HRAC D WSSA 22; bipyridylium

NOMENCLATURE

diquat dibromide

IUPAC name 1,1'-ethylene-2,2'-bipyridyldiylium dibromide
CAS RN [85-00-7]; [6385-62-2] for diquat dibromide monohydrate EEC no. 201-579-4

diquat

Common name diquat (BSI, E-ISO, (m) F-ISO, ANSI, WSSA, JMAF); deiquat (Germany); reglon* (former exception, USSR)
IUPAC name 1,1'-ethylene-2,2'-bipyridyldiylium; 9,10-dihydro-8a,10a-diazoniaphenanthrene; 6,7-dihydrodipyrido-[1,2-a:2',1'-c]pyrazine-5,8-di-ium
Chemical Abstracts name 6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium
CAS RN [2764-72-9] EEC no. 220-433-0

PHYSICAL CHEMISTRY

diquat dibromide

Mol. wt. 344.1 M.f. C12H12Br2N2 Form Colourless to yellow crystals. M.p. decomposes above 325 oC (monohydrate) V.p. <0.01 mPa (monohydrate) KOW logP = -4.60 (20 oC) Henry 5 ? 10-9 Pa m3 mol-1 (calc.) S.g./density 1.61 (25 °C) Solubility In water 700 g/l (20 oC). Slightly soluble in alcohols and hydroxylic solvents (25 g/l). Insoluble in non-polar organic solvents (<0.1 g/l). Stability Stable in neutral and acidic solutions, but readily hydrolysed in alkaline solutions. DT50 at pH 7 in simulated sunlight c. 74 d. Photochemically decomposed by u.v. irradiation, DT50 <1 w.

diquat

Mol. wt. 184.2 M.f. C12H12N2

COMMERCIALISATION

History Herbicide reported by R. C. Brian et al. (Nature (London), 1958, 181, 446). Introduced by ICI Plant Protection Division (now Syngenta AG) and first marketed in 1962. Patents GB 785732

APPLICATIONS

diquat dibromide

Biochemistry During photosynthesis, superoxide is generated, which damages cell membranes and cytoplasm. Mode of action Non-selective contact herbicide and desiccant, absorbed by the foliage, with some translocation in the xylem. Uses Pre-harvest desiccation of cotton, flax, alfalfa, clover, lupins, oilseed rape, poppies, soya beans, peas, beans, sunflowers, cereals, maize, rice, sugar beet, and other seed crops; destruction of potato haulms; and stripping of hops. Control of annual broad-leaved weeds in vines, pome fruit, stone fruit, bush fruit, strawberries (also control of runners), citrus fruit, olives, hops, vegetables, ornamental plants and shrubs, and other crops. Control of emergent and submerged aquatic weeds. Weed control on non-crop land. Weed control and tassel inhibition in sugar cane. Application rates 400-1000 g/ha. Formulation types SL; Gel. Compatibility Incompatible with alkaline materials, anionic surfactants (e.g. alkyl sulfonates or alkyl aryl sulfonates), and alkali-metal salts of hormone-type herbicides. Selected tradenames: 'Reglone' (Syngenta); 'Desiquat' (Barclay); 'Reglex' (Caffaro); mixtures: 'Seccatuttu' (+ paraquat dichloride) (Syngenta)

OTHER TRADENAMES

diquat dibromide

'Barclay Desiquat' (Barclay); 'Boomerang' (GreenCrop) mixtures: 'PDQ' (+ paraquat dichloride) (Syngenta); 'Preeglox L' (+ paraquat dichloride) (Syngenta); 'Myzet' (+ paraquat dichloride) (Otsuka); 'Spray Seed' (+ paraquat dichloride) (ICI Australia) (Crop Care) Discontinued names mixtures: 'Preglox' * (+ paraquat dichloride) (Zeneca); 'Allzett' * (+ glyphosate) (glyphosate as trimethylsulfonium salt) (Zeneca, Otsuka)

ANALYSIS

Product analysis by u.v. spectrophotometry (AOAC Methods, 1995, 969.08; CIPAC Handbook, 1970, 1, 342; 1992, E, 73-78; 1995, G, 47); impurities measured by glc (ibid., 1980, 1A, 1245; Herbicides 1977, p. 48). Residues determined by colorimetry (M. G. Ashley, Pestic. Sci., 1970, 1, 101; A. Calderbank et al., Analyst (London), 1961, 86, 569; A. Calderbank & S. H. Yuen, ibid., 1965, 90, 95; 1966, 91, 625; J. E. Pack, Anal. Methods Pestic., Plant Growth Regul. Food Addit., 1967, 5, 397; J. B. Leary, Anal. Methods Pestic. Plant Growth Regul., 1978, 10, 321; Pestic. Anal. Man., 1979, II). Residues in potatoes by rplc with dual channel u.v. detection (AOAC Methods, 1995, 992.17). Details available from Syngenta.

MAMMALIAN TOXICOLOGY

diquat dibromide

Reviews FAO/WHO 68, 70 (see part 2 of the Bibliography). Oral Acute oral LD50 for rats 408, mice 234 mg/kg. Skin and eye Acute percutaneous LD50 for rats >793 mg/kg. Irritating to skin and eyes (rabbits). Absorption through intact human skin is minimal; exposure can cause irritation and a delay in the healing of cuts and wounds. Can cause temporary damage to nails. Inhalation Extreme exposure to spray droplets may cause nose bleeding. NOEL (2 y) for rats 0.47 mg/kg b.w. daily; (4 y) for dogs 94 mg/kg diet. ADI (JMPR) 0.002 mg cation/kg b.w. [1993]; (EPA) 0.005 mg cation/kg b.w. [1995]. Water GV 10 ?g cation/kg b.w. (provisional; based on ADI). Toxicity class WHO (a.i.) II (cation); EPA (formulation) II (a.i.) EC hazard T+; R26| T; R48/25| Xn; R22| Xi; R36/37/38| R43| N; R50, R53

ECOTOXICOLOGY

diquat dibromide

Birds Acute oral LD50 for mallard ducks 155, partridges 295 mg/kg. Fish LC50 (96 h) for rainbow trout 39, mirror carp 125 mg/l. Daphnia LC50 (48 h) 2.2 ?g/l. Algae EC50 (96 h) 21 ?g/l. Bees LD50 (oral, 120 h) 22 ?g/bee. Worms LC50 (14 d) 243 mg/kg.

ENVIRONMENTAL FATE

EHC 39 (WHO, 1984). Animals In rats, following oral administration of diquat dibromide, the dose is completely eliminated in the urine and faeces within 4 days. Plants Metabolic breakdown of diquat dibromide does not occur in plants. On plant surfaces, photochemical degradation occurs. Soil/Environment Rapidly degraded by soil micro-organisms, DT50 of unadsorbed diquat <1 w; strong binding in soil increases persistence. Strongly bound and inactivated by soil and aquatic sediments and does not leach into groundwater; Kd >10 000.