Bentazon - Herbicide Profile 9/85
CHEMICAL FACT SHEET FOR: BENTAZON AND SODIUM BENTAZON
FACT SHEET NUMBER: 64
DATE ISSUED: SEPTEMBER 30, 1985
1. DESCRIPTION OF CHEMICAL
- Chemical Names: 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one
2,2-dioxide and sodium salt of above
- Common Names: bentazon and sodium bentazon (sodium salt of bentazon)
- Trade Names: Manufacturing-use product, Bentazon Manufacturer's
Concentrate; End-use product (single active ingredient), Basagran
Postemergence Herbicide; End-use product (combined with atrazine),
Laddock Postemergence Herbicide. Note: All three of these products
have sodium bentazon as the active ingredient.
- EPA Shaughnessy Code: 275200 and 103901, respectively.
- Chemical Abstracts Service (CAS) No: 50723-80-3
- Year of Initial Registration: 1975
- Pesticide Type: herbicide
- U.S. Producers: BASF Wyandotte Corporation
2. USE PATTERNS AND FORMULATIONS
- Application sites: Soybeans, rice, corn, sorghum, peanuts, beans (dry
or succulent), peas (dry or succulent), established peppermint and
spearmint, and established ornamental turf. The only additional site
under Section 24(c) (Special Local Needs) registration is Bohemian
- Percent of particular crops treated with the pesticide as of 1984:
Dry beans and peas 5%
- Percent of pesticide applied to particular crops as of 1984:
Dry beans and peas <1%
- Types and methods of application: Sodium bentazon is applied by
ground or air as a broadcast foliar spray after the crop and weeds
have emerged from the soil. It is used to control selected broadleaf
weeds and sedges only.
- Application rates: Rates, from 0.75 lb. a.1./acre to 2 lb. a.i./
acre, vary by crop, geographic region, target species, and site
- Types of formulations: The manufacturing-use product is a 46% sodium
bentazon liquid. Basagran Postemergence Herbicide is a "soluble liquid
concentrate" containing 42% sodium bentazon. Laddock Postemergence
Herbicide is a "flowable liquid concentrate" containing 18.52% sodium
bentazon and 16.96% atrazine.
- Usual carriers: The usual carrier is water. An oil concentrate is
used under certain conditions.
3. SCIENCE FINDINGS
Technical grade bentazon (isolated before formation of sodium
bentazon) is an odorless, non-volatile solid with a melting point of
137-139. Its solubility (g/100 g solvent, 20 degrees C) is 0.05 in water
and 150.7 in acetone. Sodium bentazon is considerably more soluble in
water than bentazon, with a solubility of 230 g/100 g in water.
Acute toxicity: Sodium bentazon is in Toxicity Category III (defined in
40 CFR 162.10), based upon acute oral toxicity in the rat and acute
dermal testing in the rat. An acute inhalation study is supplementary
(valid but does not meet EPA guideline requirements) and will need to be
Subchronic toxicity: Subchronic data are supplementary (90-day rat
feeding study and 13-week dog study, bentazon) or invalid (21-day dermal
study, sodium bentazon), and will require replacement. Compound-related
effects were seen at 300 and 3,000 ppm test levels in the dog study
(numerous effects at 3,000 ppm; prostatitis at 300 ppm was basis of
lowest-effect-level of 300 ppm and no-effect level of 100 ppm). A 1-year
dog study is required for hazard assessment.
All chronic toxicity data for bentazon are supplementary or
invalid, and will require replacement. Twenty-four month and 18-month
mouse studies have been invalidated and a "for cause" laboratory audit
requested, due to substantial deficiencies.
- In a supplementary mouse oncogenicity study, no specific clinical or
pathological symptoms could be associated with bentazon exposure.
- A rat 3-generation reproduction study found no compound-related
effects for bentazon up to a dietary level of 180 ppm. However,
without effects at the highest dose, the dose selection is considered
- The available rat and rabbit teratogenicity studies are inadequate,
but do not suggest that bentazon is a potent teratogen or fetotoxic
Terata were observed in one rat study at a dose of 200 mg/kg/day, but
the utility and validity of these data are in question. Additional
teratology studies in the rat and rabbit are required. - A variety of
mutagenicity studies (analytical grade bentazon or sodium salt) have
been reviewed, but none are adequate for regulatory purposes. This is
also the case for metabolism studies with labeled bentazon.
Physiological and Biochemical Behavioral Characteristics:
Mechanism of pesticidal action: Foliar application of sodium
bentazon results in photosynthesis inhibition in susceptible species.
