Parathion

Parathion

DESIGNATIONS

CAS No.: 56-38-2
Registry name: Parathion
Chemical name: O,O-Diethyl-O-4-nitrophenyl-thiophosphate
Synonyms, Trade names: Parathion-ethyl, O,O-Diethyl-O-4-nitrophenyl-phosphorothioate, E 605, Eftol, Folidol
Chemical name (German): Parathion, Ethyl-Parathion
Chemical name (French): Parathion
Appearance: yellowish to dark brown liquid with garlic odour

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula:	C₁₀H₁₄NO₅PS
Rel. molecular mass:	291.27 g
Density:	1.265 g/cm³
Boiling point:	375°C (above 160°C, parathion isomerises slowly to form O,S-Diethyl-O-4-nitrophenyl-thiophosphate which is less stable and less effective)
Melting point:	6.1°C
Vapour pressure:	5 x 10^-3 Pa
Flash point:	> 120°C
Ignition temperature:	(may be marketed in flammable mixtures)
Solvolysis/solubility:	in water: 24 mg/l at 25°C soluble in most organic solvents: in dichloromethane, 2-propanol, toluene > 200 g/l; in n-hexane 50-100 g/l; very slightly soluble in kerosene and mineral oil
Conversion factors:	1 mg/m³ = 0.083 ppm 1 ppm = 12.106 mg/m³

ORIGIN AND USE

Usage:
Parathion is a broad-spectrum insecticide which acts as a contact, feed or respiratory poison. It is widely used against biting and sucking insects in agriculture, fruit-, vegetable- and winegrowing as well as against mites, beetles and caterpillars. It is usually applied as a spray (emulsion: 500 g/l; oil: 10%).

Origin/derivation:
Emissions are mainly caused by the production and the use of parathion.

Toxicity

Humans:	LD₅₀ 3-5 mg/kg, oral (estimated)	acc. PERKOW, 1992
Humans:	LD 5-15 mg/kg (pure subst.), oral	acc. UBA, 1986
Mammals:
Rat	LD₅₀ 3.6-13 mg/kg, oral	acc. PERKOW, 1992
	LD₅₀ 6.8-21 mg/kg, dermal	acc. PERKOW, 1992
	LC₅₀ 0.05 mg/l (4h), inhalation	acc. PERKOW, 1992
	NOEL 10 mg/kg feed (2a)	acc. PERKOW, 1992
	TDLo 0.36 mg/kg (2.-22. day of pregnance), oral	acc. UBA, 1986
Mouse	LD₅₀ 12.8-25 mg/kg, oral	acc. PERKOW, 1992
Guinea pig	LD₅₀ 16-32 mg/kg, oral	acc. PERKOW, 1992
Insects:
Bees	LD₅₀ 0.11 mg/bee, contact	acc. PERKOW, 1992
Bees	LD₅₀ 0.28 mg/bee, oral	acc. PERKOW, 1992
Aquatic organisms:
Rainbow trout	LC₅₀ 1.43 mg/l (96 h)	acc. PERKOW, 1992
Perch	LC₅₀ 0.4 mg/l (96 h)	acc. PERKOW, 1992
Goldfish	LC₅₀ 1.83 mg/l (96 h)	acc. PERKOW, 1992
Golden orfe	LC₅₀ 0.57 mg/l (96 h)	acc. PERKOW, 1992
	LC₀ 0.26 mg/l, (96h)	acc. HOMMEL, 1993
	LC₅₀ 0.48 mg/l, (96h)	acc. HOMMEL, 1993
	LC₁₀₀ 1.2 mg/l, (96h)	acc. HOMMEL, 1993

Characteristic effects:

Humans/mammals: Human poisoning can result from oral intake, inhalation or dermal exposure. Parathion is readily adsorbed and distributed in the organism. It irreversibly inhibits the acetylcholinesterase enzyme and thus disrupts the normal functioning of the central nervous system. Typical symptoms of acute poisoning are headache, sweating and faintness followed by impaired vision, gastrointestinal disorders, shortness of breath, tremors, convulsions, unconsciousness, pulmonary paralysis and finally cardiac arrest. These symptoms may also appear after a delay of several hours [UBA, 1986].

Plants: Tolerance is generally good. Some strains of apples, cucumbers and tomatoes are sensitive to overfeeding.

ENVIRONMENTAL BEHAVIOUR

Water:
The half life in aqueous solutions is strongly dependent on the pH. At low pH, hydrolysis is very slow but in a neutral and especially in an alkaline environment, it takes place much faster. In addition, the hydrolysis rate rises with increasing temperature [KOCH, 1989].

pH	temperature	half-life
1-5	0°C	3000 d
	20°C	690 d
	30°C	180 d
8	20°C	99 d

In experiments carried out in a sealed glass jar (initial concentration: 10 mg/l) in sunlight and under artificial fluorescent light, residues of 50% have been detected after 1 week. After 4 weeks, residues of less then 5% have been detected and after 8 weeks no residues could be detected [VERSCHUEREN, 1983].

Soil:
The data on the persistence of parathion in soil are varying: the persistence of organophosphorus insecticides is generally low. The half-life of parathion is about 3-6 months [ULLMANN, 1989].

After 3 weeks, residues of 5% and after 15 weeks residues of 3.2% have been detected in sandy-loamy soil. In organic soil, residues of 5% have been found after 10 weeks. Residues are detectable up to 16 years following the application [PERKOW, 1992; VERSCHUEREN, 1983].

Degradation, decomposition products:
In the organism of mammals, parathion is oxidised forming the more toxic paraoxone, and hydrolysed forming nitrophenol and diethyl phosphate. It is excreted relatively fast mainly via urine (86-93%) [PERKOW, 1992].

ENVIRONMENTAL STANDARDS

Medium/ acceptor	Sector	Country/organ.	Status	Value	Cat.	Remarks	Source
Water:	Drinkw	D	L	0.1 mg/l		single substance	acc. KOCH, 1989
	Drinkw	D	L	0.5 mg/l		sum of pesticides	acc. KOCH, 1989
	Drinkw	SU	L	0.3 mg/l			acc. KOCH, 1989
	Surface	EC	G	1 mg/l	¹⁾	physical treatment	acc. LAU-BW, 1989
	Surface	EC	G	2.5 mg/l	¹⁾	physical / chemical treatment	acc. LAU-BW, 1989
	Surface	EC	G	5 mg/l	1)	physical / intensified chemical treatment	acc. LAU-BW, 1989
Air:	Workp	D	L	0.1 mg/m³	MAK	Skin	acc. AUER TECHNIKUM, 1988
	Workp	D	L	500 mg/l	BAT	2)	acc. AUER TECHNIKUM, 1988
	Workp	SU	(L)	0.05 mg/m³	PDK	Skin	acc. AUER TECHNIKUM, 1988
	Workp	USA	(L)	0.1 mg/m³	TWA	Skin	acc. AUER TECHNIKUM, 1988
	Workp	USA	(L)	0.3 mg/m³	STEL	Skin	acc. UBA, 1986

1)Quality requirements for the preparation of drinking water from surface water.
2) parameter: p-nitrophenol plus acetylcholinesterase in blood

Assessment/comments

Parathion is only moderately persistent in the environment and does not accumulate in the pedosphere or in the biosphere. On the other hand, it lacks sensitivity and is highly toxic to bees, beneficial parasites, fish, mammals and humans.

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