Description
Methyl parathion is an organophosphate insecticide. It is converted into an oxon-containing metabolite
in vivo, similar to other organophosphate pesticides, that inhibits acetylcholinesterase. Methyl parathion is lethal to lab strains and field isolates of tobacco budworm larvae (LD
50s = 7 and 81.8-128.3 μg/g, respectively). It reduces the number of stink bugs (
C. sayi) caught per 100 net sweeps when applied to alfalfa fields at a concentration of 0.4 pounds per acre. Methyl parathion increases sister chromatid exchange (SCE) in a concentration-dependent manner and induces cell cycle arrest at the M
1 phase in V79 cells at a concentration of 40 μg/ml. It is toxic to rats (LD
50 = 14 mg/kg).
Chemical Properties
Methyl parathion is a white to yellow-brown, crystalline solid with a garlic odor.It is slightly soluble in water and has a low vapor pressure (U.S. EPA, 2006b).
Uses
Parathion-methyl is an derivative of Parathion (P192220), an organophosphate insecticide used on cotton, rice and fruit trees.
Uses
Methyl parathion is an insecticide and acaricide used to control boll weevils and many biting or sucking insect pests of agricultural crops. It kills insects by contact, stomach and respiratory action. Methyl parathion is available in dust, emulsifiable concentrate, ULV liquid, microencapsules and wettable powder formulations.
Methyl parathion is one of a class of insecticides referred to as organophosphates. These chemicals act by interfering with the activities of cholinesterase, an enzyme that is essential for the proper working of the nervous systems of humans, animals and insects.
Definition
ChEBI: Parathion-methyl is a C-nitro compound that is 4-nitrophenol substituted by a (dimethoxyphosphorothioyl)oxy group at position 4. It is a synthetic organic thiophosphate compound and organophosphate acetylcholinesterase inhibitor that is the methyl homolog of parathion and is used as a pesticide. It is characterized as a colorless to white or tan crystalline solid that is odorless or has a pungent garlic-like odor, and exposure occurs by inhalation, ingestion, or contact.
Application
Parathion-methyl is a restricted use organophosphate sold under a number of trade names and formulations. First registered in 1954, it is used to control a variety of insect pests on food and feed crops. Methyl parathion is not used in residential settings due to its toxicity to humans, birds, and honey bees. The chemical is a restricted use pesticide with nearly 4 million pounds of active ingredient mainly used on cotton, corn, wheat, soybeans, and rice (U.S. EPA, 2006b).
General Description
Methyl parathion is a white crystalline solid dissolved in a liquid solvent carrier. The commercial product is a tan liquid (xylene solution) with a pungent odor. Parathion-methyl is slightly soluble to insoluble in water. Usually with the liquid solvent Parathion-methyl is a combustible liquid. Parathion-methyl is toxic by inhalation, ingestion and skin absorption. Parathion-methyl is used as an insecticide.
Air & Water Reactions
Insoluble in water.
Reactivity Profile
METHYL PARATHION is half decomposed in 8 days at 40°C. When a sample was heated in a small test tube Parathion-methyl decomposed in a few minutes, the residue exploded (Food Chem. 4(1):42. 1956).
Hazard
Explosion risk when heated. Toxicby skin absorption, inhalation, and ingestion;cholinesterase inhibitor. Use has been restricted.Questionable carcinogen.
Health Hazard
Parathion-methyl is extremely toxic; the probable oral lethal dose is 5-50 mg/kg, or between 7 drops and 1 teaspoonful for a 150-lb. person. Chronic toxicity does not appear to be a major consideration.
Fire Hazard
Poisonous gases are produced in fire and when heated. Decomposition may lead to sufficient internal pressure to cause the container to rupture violently. Avoid oxidizing materials. Unstable. High temperatures (120F) cause decomposition.
Agricultural Uses
Insecticide, Nematicide: A U.S. EPA restricted Use Pesticide (RUP). Severely
Restricted for use in EU, as parathion-methyl. This material
is used as an insecticide on over 50 crops, primarily
cotton, but also on walnuts, corn, dried beans and almonds
and on several ornamentals. It is no longer allowed to be
used on crops consumed by children.
Trade name
A-GRO®[C]; AI3-17292®; ATOMIC®[C];
AZOFOS®; AZOPHOS; BAMA BRAND®[C];
BAY 11405®; BAY E-601®; BLADAN M®;
CEKUMETHION®; CLEAN CROP®[C]; COTTON TOX
DUST®[C]; DALF®; DECLARE®; DEVITHION®;
DREXEL METHYL PARATHION 4E®[C]; DURHAM[C];
E 601®; EMMY®[C]; E-Z-FLO®[C]; FALL OUT®[C];
FMC NYNAMITE®[C]; FOLIDOC®; FOLIDOL-80®;
FOLIDOL M®; FOLIDOL M-40®; FOSFERNO M 50®;
GEARPHOS®; 8056HC®; KILEX PARATHION®;
ME-PARATHION®; MEPTOX®; METACID 50®;
METACIDE®; METAFOS®; METAPHOS®; METRON®;
METHYL-E 605®; METRON®; NITROX®; NITROX®
80; OLEOVOFOTOX®; PARAPEST M-50®; PENNCAP
M®; PENNCAP MLS®; QUINOPHOS®; SEIS-TRES
6-3®; SINAFID M-48®; SIXTY-THREE SPECIAL E.
C. INSECTICIDE®; TEKWAISA®; THIOPHENIT®;
THYLPAR M-50®; TOLL®; VERTAC METHYL
PARATHION TECHNISCH 80%®; WOFATOX 50 EC®
Contact allergens
A case of sensitization to
methyl-parathion was described in a female agricultural
worker with multiple sensitization.