Visible injury to the treated leaf surface usually occurs in 4-8 hours,
followed by plant death.
Foliar absorption and translocation: Bentazon applied
postemergence to young plants may be absorbed and translocated from the
site of application. The degree of translocation depends on the plant
species. Whether translocated or not, bentazon is rapidly metabolized,
conjugated, and incorporated into natural plant components.
Metabolism in plants and animals: The metabolism of bentazon in
tolerant plants is partially understood. The 6-hydroxy and the 8-hydroxy
metabolites are included with bentazon in the tolerances on crops.
Further work is necessary to characterize other metabolites. The
metabolism in animals is not understood, as the acid hydrolysis
procedure was not run on any of the methanol extracts of eggs and
poultry tissues. However, in animals there is no hydroxylation of
bentazon as in plants. Based on available information, the residues in
animals consist of the metabolite
AIBA and bentazon, and tolerances for residues in animal products
should be expressed in terms of these combined residues.
- Decomposition: Based on available, validated data, bentazon appears
to be stable to hydrolysis, but photodegrades in water with a half-
life of <24 hours. It also photodegrades on soil. Under aerobic
conditions in lab and field, bentazon degrades with a half-life of <1
month in soil.
- Bioaccumulation: Bentazon residues accumulate in the tail meat and
viscera of crayfish, with bioconcentration factors of <10X.
- Surface and groundwater contamination concerns: Bentazon is very
mobile in soil, but the relatively rapid degradation is expected to
prevent groundwater contamination. An aged leaching study is needed to
determine the potential for metabolites to contaminate groundwater.
Bentazon does have the potential to contaminate surface water because
of: 1) its mobility in runoff water, for all crops, and 2) its rice
use pattern that involves either direct application to water or
application to fields prior to flooding.
Hazards to fish and wildlife:
- Technical bentazon is considered slightly toxic to birds, based on
subacute dietary testing. Formulated bentazon is considered slightly
toxic to birds, based on acute oral testing with a 50% a.i. wettable
powder. Avian reproduction testing did not show effects up to the
highest dietary level tested, but the studies were found to lack
vital information and do not presently meet EPA guidelines.
- Technical bentazon is characterized by EPA as practically nontoxic to
both coldwater and warmwater fish, and slightly toxic to aquatic
invertebrates, based on review of acute testing. Formulated bentazon
is considered practically nontoxic to coldwater and warmwater fish,
based on acute testing with a 48% a.i. liquid product.
- Applications of bentazon on registered use sites are considered
unlikely to result in acute hazard to most nontarget organisms,
because of its generally low toxicity, based on available data, and
low application rates. However, a final risk assessment is deferred,
due to lack of critical environmental chemistry data and certain
ecological effects data.
Potential problems related to endangered species:
- Biological opinions (covering all registered pesticides) have been
received from the U.S. Fish and Wildlife Service Office of Endangered
Species (OES) for three of the crops for which sodium bentazon is
registered: corn, sorghum, and soybeans. To avoid jeopardy to the
Valley Elderberry Longhorn Beetle (Desmocerus californicus dimorphus),
OES indicates that herbicides should be prohibited from designated
areas in California in order to protect the host plant, elderberry
(Sambucus spp.). Labeling developed by EPA to implement this
prohibition is described below.
- The above opinions also stated that, "...to avoid jeopardy to Solano
grass.the use of any herbicides toxic to graminoides should be
prohibited within..." certain defined geographic areas of California,
because of concerns with spray drift and runoff from agricultural
areas. Solano grass (Tuctoria (= Orcuttia) mucronata) is an
endangered plant species found in a vernal lakebed in Solano County,
California. Since no grass species are claimed on existing labeling to
be controlled with sodium bentazon, and the herbicide is used on
various grass crops, Ecological Effects Branch (with informal
consultation with OES) did not consider there to be a threat to Solano
grass from the registered use of this chemical. Subsequently.
information has been located indicating that sodium bentazon may
affect certain germinating grass species with direct exposure at full
dosage rates, but that it does not affect grasses after germination.
Solano grass germinates in March and April. The earliest planting date
for corn, sorghum, or soybeans is for corn, which can be planted as
early as April 15. Since sodium bentazon is applied postemergence to
the weeds, there may be little opportunity for an application that
could affect Solano grass. Further consultation with OES will be
initiated. Label restrictions, as above, and/or plant protection data
requirements (under 40 CFR Section 158.150) may be imposed.
