NOMENCLATURE

Common name sulfosulfuron (BSI, pa ISO)

IUPAC name 1-(4,6-dimethoxypyrimidin-2-yl)-3-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-yl)sulfonylurea 

Chemical Abstracts name N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-2-(ethylsulfonyl)imidazo[1,2-a]pyridine-3-sulfonamide 

CAS RN [141776-32-1]  Development codes MON 37500 (Monsanto); TKM 19; MON 37588  (Monsanto) (for WG formulation) 

PHYSICAL CHEMISTRY

Mol. wt. 470.48  M.f. C₁₆H₁₈N₆O₇S₂  Form White, odourless solid.  M.p. 201.1-201.7 °C  V.p. <1 ´ 10^-3 mPa  K_OW logP <1 (pH 5 to 9 buffer)  Henry 8.15 ´ 10^-7 (pH 5), 8.83 ´ 10^-9 (pH 7), 2.97 ´ 10^-8 (pH 9) (calc.)  S.g./density 1.5185 (20 °C)  Solubility In water 18 (pH 5), 1627 (pH 7), 482 (pH 9) (all in ppm).  pKa 3.51 (20 °C) 

COMMERCIALISATION

History Discovered by Takeda Chemical Industries, Ltd. Reported by S. K. Parrish et al. (Proc. Br. Crop Prot. Conf. - Weeds, 1995, 1, 57). Developed jointly by Monsanto Co. and Takeda and introduced in 1997.

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. 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 Systemic herbicide, absorbed by the root system and/or leaf surface, and translocated to symplast and apoplast.  Uses Has demonstrated activity for the control of annual broad-leaved weeds and grass weeds in cereals (wheat), at 10-35 g/ha.  Phytotoxicity Barley and oats are sensitive. Tolerance of durum wheat is variety-specific.  Formulation types WG.  Compatibility Not compatible with fertiliser solutions with pH £5, nor with non-ionic surfactants or other additives that alter the pH of the spray solution below pH 5.  Not compatible with malathion. Crop injury may result if applied within 60 days of crop emergence where an organophosphate insecticide has been applied as an in-furrow treatment.

ANALYSIS

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

Oral Acute oral LD₅₀ for rats >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ for rats >5000 mg/kg. Not a skin irritant; moderate eye irritant (rabbits). Not a skin sensitiser (guinea pigs).  Inhalation Practically non-toxic.  ADI 0.24 mg/kg.  Toxicity class EPA (formulation) III 

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for bobwhite quail and mallard ducks >2250 mg/kg. Dietary LC₅₀ (5 d) for bobwhite quail and mallard ducks >5620 ppm.  Fish LC₅₀ (96 h) for rainbow trout >95, carp >91, bluegill sunfish >96, minnow >101 mg/l.  Daphnia LC₅₀ (48 h) >96 mg/l.  Algae E_bC₅₀ (3 d) for green algae (Selenastrum capricornutum) 0.221 mg/l, E_rC₅₀ (3 d) 0.669 mg/l; EC₅₀ (5 d) for blue-green algae (Anabaena flos-aquae) 0.77 mg/l.  Other aquatic spp. IC₅₀ (14 d) for Lemna gibba (G3) >1.0 mg/l.  Bees LD₅₀ (oral) >30 mg/bee; (dermal) >25 mg/bee.  Worms LC₅₀ >848 mg/kg.  Other beneficial spp. Classified as harmless to Bembidion tetracolum, Paradosa spp., Typhlodromus pyri, Apidus rhopalosiphi. 

ENVIRONMENTAL FATE

Cleavage of the sulfonylurea linkage in soil is a major pathway of metabolism, with oxidative demethylation playing a significant role in some matrices.  Animals Sulfosulfuron was eliminated rapidly from rats, with limited metabolism and negligible residues in tissues. O-Demethylation to yield desmethyl sulfosulfuron and ring-hydroxylation on the pyrimidine ring were the primary metabolic pathways. Rapid elimination was also observed in livestock. Negligible transfer and/or retention of sulfosulfuron residues to milk, eggs, organs and tissues were observed in goats and hens.  Plants Residues in wheat grain were negligible. The major component in wheat forage and straw from the post-emergent treatment was unmetabolised sulfosulfuron. The major metabolite, a sulfonamide, resulted from cleavage of the sulfonylurea bridge. Minor metabolites resulted from oxidative demethylation to yield desmethyl sulfosulfuron and the ring-opened guanidine analogue. Minimal uptake was observed in rotation crops, with the major metabolite being free and conjugated sulfonamide.  Soil/Environment The primary degradation pathway in soil is the hydrolytic cleavage of the sulfonylurea linkage to yield the corresponding sulfonamide and dimethoxypyrimidinamine. DT₅₀ (lab.) 32 d (silt loam, pH 7.6, 0.8% o.m.), 35 d (sandy loam, pH 6.8, 1.6% o.m.), 53 d (loamy sand, pH 5.8, 3.9% o.m.); DT₅₀ was longer in some other soils. Photodegradation is also a mode of environmental dissipation, DT₅₀ 3 d. In field studies at eleven sites in Europe, mean DT₅₀ after application to bare soil 24 d (range 11-47 d); mean DT₉₀ 261 d. Despite rapid degradation, rotational injury to sensitive crops can be expected; see S. K. Parrish et al., Proc. Br. Crop Prot. Conf. - Weeds, 1995, 1, 667. Degradation in water/sediment system was fairly rapid; DT₅₀ 32 d for river (pH 7.0, 1.7% o.m.), 20 d for pond (pH 7.0, 2.9% o.m.) systems (both 20 °C). In the water phase, DT₅₀ 19.5 d for river, 16 d for pond. Mobility of sulfosulfuron was limited, based on the results of field dissipation studies and an EU lysimeter study; sulfosulfuron mean concentrations in the lysimeter leachate were <0.01 mg/l over a 3 y study.