Introduction: Paraquat is a quaternary nitrogen herbicide widely used for broadleaf weed control. It is a quick-acting, nonselective compound, that destroys green plant tissue on contact and by translocation within the plant. It has been employed for killing marijuana in the U.S. and in Mexico. It is also used as a crop desiccant and defoliant, and as an aquatic herbicide.
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42% Paraquat TC,
200 g/L Paraquat SL
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Paraquat FAO standard
Common name: Paraquat
Another name: Crisquat, Cyclone, Dextrone, Dexuron, Gramoxone Extra, Herbaxone, Ortho Weed and Spot Killer, and Sweep.
Chemical Name: 1,1'-dimethyl-4,4'-bipyridinediium; 1,1'-dimethyl-4,4'-bipyridinium; 1,1'-dimethyl-4,4'-bipyridylium.
Empirical formula: C12H14Cl2N2
Mol. Weight: 186.3
CAS No.: 4685-14-7
Inhalation: Cough. Laboured breathing. Sore throat.
Skin contact: Harmful if absorbed through skin..
Eyes contact: Causes substantial but temporary eye injury
Ingestion: May be fatal if swallowed.
Product analysis by colorimetry (AOAC Methods, 17th Ed., 969.09; CIPAC Handbook, 1992, E, 166-168; 1995, G, 128); free 4,4'-bipyridyl, ibid., 1998, H, 216; in mixture with diquat, by colorimetry (CIPAC Handbook, 1992, E, 73-78; ibid., 1995, G, 49). Residues determined by colorimetry after reduction (Pestic. Anal. Man., 1979, II; A. Calderbank & S. H. Yuen, Analyst (London), 1965, 90, 99; P. F. Lott et al., J. Chromatogr. Sci., 1978, 16, 390; J. B. Leary, Anal. Methods Pestic. Plant Growth Regul., 1978, 10, 321). Residues in potatoes by rplc with dual channel u.v. detection (AOAC Methods, 17th Ed., 992.17). Details of methods available from Syngenta.
Reviews FAO/WHO 47, 49 (see part 2 of the Bibliography). Oral Acute oral LD50 for rats 157-129, guinea pigs 30-58 mg/kg. Skin and eye Acute percutaneous LD50 for rats 911 mg paraquat ion/kg. Irritating to skin and eyes (rabbits). Absorption through intact human skin is minimal; exposures can cause irritation and a delay in the healing of cuts and wounds; can cause temporary damage to nails. Not a skin sensitiser (guinea pigs). Inhalation No vapour toxicity. Extreme exposure to spray droplets may cause nose bleeding. NOEL (1 y) for dogs 0.65 mg/kg b.w. daily; (2 y) for rats 1.7 mg/kg b.w. daily. ADI (JMPR) 0.004 mg/kg b.w. (as paraquat ion) . Toxicity class WHO (a.i.) II; EPA (formulation) II (oral, a.i.); III (dermal, a.i.) EC classification T+; R26| T; R24/25, R48/25| Xi; R36/37/38| N; R50, R53
Birds Acute oral LD50 for bobwhite quail 175, mallard ducks 199 mg/kg. LC50 (5 d) for bobwhite quail 981, Japanese quail 970, mallard ducks 4048, ring-necked pheasant 1468 mg/kg. Fish LC50 (96 h) for rainbow trout 26, mirror carp 135 mg/l. Daphnia EC50 (48 h) 6.1 mg/l. Algae EbC50 (96 h) 0.10 mg/l; ErC50 0.28 mg/l. Bees LD50 (72 h) (oral) 36 mg/bee; (contact) 150 mg/bee. Worms LC50 >1380 mg/kg soil.
EHC 39 (WHO, 1984). Animals In rats, following oral administration, 76-90% of the dose was excreted in the faeces, and 11-20% in the urine. Paraquat does not bioaccumulate, with >90% of the dose eliminated in 72 h. Plants On plant surfaces, photochemical degradation occurs. Degradation products which have been isolated include 1-methyl-4-carboxypyridinium chloride and methylamine hydrochloride. Soil/Environment Paraquat is rapidly degraded by soil micro-organisms (DT50 of unadsorbed paraquat <1 w). Strong binding in soil increases persistence. Paraquat is strongly bound and inactivated by soil and aquatic sediments, and does not leach into groundwater; Kd >10 000.
Usage: Broad-spectrum control of broad-leaved weeds and grasses in fruit orchards (including citrus), plantation crops (bananas, coffee, cocoa palms, coconut palms, oil palms,
rubber, etc.), vines, olives, tea, alfalfa, onions, leeks, sugar beet, asparagus, ornamental trees and shrubs, in forestry, etc. Also used for general weed control on non-crop land; as a defoliant for cotton and hops; for destruction of potato haulms; as a desiccant for pineapples, sugar cane, soya beans, and sunflowers; for strawberry runner control; in pasture renovation; and for control of aquatic weeds. For control of annual weeds.
Application: Biochemistry During photosynthesis, superoxide is generated, which damages cell membranes and cytoplasm. Mode of action Non-selective contact herbicide, absorbed by the foliage, with some translocation in the xylem. Uses Broad-spectrum control of broad-leaved weeds and grasses in fruit orchards (including citrus), plantation crops (bananas, coffee, cocoa palms, coconut palms, oil palms, rubber, etc.), vines, olives, tea, alfalfa, onions, leeks, sugar beet, asparagus, ornamental trees and shrubs, in forestry, etc. Also used for general weed control on non-crop land; as a defoliant for cotton and hops; for destruction of potato haulms; as a desiccant for pineapples, sugar cane, soya beans, and sunflowers; for strawberry runner control; in pasture renovation; and for control of aquatic weeds. For control of annual weeds, applied at 0.4-1.0 kg/ha.