IDENTIFICATION
Common name: Paraquat dichloride
Other name: methyl viologen
paraquat (BSI, E-ISO, (m) F-ISO, ANSI, WSSA, JMAF); no name (Germany)
Chemical abstracts name: 1,1`-dimethyl-4,4`-bipyridinium dichloride/1 ,l`-dimethyl-4,4`-bipyridinium [paraquat]
Type: Herbicide
CAS RN: [1910-42-5]; [2074-50-2] bis(methyl sulfate) /[4685-14-7] (paraquat)
M.F.: C12H14Cl2N2 / C12H14N2 [paraquat]
Mol Wt: 257.2 /186.3 [paraquat]
PHYSICAL CHEMISTRY
Form (appearance): Colourless, hygroscopic crystals.
Composition: Not normally isolated from the tech. products, which are >95% pure. / M.P.: Decomposes at c. 340℃
V.P.: <1 × 10-2 mPa (25℃)
S.G.: 1.24-1.26 (20℃)
Solubility.: In water c. 620 g/l (20℃). Practically insoluble in most organic solvents.
Stability: Stable in neutral and acidic media, but readily hydrolysed in alkaline media.
Photochemically decomposed by u.v, irradiation in aqueous solution.
Henry: <4 × 10-9 Pa m3 mol-1 (catc.)
KowlogP: -4.5 (20℃)
APPLICATION
Formulation types: SL
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.
Compatibility: Incompatible with all< materials. inert clay-containing and surfactants, anionic materials,
MAMMALIAN TOXICOLOGY
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) [1986].
Toxicity: WHO (a.i.) II; EPA (formulation) II (oral, a.i.); III (dermal, a.i.)
EC hazard: T; R24/25|Xi; R36/37/38 (applies to all salts)
ECOTOXICOLOGY
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 pheasants 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.
Worms: LC50 >1380 mg/kg soil.
/Bees LD50 (72 h) (oral) 36 μg/bee; (contact) 150 μg/bee.
ENVIRONMENTAL FATE
Plant: EHC 39 (WHO, 1984).
On plant surfaces, photochemical degradation occurs. Degradation products which have been isolated include 1-methyl-4-carboxypyridinium chloride and methylamine hydrochloride.
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.
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 >10000.
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