Benomyl

Description

Benomyl, a tan-coloured crystalline solid/powder, is a systemic fungicide with a characteristic odour. It belongs to the benzimidazole family. Benomyl decomposes at high temperature. Benomyl is essentially insoluble in water. It is stable under normal storage conditions but will decompose to carbendazim in water. On decomposition by heat, benomyl produces toxic fumes including nitrogen oxides. Benomyl is a systemic and broad-spectrum fungicide that is currently registered for use in more than 50 countries on more than 70 crops for the control of diseases in fruit trees, nut crops, vegetables, cereals, tropical crops and ornamentals, turf, and many field crops. Benomyl is marketed as a wettable powder and as a dry flowable formulation (dispersible granules).

Chemical Properties

Benomyl is a white crystalline solid. Faint acrid odor.

Uses

Post-harvest systemic fungicide used to control fungi and mildew on cotton, roses, soft fruits, tomatoes, cucumbers and other vegetables.

Uses

Fungicide; ascaricide.

Uses

Benomyl is a systemic fungicide with both protective and curative activities. It is effective against more than 190 different fungal diseases in stone fruits, pome fruits, tropical and subtropical fruit crops, grapes, fruiting vegetables, cereals, etc. It is effective against fungal diseases caused by Ascomycetes and Basidiomycetes spp., including leaf spots, blotches and blights; fruit spots and rots; sooty mould; scabs, bulb, corm and tuber decays; blossom blights; powdery mildew; certain rusts; common soil borne crown and root rots.

Definition

ChEBI: A member of the class of benzimidazoles that is the methyl ester of [1-(butylcarbamoyl)-1H-benzimidazol-2-yl]carbamic acid. A foliar fungicide used to control a wide range of Ascomycetes and Fungi Imperfecti in a wide range of crops.

General Description

Colorless to white crystals or off-white powder. Faint acrid odor.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Benomyl is incompatible with strong acids, peroxides and strong oxidizers. Decomposed by strong alkalis. Also decomposes on storage with water .

Hazard

High toxicity by ingestion. Upper respira- tory tract irritant, male reproductive, testicular, and embryo/fetal damage. Possible carcinogen.

Health Hazard

Mildly toxic in rodent by ingestion, inhalation, and absorption through skin; large dosescan produce effects of carbamate poisoning;teratogenic and mutagenic effects reported;carcinogenic potential not known; mild skinirritant.
LD50 oral (rat): 10,000 mg/kg
LD50 skin (mouse): 5600 mg/kg
LD50 skin (wild bird): 100 mg/kg
Benomyl metabolizes to carbendazim(MBC) and 5-HBC. Animal studies indicatedthat benomyl and its metabolites rapidlyeliminated out within 24 hours of exposure.They do not accumulate in tissues over longterm exposure..

Fire Hazard

Literature sources indicate that Benomyl is nonflammable.

Agricultural Uses

Fungicide: Used as a pre-harvest systemic fungicide and as a post-harvest dip. Used on arable and vegetable crops, apples, soft fruit, nuts, mushrooms, lettuce, tomatoes and turf. In California, the top five crops for which benomyl is used are pistachios, table and raisin grapes, almonds, strawberries and wine grapes. All uses of benomyl products in the United States was phased out with a deadline of December 31, 2003. Not approved for use in EU countries.

Trade name

ABORTRINE®; AGROCITE®; ARILATE®; BBC 6597®; BENEX®; BENLAT®[C]; BENLATE®, withdrawn 5/7/01; BENLATE 50®; BENLATE 50 W®; BENLATE 50WP®; BENOMYL® 50 W; BENOSAN®; D 1991®[C]; F 1991®; FUNDAZOL®; FUNGICIDE 1991®; FUNGACIDE D-1991®; FUNGOCHROM®; TARSAN®; TERSAN®; TERSAN 1991®; UZGN®

Contact allergens

Benomyl is a fungicide, derived from benzimidazole. Cases of sensitization were reported in horticulturists and florists. It is however, at most, a weak sensitizer, with possible false-positive patch reactions, or with crossreactions after previous exposure to other fungicides.

Safety Profile

Poison by ingestion. Mildly toxic by inhalation. Experimental teratogenic and reproductive effects. Human mutation data reported. A human skin irritant. When heated to decomposition it emits toxic fumes of NO,. See also CARB AMATES.

Potential Exposure

Benomyl is used as an agricultural chemical and pesticide, pharmaceutical, and veterinary drug.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.

Carcinogenicity

Benomyl was genotoxic, causing chromosome aberrations in vitro and in vivo, but it does not directly act with DNA.

