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The information in this profile may be out-of-date.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

Bensulide

Trade and Other Names: Trade names for bensulide include Betamec, Betasan, Bensumec, Benzulfide, Disan, Exporsan, Prefar, Pre-San, and R-4461. It is used in combination with other pesticides such as thiobencarb and molinate.

Regulatory Status: Bensulide is classified as a General Use Pesticide (GUP) by the U.S. Environmental Protection Agency. It is classified toxicity class III - slightly toxic. Products with bensulide bear the Signal Word CAUTION.

Chemical Class: organophosphate

Introduction: Bensulide is a selective organophosphate herbicide. It is one of a few organophosphate compounds that are used as a herbicide. Most of the others are used as insecticides. It is used on vegetable crops such as carrots, cucumbers, peppers, and melons and in cotton and turfgrass to control annual grasses such as bluegrass and crabgrass and broadleaf weeds. It is often applied before the weed seeds germinate (pre-emergence) in order to prevent them from germinating. It is available as granules or an emulsifiable concentrate. Estimates place the total U.S. use of bensulide at about 632,000 pounds annually. Application rates may be relatively heavy (up to 22.6 kg/ha) when it is used.

Formulation: It is available as granules or an emulsifiable concentrate.

Toxicological Effects:

• Acute toxicity: Although its toxicity is not high, bensulide can cause convulsions in humans when large amounts are ingested. Other symptoms of acute poisoning range from nausea and vomiting at mild exposure levels to abdominal cramps, loss of muscle coordination, slurring of speech, coma and death at higher levels of acute exposure [8]. The oral LD50 in rats ranges from 271 mg/kg to 770 mg/kg [13,40]. The dermal LD50 is 3950 mg/kg in rats and 2000 mg/kg in rabbits. Thus, bensulide's dermal acute toxicity is low. In tests with rodents, Betasan, a bensulide containing product, did not cause eye irritation. Rabbits exposed to bensulide suffered minor eye irritation [8].
• Chronic toxicity: Bensulide inhibits cholinesterase, a chemical which is critical to the proper functioning of the nervous system. Symptoms of human chronic exposure are fairly typical of other organophosphate pesticides and may include chest tightness, nausea, abdominal cramps, diarrhea, headache, dizziness, weakness, blurring, tearing, loss of muscle coordination, and face muscle twitches [8]. The lowest dose that resulted in no adverse effects for a 90-day feeding study with rats was 25 mg/kg/day [8].
• Reproductive effects: No data are currently available.
• Teratogenic effects: No data are currently available.
• Mutagenic effects: Bensulide was not mutagenic in the one bacterial assay that was performed [8]. No other data are currently available.
• Carcinogenic effects: Bensulide does not appear to be carcinogenic. In a 90-day feeding trial, rats and dogs tolerated daily doses close to the lethal dose without any noticeable tumor growth [8].
• Organ toxicity: Bensulide can inhibit the enzyme cholinesterase and affect brain, nerve, and some blood cells [41]. It may cause mild eye irritation.

• Fate in humans and animals: No data are currently available.

Ecological Effects:

• Effects on birds: Bensulide is only slightly toxic to birds. The bensulide herbicide, Betasan, was fed to adult Japanese quail for 3 weeks, and egg hatchability was significantly reduced at the highest dose (about 50 mg/kg/day), but fertility was not affected. Blood cholinesterase was inhibited at lower doses, but recovered within 2 weeks after the treatments stopped [8]. The oral LD50 in bobwhite quail is 1386 mg/kg [13].
• Effects on aquatic organisms: Bensulide is moderately to highly toxic to aquatic organisms, including rainbow trout and bluegill [8]. The LC50 for bensulide is 1.1 mg/L in rainbow trout, 1.4 mg/L in bluegill, and 1 2 mg/L in goldfish. The compound is moderately toxic to aquatic invertebrates like the amphipod Gammarus lacustrus [6]. The calculated bioconcentration is low and it is not expected to bioaccumulate [6].
• Effects on other organisms: Bensulide is very highly toxic to bees [13]. The LD50 of bensulide is 0.0016 mg per bee [13].

Environmental Fate:

• Breakdown in soil and groundwater: Bensulide is highly persistent in both plants and soil [8]. Because it strongly binds to the top 0 to 2 inches of soil, bensulide does not evaporate easily but can be carried off site with sediment or dust. The rate of application, temperature, soil organic matter, and soil acidity can all affect its breakdown. Bensulide leaches very little in sand, clay, or organic soils. Bensulide is slowly broken down by soil microorganisms. The rate of degradation increases with increasing soil temperature and organic matter, but decreases with increasing basicity [8]. At 70 to 80 F, the half-life of bensulide is 4 months in a moist loam soil and 6 months in a moist, loamy sand [13]. As of 1988, it had not been found in groundwater or in well water [42].
• Breakdown in water: In flooded rice fields the half-life of bensulide averages 4 to 6 days [13]. Some decomposition by sunlight occurs over several days [8].
• Breakdown in vegetation: Bensulide is rapidly absorbed by roots and foliage and is translocated to the active growing portions of the plant (root or stem tips) where it works to stop cell division and plant growth [13]. When applied to roots, bensulide is not translocated to leaves except as metabolites [8].

Physical Properties:

• Appearance: Bensulide is a viscous, colorless liquid or a white crystalline solid [13]
• Chemical Name: O,O-diisopropyl S-2-phenylsulfonylaminoethyl phosphorodithioate [13]
• CAS Number: 741-58-2
• Molecular Weight: 397.54
• Water Solubility: 25 mg/L @ 20 C [13]
• Solubility in Other Solvents: kerosene s.; acetone v.s., ethanol v.s., xylene v.s. [13]
• Melting Point: 34.4 C [13]
• Vapor Pressure: 0.133 mPa @ 25 C [13]
• Partition Coefficient: 4.2175 [13]
• Adsorption Coefficient: 1000 (estimated) [19]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

ICI Americas, Inc.
Agricultural Products
New Murphey Road
Wilmington, DE 19897

• Phone: 302-866-1000
• Emergency: 800-323-8633
  

References:

References for the information in this PIP can be found in Reference List Number 5

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.