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DESIGNATIONS
CAS No.: 121-75-5
Registry name: Malathion
Chemical name: S-[1,2-bis-(Ethoxy-carbonyl)ethyl]-O,O-dimethyl-dithiophosphate
Synonyms, Trade names: O,O-Dimethyl-S-[1,2-bis(ethoxy-carbonyl)ethyl] dithiophosphate, American Cyanamide 4049, Aphisan, Carbophos, Mercaptothion and many others
Chemical name (German): Malathion
Chemical name (French): Malathion
Appearance: clear, yellowish liquid (oil); technical product (95%) is brown
BASIC CHEMICAL AND PHYSICAL DATA
| Empirical formula: | C10H19O6PS2 |
| Rel. molecular mass: | 330.36 g |
| Density: | 1.23 g/cm3 at 25°C |
| Relative gas density: | 11.4 |
| Boiling point: | 156-157°C at 1hPa |
| Melting point: | 2.8-3.7°C |
| Vapour pressure: | 16.6 x 10-3 Pa |
| Solvolysis/solubility: | in water: 145 mg/l at 25°C; soluble in organic solvents slightly soluble in petroleum ether and certain mineral oils |
| Conversion factors: | 1 ppm = 13.7 mg/m3 1 mg/m3 = 0.07 ppm |
ORIGIN AND USE
Usage:
Malathion is used in agriculture primarily as a contact pesticide
(insecticide and acaricide) to combat insects which damage by
sucking.
Origin/derivation:
Reaction of O,O-dimethyl hydrogen phosphorodithioate with diethyl
maleate in the presence of triethylamine as catalyst and
hydroquinone to prevent polymerisation of maleate.
Production figures:
| USA | 1978 | 14,000 t | (WHO, 1983) |
| India | 1980/81 | 1,264 t | (WHO, 1983) |
There are also production facilities in Denmark, France, Italy, Spain, Germany, Japan, Brazil, Mexico and Taiwan.
Consumption:
| Mexico | 1982 | 1800 t | (WHO, 1986) |
| USA | 1982 | 1500 t | (WHO, 1986) |
| India | 1982 | 800 t | (WHO, 1986) |
| Italy | 1981 | 552 t | (WHO, 1986) |
| Jordan | 1982 | 450 t | (WHO, 1986) |
| Hungary | 1982 | 313 t | (WHO, 1986) |
| Argentina | 1982 | 235 t | (WHO, 1986) |
| Egypt | 1981 | 208 t | (WHO, 1986) |
| Poland | 1982 | 104 t | (WHO, 1986) |
| Niger | 1981 | 69 t | (WHO, 1986) |
| Pakistan | 1982 | 68 t | (WHO, 1986) |
| Turkey | 1982 | 58 t | (WHO, 1986) |
Toxicity
| Mammals: | ||
| Mouse: | LD50 1,260 mg/kg, oral | acc. WHO, 1983 |
| Mouse: | LD50 193 mg/kg, intravenous | acc. WHO, 1983 |
| Rat: | LD50 1375 mg/kg, oral | acc. PERKOW, 1993 |
| Rat: | LD50 4,400 mg/kg, dermal | acc. WHO, 1983 |
| Dog: | LD50 1,600 mg/kg, intravenous | acc. WHO, 1983 |
| Guinea pig: | LD50 500 mg/kg, intravenous | acc. WHO, 1983 |
| Aquatic organisms: | ||
| American minnow: | LC50 12.5 mg/l (96 h) | acc. ATRI, 1985 |
| Rainbow trout: | LC50 0.1 mg/l (24 h) | acc. ATRI, 1985 |
| Blue perch: | LC50 0.12 mg/l (24 h) | acc. ATRI, 1985 |
| Water flea: | LC50 0.0009 mg/l (24-25h) | acc. ATRI, 1985 |
Note:
ATRI (1985) quotes countless toxicity levels for fish,
aquatic organisms in general and aquatic plants.
Characteristic effects:
Humans/mammals: Malathion is a nerve toxin and damages the central nervous system (it inhibits the enzyme acetyl cholinesterase). Acute poisoning takes the form of bouts of sweating, increased production of saliva, diarrhoea, bronchitis, heart attack and coma. Death occurs as a result of apnoea.
There are no conclusive findings on teratogeny and fertility yet. The carcinogenic and mutagenic potential has likewise not yet been proved (WHO, 1983).
Aquatic organisms: There are numerous toxicity values available for various fish species. Several months of exposure caused deformation in blue perch and inhibited lactate dehydrogenase in the liver of carp spawn. 0.1-5 ppm may prove lethal. Malathion inhibits the growth of algae.