- An oyster study and further environmental chemistry data are required,
in part, to evaluate whether there is any hazard to endangered mussel
species from sodium bentazon use.
- The Agency is not aware of any other data which would suggest that the
risk criteria of Section 162.11 have been met or exceeded for the uses
of sodium bentazon at the present time.
- In the United States, tolerances are currently established in 40 CFR
Section 180.355 for combined residues of bentazon (3-isopropyl-1H-
2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide) and its 6- and 8-hydroxy
metabolites in or on agricultural commodities as follows:
Commodity Parts per million
Beans (except soybeans), dried 0.05
Beans (exc. soybeans), dried, vine hays 3
Beans (exc. soybeans), forage 3
Beans, lima (succulent) 0.05
Beans, succulent 0.05
Bohemian chili peppers 0.5*
Corn, fodder 3
Corn, forage 3
Corn, grain 0.05
Corn, fresh (incl. sweet K+CWHR) 0.05
Peanuts, hay 3
Peanuts, hulls 0.3
Peanuts, forage 3
Peas (dried) 0.05
Peas (dried), vine hays 3
Peas, forage 3
Peas, succulent 0.5
Rice, straw 3
Sorghum, fodder 0.05
Sorghum, forage 0.20
Sorghum, grain 0.05
Soybeans, forage 3
Soybeans, hay 0.3
*The misprinted tolerance of 0.5 ppm for Bohemian chili peppers will be
corrected to read 0.05 ppm and combined residues of bentazon (3-
isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide) and its
metabolite 2-amino-Nisopropyl benzamide in raw agricultural commodities
Commodity Parts per million
Cattle, fat 0.05
Cattle, mbyp 0.05
Cattle, meat 0.05
Goats, fat 0.05
Goats, mbyp 0.05
Goats, meat 0.05
Hogs, fat 0.05
Hogs, mbyp 0.05
Hogs, meat 0.05
Poultry, fat 0.05
Poultry, mbyp 0.05
Poultry, meat 0.05
Sheep, fat 0.05
Sheep, mbyp 0.05
Sheep, meat 0.05
- Tolerance reassessment cannot be conducted because of toxicology and
residue chemistry data gaps.
- International tolerances: There are 0.1 ppm Canadian tolerances for
bentazon on soybeans, beans, peas, corn, rice, and peanuts. Presently,
there are no Mexican or Codex Alimentarius tolerances for bentazon.
4. SUMMARY OF REGULATORY POSITION AND RATIONALE
The available data do not indicate that any of the risk criteria
listed in Section 162.11(a) of Title 40 of the U.S. Code of Federal
Regulations have been met or exceeded for the uses of sodium bentazon at
the present time. However, substantial data gaps exist (see below).
Under FIFRA Section 3(c)(2)(B), the registrant must provide or agree to
develop this data to maintain the existing MP registration or to permit
new registrations of substantially similar sodium bentazon MP's.
The Agency will complete its hazard evaluation, or determine what
further data are necessary to do so, upon review of the data being
required under this Registration Standard. The Agency will determine at
that time if such data will affect the registrations of bentazon. If
such review determines that criteria for determinations of unreasonable
adverse effects are met or exceeded (as specified under Section 162.11),
a rebuttable presumption shall arise that a notice of intent to cancel
registration(s) pursuant to FIFRA Section 6(b)(1) (or a notice of intent
to hold a hearing to determine whether the registration(s) should be
cancelled) may be issued. If, at any time, review of the data indicates
that an imminent hazard (as defined by FIFRA Section 2(1)) is posed by
continued bentazon use, immediate suspension procedures may be initiated
as per FIFRA Section 6(c)(1).
No new uses of sodium bentazon will be permitted until the data
base is adequate to complete a hazard assessment. As per Conditional
Registration Interim Final Regulations (FR Vol. 44, No. 93, May 11,
1979), no new uses or new products may be registered without "data
sufficient to allow the Agency to determine that approval of the
application would not cause a significant increase in the risk of
unreasonable adverse effects on the environment." For bentazon, the
entire subchronic and chronic toxicology data base (required to evaluate
hazards to humans/domestic animals from existing uses) is invalid or
otherwise inadequate, and thus totally insufficient to evaluate any new
uses. The Agency is unable to complete a tolerance reassessment of
bentazon because of these gaps, as well as residue chemistry data gaps.
The Agency is unable to fully assess potential human exposure,
potential for groundwater contamination, or complete an ecological
effects hazard assessment of existing sodium bentazon uses because of
exposure assessment/environmental chemistry data gaps. There are also
certain product chemistry, wildlife/aquatic organism, and nontarget
insect data gaps that prevent full assessment of existing use.
