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in 1996. EXTOXNET no longer updates this information, but it may be useful
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E X T O X N E T
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
EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
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.
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
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.
- Acute toxicity: Bentazon is slightly
toxic by ingestion and by dermal absorption . 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 . Severe eye
irritation from this material healed after 1 week .
Symptoms which have occurred in test animals include
apathy, incoordination, prostration, tremors, anorexia,
vomiting, and diarrhea . 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 . Prolonged or repeated
exposure of the skin or eyes to bentazon may cause
dermatitis or conjunctivitis . 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 .
- Reproductive effects: No data are
- 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 . No
further data are currently available.
- Mutagenic effects: No data are currently
- Carcinogenic effects: Tumors have been
seen in rats given 200 mg/kg/day of bentazon, but these
results are questionable . No further data are
currently available .
- 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
- 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
- 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
- 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].
- Breakdown in soil and groundwater:
Bentazon has a low persistence in soil. Its half-life is
less than 2 weeks . 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
. 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 .
- 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 . 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 .
- 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 .
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 . Bentazon has little effect on
germinating seeds . 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 .
- Appearance: Pure bentazon is a colorless
to slightly brown, odorless crystalline solid .
- Chemical Name:
- CAS Number: 25057-89-0
- Molecular Weight: 240.28
- Water Solubility: 500 mg/L @ 20 C 
- Solubility in Other Solvents: acetone
v.s.; ethanols, ethyl acetates, and benzene s.s.;
cyclohexane s.s. 
- Melting Point: 137-139 C 
- Vapor Pressure: Negligible; <0.46 mPa
@ 20 C 
- Partition Coefficient: 0.4559 
- Adsorption Coefficient: 34 (parent acid)
- ADI: 0.1 mg/kg/day 
- MCL: Not Available
- RfD: 0.0025 mg/kg/day 
- PEL: Not Available
- HA: 0.02 mg/L (lifetime) 
- TLV: Not Available
Agricultural Products Group
P.O. Box 13528
Research Triangle Park, NC 27709-3528
- Phone: 800-669-2273
- Emergency: 800-832-4357
References for the information in this PIP can be found in
Reference List Number 10
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