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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Azinphos-methyl

Trade and Other Names: Common names include azinphos-methyl and metiltriazotion. Trade names include Azimil, Bay 9027, Bay 17147, Carfene, Cotnion-methyl, Gusathion, Gusathion-M, Guthion, and Methyl-Guthion.

Regulatory Status: All azinphos-methyl liquids with a concentration greater than 13.5% are classified as Restricted Use Pesticides (RUP) by the U.S. Environmental Protection Agency (EPA) because of the inhalation hazard and acute toxicity they present, as well as their potential adverse effects on mammalian species, birds, and aquatic organisms. RUPs may be purchased and used only by certified applicators. The EPA has imposed a 24-hour reentry interval for this material. It is toxicity class I - highly toxic. Products containing azinphos-methyl bear the Signal Words DANGER and POISON.

Chemical Class: OP insecticide

Introduction: Azinphos-methyl is a highly persistent, broad spectrum insecticide. It is also toxic to mites and ticks, and poisonous to snails and slugs. It is a member of the organophosphate class of chemicals. It is nonsystemic, meaning that it is not transported from one plant part to another. It is used primarily as a foliar application against leaf feeding insects. It works as both a contact insecticide and a stomach poison. Azinphos-methyl is registered for use in the control of many insect pests on a wide variety of fruit, vegetable, nut, and field crops, as well as on ornamentals, tobacco, and forest and shade trees. Outside of the U.S., azinphos-methyl is used in lowland rice production. Azinphos-methyl is available in emulsifiable liquid, liquid flowable, ULV liquid, and wettable powder formulations.

Formulation: Azinphos-methyl is available in emulsifiable liquid, liquid flowable, ULV liquid, and wettable powder formulations.

Toxicological Effects:

