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in 1996. EXTOXNET no longer updates this information, but it may be useful
as a reference or resource.
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E X T O X N E T
A Pesticide Information Project of Cooperative Extension
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and the Institute for Environmental Toxicology, Michigan State
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USDA/Extension Service/National Agricultural Pesticide Impact
EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names for products containing this compound include
Apl-Luster, Arbotect, Mertect, Mycozol, TBZ, Tecto, and
Thibenzole. The product is often used in combination with other
fungicides and insecticides.
Thiabendazole is a General Use Pesticide (GUP). It is in EPA
toxicity class III - slightly toxic, and products containing it
carry the Signal Word CAUTION on the label.
Thiabendazole is a systemic benzimidazole fungicide used to
control fruit and vegetable diseases such as mold, rot, blight,
and stain. It is also active against storage diseases and Dutch
Elm disease. In livestock and humans, thiabendazole is applied to
treat several helminth species such as roundworms. Thiabendazole
is also used medicinally as a chelating agent to bind metals. It
is available as a wettable powder, suspension concentrate,
flowable concentrate, and liquid.
Formulation: It is
available as a wettable powder, suspension concentrate, flowable
concentrate, and liquid.
- Acute toxicity: Effects of acute
overexposure to the fungicide include dizziness,
anorexia, nausea, and vomiting. Other symptoms such as
itching, rash, chills, and headache occur less
frequently. The symptoms are brief and are related to the
dose level . The oral LD50 is 3100 to 3600 mg/kg in
the rat, 1395 to 3810 mg/kg in mice, and greater than
3850 mg/kg in the rabbit [1,3]. The lethal dose in sheep
is 1200 mg/kg. The dermal LC50 in rabbits is greater than
5000 mg/kg. Thiabendazole is not a skin irritant or a
- Chronic toxicity: Rats fed 200 mg/kg/day
or less showed few or no growth effects. At higher doses
(400 mg/kg/day), there was growth suppression. Death
occurred in a few days at 1200 mg/kg/day and 30%
mortality occurred within 30 days at 800 mg/kg/day. A
decrease of active bone marrow at high doses was also
noted . At doses somewhat below the LD50, mice
experienced significant liver, spleen, and intestinal
effects. In dogs, high daily doses (200 mg/kg/day) for 2
years produced few effects other than occasional attacks
of vomiting and persistent anemia. Sheep experienced
toxic depression and anorexia at very high doses (800 to
1000 mg/kg/day). Studies on cattle, sheep, goats, swine,
horses, and zoo animals have shown few chronic symptoms
at low doses .
- Reproductive effects: A three-generation
study in rats showed no adverse effects on reproduction
at 20 to 80 mg/kg/day. However, four times this low
therapeutic dose produced serious pregnancy related
disorders (eclampsia) in sheep . Mice studied for five
generations showed no effects at 10 mg/kg/day, decreased
weanling weights at 50 mg/kg/day, and decreased weanling
weight and size at 250 mg/kg/day [3,8]. Reproductive
effects in humans are not likely at anticipated levels of
- Teratogenic effects: Pregnant rabbits
fed doses of 75, 150, and 600 mg/kg/day produced pups
with lower fetal weights at the highest dose tested. No
birth defects were observed with thiabendazole at any
dose tested [3,8]. Teratogenic effects are not likely
from thiabendazole exposure.
- Mutagenic effects: Several studies with
bacteria have failed to produce any chromosome changes or
mutations due to thiabendazole . It appears that the
compound is not mutagenic.
- Carcinogenic effects: A 2-year feeding
study with rats at levels of 10 to 160 mg/kg/day produced
no cancer-related effects attributable to thiabendazole
[3,8]. Another study conducted over 18 months at the
maximum tolerated dose in mice produced no evidence of
cancer related effects [3,8]. It does not appear that
thiabendazole is carcinogenic.
- Organ toxicity: Dogs autopsied after a
2-year feeding study had incomplete development of bone
marrow, a wasting away of lymph tissue, and other
abnormalities . Most dogs tested at about 100
mg/kg/day for 2 years developed anemia. The dogs
recovered at the end of the study .
- Fate in humans and animals: In four men
given 1000 mg (approximately 14 mg/kg) thiabendazole
orally, plasma concentrations peaked at 13 to 18 ppm
within an hour . Within 4 hours, 40% of the dose was
excreted, and within 24 hours, 80% was excreted, mostly
in the urine as metabolites of the compound .
Elimination is rapid in other species as well. Rats
almost completely eliminate the compound after 48 hours
and sheep after 96 hours . Metabolites are distributed
throughout most body tissues in sheep, but detectable in
only a few tissues at low levels (less than 0.2 ppm) at
16 days and at very low levels (0.06 ppm or less) after
30 days .
- Effects on birds: No data are currently
- Effects on aquatic organisms:
Thiabendazole is of low toxicity to fish . The
compound is not expected to appreciably accumulate in
aquatic organisms. The bioconcentration factor for
thiabendazole in whole fish is 87 times the ambient water
concentrations. Fish eliminated the compound within 3
days after being placed in thiabendazole-free water 
- Effects on other organisms: Earthworms
are sensitive to the compound (LD50 = approx. 20
ug/worm), while bees are not . It is nontoxic to bees.
- Breakdown in soil and groundwater:
Thiabendazole's affinity for binding to soil particles
increases with increasing soil acidity. It is highly
persistent. The field half-life for thiabendazole has
been reported as 403 days . In one study, 9 months
following application, most of the residues (85 to 95%)
were recovered from soil. Due to its binding and slight
solubility in water, it is not expected to leach readily
- Breakdown in water: Thiabendazole is
stable in aqueous suspension and acidic media . Its
low water solubility will make it unlikely to be in
solution, and it will most likely be bound to sediment.
- Breakdown in vegetation: No metabolism
was seen with seed potatoes, but photoproducts were
detected on sugar beet leaves . Total residues in
sugar beets were 78% parent compound with the remaining
22% being benzimidazole, benzimidazole-2-carboxamide, and
unidentified products. Thiabendazole is readily absorbed
by roots and translocated to all parts of a plant, but
predominantly to the leaf margins .
- Appearance: Thiabendazole is an
odorless, colorless powder .
- Chemical Name:
- CAS Number: 148-79-8
- Molecular Weight: 201.20
- Water Solubility: <50 mg/L @ pH 5 to
- Solubility in Other Solvents: s. in
acetone and ethanol; s.s. in benzene and chloroform 
- Melting Point: 304-305 C 
- Vapor Pressure: Negligible at room
- Partition Coefficient: Not Available
- Adsorption Coefficient: 2500 
- ADI: 0.1 mg/kg/day 
- MCL: Not Available
- RfD: 0.1 mg/kg/day 
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
Division of Merck & Co., Inc.
P.O. Box 2000
Rahway, NJ 07065-0912
- Phone: 908-855-4277
- Emergency: Not Available
References for the information in this PIP can be found in
Reference List Number 10
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