ENVIRONMENTAL BEHAVIOUR
Air:
Malathion is released into the atmosphere as a result of the
application method used in agriculture (use as spray 0.03 -
0.08%, as vapour 4% and as aerosol 2.5-5%, WHO, 1983). After
application, a concentration of approx. 0.1 ng/m3 is
found in the air over farmland (WHO, 1983).
Half-life:
The substance is degraded within about 24 hours in the body of an
animal and excreted with its urine (substantiated in animal
experiments with hens and cows, WHO 1983).
The half-life for chemical decomposition in water (pH = 7.4, 20°C) is roughly 11 days and depends on the pH-value (slow hydrolysis with pH < 7 and rapid hydrolysis with pH >7) (ATRI, 1985).
Degradation, decomposition products:
In the organism of insects, malathion is oxidised forming malaoxon. Besides, derivatives of succinic acid and other carboxylic acids, O,O-dimethylthiophosphoric acid and phosphoric acid result from hydrolysis [acc. PERKOW,1994].
Malathion is rapidly degraded in vitro by salt-marsh bacteria to malathion monocarboxylic acid, malathion dicarboxylic acid and various phosphothionates as a result of carboxyesterase cleavage. In addition, phosphatase activity produces desmethyl malathion, phosphomono- and dithionates, 4-carbon dicarboxylic acids and the corresponding ethylesters [acc. VERSCHUEREN, 1983].
Food chain:
Malathion is assimilated by respiration and skin contact and is
absorbed in the intestines. There are no reported cases of
malathion polluting groundwater and drinking water (ATRI, 1985).
Malathion enters the food chain as a residual substance in
foodstuffs such as grain, pulses and vegetables if the areas
where they are grown are treated with malathion. This path is
significant and has caused the WHO, FAO and EC to publish
recommendations on tolerable residue concentrations.
ENVIRONMENTAL STANDARDS
| Medium/ acceptor | Sector | Country/ organ. | Status | Value | Cat. | Remarks | Source |
| Air: | Workp | B | (L) |
10 mg/m3 | acc. WHO, 1983 | ||
| Workp | BG | (L) |
0.06 mg/m3 | Maximum value | acc. WHO, 1983 | ||
| Workp | CH | (L) |
10 mg/m3 | Long-time value | acc. WHO, 1983 | ||
| Workp | D | (L) |
15 mg/m3 | MAK | DFG, 1989 | ||
| Workp | I | (L) |
10 mg/m3 | Long-time value | acc. WHO, 1983 | ||
| Workp | NL | (L) |
10 mg/m3 | acc. WHO, 1983 | |||
| Workp | PL | (L) |
15 mg/m3 | acc. WHO, 1983 | |||
| Workp | RO | (L) |
10 mg/m3 | Long-time value | acc. WHO, 1983 | ||
| Workp | RO | (L) |
15 mg/m3 | Max. | acc. WHO, 1983 | ||
| Workp | SF | (L) |
10 mg/m3 | acc. WHO, 1983 | |||
| Workp | USA | (L) |
10 mg/m3 | TWA | Skin | ACGIH, 1986 | |
| Workp | YU | (L) |
0.5 mg/m3 | acc. WHO, 1983 | |||
| Water: | Drinkw | D | L |
0.1 µg/l | single substance | acc. LAU BW, 1989 | |
| Drinkw | D | L |
0.5 µg/l | sum of pesticides | acc. LAU BW, 1989 | ||
| Drinkw | EC | L |
0.1 µg/l | single substance | acc. LAU BW, 1989 | ||
| Drinkw | EC | L |
0.5 µg/l | sum of pesticides | acc. LAU BW, 1989 | ||
| Surface | EC | L |
1 µg/l | sum of pesticides | acc. LAU BW, 1989 | ||
| Surface | EC | L |
2.5 µg/l | sum of pesticides | acc. LAU BW, 1989 | ||
| Surface | EC | L |
5 µg/l | sum of pesticides | acc. LAU BW, 1989 |
Quality requirements for surface water designated for drinking water
- simple physical treatment
- normal physical and chemical treatment
- physical and enhanced chemical treatment
Comparison/reference values
| Medium/origin | Country | Value | Source |
| Water: | |||
| Rhine: (Lobith, 1972) | D | 0.01 mg/m3 | acc. ATRI, 1985 |
| Cistern water | USA | 0.01 ppb (1970) | acc. ATRI, 1985 |
| Foodstuffs: | |||
| Fruit | D | 0.5 ppm (max.) | acc. ATRI, 1985 |
| Grain | D | 3 ppm (max.) | acc. ATRI, 1985 |
Assessment/comments
Malathion is one of the agricultural pesticides used particularly in developing countries. Special precautions must be taken when using it because of the high, acute toxicity for humans and aquatic organisms. Particular attention should be paid to residues in foodstuffs.
Special sources: ATRI (1985)