Common name: terbutryn; terbutryne
IUPAC name: N2-tert-butyl-N4-ethyl-6-methylthio-1,3,5-triazine-2,4-diamine
Chemical Abstracts name: N-(1,1-dimethylethyl)-N'-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine
CAS RN: [886-50-0]
PHYSICAL CHEMISTRY
Composition: Tech. is 98%. Mol. wt.: 241.4; M.f.: C10H19N5S; Form: White powder. M.p.: 104-105 ºC. B.p.: 274 °C/101 kPa. V.p.: 0.225 mPa (25 ºC) (OECD 104). KOW: logP = 3.65 (25 ºC, unionised). Henry: 1.5x10-3 Pa m3 mol-1 (calc.) S.g./density: 1.12 (20 ºC). Solubility: In water 22 mg/l (22 ºC). In acetone 220, hexane 9, n-octanol 130, methanol 220, toluene 45 (all in g/l, 20 ºC). Also readily soluble in dioxane, diethyl ether, xylene, chloroform, carbon tetrachloride, dimethylformamide. Slightly soluble in petroleum ether. Stability: Stable under normal conditions. The methylthio group is hydrolysed in the presence of strong acids or alkalis. At 70 ºC, no significant hydrolysis occurs at pH 5, 7, or 9. pKa: 4.3, weak base.
APPLICATIONS
Biochemistry: Photosynthetic electron transport inhibitor at the photosystem II receptor site.
Mode of action: Selective herbicide, absorbed by the roots and foliage, with translocation acropetally through the xylem, and accumulation in the apical meristems.
Uses: Used pre-emergence in winter cereals, at 1-2 kg a.i./ha, to control blackgrass and annual meadow grass. Among the autumn-germinating broad-leaved weeds controlled are chickweed, mayweed, poppies and speedwell, but cleavers are rather resistant. Other pre-emergence uses are on sugar cane and sunflowers; and, in mixture with terbuthylazine, on beans, peas and potatoes. In mixture with metolachlor, used in cotton and peanuts. Also used post-emergence (0.2-0.4 kg/ha) in cereals, (1-3 kg/ha) in sugar cane, and as a directed spray in maize. As 'Clarosan', it is used to control algae and submerged vascular plants in waterways, reservoirs and fish ponds.
Phytotoxicity: Not safe for post-emergence use in cereals which are under stress.
Formulation types: FW; GR; MG; SC; WP.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for rats 2500, mice 500 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats >2000, rabbits >20 000 mg/kg. Not a skin or eye irritant (rabbits). Not a skin sensitiser (guinea pigs).
Inhalation: LC50 (4 h) for rats >2200 mg/m3 air.
NOEL: (2 y) for rats 300 ppm, for mice 3000 ppm; (1 y) for dogs 100 mg/kg diet daily.
ADI: 0.027 mg/kg b.w.
Other: Non-mutagenic.
Toxicity class: WHO (a.i.) III (Table 5); EPA (formulation) III
ECOTOXICOLOGY
Birds: Dietary LC50 (5 d) for bobwhite quail 5000, mallard ducks >4640 mg/kg b.w.
Fish: LC50 (96 h) for rainbow trout 1.1, bluegill sunfish 1.3, carp 1.4.
Daphnia: LC50 (48 h) 2.66 mg/l.
Algae: EC50 (7 d) for Selenastrum capricornutum 0.013 mg/l.
Other aquatic spp.: EC50 (48 h) for Quahog clam 5.6 mg/l.
Bees: Not toxic to bees. LD50 (oral) >225 ug/bee; (contact) >100 ug/bee.
Worms: LC50 for Eisenia foetida 170 mg/kg.
ENVIRONMENTAL FATE
Animals: In mammals, following oral administration, 73-85% is eliminated as the dealkylated hydroxy metabolite in the faeces within 24 hours.
Plants: In plants, terbutryn is degraded in a manner similar to other methylthio-s-triazines, viz. by oxidation of the methylthio group to hydroxy metabolites, and by dealkylation of the side-chains. Conjugates are also formed.
Soil/Environment: Soil micro-organisms play an important role in the degradation of terbutryn. Residual activity in soil is 3-10 weeks, depending upon rate of application, soil type, and weather. DT50 in soil 14-50 d. Koc 2000, indicating a low leaching potential. Degradation in aquatic systems is caused by microbial processes; photolysis also contributes. Considerable amounts of terbutryn are removed from the water by adsorption to the sediment.