Clarification or verification of all test materials used in studies
submitted by the registrant is required. The Agency reserves the right
to impose additional testing of either bentazon or sodium bentazon
following review of this information and/or review of new studies
submitted to fulfill data gaps identified in this Standard.
All manufacturing-use and end-use products containing sodium
bentazon must bear appropriate labeling as specified in 40 CFR Section
162.10. The following statements are also required. All labeling changes
must appear on all products released for shipment by September, 1986.
All labeling changes must appear on all products in channels of trade by
- Manufacturing-use products:
- Do not discharge effluent containing this product into lakes, streams,
ponds, estuaries, oceans, or public waters unless this product is
specifically identified and addressed in a National Pollutant
Discharge Elimination System (NPDES) permit. Do not discharge effluent
containing this product to sewer systems without previously notifying
the sewage treatment plant authority. For guidance, contact your State
Water Board or Regional Office of the U.S. Environmental Protection
- Note: When citing the bentazon equivalent, the chemical name for
bentazon should be written as "3-(1-methylethyl)-1H-2,1,3-
benzothiadiazin-4(3H)-one 2,2 dioxide."
- Do not graze treated corn fields for at least 12 days after the last
sodium bentazon treatment.
- Do not graze treated peanut fields for at least 50 days after the last
sodium bentazon treatment.
- Do not rotate crops used for food or feed, which are not registered
for use with sodium bentazon, on areas previously treated with this
- Do not use water containing bentazon or sodium bentazon residues from
rice cultivation to irrigate crops used for food or feed unless sodium
bentazon is registered for use on these crops.
- For all uses except rice: Do not apply directly to water or wetlands.
Do not contaminate water by cleaning of equipment or disposal of
For rice use: Do not contaminate water by cleaning of equipment or
disposal of wastes.
For corn, soybean, and sorghum uses:
- Notice: It is a violation of federal laws to use any pesticide in a
manner that results in the death of an endangered species or adverse
modification of its habitat.
- The use of this product may pose a hazard to certain federally
designated endangered species known to occur in specific areas within
the California counties of Merced, Sacramento. and Solano. Before
using this product in these counties, you must obtain the EPA
Endangered Species Bulletin specific for these areas. The bulletin
(EPA/ES-85-6) is available from either your County Agricultural
Extension Agent, the Endangered Species Specialist in your State
Wildlife Agency Headquarters, or the Regional Office of the U.S. Fish
and Wildlife Service (Portland, Oregon). This bulletin must be
reviewed prior to pesticide use. The use of this product is prohibited
in these counties unless specified otherwise in the bulletin.
- Note: When citing the bentazon equivalent, the chemical name for
bentazon should be written as "3-(1-methylethyl)-1H-2,1,3
benzothiadiazin-4(3H)-one 2,2 dioxide."
5. SUMMARY OF MAJOR DATA GAPS
There are numerous generic data gaps in the areas of product
chemistry, residue chemistry, environmental fate, and ecological
effects. Generic toxicology data gaps and time frames for submittal
are as follows:
- Acute inhalation toxicity, rat 9 months
- 90-day feeding, rodent 15 months
- 90-day feeding, nonrodent (dog) 18 months
- 21-day dermal, rabbit 12 months
- Chronic toxicology, rodent 50 months
- Chronic toxicology, nonrodent (dog) 50 months
- Oncogenicity, rat (preferred) 50 months
- Oncogenicity, mouse (preferred) 50 months
- Teratogenicity, rat 15 months
- Teratogenicity, rabbit 15 months
- Reproduction, rat (2-generation) 39 months
- Mutagenic ty, gene mutation (Ames test) 9 months
- Mutagenicity, structural chromosomal aberration 12 months
- Mutagenicity, other genotoxic effects 12 months
- General metabolism (using bentazon and sodium
bentazon) 24 months
- Dermal penetration 12 months
- Product-specific data gaps on the manufacturing-use product include
product chemistry data and two acute toxicology studies.
6. CONTACT PERSON AT EPA
Product Manager 25
Environmental Protection Agency
401 M Street S.W.
Washington, DC 20460
DISCLAIMER: THE INFORMATION PRESENTED IN THIS CHEMICAL INFORMATION FACT
SHEET IS FOR INFORMATIONAL PURPOSES ONLY AND NOT TO BE USED TO FULFILL
DATA REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.