Chemical Properties
Acephate is an organophosphate foliar spray insecticide of moderate persistence with
residual systemic activity. It is a contact and systemic insecticide and very effective against
a large number of crop pests, such as alfalfa looper, aphids, armyworms, bagworms, bean
leafbeetle, bean leafroller, blackgrass bugs, bollworm, budworm, and cabbage looper.
Chemical Properties
White Solid
Uses
Contact and systemic insecticide
Definition
ChEBI: A phosphoramide that is methamidophos in which one of the hydrogens is replaced by an acetyl group.
General Description
A white solid. Used as a contact and systemic insecticide.
Air & Water Reactions
Soluble in water.
Reactivity Profile
A thiophosphate ester. Organothiophosphates are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.
Biological Activity
Anticholinesterase insecticide that produces cholinotoxicity. Displays weak inhibition of rat acetylcholinesterase (AChE) but potently inhibits cockroach AChE.
Health Hazard
Acephate is a colorless to white, solid organophosphate insecticide. Exposures to acephate
cause poisoning to animals and humans. Acephate inhibits acetylcholine esterase (AchE),
the essential nervous system enzyme, and causes characteristic organophosphate poi-
soning. The symptoms of toxicity include, but are not limited to, headache, nervousness,
blurred vision, weakness, nausea, fatigue, stomach cramps, diarrhea, diffi
culty breathing,
chest pain, sweating, pin-point pupils, tearing, salivation, clear nasal discharge and spu-
tum, vomiting, muscle twitching, muscle weakness, and in severe poisonings, convulsions, respiratory depression, coma, and death. Acephate causes cholinesterase inhibition lead-
ing to overstimulation, respiratory paralysis, and death.
Potential Exposure
Acephate is a general use contact and systemic insecticide. Banned in the EU for use as a biocide and agricultural insecticide. Used on green- and limabeans, Brussels sprouts, cauliflower, celery, cotton, cottonseed, cranberries, head lettuce, macadamia nuts, peanuts, bell-and nonbell peppers, peppermint, spearmint, tobacco, and soybeans (Special Local Need Registration required in Mississippi and Texas only). Also used to control cockroach (spot treatment only) in residential and industrial buildings and insect control in forests, and on ornamental plants and to target armyworms, aphids, beetles, bollworms, borers, budworms, cankerworms, crickets, cutworms, fire ants, fleas, grasshoppers, leafhoppers, loopers, mealybugs, mites, moths, roaches, spiders, thirps, wasps, weevils, whiteflies, etc. banned for use in the EU.
First aid
Treatment for organophosphate poisoning consists of thorough decontamination, cardiorespiratory support, and administration of the antidotes atropine and pralidoxime. In cases of severe poisoning, diazepam, an anticonvulsant, should also be administered. Antidotes should be administered as prevention even if the diagnosis is in doubt. Speed in removing material from eyes and skin is of extreme importance. Eyes: Contact can cause dangerous amounts of these chemicals to be quickly absorbed through the mucous membrane into the bloodstream. Immediately and gently flush eyes with plenty of warm or cold water (NO hot water) for at least 15 minutes, occasionally lifting the upper and lower eyelids. Get medical aid immediately. Skin: Get medical aid. Dermal contact can cause dangerous amounts of these chemicals to be absorbed into the bloodstream. Wearing the appropriate PPE equipment and respirator for organophosphate pesticides, immediately flush skin with plenty of soap and water for at least 15 minutes while removing contaminated clothing and shoes. Shampoo hair promptly if contaminated. The removed, contaminated clothing and shoes should be double-bagged and left in Hot Zone for later disposal by hazardous materials experts. Skin may also be decontaminated with diluted hypochlorite solution. Inhalation: Get medical aid. Do not contaminate yourself. Wearing the appropriate PPE equipment and respirator for organophosphate pesticides, immediately remove the victim from the contaminated area to fresh air. If the victim is not breathing, administer artificial respiration. Do not use mouth-tomouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. If breathing is difficult, administer oxygen through bag/mask apparatus until medical help arrives. Do not leave victim unattended. Ingestion: Call poison control. Loosen all clothing. Never give anything by mouth to an unconscious person. If victim is unconscious or having convulsions, do nothing except keep victim warm. Get medical aid. Transfer promptly to a medical facility. In cases of ingestion, do not induce vomiting. If the victim isalert and asymptomatic, administer a slurry of activated charcoal at a dose of 1 g/kg (infant, child, and adult dose). A soda can and straw may be of assistance when offering charcoal to a child. In some cases you may be specifically instructed by poison control to induce vomiting by way of 2 tablespoons of syrup of ipecac (adult) washed down with a cup of water. Do NOT give activated charcoal before or with ipecac syrup.
Shipping
UN2783 Organophosphorus pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials. UN3018 Organophosphorus pesticides, liquid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous material
Incompatibilities
May react with strong oxidizers such as chlorates, peroxides, nitrates, etc. In the presence of strong reducing agents such as hydrides, organophosphates form highly toxic and flammable phosphine gas. Contact with oxidizers can cause the release of toxic oxides of phosphorus. Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines) releasing substantial heat, water, and a salt that may be harmful. Incompatible with arsenic compounds(releases hydrogen cyanide gas), diazo compounds, dithiocarbamates, isocyanates, mercaptans, nitrides, and sulfides (releasing heat, toxic and possibly flammable gases), thiosulfates and dithionites (releasing hydrogen sulfate and oxides of sulfur).
Waste Disposal
Alkaline hydrolysis or incineration. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Containers must be disposed of properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office.
Production Methods
Acephate is manufactured through a continuous chemical process that enhances efficiency and yield. The synthesis begins by reacting O,O-dimethyl phosphoroamidothioate with dimethyl sulfate to produce methamidophos, a key intermediate. This compound is then acetylated using an acetylating agent to form acephate.
