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The information in this profile may be out-of-date.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 pesticidefact sheets. If you don't find a fact sheet related toyour 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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A Pesticide Information Project of Cooperative ExtensionOffices of Cornell University, Oregon State University, theUniversity of Idaho, and the University of California at Davisand the Institute for Environmental Toxicology, Michigan StateUniversity. Major support and funding was provided by theUSDA/Extension Service/National Agricultural Pesticide ImpactAssessment Program.

EXTOXNET primary files maintained and archived at Oregon StateUniversity

Revised June 1996

Trade names of this product include Basudin, Dazzel, Gardentox,Kayazol, Knox Out, Nucidol, and Spectracide. Diazinon may befound in formulations with a variety of other pesticides such aspyrethrins, lindane, and disulfoton.

Diazinon is classified as a Restricted Use Pesticide (RUP) and isfor professional pest control operator use only. In 1988, EPAcanceled registration of diazinon for use on golf courses and sodfarms because of die offs of birds that often congregated inthese areas. It is classified toxicity class II - moderatelytoxic, or toxicity class III - slightly toxic, depending on theformulation. Products containing diazinon bear the Signal WordWARNING or CAUTION.

organophosphate

Diazinon is a nonsystemic organophosphate insecticide used tocontrol cockroaches, silverfish, ants, and fleas in residential,non-food buildings. Bait is used to control scavenger yellowjackets in the western U.S. It is used on home gardens and farmsto control a wide variety of sucking and leaf eating insects. Itis used on rice, fruit trees, sugarcane, corn, tobacco, potatoesand on horticultural plants. It is also an ingredient in peststrips. Diazinon has veterinary uses against fleas and ticks. Itis available in dust, granules, seed dressings, wettable powder,and emulsifiable solution formulations.

It isavailable in dust, granules, seed dressings, wettable powder, andemulsifiable solution formulations.

• Acute toxicity: Toxic effects of diazinon are due to the inhibition of acetylcholinesterase, an enzyme needed for proper nervous system function. The range of doses that results in toxic effects varies widely with formulation and with the individual species being exposed. The toxicity of encapsulated formulations is relatively low because diazinon is not released readily while in the digestive tract. Some formulations of the compound can be degraded to more toxic forms. This transformation may occur in air, particularly in the presence of moisture, and by ultraviolet radiation. Most modern diazinon formulations in the U.S. are stable and do not degrade easily [8]. The symptoms associated with diazinon poisoning in humans include weakness, headaches, tightness in the chest, blurred vision, nonreactive pinpoint pupils, salivation, sweating, nausea, vomiting, diarrhea, abdominal cramps, and slurred speech. Death has occurred in some instances from both dermal and oral exposures at very high levels [2,8]. The LD50 is 300 to 400mg/kg for technical grade diazinon in rats (2,13). The inhalation LC50 (4-hour) in rats is 3.5 mg/L [13]. In rabbits, the dermal LD50 is 3600 mg/kg [13].
• Chronic toxicity: Chronic effects have been observed at doses ranging from 10 mg/kg/day for swine to 1000 mg/kg/day for rats. Inhibition of red blood cell cholinesterase, and enzyme response occurred at lower doses in the rats. Enzyme inhibition has been documented in red blood cells, in blood plasma, and in brain cells at varying doses and with different species [2].
• Reproductive effects:No data are currently available.
• Teratogenic effects:The data on teratogenic effects due to chronic exposure are inconclusive. One study has shown that injection of diazinon into chicken eggs resulted in skeletal and spinal deformities in the chicks. Bobwhite quail born from eggs treated in a similar manner showed skeletal deformities but no spinal abnormalities. Acetylcholine was significantly affected in this latter study [56]. Tests with hamsters and rabbits at low doses (0.125 0.25 mg/kg/day) showed no developmental effects, while tests with dogs and pigs at higher levels (1.0 10.0 mg/kg/day) revealed gross abnormalities [57].
• Mutagenic effects: While some tests have suggested that diazinon is mutagenic, current evidence is inconclusive [2].
• Carcinogenic effects: Diazinon is not considered carcinogenic. Tests on rats over a 2-year period at moderate doses (about 45 mg/kg) did not cause tumor development in the test animals [2].
• Organ toxicity: Diazinon itself is not a potent cholinesterase inhibitor. However, in animals, it is converted to diazoxon, a compound that is a strong enzyme inhibitor [2].

