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The information in this profile may be out-of-date.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

Benomyl

Trade and Other Names: Commercial names for products containing benomyl include Agrocit, Benex, Benlate, Benosan, Fundazol, Fungidice 1991, and Tersan 1991. Benomyl is compatible with many other pesticides.

Regulatory Status: Benomyl is a General Use Pesticide (GUP). The EPA categorizes it as toxicity class IV - practically nontoxic. Benomyl-containing products carry the Signal Word CAUTION.

Chemical Class: benzimidazole

Introduction: Benomyl is a systemic, benzimidazole fungicide that is selectively toxic to microorganisms and to invertebrates, especially earthworms. It is used against a wide range of fungal diseases of field crops, fruits, nuts, ornamentals, mushrooms, and turf. Formulations include wettable powder, dry flowable powder, and dispersible granules.

Formulation: Formulations include wettable powder, dry flowable powder, and dispersible granules.

Toxicological Effects:

• Acute toxicity: Benomyl is of such a low acute toxicity to mammals, it has been impossible or impractical to administer doses large enough to firmly establish an LD50. Thus the LD50 is greater than 10,000 mg/kg in rats and greater than 3400 mg/kg in rabbits (using a 50% wettable powder formulation). Because of its high LD50 there is a low risk for acute poisoning from this compound [1]. Skin irritation may occur for workers exposed to benomyl. Skin reactions have also been seen in rats and guinea pigs. Most organisms can become sensitized to the compound as well. Benomyl is readily absorbed into the body by inhaling the dust, but there are no reports of toxic effects to humans by this route of exposure. The inhalation LC50 in rats is greater than 2 mg/L [2].
• Chronic toxicity: When rats were fed diets containing about 150 mg/kg/day for 2 years, no toxic effects were observed [3]. Dogs fed benomyl in their diets for 3 months had no major toxic effects, but did show evidence of altered liver function at the highest dose (150 mg/kg). The damage progressed to more severely impaired liver function and liver cirrhosis after 2 years [6].
• Reproductive effects: A three-generation study on rats showed no reproductive or lactational differences at a dose of 150 mg/kg/day administered in the diet [3]. In another study in rats, the testes were the most affected sites at relatively low doses of about 15 mg/kg/day. Male rats had decreased sperm counts, decreased testicular weight, and lower fertility rates. The animals recovered from these effects 70 days after feeding with the pesticide had stopped [3]. Reproductive effects in humans are unlikely at expected exposure levels.
• Teratogenic effects: Very high doses of benomyl can cause birth defects in test animals [4]. Rats fed 150 mg/kg/day in the diet for three generations showed no birth defects. No teratogenicity was observed in another study of rats given 300 mg/kg/day on days 6 to 15 of gestation [4]. At higher doses, some birth defects were noted, but they were accompanied by toxicity to the fetus [4]. In another rat study where mothers were fed 1000 mg/kg/day for 4 months, the offspring showed a decrease in viability and fertility [1]. These data suggest that benomyl is not likely to cause teratogenic effects under normal circumstances.
• Mutagenic effects: Conflicting negative and positive results have been found in numerous mutagenicity assays. As a result, no conclusions about the mutagenicity of benomyl can be drawn [3].
• Carcinogenic effects: Tumors in the livers of both male and female mice were observed in lifetime studies at doses of benomyl at 40 to 400 mg/kg/day. In a 2-year dietary study when albino rats were fed up to 2500 mg/kg/day of benomyl, there were no significant adverse effects at any dose level attributable to benomyl [1]. Based on these data, it is not possible to determine the carcinogenicity of benomyl [5].
• Organ toxicity: Target organs identified in animal studies included the liver and testes.

• Fate in humans and animals: Benomyl's metabolism has been studied in the mouse, rat, rabbit, dog, sheep, and cow. Benomyl is rapidly broken down to carbendazim, further to other compounds, such as 5-hydroxy-2-benzimidazole carbamate (5 HBC), and then eliminated. In a rat study, benomyl, carbendazim (MBC), and 5-HBC were found in rat blood in the first 6 hours. After 18 hours, only 5-HBC was present. The urine contained about 40 to 70% of the dose, and the feces 20 to 45%. No residues were found in muscle or fat. Benomyl and its metabolites do not accumulate in tissues over long-term exposure periods [2,3]. Carbendazim (MBC) and the parent compound benomyl have similar toxicological properties, but the former is not a skin sensitizer [2].

Ecological Effects:

• Effects on birds: In bobwhite quail and mallard ducks, the 5-day dietary LC50 for benomyl is greater than 10,000 ppm. In redwing blackbirds, the LD50 value is 100 mg/kg, which indicates that benomyl is moderately toxic to this species [4].
• Effects on aquatic organisms: Benomyl is highly to very highly toxic to fish. The order of susceptibility to benomyl for various fish species from least susceptible to most susceptible is catfish, bluegill, rainbow trout, and goldfish. The LC50 values for the compound in fish are 0.05 mg/L to 14 mg/L in adults, and 0.006 mg/L in catfish fry [8]. The main breakdown product, carbendazim, had the same order of toxicity as benomyl. Crayfish have an LC50 greater than 100 mg/L. The estimated bioconcentration factor (BCF) ranges from 159 in rainbow trout up to 460 in bluegill sunfish, indicating that benomyl does not tend to significantly concentrate in living tissue [8,9].
• Effects on other organisms: A single application of benomyl to turf grass can substantially reduce some soil dwelling organisms. The compound is very lethal to earthworms at low concentrations over a long time period. The 7-day LC50 in earthworms is 1.7 mg/L and the 14-day LC50 is 0.4 mg/L [6]. Benomyl also decreases the mixing of soil and thatch. The effects last for up to 20 weeks [10]. Benomyl is relatively nontoxic to bees [2].

Environmental Fate:

• Breakdown in soil and groundwater: Benomyl is strongly bound to soil and does not dissolve in water in flooded rice fields to any significant extent [2,11]. It is highly persistent. When applied to turf, it has a half-life of 3 to 6 months and, when applied to bare soil the half-life is 6 to 12 months. Where four successive annual applications were applied, residues did not accumulate from one year to the next [6].
• Breakdown in water: Benomyl completely degrades to carbendazim within several hours in acidic or neutral water. The half-life of carbendazim is 2 months [1].
• Breakdown in vegetation: Since benomyl is a systemic fungicide, it is absorbed by plants. Once it is in the plant, it accumulates in veins and at the leaf margins [6]. The metabolite carbendazim seems to be the fungicidally active agent. Benomyl residues are quite stable, with 48 to 97% remaining as the parent compound 21 to 23 days after application [6].

Physical Properties:

• Appearance: Benomyl is a tan crystalline solid compound. It has little or no odor [1].
• Chemical Name: methyl-1-[(butylamino)carbonyl]-H-benzimidazol-2-ylcarbamate [1]
• CAS Number: 17804-35-2
• Molecular Weight: 290.62
• Water Solubility: 2 mg/L [1]
• Solubility in Other Solvents: chloroform s.; heptane s.; ethanol s.; acetone s. [1]
• Melting Point: Decomposes without melting above 300 C [1]
• Vapor Pressure: Negligible (<1 mPa) at 20 C [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 1900 [1]

Exposure Guidelines:

• ADI: 0.02 mg/kg/day [12]
• MCL: Not Available
• RfD: 0.05 mg/kg/day [13]
• PEL: 5 mg/m3 (8-hour) (respirable fraction) [14]
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 80038
Wilmington, DE 19880-0038

• Phone: 800-441-7515
• Emergency: 800-441-3637
  

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.