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)  K_OW 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. 

COMMERCIALISATION

History Herbicidal properties of metsulfuron-methyl reported by R. I. Doig et al. (Proc. Int. Congr. Plant Prot., 10th, 1983, 1, 324). Introduced by E. I. du Pont de Nemours and Co.  Patents US 4370480 

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. 

ANALYSIS

Product analysis by hplc (L. W. Hershberger & D. E. Brennan, Anal. Methods Pestic. Plant Growth Regul., 1988, 16, 83). Residues determined by hplc (idem, ibid.). Methods for sulfonylurea residues in crops, soil and water reviewed (A. C. Barefoot et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 2, 707). 

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. K_oc 35 (pH 7).