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DESIGNATIONS
CAS No.: 1910-42-5; 4685-14-7 (Paraquat dichloride)
Registry names: Paraquat
Chemical name: 1,1'-Dimethyl-(4,4'-bipyridinium) cation
Synonyms, Trade names: 1,1'-Dimethyl-(4,4'-bipyridinium) [dichloride], N,N'-dimethyl-4,4'-bipyridinium chloride, methylviologen, Gramoxone, Gramoxon, Terraklene, Weedol, Dextrone X and many others
Chemical name (German): Paraquat [Dichlorid];1,1'-Dimethyl-(4,4'-bipyridinium) [Dichlorid]
Chemical names (French): [Dichlorure de] paraquat, [dichlorure de] 1,1'-diméthyl-(4,4'-dipyridinium)
Appearance: pure paraquat salt is a white, crystalline, odourless powder; the technical product has a yellowish appearance.
BASIC CHEMICAL AND PHYSICAL DATA
Note: |
All data refer to the dichloride. |
Empirical formula: |
C12H14N2 [ C12H14Cl2N2 ] |
Rel. molecular mass: |
257.2 g |
Density: |
1.25 g/cm3 at 20°C |
Relative gas density: |
8.88 |
Boiling point: |
decomposition |
Melting point: |
above » 300°C decomposition |
Vapour pressure: |
very low (<10-3 Pa at 20°C; also 10-5 Pa at 20°C cited) |
Ignition temperature: |
(may be marketed in flammable mixtures) |
Solvolysis/solubility: |
in water 700 g/l at 20°C; soluble in alcohol; insoluble in organic solvents |
Conversion factors: |
1 ppm = 10.7 mg/m3 |
1 mg/m3 = 0.094 ppm |
ORIGIN AND USE
Usage:
Paraquat is a non-selective contact herbicide used in particular in the cultivation of
fruit and vines to combat weeds directly before cultivating useful plants. The sulphate or
chloride is normally used. There is a ban in Germany on substances which have only
paraquat as active substance for treating plants.
Origin/derivation:
Paraquat is produced synthetically. There are no known natural sources. Paraquat is part
of the bipyridinium derivative group. Two technical products are manufactured:
1,1'-dimethyl-4,4'-bipyridinium dichloride and 1,1'-dimethyl-4,4'-bipyridinium dimethyl
sulphate. The product is synthesised from pyridine, by treatment with sodium in liquid
ammonia, followed by oxidation to form 4,4'-bipyridine, and subsequent methylation.
Production figures:
Paraquat is produced in a number of countries (e.g. People's Republic of China,
Taiwan, Italy, Great Britain, USA). It is applied in more than 130 countries (normally as
paraquat dichloride, in the (former) USSR as paraquat dimethyl phosphate). Production
figures are not available (WHO, 1984).
Toxicity
Humans: |
DTA 0.008 mg/kg |
acc. DFG, 1985 |
Mammals: |
||
Mouse: |
LD50 100-120 mg/kg, oral |
acc. DVGW, 1988 |
Mouse: |
LD50 62 mg/kg, dermal |
acc. WHO, 1984 |
Rat: |
LD50 100-150 mg/kg, oral |
acc. DVGW, 1988 |
Rat: |
LD50 80-90 mg/kg, dermal |
acc. DVGW, 1988 |
Rat: |
LC50 1-10 mg/m3, inhalation |
acc. WHO, 1984 |
Dog: |
LD50 25-50 mg/kg, oral |
acc. DVGW, 1988 |
Cat: |
LD50 30-50 mg/kg, oral |
acc. DVGW, 1988 |
Rabbit: |
LD50 120-130 mg/kg, oral |
acc. DVGW, 1988 |
Rabbit: |
LD50 236-500 mg/kg, dermal |
acc. WHO, 1984 |
Guinea pig: |
LD50 20-40 mg/kg, oral |
acc. DVGW, 1988 |
Guinea pig: |
LD50 319 mg/kg, dermal |
acc. WHO, 1984 |
Guinea pig: |
LC50 4 mg/m3, inhalation |
acc. WHO, 1984 |
Monkey: |
LD50 50 mg/kg, oral |
acc. WHO, 1984 |
Aquatic organisms: |
||
Guppy: |
LC50 21.8-46.4 mg/l (96h) |
acc. DVGW, 1988 |
Sun perch: |
LC50 100 mg/l (48h) |
acc. DVGW, 1988 |
Sun perch: |
LC50 12 mg/l (96h) |
acc. DVGW, 1988 |
Trout: |
LC50 4.5-32 mg/l (96h) |
acc. DVGW, 1988 |
Crawfish: |
LC50 11 mg/l (96h) |
acc. DVGW, 1988 |
Characteristic effects:
Humans/mammals: Paraquat is toxic for humans and damages the kidneys, liver and lungs. In aqueous form the herbicide has a caustic effect on the skin, mucous membranes and conjunctiva; it is absorbed through the skin. There is also good absorption of paraquat via the lungs where the substance is stored. However, resorption is usually minimal (5% of the amount absorbed) (DVGW, 1988). Metabolisation in the body is likewise very limited; most of the substance is excreted without undergoing change.
