Primisulfuron-Methyl - Herbicide Profile 6/90
EPA Pesticide Fact Sheet
Name of Chemical: Primisulfuron-methyl
Reason for Issuance: Registration
Date Issued: June 12, 1990
Fact Sheet Number: 214
1. DESCRIPTION OF CHEMICAL
- Generic Name: 3-[4,6-Bis-(difluoromethoxy)-pyrimidin-2-yl]-1-(2-
- Common Name: CGA-136872 and primisulfuron-methyl
- Trade Names: Beacon Herbicide and Rifle Herbicide
- EPA Shaughnessy Code: 128973-5
- Chemical Abstracts Service (CAS) Number: 86209-51-0
- Year of Initial Registration: 1990
- Pesticide Type: Herbicide
- Chemical Family: Sulfonylurea
- U.S. Producer: CIBA-GEIGY Corporation
2. USE PATTERNS AND FORMULATIONS
- Application sites: Terrestrial food crops and terrestrial noncrop
sites. Postemergence to actively growing weeds in corn; and in
noncropland areas such as fence rows, airports, highway rights-of-way,
industrial sites, lumber yards, petroleum tank farms, pipeline rights-
of-way, plant sites, railroads, storage areas, and utility rights-of-
- Types of formulations: The two end-use products (75.0% a.i) are
identical in composition. They are water dispersible granules
packaged in water soluble bags. The technical product which is a
crystalline solid containing 95% a.i. is used in the manufacture of
the two end-use products. The technical product is packaged in a
- Amount and Method of Application: Maximum application of 0.56 oz.
active ingredient per acre per season is claimed for postemergence
weed control in the culture of corn. For low maintenance turfgrass
sites along roadsides, airports, industrial sites, fence rows, etc. in
common bermudagrass and buffalograss turf, dosages of 0.4 to 2.5 ozs
per acre may be applied. These same dosages are claimed for noncrop
sites such as fence rows, highway rights-of-way, industrial sites,
lumberyards, petroleum tank farms, pipeline rights-of-way, plant
sites, railroads, storage areas, and utility rights-of-way. The
dosage to be used depends on the target weed species to be controlled.
Only ground application directions are given on the proposed labeling.
Measures to avoid spray drift and washing onto nontarget areas are
described on the labeling.
- Carrier: Water
3. SCIENCE FINDINGS
Summary Science Statements:
Adequate toxicological, product and residue chemistry ecological
effects environmental fate and ground water data have been submitted and
reviewed to support the registration of primisulfuron-methyl for use as
a postemergence herbicide in the culture of corn and perennial turf
grasses. Registration as a postemergence, non-selective herbicide on
noncropland such as fence rows, highway rights-of-ways, industrial
sites, lumber yards, petroleum tank farms, pipe line right-of-ways,
plant sites, railroads, storage areas, and utility rights-of-way is also
supported. Primisulfuron-methyl is classified as a Toxicity Category
III pesticide and is labeled with the signal word CAUTION, based on
acute dermal, acute inhalation and eye irritation studies. A 21-day
dermal study in rabbits indicated a no observable effect level (NOEL) of
greater than 1,000 mg/kg/day for systemic toxicity. Primisulfuron-
methyl was non-mutagenic and in developmental toxicity studies it did
not appear to be a potential teratogen. Based on results of a mouse
oncogenic lifetime study it was classified as a Group D carcinogen - not
classifiable as to human carcinogenicity. Ecological effects data
characterize primisulfuron-methyl as practically nontoxic to birds on
subacute dietary and acute oral bases. Toxicological data demonstrated
that it is of low toxicity to mammals. Low levels of contamination of
ground water is possible in vulnerable soils with high water tables.
The chemical is essentially nontoxic to honey bees. It is stable to
hydrolysis in neutral and mildly alkaline solutions (pH 7 and 9), and
hydrolyzed slowly (half-life >30 days) in acidic (pH 5) solutions.
- Physical State: Crystalline Solid
- Color: Colorless to yellow
- Odor: Odorless
- Melting Point: ca. 200 degrees C (Decomposition at melting Point)
- Density: 1.62 gm/cm3 at 20 degrees (typical)
- Solubility Solvent Based on gm/100 cm3/20 degrees C
Water 1 ppm (pH 5)
9 ppm (pH 6)
70 ppm (pH 7)
600 ppm (pH 8)
4500 ppm (pH 9)
N-Octanol 120 ppm
Methyl Chloride 0.4%
- Vapor Pressure: < 1.5 x 10-10 Torr. at 25 degrees C
- Dissociation Constant: PKa value = 5.1 (Acid)
- Octanol/Water Partition Coefficient: P = 0.059
- pH: 5.56 at 25 degrees C + or - 1 degree C (Saturated Solution)
The technical material decomposes on melting. Technical
primisulfuron-methyl is stable at room temperatures. At 35 degrees C it
degraded less than 1.0 percent during 12 months of storage. At 54
degrees C there was no degradation up to 3 months of storage. The
formulated products Beacon Herbicide and Rifle Herbicide were stable up
to 28 weeks at 50 degrees C and after 7 weeks at 70 degrees C there
occurred 2.0% degradation.
- Acute Toxicity (Technical, 94% ai)
- Acute oral toxicity (rat): LD50 > 5050 mg/kg, Toxicity Category IV.