• Acute toxicity: Azinphos-methyl is one of the most toxic of the organophosphate insecticides [2,23]. It is highly toxic by inhalation, dermal absorption, ingestion, and eye contact [2]. Like all organophosphate chemicals, azinphos-methyl is a cholinesterase inhibitor. It damages normal functioning of cholinesterase, an enzyme which is essential to proper nervous system function. Individuals with a history of reduced lung function, convulsive disorders, or recent exposure to other cholinesterase inhibitors are at increased risk from exposure to azinphos-methyl [2,8]. There is wide variation in the recorded LD50 values for azinphos-methyl depending on the route of exposure and the test animal. The oral LD50 for azinphos-methyl is 4.4 to 16 mg/kg in rats, 80 mg/kg in guinea pigs, and 8 to 20 mg/kg in mice [2,8,13]. The dermal LD50 is 88 to 220 mg/kg in rats, and 65 mg/kg in mice [2,8,13]. The 1-hour inhalation LC50 for azinphos-methyl in rats is 0.4 mg/L [13]. For humans, ingestion of azinphos-methyl in amounts above 1.5 mg/day can cause severe poisoning with symptoms such as dimness of vision, salivation, excessive sweating, stomach pain, vomiting, diarrhea, unconsciousness, and death [2,23]. Inhalation of the dust or aerosol preparation of azinphos-methyl may cause wheezing, tightness in the chest, blurred vision, and tearing of the eyes. Complete symptomatic recovery may occur within 1 week after sublethal poisoning; i.e., poisoning from an exposure that is just below the amount necessary to be fatal [23]. Pure azinphos-methyl is easily absorbed by the skin and lethal amounts can build up in the body after dermal exposure. Symptoms of illness caused by this type of exposure include nausea, vomiting, blurred vision, and muscle cramps [2,23]. Eye contact with concentrated solutions of azinphos-methyl can be life-threatening. Within a few minutes of eye exposure, azinphos-methyl may cause pain, blurring of distant vision, tearing, and other problems. Symptoms of cholinesterase inhibition may also occur, such as respiratory difficulties, gastrointestinal problems, and central nervous systems disturbances [23]. Some organophosphates may cause delayed symptoms beginning 1 to 4 weeks after an acute exposure which may or may not have produced immediate symptoms. In such cases, numbness, tingling, weakness, and cramping may appear in the lower limbs and progress to incoordination and paralysis. Improvement may occur over months or years, and in some cases residual impairment will remain [2,23].
• Chronic toxicity: Long term exposure to azinphos-methyl, above the average 8-hour standard set by the Occupational Safety and Health Administration (OSHA), can impair concentration and memory, and cause headache, irritability, nausea, vomiting, muscle cramps, and dizziness [23]. Cholinesterase inhibition from exposure to azinphos-methyl may persist for 2 to 6 weeks [1]. Repeated exposure to small amounts may result in an unexpected inhibition of cholinesterase, causing symptoms that resemble other flu-like illnesses, including general discomfort, weakness, and lack of appetite [1,2]. The effects of azinphos-methyl exposure may be greater in a previously exposed person than in an individual with no previously exposure. Rats tolerated dietary doses of 0.25 mg/kg/day for 60 days without cholinesterase inhibition, 1 mg/kg/day resulted in questionable growth effects and a slight inhibition of brain and red blood cell cholinesterase. In chronic oral toxicity studies, rats and dogs were fed doses of 0.125, 0.5, 1, or 2.5 mg/kg/day. The 2.5 mg/kg/day dose was increased to 5 mg/kg/day after 47 weeks. At 0.125 mg/kg/day, cholinesterase was not affected in rats and dogs. At 1 mg/kg/day, the plasma and red blood cell cholinesterases in the rat were initially inhibited, but returned to normal after 65 weeks. Five mg/kg/day doses produced convulsions in some animals. In dogs, 0.5 mg/kg/day produced a slight, irregular decrease in red blood cell cholinesterase [24,25]. Rats fed about 5 to 10 mg/kg/day azinphos-methyl for 2 years, had depressed red blood cell counts and brain cholinesterase activity. Dietary levels of about 0.5 mg/kg/day or less had no negative effects [2].
• Reproductive effects: In a two generation reproduction study, there were no observed reproductive and maternal effects in rats at 0.25 mg/kg/day [25]. However, at oral doses of 20 mg/kg to 8 day pregnant mice, Guthion was toxic to the fetus [25]. These data indicate that reproductive effects in humans are unlikely at expected exposure levels.
• Teratogenic effects: In a teratology study, no maternal or developmental effects were observed in rats at doses of 2 mg/kg/day [25]. A 16 mg/kg oral dose to 8-day pregnant rats caused specific development abnormalities in the muscles and bones. It appears the teratogenic effects are not likely in humans under expected exposure conditions.
• Mutagenic effects: No mutagenic effects were observed in the Ames test on bacteria and a test on human cell cultures [25]. These data suggest that azinphos-methyl is not mutagenic.
• Carcinogenic effects: Although one carcinogenicity study on rats suggested that tumors of the pancreas and selected thyroid cells may have been associated with azinphos-methyl [2], two other studies at doses up to 10 mg/kg/day did not show an increase in the incidence of tumors in mice from azinphos-methyl [2,17]. The carcinogenicity of azinphos-methyl is not clear from current evidence.
• Organ toxicity: Toxicity from azinphos-methyl is primarily manifested in cholinesterase inhibition which affects the nervous system. Dogs fed 9 mg/kg/day showed tremors, weakness, abnormal quietness, and some weight loss [2].

• Fate in humans and animals: One study suggests that Guthion is rapidly broken down into nonpoisonous forms in the body [24]. Azinphos-methyl is eliminated in feces and urine of mammals within 2 days of administration.

Ecological Effects:

• Effects on birds: Azinphos-methyl is slightly to moderately toxic to birds. Acute symptoms of azinphos-methyl poisoning include regurgitation, wing drop, wing spasms, diarrhea, and lack of movement [26]. Chickens fed azinphos-methyl at doses of 40 mg/kg developed leg weakness. The oral LD50 for azinphos-methyl is 136 mg/kg in young mallards, 74.9 mg/kg in young pheasant, 84.2 mg/kg in young chukar partridges, 262.0 mg/kg in chickens, and 32.2 mg/kg in bobwhite quail [13,17,27]. The dietary LC50 for azinphos-methyl is 639 ppm in Japanese quail, 1821 ppm in ring necked pheasant, and 1940 ppm in mallard duck [13,17].

