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The information in this profile may be out-of-date.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

Bentazon

Trade and Other Names: Trade names include Adagio, Bas 351H, Basagran, Bendioxide, Bentazone, Entry, Leader, and Pledge. All products currently marketed in the U.S. contain the sodium salt of bentazon, referred to as sodium bentazon, as the active ingredient.

Regulatory Status: Bentazon is A General Use Pesticide (GUP) that is classified as toxicity class III - slightly toxic. Products containing bentazon bear the Signal Word CAUTION.

Chemical Class: Not Available

Introduction: Bentazon is a post-emergence herbicide used for selective control of broadleaf weeds and sedges (a weed) in beans, rice, corn, peanuts, mint, and others. Bentazon is a contact herbicide, which means that it causes injury only to the parts of the plant to which it is applied. It interferes with the ability of susceptible plants to use sunlight for photosynthesis. Visible injury to the treated leaf surface usually occurs within 4 to 8 hours, followed by plant death. It should not be used on blackeyed peas or garbanzo beans.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Bentazon is slightly toxic by ingestion and by dermal absorption [22]. Human ingestion of high doses of this herbicide has caused vomiting, diarrhea, trembling, weakness, and irregular or difficult breathing. It is moderately irritating to the skin, eyes, and respiratory tract [68]. Severe eye irritation from this material healed after 1 week [8]. Symptoms which have occurred in test animals include apathy, incoordination, prostration, tremors, anorexia, vomiting, and diarrhea [58]. The LD50 for bentazon in cats is 500 mg/kg, in rabbits is 750 mg/kg, in mice is 400 mg/kg, and in rats is 1100 to 2063 mg/kg [1,58]. When bentazon was applied to the shaven skin of rabbits, it did not cause irritation [1,58]. Its dermal LD50 is 4000 mg/kg in rabbits.
• Chronic toxicity: Consumption of bentazon at high levels for a long time results in excessive weight loss and inflammation of the prostrate gland in animal studies [69]. Prolonged or repeated exposure of the skin or eyes to bentazon may cause dermatitis or conjunctivitis [22]. When dogs were given 2.5, 7.5, 25, or 75 mg/kg/day for 13 weeks, weight loss, general ill health, and inflammation of the prostrate occurred at the highest dose tested [69].
• Reproductive effects: No data are currently available.
• Teratogenic effects: Birth defects were observed in one rat study at a dose of 200 mg/kg/day, but the validity of these data are in question [70]. No further data are currently available.
• Mutagenic effects: No data are currently available.
• Carcinogenic effects: Tumors have been seen in rats given 200 mg/kg/day of bentazon, but these results are questionable [71]. No further data are currently available [1].
• Organ toxicity: Animal studies have shown that the prostate gland may be affected.
• Fate in humans and animals: Bentazon is rapidly absorbed and readily excreted, unchanged, in the urine. About 91% of a 0.8 mg dose administered to rats by stomach tube was excreted in the urine within 24 hours of ingestion, with less than 1% in feces. This suggests that bentazon is almost completely absorbed from the gastrointestinal tract into the bloodstream when it is ingested [69].

Ecological Effects:

• Effects on birds: Technical and formulated bentazon are both slightly toxic to birds. The oral LD50 of formulated bentazon (BAS 3510H) is 2000 mg/kg in mallard ducks and 720 mg/kg in Japanese quail [58].
• Effects on aquatic organisms: Bentazon is practically nontoxic to both coldwater and warmwater fish. Bentazon is slightly toxic to aquatic invertebrates. The LC50 (96-hour) for bentazon in rainbow trout is 510 mg/L for wettable powder. The LC50 (96-hour) for technical bentazon is 616 mg/L in bluegill sunfish, and in rainbow trout it is 190 mg/L. For formulated bentazon (BAS 35- H), the LC50 (96-hour) in bluegills is 1060 mg/L, and in rainbow trout is 636 mg/L [1,58]. The bioconcentration factor for bentazon predicted from its water solubility is 19, indicating low bioaccumulation potential.
• Effects on other organisms: Applications of bentazon are not considered hazardous to most non-target organisms because of its generally low toxicity. Bentazon is not toxic to bees [8,70].

Environmental Fate:

• Breakdown in soil and groundwater: Bentazon has a low persistence in soil. Its half-life is less than 2 weeks [11]. Bentazon reaches undetectable levels in soil 6 weeks after its application [58,71]. It is subject to breakdown by ultraviolet (UV) light from the sun and rapid degradation by soil bacteria and fungi [8]. Bentazon does not bind to soil particles and it is highly soluble in water. These characteristics usually suggest a strong potential for groundwater contamination. However, its rapid degradation is expected to prevent significant contamination of groundwater [72,11]. Based on a national survey, EPA estimates that bentazon may be found in about 0.1% of the rural drinking water wells nationwide. Bentazon was not detected in any community water systems. It was also not detected at concentrations above 0.02 mg/L in any well [73].
• Breakdown in water: Bentazon has the potential to contaminate surface water because of both its mobility in runoff water from treated crops, and its pattern of use on rice, which involves either direct application to water, or application to fields prior to flooding. Commercial formulations are readily water-soluble [72]. Bentazon appears to be stable to hydrolysis, a chemical reaction with water. However, it has a half-life of less than 24 hours in water because it is readily broken down by sunlight [72].
• Breakdown in vegetation: Bentazon is absorbed by plant leaves. In resistant (tolerant) plants, it is rapidly broken down into natural plant components [8,58]. It may be also be absorbed by the roots and translocated from the roots to other plant parts [58]. The degree of translocation depends on the type of plant. Whether translocated or not, bentazon is quickly metabolized, reorganized, and incorporated into natural plant components [72]. Bentazon has little effect on germinating seeds [58]. Some leaf speckling and leaf bronzing may occur under certain conditions of bentazon usage. Crop injury may result if bentazon is applied to crops that have been subjected to stress conditions, such as drought or widely fluctuating temperatures [8].

Physical Properties:

• Appearance: Pure bentazon is a colorless to slightly brown, odorless crystalline solid [1].
• Chemical Name: 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide [1]
• CAS Number: 25057-89-0
• Molecular Weight: 240.28
• Water Solubility: 500 mg/L @ 20 C [1]
• Solubility in Other Solvents: acetone v.s.; ethanols, ethyl acetates, and benzene s.s.; cyclohexane s.s. [1]
• Melting Point: 137-139 C [1]
• Vapor Pressure: Negligible; <0.46 mPa @ 20 C [1]
• Partition Coefficient: 0.4559 [1]
• Adsorption Coefficient: 34 (parent acid) [11]

Exposure Guidelines:

• ADI: 0.1 mg/kg/day [12]
• MCL: Not Available
• RfD: 0.0025 mg/kg/day [13]
• PEL: Not Available
• HA: 0.02 mg/L (lifetime) [69]
• TLV: Not Available

Basic Manufacturer:

BASF Corporation
Agricultural Products Group
P.O. Box 13528
Research Triangle Park, NC 27709-3528

• Phone: 800-669-2273
• Emergency: 800-832-4357
  

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.