Environmental Fate

Biological. Mixed cultures can grow on benomyl as the sole carbon source. It was proposed that benomyl degraded to butylamine and methyl 2-benzimidazole-carbamate (MBC), the latter undergoing further degradation to 2-aminobenzimidazole then to carbon dioxide and other products (Fuchs and de Vries, 1978).
Soil. In soil and water, benomyl is transformed to methyl-2-benzimidazole and 2- aminobenzimidazole (Rhodes and Long, 1974; Ramakrishna et al., 1979; Rajagopal et al., 1984). Benomyl is easily hydrolyzed in soil to methyl-2-benzimidazole carbamat
Plant. On apple foliage treated with a Benlate formulation, benomyl was transformed to MBC. Benomyl dissipated quickly and the reported half-life on foliage was 3–7 days (Chiba and Veres, 1981).
Chemical/Physical. In aqueous solutions, especially in the presence of acids, benomyl hydrolyzes to the strongly fungicidal methyl-2-benzimidazolecarbamate (carbendazim) (Clemons and Sisler, 1969; Peterson and Edgington, 1969; Zbozinek, 1984; Cremlyn, 1991; Worthing and Hance, 1991) and butyl isocyanate (Zbozinek, 1984; Worthing and Hance, 1991). The latter is unstable in water and decomposes to butylamine and carbon dioxide (Zbozinek, 1984). In highly acidic and alkaline aqueous solutions (pH <1 and pH >11), benomyl is completely converted to 3-butyl-2,4-dioxo-[1,2-a]-s-triazinobenzimida zole (STB) with smaller quantities of methyl 2-benzimidazolecarbamate (MBC). In addi tion 1-(2-benzimidazolyl)-3-n-butylurea was identified but only under highly alkaline conditions (Singh and Chiba, 1985).
Emits toxic fumes of nitrogen oxides when heated to decomposition (Lewis, 1990).

Metabolic pathway

When benlate is degraded by the singlet oxygen photoreaction either in methanol or in aqueous hydrochloric solutions, carbendazim is identified as a major degradation product with the other nine degradation products from both reactions, including 2-guanidinobenzimidazole, benzimidazole, and 2,4'-and 2,5'-bibenzimidazoles which are identical to the photodegradation products of carbendazim by the singlet oxygen photoreaction in aqueous hydrochloric acid solution.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Store in a cool, dry place or ina refrigerator away from strong bases, strong acids, heat.

Shipping

UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9—Miscellaneous hazardous material, Technical Name Required.

Degradation

Benomyl (1) was stable under strongly acidic conditions (i.e. 5N HCl; Singh et al., 1992). Under mildly acidic conditions, benomyl was converted into carbendazim (MBC, 2) through the loss of n-butyl isocyanate (3). The mechanism of this reaction involves interaction between the electron pair at the N-1 position and the proton on the n-butylcarbamoyl nitrogen. The formation of this hydrogen bond leads to proton abstraction and the release of 3 (Calmon and Sayag, 1976a). Under alkaline conditions, the formation of MBC became secondary to the formation of 3- butyl-2,4-dioxo-s-triazino[1,2-a]benzimidazole(4 ) such that compound 4 was the major degradate at pH 13 (Calmon and Sayag, 1976b; Singh and Chiba, 1985). The DT₅₀ values of benomyl at 25 °C in pH 5,7 and 9 solutions were 3.5, 1.5 and <1 hour, respectively (WHO, 1993). The relative stability of benomyl in strongly acidic solution was attributed to the protonation of the molecule (Singh et al., 1990).
Carbendazim (2) decomposed under alkaline conditions via the cleavage of the amide linkage to yield 2-aminobenzimidazole (2-AB, 5) (Watkins, 1976; Zbozinek, 1984). In pH 9 solution, the hydrolytic DT₅₀ for MBC was ca. 54 days (WHO, 1993). Under extreme alkaline conditions, compound 4 was converted into 1-(2-benzimidazolyl)-3-n-butylurea (6) via the cleavage of the carbamoyl moiety (White et al., 1973). Butyl isocyanate (3), once formed, hydrolysed rapidly in aqueous solution to yield n-butylcarbamic acid (7) and n-butylamine (8) (Calmon and Sayag, 1976a). These products are shown in Scheme 1.
Photolysis was not a significant degradation pathway for benomyl in sterile pH 5 solution (Powley, 1985) under natural sunlight.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides (forms toxic oxides of nitrogen). Decomposed in water or otherwise moist conditions.

Waste Disposal

In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office.