Safety Profile
Poison by inhalation,
ingestion, skin contact, subcutaneous,
intravenous, and intraperitoneal routes. Fatal
poisoning can result from skin or eye
contact after very brief exposure to
concentrated solution. Experimental
teratogenic and reproductive effects.
Questionable carcinogen. Human mutation
data reported. A cholinesterase inhibitor
type of insecticide. When heated to
decomposition it emits very toxic fumes of
NOx, POx, and SOx.
Potential Exposure
A severely hazardous pesticide formulation. Alert: This material is used as an insecticide on over
50 crops, primarily cotton, and on several ornamentals
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Speed in removing material from skinis of extreme importance. Shampoo hair promptly if contaminated. Seek medical attention immediately. If thischemical has been inhaled, remove from exposure, beginrescue breathing (using universal precautions, includingresuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.Effects of exposure may be delayed. Medical monitoring isadvised.
Carcinogenicity
When rats were given diets with
0, 0.5, 2.5, 12.5, and 50 ppm (0, 0.02, 0.1, 0.5, or 2 mg/kg/day
(males); 0, 0.02, 0.1, 0.7, or 3 mg/kg/day (females) for
12 months, neuronal degeneration and plasma, erythrocyte,
and brain cholinesterase inhibition occurred at 12.5 and
50 ppm .
Environmental Fate
Methyl parathion is mobile in soils and can leach into groundwater and enter surface water as runoff. The chemical breaks down though microbial degradation, aqueous photolysis, hydrolysis, and incorporation into soil organic matter; thus, it degrades rapidly in soil and water with a half-life <5 days. Photodegradation is rapid in aquatic environments with a half-life of 49 h. Bioconcentration is not expected to occur (U.S. EPA, 2006b).
Metabolic pathway
Parathion-methyl is a non-systemic insecticide and, where studied,
metabolism parallels that of parathion and f enitrothion. The major routes
of biotransformation involve desulfuration to the oxon analogue
(paraoxon-methyl) and hydrolysis to give dimethyl phosphate, dimethyl
phosphorothionate and 4-nitrophenol. Demethylation to give desmethylparathion-
methyl and reduction of the nitro group also occurs. As with
organophosphates, demethylation via glutathione-S-methyl transferases
in the liver and some other tissues is an important mechanism in
mammals. The major route of phase II metabolism involves conjugation
of 4-nitrophenol followed by excretion.
storage
Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Store in tightly closed containers in a cool, well-ventilated area away from heat sourcessince violent reactions may occur. See incompatible material listed above. Sources of ignition, such as smoking andopen flames, are prohibited where this chemical is handled,used, or stored. Metal containers involving the transfer of 5gallons or more of this chemical should be grounded andbonded. Drums must be equipped with self-closing valves,pressure vacuum bungs, and flame arresters. Use only nonsparking tools and equipment, especially when opening andclosing containers of this chemical. Wherever this chemicalis used, handled, manufactured, or stored, use explosionproof electrical equipment and fittings.
Shipping
UN3017 Organophosphorus pesticides, liquid,
toxic, flammable, flash point not ,23C, Hazard class: 6.1;
Labels: 6.1-Poisonous materials, 3.-Flammable liquid.
UN2783 Organophosphorus pesticides, solid, toxic, Hazard
Class: 6.1; Labels: 6.1-Poisonous material. UN2811 Toxic
solids, organic, n.o.s., Hazard Class: 6.1; Labels: 6.1-
Poisonous materials, Technical Name Required
Degradation
Parathion-methyl (1) is hydrolysed under acidic and alkaline conditions.
The rate is five times faster than for parathion. Upon heating it isomerises
via a thonwthiolo rearrangement to yield S-methylparahon-methyl (2)
(PM). The hydrolysis of the active anticholinesterase oxon analogue
(paraoxon-methyl) (3) is much faster than that of parathion-methyl. The
products of parathion-methyl hydrolysis were 4-nitrophenol (4) and
dimethyl phosphorothioate (5) (Thuma et al., 1983). Hydrolysis is much
more rapid in alkaline than in acidic or neutral media. Photodegradation
in natural sunlight led to the formation of O,O,S-trimethyl phosphorothioate
(6) and trimethyl phosphate (7) (Chukwudebe et al., 1989).
Zweiner et al. (1994) examined the photolysis of parathion-methyl in
aqueous solution after irradiation by unfiltered UV light. The major
metabolites, which were detected by GC-MS, were paraoxon-methyl (3)
and 4-nitrophenol (4). These conversions are shown in Scheme 1.
Incompatibilities
Incompatible with oxidizers, strong
bases; heat. Mixtures with magnesium, or endrin may be
violent or explosive. Slightly decomposed by acid solutions. Rapidly decomposed by alkalies. Explosive risk
when heated above 50C. The liquid xylene solution
decomposes violently @ 120C
Waste Disposal
Consult with environmental
regulatory agencies for guidance on acceptable disposal
practices. Generators of waste containing this contaminant
(≥100 kg/mo) must conform to EPA regulations governing
storage, transportation, treatment, and waste disposal.
Incineration (816C, 0.5 second minimum for primary combustion; 1204C, 1.0 second for secondary combustion)
with adequate scrubbing and ash disposal facilities.
In accordance with 40CFR165, follow recommendations
for the disposal of pesticides and pesticide containers.
Must be disposed properly by following package label
directions or by contacting your local or federal environmental control agency, or by contacting your regional
EPA office
