Parathion-methyl Chemical Properties

Melting point:

36°C

Boiling point:

143°C (1.0 mmHg)

Density 

1.36

vapor pressure 

4.1×10^-4 Pa (20 °C)

refractive index 

nD25 1.5367

Flash point:

46.1°C

storage temp. 

APPROX 4°C

solubility 

Chloroform: Slightly Soluble,Methanol: Slightly Soluble

form 

solid

Water Solubility 

0.005 g/100 mL

BRN 

8905814

Stability:

Stable. Flammable.

CAS DataBase Reference

298-00-0(CAS DataBase Reference)

NIST Chemistry Reference

Phosphorothioic acid, o,o-dimethyl-o-p-nitrophenyl ester(298-00-0)

IARC

3 (Vol. 30, Sup 7) 1987

EPA Substance Registry System

Methyl parathion (298-00-0)

Safety Information

Hazard Codes 

T+;N,N,T+,Xn,F

Risk Statements 

5-24-26/28-48/22-50/53-10-67-66-51/53-36-20/22-11-65-38

Safety Statements 

28-36/37-45-60-61-26-62-16

RIDADR 

UN 2052/2783/2811

OEB

C

OEL

TWA: 0.2 mg/m3 [skin]

WGK Germany 

3

RTECS 

TG0175000

HazardClass 

6.1(a)

PackingGroup 

II

HS Code 

29201100

Hazardous Substances Data

298-00-0(Hazardous Substances Data)

Toxicity

LD50 in male, female rats (mg/kg): 14, 24 orally; 67, 67 dermally (Gaines)

Parathion-methyl Usage And Synthesis

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 (LD₅₀s = 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 M₁ phase in V79 cells at a concentration of 40 μg/ml. It is toxic to rats (LD₅₀ = 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

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