Animal experiments have not revealed any increase in the tumour rate due to paraquat. Genetic toxicity and teratogenic effects have been substantiated with certain species of animal.
Plants: Paraquat is absorbed by plant leaves only from the aqueous solutions of its salts. Absorption takes place more readily and more effectively in the dark than in daylight. It is transported with the perspiration flow in the xylem. Phytotoxicity is only encountered in daylight and with sufficient oxygen content. There is a sustained
ENVIRONMENTAL BEHAVIOUR
Water:
Paraquat is adsorbed on suspended matter and on sediment in water or absorbed by plants.
The herbicide finds its way into the water either following direct usage or by erosion
from neighbouring areas. If paraquat is not subject to sorption, it is rapidly degraded by
microorganisms and thus no longer effective. Because of this, there is only a low risk of
groundwater pollution.
Air:
Small quantities of paraquat are released into the air as a function of the type of
application (as spray or mixed with liquid). The crucial factor is, however, whether
paraquat is inhaled during application or resorbed through the skin. Passage through the
skin represents the principal way of assimilation. The half-life in air is reported
between a period of several hours up to 64 days.
Soil:
Paraquat is subject to considerable sorption in clay soils. In topsoils with a high
content of organic matter, it is more or less immobile and then it may not be absorbed by
plants. Depending on the type of soil, paraquat remains in the uppermost soil horizon.
Because of the high sorption rate, there is no elution by seepage water and no
metabolisation by microorganisms.
Half-life:
When used in water, paraquat could not be detected after 1-4 days; residues were still
found in sludge after more than 400 days. The half-life in sandy clays is about 7 years.
Degradation, decomposition products:
Photochemical degradation results in less toxic decomposition products. Biological
degradation in the soil leads to rapid decline of the amount applied, but also to a
reduction in the population density of the microorganisms.
Food chain:
No accumulation by way of food chains.
ENVIRONMENTAL STANDARDS
| Medium/acceptor | Sector | Country/organ. | Status | Value | Cat. | Remarks | Source |
| Water: | Drinkw | D | L |
0.1 µg/l |
acc. DVGW, 1988 | ||
| Drinkw | EC | L |
0.1 µg/l |
acc. DVGW, 1988 | |||
| Surface | EC | L |
0.001 mg/l |
1) | acc. DVGW, 1988 | ||
| Surface | EC | L |
0.0025 mg/l |
2) | acc. DVGW, 1988 | ||
| Surface | EC | L |
0.005 mg/l |
3) | acc. DVGW, 1988 | ||
| Air: | Workp | BG | (L) |
0.01 mg/m3 |
acc. WHO, 1984 | ||
| Workp | D | L |
0.1 mg/m3 |
MAK | acc. DFG, 1994 | ||
| Workp | H | (L) |
0.02 mg/m3 |
acc. WHO, 1984 | |||
| Workp | USA | (L) |
0.1 mg/m3 |
TWA | ACGIH, 1986 |
Notes:
The use of paraquat in the cultivation of cereals is banned in the Federal Republic of
Germany (Order Governing Use of Pesticides, as at 1988).
1) Limit value for physical treatment and sterilisation of drinking water
2) Limit value for physical and chemical treatment/sterilisation of drinking
water
3) Limit value for physical and refined chemical treatment of drinking water
Assessment/comments
Paraquat is a strong contact herbicide; inhalation and skin contact should be avoided when using it. Use of the substance is not recommended because of the high toxicity for humans and animals. This recommendation is further strengthened by the high persistence in soil.