Herbicide
HRAC  K1 WSSA  3; dinitroaniline



NOMENCLATURE
Common name trifluralin (BSI, E-ISO, ANSI, WSSA, JMAF); trifluraline ((f) F-ISO)
IUPAC name a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine 
Chemical Abstracts name 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine 
CAS RN [1582-09-8]  EEC no. 216-428-8  Development codes L-36 352 (DowElanco); EL-152

PHYSICAL CHEMISTRY
Mol. wt. 335.3  M.f. C₁₃H₁₆F₃N₃O₄  Form Yellow-orange crystals.  M.p. 48.5-49 ºC; (tech., 43-47.5 ºC)  B.p. 96-97 °C/24 Pa  V.p. 6.1 mPa (25 ºC) (EEC A4)  K_OW logP = 4.83 (20 ºC) (EEC A8)  Henry 15 Pa m³ mol^-1 (calc.)  S.g./density 1.36 (22 ºC) (EEC A3)  Solubility In water 0.184 (pH 5), 0.221 (pH 7), 0.189 (pH 9) (all in mg/l) (EEC A6); tech. 0.343 (pH 5), 0.395 (pH 7), 0.383 (pH 9) (all in mg/l) (EEC A6). In acetone, chloroform, acetonitrile, toluene, ethyl acetate >1000, methanol 33-40, hexane 50-67 (all in g/l, 25 ºC).  Stability Stable at 52 ºC (highest storage temperature tested). Stable to hydrolysis at pH values of 3, 6 and 9 (52 ºC). Decomposed by u.v. irradiation (E. Leitis & D. G. Crosby, J. Agric. Food Chem., 1974, 22, 842).  F.p. 151 ºC (closed cup); tech. 153 ºC (open cup) (both Pensky-Martens) 

COMMERCIALISATION
History Herbicide reported by B. C. Byrd et al. (Proc. West. Soc. Weed Sci., 1975, 28, 44). Introduced by Dow Chemical Co. (now Dow AgroSciences).  Manufacturers Agriphar; Aimco; Dow AgroSciences; Gharda; Punjab

APPLICATIONS
Biochemistry Microtubule assembly inhibition.  Mode of action Selective soil-herbicide, which acts by entering the seedling in the hypocotyl region. Also inhibits root development.  Uses Pre-emergence control of many annual grasses and broad-leaved weeds in brassicas, beans, peas, carrots, parsnips, lettuce, capsicums, tomatoes, artichokes, onions, garlic, vines, strawberries, raspberries, citrus fruit, oilseed rape, peanuts, soya beans, sunflowers, safflowers, ornamentals, cotton, sugar beet, sugar cane, and in forestry. Used with linuron or isoproturon for control of annual grasses and broad-leaved weeds in winter cereals. Normally applied pre-planting with soil incorporation, at 0.5-1.0 kg a.i./ha, but post-planting application is also possible for some crops.  Formulation types EC; GR.

ANALYSIS
Product analysis by glc with FID (CIPAC Handbook, 1980, 1A, 1362; AOAC Methods, 1995, 973.14) or by u.v. spectrometry (ibid., 973.13). Residues determined by glc with ECD (J. B. Tepe & R. E. Scroggs, Anal. Methods Pestic., Plant Growth Regul. Food Addit., 1967, 5, 527; Anal. Methods Pestic. Plant Growth Regul., 1972, 6, 703). In drinking water by gc with ECD (AOAC Methods, 1995, 990.06). Details from Dow AgroSciences. 

MAMMALIAN TOXICOLOGY
IARC ref. 53  class 3  Oral Acute oral LD₅₀ for rats >5000 mg/kg.  Skin and eye Acute percutaneous LD₅₀ >5000 mg/kg (rabbits). Non-irritating to skin; slightly irritating to eyes (rabbits).  Inhalation LC₅₀ (4 h) for rats >4.8 mg/l.  NOEL In 2 y feeding trials in rats, the only effect at the low dose of 813 mg/kg in diet was the formation of renal calculi. This has been shown to be reversible in a 90 d study in dogs, and a NOEL established at 2.4 mg/kg daily. NOEL in mice was 73 mg/kg daily.  ADI 0.024 mg/kg.  Water GV 20 mg/l (TDI 7.5 mg/kg b.w.).  Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) III, IV  EC hazard Material containing <0.5 ppm NPDA is Xi; R36| R43 

ECOTOXICOLOGY
Birds Acute oral LD₅₀ for bobwhite quail >2000 mg/kg. Dietary LC₅₀ (5 d) for bobwhite quail and mallard ducks >5000 mg/kg.  Fish LC₅₀ (96 h) for young rainbow trout 0.088, young bluegill sunfish 0.089 mg/l.  Daphnia LC₅₀ (48 h) 0.245 mg/l; NOEC (21 d) 0.051 mg/l.  Algae EC₅₀ (7 d) for Selenastrum capricornutum 12.2 mg/l; NOEC 5.37 mg/l.  Other aquatic spp. LD₅₀ (96 h) for grass shrimp (Palaemonetes sp.) 0.64 mg/l.  Bees LD₅₀ (oral and contact) >100 mg/bee.  Worms LC₅₀ (14 d) >1000 mg/kg dry soil; NOEC (reduced bodyweight) <171 mg/kg.

ENVIRONMENTAL FATE
Animals Degradation in animals is as for soil (J. L. Emmerson & R. C. Anderson, Toxicol. Appl. Pharmacol., 1966, 9, 84-97). Following oral administration, c. 70% is eliminated in the urine and 15% in the faeces within 72 h.  Plants Degradation in plants is as for soil.  Soil/Environment Adsorbed by the soil, and is extremely resistant to leaching. Little lateral movement in the soil. Metabolism involves dealkylation of the amino group, reduction of the nitro group to an amino group, partial oxidation of the trifluoromethyl group to a carboxy group, and subsequent degradation to smaller fragments (T. Golab et al., J. Agric. Food Chem., 1979, 27, 163); DT₅₀ 57-126 d. Duration of residual activity in soil is 6-8 mo. In laboratory studies, degradation was more rapid under anaerobic conditions, e.g. for loam soil, DT₅₀ (anaerobic) 25-59 d, DT₅₀ (aerobic) 116-201 d. Soil photolysis DT₅₀ 41 d; aqueous photolysis DT₅₀ 0.8 h. K_oc 4400-40 000; K_d ranges from 3.75 (0.01% o.m., pH 6.6) to 639 (16.9% o.m., pH 6.8) (H. J. Pedersen et al., Pestic. Sci., 44, 131 (1995)).