the roots and foliage, with rapid translocation both acropetally and basipetally. Susceptible plants cease growth almost immediately after post-emergence treatment, and are killed in 7-21 days. Surfactants increase the activity of metsulfuron-methyl on certain broad-leaved weeds. Uses Metsulfuron-methyl controls a wide range of annual and perennial broad-leaved weeds in wheat, barley, rice and oats, by either pre- or post-emergence application, at 4-7.5 g/ha post-emergence. Formulation types WG.
MAMMALIAN TOXICOLOGY
metsulfuron-methyl
Oral Acute oral LD50 for male and female rats >5000 mg/kg. Skin and eye Acute percutaneous LD50 for rabbits >2000 mg/kg. Mild skin irritant to guinea pigs, but not a skin sensitiser; moderate but reversible eye irritant. Inhalation LC50 (4 h) for male and female rats >5 mg/l air. NOEL (2 y) for rats 500, male dogs 500, female dogs 5000 mg/kg diet. ADI 0.25 mg/kg (Germany). Other Non-mutagenic in the Ames test. Non-teratogenic. Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) IV
metsulfuron
EC hazard N; R50, R53
ECOTOXICOLOGY
metsulfuron-methyl
Birds Acute oral LD50 for mallard ducks >5000 mg/kg. Dietary LC50 (8 d) for mallard ducks and bobwhite quail >5620 mg/kg diet. Fish LC50 (96 h) for rainbow trout and bluegill sunfish >150 mg/l. Daphnia EC50 (48 h) >150 mg/l. Algae NOEC for green algae 100 mg/l. Other aquatic spp. NOEC for Lemna gibba 0.16 mg/l. Bees Non-toxic to bees; LD50 >25 mg/bee. Worms >1000 mg/kg.
ENVIRONMENTAL FATE
metsulfuron-methyl
Animals In mammals, following oral administration, metsulfuron-methyl is excreted predominantly unchanged. The methoxycarbonyl and sulfonylurea groups are only partly degraded, by O-demethylation and hydroxylation. Plants In plants, undergoes complete degradation within a few days, by hydrolysis and conjugation. In addition to the hydroxymethyl analogue, other metabolites identified include methyl 2-(aminosulfonyl)benzoate and 2-(aminosulfonyl)benzoic acid. Rapidly metabolised within cereal plants. Soil/Environment In soil, metsulfuron-methyl is broken down both by chemical hydrolysis and by microbial degradation. DT50 varies from 1 to 5 weeks, with breakdown being more rapid at lower soil pH, at higher temperatures, and at higher levels of soil moisture. Koc 35 (pH 7).
