Nicosulfuron

Common name: nicosulfuron

IUPAC name: 2-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-N,N-dimethylnicotinamide; 1-(4,6-dimethoxypyrimidin-2-yl)-3-(3-dimethylcarbamoyl-2-pyridylsulfonyl)urea

Chemical Abstracts name: 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide

CAS RN: [111991-09-4]

PHYSICAL CHEMISTRY

Mol. wt.: 410.4; M.f.: C15H18N6O6S; Form: Colourless crystals. M.p.: 169-172 °C; V.p.: <8x10-7 mPa (25 °C). KOW: logP = -0.36 (pH 5), -1.8 (pH 7), -2 (pH 9). Henry: <4.68x10-9 Pa m3 mol-1 (25 °C). S.g./density: 0.313 (bulk). Solubility: In water 0.07 g/l. In acetone 18, ethanol 4.5, chloroform, dimethylformamide 64, acetonitrile 23, toluene 0.370, hexane <0.02, dichloromethane 160 (all in g/kg, 25 ºC). Stability: Hydrolysis DT50 15 d (pH 5); stable at pH 7 & 9. pKa: 4.6 (25 ºC). F.p.: >200 °C (Cleveland open cup).

APPLICATIONS

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. Maize selectivity derives from selective metabolism (P450-mediated pyrimidine-5-hydroxylation, followed by conjugation with glucose).

Mode of action: Selective systemic herbicide, absorbed by the foliage and roots, with rapid translocation in xylem and phloem to the meristematic tissues.

Uses: Selective post-emergence control in maize of annual grass weeds including Setaria, Echinochloa, Digitaria, Panicum, Lolium, and Avena spp., broad-leaved weeds including Amaranthus spp. and Cruciferae, and perennials such as Sorghum halepense and Agropyron repens. Applied at 35-70 g/ha.

Formulation types: SC; WG.

MAMMALIAN TOXICOLOGY

Oral: Acute oral LD50 for male and female rats and mice >5000 mg/kg.

Skin and eye: Acute percutaneous LD50 for male and female rats >2000 mg/kg. Moderate eye irritant; not a skin irritant (rabbits); not a skin sensitiser (guinea pigs). The 75% formulation is not an eye irritant.

Inhalation: LC50 for rats (4 h) 5.47 mg/l.

NOEL: In 28 d feeding trials on rats and mice, no adverse effect up to 30 g/kg diet.

Other: Non-mutagenic in the Ames test.

Toxicity class: WHO (a.i.) III (Table 5); EPA (formulation) IV

ECOTOXICOLOGY

Birds: Dietary oral LD50 for bobwhite quail >2250 mg/kg. Dietary LC50 for mallard ducks and bobwhite quail >5620 ppm.

Fish: LC50 (96 h) for bluegill sunfish and rainbow trout >1000 mg/l.

Daphnia: LC50 (48 h) >1000 mg/l.

Algae: NOEC (96 h) for green algae 100 mg/l.

Bees: LD50 (contact) >20 ug/bee; dietary LC50 (48 h) >1000 ppm. NOEC 500 ppm.

Worms: LC50 (14 d) for earthworms >1000 mg/kg.

ENVIRONMENTAL FATE

Animals: In goats, following a dose of 60 ppm, <0.1 ppm was found in tissues and milk; therefore nicosulfuron and its metabolites do not bioaccumulate. Hydrolysis of the sulfonylurea bridge and hydroxylation were the main metabolic pathways.

Plants: Degraded rapidly in maize, DT50 1.5-4.5 d. Residues <0.02 ppm in all crops. Hydrolysis of the sulfonylurea bridge to form the pyridine sulfonamide and pyrimidine amine, and hydroxylation on the pyrimidine ring, were the main metabolic pathways.

Soil/Environment: Soil DT50 (aerobic) 26 d (pH 6.1, 5.1% o.m., 25 °C). In four sandy loams, Kd (25 °C) 0.16 (pH 6.6, 1.1% o.m.) to 1.73 (pH 5.4, 4.3% o.m.). Photolysis DT50 (soil) 60-67 d; (water) 14-19 d (pH 5), 200-250 d (pH 7), 180-200 d (pH 9). Values from separate studies were: Soil DT50 24-43 d (20 °C); DT90 80-143 d (20 °C). Kd 0.05-0.7. In water, DT50 15 d (pH 5, 20 °C).