• Effects on aquatic organisms: Azinphos-methyl is moderately to very highly toxic to freshwater fish. For most species, the LC50 values are less than 1 mg/L. The 96-hour LC50 for azinphos-methyl in rainbow trout is 0.003 mg/L [8,13]. Guthion-poisoned fish exhibit central nervous system impairment, including erratic swimming accompanied by uncontrolled convulsions. Rapid gill movements, paralysis, and death follow in rapid succession [8]. Azinphos-methyl is highly toxic to aquatic invertebrates, shellfish, frogs, and toads [8]. The LC50 values are below 1 ug/L for many of the species [8,17].
• Effects on other organisms: Several studies have indicated that azinphos-methyl causes adverse effects in wildlife. Wild mammals and aquatic organisms appear to be more vulnerable than birds to hazards created by this material [29]. The EPA requires endangered species labeling for certain azinphos-methyl uses [17]. Azinphos-methyl is toxic to honeybees and other beneficial insects [8,24]. It will cause severe bee losses if used when bees are present at treatment time or within a day thereafter [30]. A 90% mortality rate is seen in pollinating leaf cutting bees after a 9-day exposure to greenhouse alfalfa treated with azinphos-methyl [27].

Environmental Fate:

• Breakdown in soil and groundwater: Persistence of azinphos-methyl in soil is quite variable but is generally low under field conditions [19,31]. The half-life in sandy loam soil is 5 days. Its half-life in nonsterile soil is 21 days when oxygen is present or 68 days under oxygen-free conditions. In sterile soil, the half-life is reported to be 355 days. Azinphos-methyl is fairly immobile in soil because it adsorbs strongly to soil particles and has low water solubility. It has low leaching potential and is unlikely to contaminate groundwater [19,31]. It was not detected in 54 groundwater samples collected in New York state [32]. Azinphos-methyl is one of 118 synthetic organic chemicals that the state of Florida has designated for groundwater monitoring [33]. It was detected in only 5 out of 1628 wells sampled in 10 states from 1983 to 1991 [34]. The disappearance of azinphos-methyl from soil is more rapid in the surface layers (0 2.5 centimeters deep) than it is in the next deeper layer (2.4 to 7.5 cm). Biodegradation and evaporation are the primary routes of disappearance for azinphos-methyl. Azinphos-methyl is also subject to degradation by ultraviolet (UV) light from the sun and hydrolytic decomposition. Photodecomposition is particularly rapid at high levels of soil moisture and in the presence of UV light [31]. Rapid degradation of Gusathion was observed at temperatures higher than 37 C [29].
• Breakdown in water: In general, organophosphates, such as azinphos-methyl, are dissipated rapidly in water [35]. In pond water, it is subject to degradation by sunlight and microorganisms, with a half-life of up to 2 days. Volatilization from water is unlikely. Chemical hydrolysis is important in alkaline waters [12]. Azinphos-methyl is very stable in water below pH 10.0. Above pH 11.0, it is rapidly hydrolyzed to anthranilic acid, benzamide, and other metabolites. Azinphos-methyl has a low to medium tendency to adsorb to sediments or suspended solids [12].
• Breakdown in vegetation: Residue levels of azinphos-methyl in crops are dependent on the rate and frequency of application, nature of the plant surface, and weather conditions such as rainfall, temperature, sunlight, humidity, and wind [24]. The half-life on vegetable and forage crops is 3 to 5 days under field conditions [24]. It gives effective protection for 2 or more weeks [36]. On treated apple trees, the half-life of this pesticide was about 2.6 to 6.3 days [28]. Hawthorn and American Linden trees have been injured by this material. It has also caused russeting on certain varieties of fruit [24].

Physical Properties:

• Appearance: Pure azinphos-methyl is a white crystalline solid. Technical azinphos-methyl is a brown waxy solid [13,37].
• Chemical Name: S-(3,4-dihydro-4-oxobenzo[d]-[1,2,3]-triazin-3-ylmethyl) O,O-dimethyl phosphordithioate [13]
• CAS Number: 86-50-0
• Molecular Weight: 317.33
• Water Solubility: 30 mg/L @ 25 C [13]
• Solubility in Other Solvents: dichloromethane v.s.; toluene v.s. [13]
• Melting Point: 65-68 C (technical) [13]; 73-74 C (pure form) [13]
• Vapor Pressure: <1 mPa @ 20 C [13]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 1000 [19]

Exposure Guidelines:

• ADI: 0.005 mg/kg/day [38]
• MCL: Not Available
• RfD: Not Available
• PEL: 0.2 mg/m3 (8-hour) (skin) [39]
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Miles, Inc.
P.O. Box 4913
8400 Hawthorn Road
Kansas City, MO 64120

• Phone: 816-242-2429
• Emergency: 816-242-2582
  

References:

References for the information in this PIP can be found in Reference List Number 5

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.