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Malathion

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 25C
Relative gas density: 11.4
Boiling point: 156-157C at 1hPa
Melting point: 2.8-3.7C
Vapour pressure: 16.6 x 10-3 Pa
Solvolysis/solubility: in water: 145 mg/l at 25C;

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, 20C) 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 g/l   single substance acc. LAU BW, 1989
Drinkw D

L

0.5 g/l   sum of pesticides acc. LAU BW, 1989
Drinkw EC

L

0.1 g/l   single substance acc. LAU BW, 1989
Drinkw EC

L

0.5 g/l   sum of pesticides acc. LAU BW, 1989
Surface EC

L

1 g/l   sum of pesticides acc. LAU BW, 1989
Surface EC

L

2.5 g/l   sum of pesticides acc. LAU BW, 1989
Surface EC

L

5 g/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)


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