E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade names for bensulide include Betamec, Betasan, Benzulfide,
Disan, Exporsan, Prefar, Pre-San, and R-4461. It may be used in
combination with other pesticides such as thiobencarb and molinate.
Bensulide is a selective organophosphate herbicide. 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 formulated as an
emulsifiable liquid and applied before the weed seeds germinate in order
to prevent them from germinating (10).
This slightly toxic herbicide is labeled with a CAUTION signal
word. Although its toxicity is not high, it 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 and slurring of speech,
coma and death at higher levels of acute exposure (4). Specific
concentrations or doses were not noted with the listed symptoms.
The oral LD50 for rats ranges from 271 mg/kg (5) to 770 mg/kg (2).
The dermal LD50 is 3,950 mg/kg for rats and 2,000 mg/kg for rabbits. In
tests with rodents, Betasan, a bensulide containing product, did not
cause eye irritation (4).
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. No information was found about its potential to
cause birth defects.
Bentasan fed to adult Japanese quail for three weeks at moderate
doses (50 mg/kg) adversely affected egg hatchability. Fertility however
was unaffected (4). This evidence is not sufficient to draw any
conclusions about the risk of bensulide to human reproduction.
This chemical was not mutagenic in the one bacterial assay that was
performed (4). More information is needed before bensulide's mutagenic
potential can be appropriately assessed.
Appropriate studies for establishing carcinogenic potential have
not been performed. However, in a 90-day feeding trial, rats and dogs
tolerated daily doses close to the lethal dose without any noticeable
tumor growth (7).
Bensulide can inhibit the enzyme cholinesterase and affect brain,
nerve, and some blood cells (6). Rabbits exposed to bensulide have
suffered mild eye irritation.
Bensulide is moderately to highly toxic to aquatic organisms,
including rainbow trout and bluegill (4). The LC50 for bensulide in
rainbow trout is 0.7 mg/l, in the bluegill it is 0.8 mg/l and is 1-2
mg/l in the goldfish.
It is only slightly toxic to wild birds. The bensulide herbicide,
Betasan, was fed to adult Japanese quail for three weeks and egg
hatchability was significantly reduced at the highest dose (about 50
mg/kg), but fertility was not affected. Blood cholinesterase was
inhibited at lower doses, but recovered within two weeks after the
treatments stopped (4).
The compound is very highly toxic to bees (9). The LC50 of
bensulide is about 12.5 ug/bee (4).
Bensulide is persistent in both plants and soil. Because it
strongly binds to soils, bensulide does not evaporate easily but can be
carried off site with sediment or in dust. The rate of application,
temperature, soil organic matter, and soil acidity can all affect the
breakdown of the product.
Root growth of target plants can be inhibited or delayed by
bensulide treatment. In one study, root growth of bermudagrass was
greatly reduced by low dose bensulide applications (1). The compound 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 (9). When applied to roots, bensulide is
not translocated to leaves except as metabolites (4). Bensulide is
effective for four months to one year, depending on the rate of
Bensulide leaches very little in sand, clay, or organic soils. It
is tightly bound in the top 0 to 2 inches of soil. Thus, it persists
long enough to control summer weeds like crabgrass, barnyard grass,
lambsquarters, and deadnettle.
The rate of degradation increases with increasing soil temperature
and organic matter, but decreases with increasing basicity (4).
Bensulide is slowly broken down by soil micro-organisms. At 70-80
degrees F, the half of the compound is still present after four months
in a moist loam soil, and after six months in a moist, loamy sand (4).
Since bensulide binds to soil, it can be transported to surface water
through runoff. As of 1988 it had not been found in groundwater or in
wellwater (8). In rice fields the half-life of the compound averages
only four to six days (9).
Some decomposition by sunlight occurs over several days (4).
PHYSICAL PROPERTIES AND GUIDELINES
Bensulide is a viscous, colorless liquid or a white crystalline
solid, with a molecular weight of 397.52. It is a member of the
organophosphates. Products containing bensulide may be amber colored
liquids. While it is corrosive to copper, it is non-corrosive to other
metals. No incompatibilities are known. Bensulide shows little
reactivity, and is of low fire hazard.
Its chemical name is S-(O,O-diisopropyl phosphorodithioate) ester
of N-(2-mercaptoethyl) benzenesulfonamide. Bensulide is stable and has
an indefinite storage life under normal conditions.
|NOEL: ||25 mg/kg/day for 90 days (rat); 12.5 mg/kg/day for 90 days (dog).
|CAS #: ||741-58-2
|Solubility in water: ||25 mg/L at 20 degrees C (low solubility)
|Solubility in solvents: ||soluble in 300 mg/l kerosene at 20 degrees C. It is also miscible with acetone, ethanol, xylene, and methyl-isobutyl ketone.
|Melting point: ||34.4 degrees C
|Boiling point: ||decomposes at 200 degrees C in 18 to 48 hours.
|Vapor pressure: ||<133 uPa at 20 degrees C.
Zeneca Ag Products
Wilmington, DE 19897
Telephone: (302) 886-1000
Review by Basic Manufacturer:
Comments solicited: November, 1992
Ashton, F.M. and Crafts, A.S. Bensulide, Mode of Action of
Herbicides. pp. 396-398. New York: John Wiley & Sons Inc., 1973.
Buchel, K.H., ed. and Holmwood, G.M., translator. Chemistry of
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Clinical Toxicology of Commercial Products, 5th edition. Williams &
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Occupational Health Services Inc. Material Safety Data Sheet:
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Worthing, C.R., ed. 1983 "Bensulide." The Pesticide Manual. 7th
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US Environmental Protection Agency. 1988. Pesticides in Ground
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