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The information in this profile may be out-of-date.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

Amitrole

Trade and Other Names: Amitrole is known as amino-triazole in Great Britain, France, New Zealand, and the former U.S.S.R. Trade names include Amerol, Amino Triazole, Amitrol, Amizine, Amizol, Azolan, Azole, Cytrol, Diurol, and Weedazol.

Regulatory Status: Amitrole is a Restricted Use Pesticide (RUP). RUPs may be purchased and used only by certified applicators. Amitrole is classified as toxicity class III - slightly toxic. Products containing amitrole bear the Signal Word CAUTION. All use of amitrole on food crops was canceled by the EPA in 1971 because it caused cancer in experimental animals.

Chemical Class: triazole

Introduction: Amitrole is a nonselective systemic triazole herbicide. It is used on non-cropland for control of annual grasses and perennial and annual broadleaf weeds, for poison ivy control, and for control of aquatic weeds in marshes and drainage ditches (1). This compound is compatible with many other herbicides. It is available as wettable powders, soluble concentrates, and water dispersable granules.

Amitrole was involved in the Delaney Clause's first enforcement. The Delaney Clause prohibits any amount of any cancer causing substance to be a food additive, prompting growers to follow pesticide label directions carefully. In 1959, amitrole was registered for post harvest use on cranberries. Misuse left small residues on portions of cranberry crops. Just 13 days before Thanksgiving, 1587 metric tons of cranberries were seized by the Food and Drug Administration; and just 3 days before Thanksgiving, the FDA certified sufficient cranberries to meet holiday demands and end the "Cranberry Crisis".

Formulation: It is available as wettable powders, soluble concentrates, and water dispersable granules.

Toxicological Effects:

• Acute toxicity: Amitrole has a very low acute toxicity to humans and animals. Associated symptoms in humans include skin rash, vomiting, diarrhea, and nose bleeds. Poisoning by amitrole is characterized by increased intestinal peristalsis (this may lead to diarrhea), fluid in the lungs, and hemorrhages of various organs. No toxic effects were observed in a woman who ingested 20 mg/kg, but a single dose of 1200 mg/kg reduced iodine uptake by the thyroid in healthy persons [3,15]. Amitrole is a mild skin and eye irritant [3,15]. The oral and dermal LD50 values for amitrole in rats are greater than 5000 mg/kg. Studies have reported oral LD50 values as high as 15,000 mg/kg in mice and 24,600 mg/kg in rats. In one study, the largest doses tested, 4080 mg/kg orally and 2500 mg/kg dermally, produced no toxic effects on rats. The dermal LD50 in rabbits is greater than 200 mg/kg [3,15].
• Chronic toxicity: Feeding of amitrole to rats at dietary doses of 3 or 6 kg/mg/day for 2 weeks caused enlargement of the thyroid and reduced uptake of iodine. A dietary dose of 50 mg/kg/day produced significant enlargement of the thyroid after 3 days of feeding. Several studies have shown that amitrole inhibits the activity of various liver enzymes. Long-term exposure to amitrole can cause reversible goiters [16,19].
• Reproductive effects: In a two-generation study in rats, dams fed 5 or 25 mg/kg/day of amitrole had fewer pups per litter, and their weight at weaning was reduced. Dietary doses of 1.25 mg/kg/day had no significant effect on reproduction [3]. It is unlikely that reproductive effects will occur in humans in normal circumstances.
• Teratogenic effects: Birth defects have occurred in the pups of pregnant rabbits, rats, and mice exposed to amitrole, but only at doses high enough to also produce signs of toxicity in the mothers [14]. Atrophy of the thymus and spleen occurred at high doses (5 or 25 mg/kg/day). Within a week after weaning, most of these pups died of a condition resembling runt disease. Similar effects have been observed in mice. Teratogenic effects in humans are unlikely in normal circumstances.
• Mutagenic effects: One laboratory assay has shown amitrole to be weak mutagen. All other assays have shown no mutagenic effects (3,14). These data suggest that amitrole is weakly or nonmutagenic.
• Carcinogenic effects: Amitrole has induced thyroid and liver tumors in rats and mice after lifetime high dose exposures [3,14,18].
• Organ toxicity: Animal studies have shown that amitrole's main effects are on the thyroid and liver.

• Fate in humans and animals: Amitrole is rapidly and completely absorbed into the body through the gastrointestinal tract when eaten. Amitrole is excreted through the urine. The highest concentrations in all tissues generally occur within 1 hour after exposure. Concentrations begin to decline after 2 to 6 hours [3]. Most (70 to 95.5%) of amitrole administered to rats by stomach tube was excreted in the urine during the first 24 hours. Some was detected in the rats' feces for 2 to 5 days after dosing. After 6 days, only 0.28 to 1.36% of the total dose remained, mainly in the liver [3].

Ecological Effects:

• Effects on birds: Amitrole is practically nontoxic to upland game birds [6,18]. The LD50 for amitrole in mallard ducks is 2000 mg/kg [18].
• Effects on aquatic organisms: Amitrole is slightly toxic to various species of freshwater fish and freshwater invertebrates [18].
• Effects on other organisms: Amitrole inhibits the growth of bacteria [16]. It is nontoxic to bees [6].

Environmental Fate:

• Breakdown in soil and groundwater: Amitrole has low soil persistence. Its half-life is 14 days [20]. Microbial breakdown of amitrole takes 2 to 3 weeks in warm, moist soil [15]. Some chemical degradation may also occur in soils. Loss of amitrole from soils by volatilization or photodegradation is minor [21]. Amitrole has a moderate potential for groundwater contamination because it does not adsorb strongly to soil particles and is readily soluble in water.
• Breakdown in water: In aquatic environments, amitrole does not break down by hydrolysis or photolysis, volatilize, nor bioaccumulate in aquatic organisms. The biodegradation half-life for amitrole in water is about 40 days. Degradation of amitrole in open waters may occur through oxidation by other chemicals [21].
• Breakdown in vegetation: Amitrole is readily absorbed and rapidly translocated in the roots and leaves of higher plants [18]. But, plants are able to metabolize amitrole in 1 to 4 weeks [15]. Amitrole residues were not detected in crops planted into soil 1 to 50 days after treatment with amitrole [18].

Physical Properties:

• Appearance: Amitrole is a white to off-white, odorless crystalline powder with a bitter taste (6).
• Chemical Name: 1H-1,2,4-triazole-3-ylamine [6]
• CAS Number: 61-82-5
• Molecular Weight: 84.08
• Water Solubility: 280,000 mg/L @ 23 C [6]
• Solubility in Other Solvents: chloroform, methanol, acetonitrile; acetone and nonpolar solvents, i.s. [6]
• Melting Point: 157 C [6]
• Vapor Pressure: <1 mPa @ 20 C [6]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 100 [21]

Exposure Guidelines:

• ADI: 0.0005 mg/kg/day [22]
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: 0.2 mg/m3 (8-hour) [16]

Basic Manufacturer:

Rhone-Poulenc Ag. Co.
P.O. Box 12014
2 T.W. Alexander Dr.
Research Triangle Park, NC 27709

• Phone: 919-549-2000
• Emergency: 800-334-7577
  

References:

References for the information in this PIP can be found in Reference List Number 8

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.