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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
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.
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.
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
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
- 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
- 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 . 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 .
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
- 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 .
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 .
- Effects on birds: Amitrole is
practically nontoxic to upland game birds [6,18]. The
LD50 for amitrole in mallard ducks is 2000 mg/kg .
- Effects on aquatic organisms: Amitrole
is slightly toxic to various species of freshwater fish
and freshwater invertebrates .
- Effects on other organisms: Amitrole
inhibits the growth of bacteria . It is nontoxic to
- Breakdown in soil and groundwater:
Amitrole has low soil persistence. Its half-life is 14
days . Microbial breakdown of amitrole takes 2 to 3
weeks in warm, moist soil . Some chemical degradation
may also occur in soils. Loss of amitrole from soils by
volatilization or photodegradation is minor .
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
- Breakdown in vegetation: Amitrole is
readily absorbed and rapidly translocated in the roots
and leaves of higher plants . But, plants are able to
metabolize amitrole in 1 to 4 weeks . Amitrole
residues were not detected in crops planted into soil 1
to 50 days after treatment with amitrole .
- Appearance: Amitrole is a white to
off-white, odorless crystalline powder with a bitter
- Chemical Name:
- CAS Number: 61-82-5
- Molecular Weight: 84.08
- Water Solubility: 280,000 mg/L @ 23 C
- Solubility in Other Solvents:
chloroform, methanol, acetonitrile; acetone and nonpolar
solvents, i.s. 
- Melting Point: 157 C 
- Vapor Pressure: <1 mPa @ 20 C 
- Partition Coefficient: Not Available
- Adsorption Coefficient: 100 
- ADI: 0.0005 mg/kg/day 
- MCL: Not Available
- RfD: Not Available
- PEL: Not Available
- HA: Not Available
- TLV: 0.2 mg/m3 (8-hour) 
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 for the information in this PIP can be found in
Reference List Number 8
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