Herbicide
HRAC  B WSSA  2; sulfonylurea



NOMENCLATURE
Common name nicosulfuron (BSI, ANSI, draft E-ISO); no name (Brazil)
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. <8 × 10^-7 mPa (25 °C)  K_OW logP = -0.36 (pH 5), -1.8 (pH 7), -2 (pH 9)  Henry <4.68 × 10^-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. 

ANALYSIS
Product by hplc. Methods for sulfonylurea residues in crops, soil and water reviewed (A. C. Barefoot et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 2, 707). Details from Ishihara Sangyo

MAMMALIAN TOXICOLOGY
Reviews Material Safety Data Sheets (available from Du Pont).  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 mg/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, K_d (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). K_d 0.05-0.7. In water, DT₅₀ 15 d (pH 5, 20 °C).