• Fate in humans and animals: Metabolism and excretion rates for diazinon are rapid. The half-life of diazinon in animals is about 12 hours. The product is passed out of the body through urine and in the feces. The metabolites account for about 70% of the total amount excreted. Cattle exposed to diazinon may store the compound in their fat over the short term [8]. One study showed that the compound cleared the cows within 2 weeks after spraying stopped. Application of diazinon to the skin of cows resulted in trace amounts in milk 24 hours after the application [8].

• Effects on birds: Birds are quite susceptible to diazinon poisoning. In 1988, the EPA concluded that the use of diazinon in open areas poses a "widespread and continuous hazard" to birds. Bird kills associated with diazinon use have been reported in every area of the country and at all times of the year. Canadian geese and mallard ducks may be exposed to LC50 concentrations in very short periods of time after application (from 15 to 80 minutes depending on the application rate of the pesticide). Birds are significantly more susceptible to diazinon than other wildlife. LD50 values for birds range from 2.75 mg/kg to 40.8 mg/kg [8].
• Effects on aquatic organisms: Diazinon is highly toxic to fish. In rainbow trout, the diazinon LC50 is 2.6 to 3.2 mg/L [13]. In hard water, lake trout and cutthroat trout are somewhat more resistant. Warm water fish such as fathead minnows and goldfish are even more resistant with diazinon LC50 values ranging up to 15 mg/L [8]. There is some evidence that saltwater fish are more susceptible than freshwater fish. Bioconcentration ratios range from 200 in minnows to 17.5 for guppies. These studies show that diazinon does not bioconcentrate significantly in fish [12].
• Effects on other organisms: Diazinon is highly toxic to bees [13].

• Breakdown in soil and groundwater: Diazinon has a low persistence in soil. The half-life is 2 to 4 weeks [19]. Bacterial enzymes can speed the breakdown of diazinon and have been used in treating emergency situations such as spills [12]. Diazinon seldom migrates below the top half inch in soil, but in some instances it may contaminate groundwater. The pesticide was detected in 54 wells in California and in tap water in Ottawa, Canada, and in Japan [12].
• Breakdown in water: The breakdown rate is dependent on the acidity of water. At highly acidic levels, one half of the compound disappeared within 12 hours while in a neutral solution, the pesticide took 6 months to degrade to one half of the original concentration [12].
• Breakdown in vegetation: In plants, a low temperature and a high oil content tend to increase the persistence of diazinon [58]. Generally the half-life is rapid in leafy vegetables, forage crops and grass. The range is from 2 to 14 days. In treated rice plants only 10% of the residue was present after 9 days [58]. Diazinon is absorbed by plant roots when applied to the soil and translocated to other parts of the plant [13].

• Appearance: Diazinon is a colorless to dark brown liquid. It has a flashpoint of 180 F [13].
• Chemical Name: O,O-diethyl 0-2-isopropyl-6-methyl(pyrimidine-4-yl) phosphorothioate [13]
• CAS Number:333-41-5
• Molecular Weight: 304.35
• Water Solubility: 40 mg/L @ 20 C [13]
• Solubility in Other Solvents: petroleum ether v.s.; alcohol v.s.; benzene v.s. [13]
• Melting Point:Decomposes @ >120 C [8]
• Vapor Pressure: 0.097 mPa @ 20 C [13]
• Partition Coefficient: Not Available
• Adsorption Coefficient:1000 (estimated) [19]

• ADI:0.002 mg/kg/day [38]
• MCL: Not Available
• RfD: 9 x 10-5 mg/kg/day [53]
• PEL: Not Available
• HA: 6 x 10-4 mg/L (lifetime) (8)
• TLV: 0.1 mg/m3 (8-hour) [47]

Ciba-Geigy Corp.
P.O. Box 18300
Greensboro, NC 27419-8300

• Phone: 800-334-9481
• Emergency: 800-888-8372
  

References for the information in this PIP can be found inReference ListNumber 5

Theinformation in this profile does not in any way replace orsupersede the information on the pesticide product labeling orother regulatory requirements. Please refer to the pesticideproduct labeling.