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]

metsulfuron
Common name: metsulfuron
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.: 3.3x10-7 mPa (25 ºC) KOW: logP = -1.74 (pH 7). Henry: 2.3x10-10 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.
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.
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 ug/l.
Bees: Non-toxic to bees; LD50 >25 ug/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).