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The information in this profile may be out-of-date.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

Thiabendazole

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.

Regulatory Status: 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.

Chemical Class: benzimidazole

Introduction: 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.

Toxicological Effects:

• 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 [3]. 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 sensitizer [3].
• 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 [8]. 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 [3].
• 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 [3]. 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 exposure.
• 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 [8]. 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 [30]. Most dogs tested at about 100 mg/kg/day for 2 years developed anemia. The dogs recovered at the end of the study [3].

• 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 [3]. 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 [3]. Elimination is rapid in other species as well. Rats almost completely eliminate the compound after 48 hours and sheep after 96 hours [3]. 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 [8].

Ecological Effects:

• Effects on birds: No data are currently available.
• Effects on aquatic organisms: Thiabendazole is of low toxicity to fish [8]. 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 [49]
• Effects on other organisms: Earthworms are sensitive to the compound (LD50 = approx. 20 ug/worm), while bees are not [8]. It is nontoxic to bees.

Environmental Fate:

• 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 [11]. 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 from soil.
• Breakdown in water: Thiabendazole is stable in aqueous suspension and acidic media [1]. 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 [8]. 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 [8].

Physical Properties:

• Appearance: Thiabendazole is an odorless, colorless powder [1].
• Chemical Name: 2-(thiazol-4-yl)benzimidazole [1]
• CAS Number: 148-79-8
• Molecular Weight: 201.20
• Water Solubility: <50 mg/L @ pH 5 to 12 [1]
• Solubility in Other Solvents: s. in acetone and ethanol; s.s. in benzene and chloroform [1]
• Melting Point: 304-305 C [1]
• Vapor Pressure: Negligible at room temperature [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 2500 [1]

Exposure Guidelines:

• ADI: 0.1 mg/kg/day [12]
• MCL: Not Available
• RfD: 0.1 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Merck Agvet
Division of Merck & Co., Inc.
P.O. Box 2000
Rahway, NJ 07065-0912

• Phone: 908-855-4277
• Emergency: Not Available
  

References:

References for the information in this PIP can be found in Reference List Number 10

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.