Agricultural Uses
Insecticide: Acephate is a general use contact and systemic
insecticide. Not approved for use in EU countries.
Actively registered in the U.S., homeowner use for lawns
is discontinued except for treatment of fire ant mounds.
Other indoor treatment has been discontinued. Used on
green and lima beans, Brussels sprouts, cauliflower, celery, cotton, cottonseed, cranberries, head lettuce, macadamia nuts, peanuts, bell-and non-bell peppers, peppermint,
spearmint, tobacco, and soybeans (Special Local Need
Registration required in Mississippi and Texas only). Also
used to control cockroach (spot treatment only) in residential and industrial buildings and insect control in forests, and on ornamental plants and to target armyworms,
aphids, beetles, bollworms, borers, budworms, cankerworms, crickets, cutworms, fire ants, fleas, grasshoppers,
leafhoppers, loopers, mealybugs, mites, moths, roaches,
spiders, thirps, wasps, weevils, whiteflies, etc.
Trade name
ACECAP SYSTEMIC INSECTICIDE
IMPLANTS®; ACEFAL 75 PS®; ACEHERO®;
ACEPHATE 97 EG®; ACEPHATE 75SP®; ACEPHATE
PCO SP INSECTICIDE®; ACESUL®; ACE-TOX®;
ACHERO®; ACIFAT®; ADDRESS®; AIMTHENE®;
AMCOTHENE®; ASATAF®; ASIFY®; ATTACK®;
CHEVRON RE 12420®; CLEAN CROP ACEPHATE 80
DF SEED PROTECTORANT®; DREXEL ACEPHATE 75
WSP®; DREXEL ACEPHATE PCO SP INSECTICIDE®;
FATEL®; FORPHATE®, FORWARD®; KITRON®;
KORANDA® (acephate + fenvelerate); LANCER®;
ORCEPHATE®; ORTHENE®; ORTHENE 755®;
Acephate 3
ORTHO 12420®; ORTRAN®; ORTRIL®; PACE®;
PAYLOAD®; PILARTHENE®; PINPOINT®; PRECISE
ACEPHATE®; RACET®; RE 12420®; SAPHATE®; 75
SP®; VALENT ORTHENE TECHNICAL®; VEGFRU
TARGET®
Mechanism of action
Broad-spectrum, contact and ingestion systemic action. Weak acetylcholinesterase (AChE) inhibitor.
Carcinogenicity
Acephate showed no evidence of
carcinogenicity among rats given diets with 0, 5, 50, or
700 ppm (equivalent to about 0, 0.25, 2.5, and 35.0 mg/kg/
day, respectively) for 28 months .
Environmental Fate
Soil. In aerobic and anaerobic soils, methamidophos and carbon dioxide were identified
as the major soil metabolites (Hartley and Kidd, 1987). The estimated half-life in soil is
3 days (Wauchope, 1988)
Plant. Acephate is quickly absorbed, translocated and transformed in pine seedlings
(Werner, 1974) and cotton plants (Bull, 1979). The chemical was metabolized via cleavage
of the amide bond to form methamidophos (O,S-dimethyl phosphoramidothioat
Chemical/Physical. Emits toxic fumes of phosphorus, nitrogen and sulfur oxides when
heated to decomposition (Sax and Lewis, 1987)
Metabolic pathway
Acephate is a systemic insecticide with a very favourable mammalian
toxicity. The initial reaction of the biotransformation of acephate is by
hydrolysis to the active acetylcholinesterase inlubitor methamidophos. In
every case where the metabolism of acephate has been studied in biological
systems, the production of methamidophos has been demonstrated;
however, the amount of this presumed active metabolite varies
greatly from organism to organism. In mammals, which are relatively
insensitive to the insecticide, the primary route of stage I metabolism is
mainly degradative via O-demethylation to give des-O-methylacephate.
Further metabolism in mammals and birds leads to incorporation of the
molecule into proteins, carbohydrates and lipids as well as to excretion.
Conjugates have not been identified.
Degradation
Acephate is relatively stable to hydrolysis, with DT50s of 60 hours at pH 9
and 710 hours at pH 3 and 40 °C (PM).
Chukwudebe et al. (1984) studied the breakdown of acephate in 0.1M
Tris-HCl buffer at pH 7.2, 8.1 and 8.6 at 37 °C. The hydrolysis products
were analysed by GLC with FID for acephate and methamidophos and
TLC separation and GLC analysis for the other products. Authenticated
standards [methamidophos (2), des-O-methylacephate (3), des-S-methylacephate
(4) and O,S-dimethyl phosphorothioate (5)] were used to
calibrate the analysis. The major metabolite at all pH values was O,S-dimethyl
phosphorothioate (5). This reached a maximum concentration
of 40-55% in 1-3 days depending on pH. Its concentration then declined
as it was itself hydrolysed. The hydrolysis of acephate was strongly
biphasic, with hydrolysis becoming very slow after about 2 days. The
amounts of methamidophos (2) (3%) and des-S-methylacephate (4) (10%)
produced after 7 days were minor. Major and minor routes for the
hydrolysis of methamidophos are shown in Scheme 1.
Toxicity evaluation
Although methamidophos is highly toxic to mammals
(LD50 mice = 27 mg/kg), the acetylation causes a dramatic
decrease in the mammalian toxicity; the acute oral
LD50 values of acephate for mice and rats are 361 and
945 mg/kg, respectively. Inhalation LC50 is >15 mg/L air.
In 2 years of feeding trials, dogs showed depression of
cholinesterase at 100 mg/kg diet (5 mg/kg/d) (maximum
dose level). ADI is 0.03 mg/kg.
Pesticide Type
Insecticide