- Acute dermal toxicity (rabbit): LD50 > 2,010 mg/kg, Toxicity
- Primary dermal irritation (rabbit): No edema, no erythema in male
rabbits, Erythema in one female rabbit cleared within 72 hours,
Toxicity Category IV.
- Primary eye irritation (rabbit): No corneal opacity, conjunctivitis
clearing within 3 days, Toxicity Category III.
- Acute inhalation toxicity (rat): No deaths, LC50 > 4.81 mg/L for 4
hours, Category III.
- Dermal sensitization (guinea pig): Negative for skin sensitization in
male guinea pigs (not tested in females), not a skin sensitizer.
- Acute Toxicity (Beacon Herbicide, 75% ai) Acute dermal toxicity
(rabbit): No deaths, LD5050 >2010 mg/kg, Category III.
- Acute inhalation toxicity (rat): No deaths, LC5050 >3.28 mg/L for
4 hours, Category III.
- Primary eye irritation (rabbit): No corneal opacity, conjunctivitis
clearing in day 4, Category III.
- Primary dermal irritation (rabbit): No edema, slight erythema in one
male and one female clearing by 24 hours, Category IV.
- Dermal sensitization (guinea pig): Negative for skin sensitization in
male guinea pigs, females not tested, not a skin sensitizer.
- A 21-day dermal study in rabbits was conducted using levels of 0, 10,
100 and 1,000 mg/kg/day. No effect was observed on any parameter
examined, NOEL was > 1,000 mg/kg/day.
- A 13-week dog feeding study at 0, 25, 1,00 and 10,000 ppm was
conducted. Effects were increased platelet values in females and
thickened gall bladder mucosa in one female dog macroscopically. One
male and three female dogs had mild epithelial hyperplasia of the gall
bladder. The NOEL was 25 ppm and the LEL was 1,000 ppm.
- A 13-week rat feeding study at 0, 10, 300, 3,000, 10,000, 20,000 ppm
was conducted. The effects were decreased body weight in males,
decreased food consumption in males, decreased absolute and relative
spleen weight in males. The NOEL was 300 ppm and the LEL was 3, 000
- A l-year dog feeding study was conducted at 0, 25, 1,000 and 10,000/
5,000 ppm (changed after week 10). Results were decreased body weight
gain at 10,000 ppm (weeks 1 to 10); anemia at 10/5,000 ppm; liver
weight increases (absolute and relative) and vacuolar changes at
10/5,000 ppm; thyroid hyperplasia at 10/5,000 ppm; systemic NOEL was
1,000 (25 mg/kg/day) and the systemic LEL was 5,000 ppm (125
mg/kg/day). The effects were anemia, increase in platelets, lower
cholesterol values, pale livers, moderate to trace vacuolar changes
and thyroid hyperplasia.
- A 2-generation reproduction study in rats was conducted at doses of 0,
10, 1,000 and 5,000 ppm. An effect noted at 5,000 ppm was decrease in
testicular/spermatic function and decreased body weight gains in
males. There was also a decrease in pup weights. The systemic
parental NOEL was 1000 ppm and the LEL was 5,000 ppm based on
decreased body weight gain. The reproductive NOEL was 1,000 ppm and
the LEL was 5,000 ppm based on paternal decrease in
testicular/spermatic function and a decrease in pup body weight.
The following mutagenicity studies indicated that primisulfuron-
methyl is not mutagenic at doses tested:
- Ames Assays for mutagenicity with and without metabolic activation in
Salmonella TA98, TA100, TA1535, and TA1537 up to 1024 ug/plate.
- Chromosome Aberration (micronucleus) in Chinese hamster up to 5,000
mg/kg. There was no evidence of toxicity.
- Unscheduled DNA synthesis (UDS) Assay with rat liver cells
(hepatocytes) up to 400 ug/ml.
- UDS Assay with human fibroblasts up to 1,000 ug/ml without activation
- In a rabbit teratology study at doses of 0, 10, 300, 600 mg/kg/day by
gavage there was no evidence of development effects. The effect
observed in this study was abortion, decreased body weight, stool
alterations. The maternal NOEL was 10 mg/kg/day and the LEL was 300
- In a rat study at doses of 0, 100, 500, and 1000 mg/kg/day by gavage
there was delayed skeletal development and incomplete or lack of
ossification of several bones. The developmental NOEL was 100
mg/kg/day and the LEL was 500 mg/kg/day.
- In a second rat study at doses of 0, 10, 50 and 100 mg/kg/day there
was possible increase in number of litters (not fetuses) having
incomplete ossification of the os pubis at 100 mg/kg/day. Maternal
NOEL was > 100 mg/kg/day at the highest dose tested (DT).
- These three studies indicate that primisulfuron-methyl is not a
- A 104-week rat feeding oncogenic study was conducted at doses of 0,
10, 300, 3,000 and 10,000/8,000 ppm. The systemic NOEL was 300 ppm (15
mg/kg/day) and the systemic LEL was 3,000 ppm (150 mg/kg/day) based on
decreased weight gain in males. At 10,000/8,000 ppm testes of males
were soft and atrophied; at 10,000/8,000 ppm food consumption in both
males and female was decreased. The study was evaluated as showing a
negative oncogenicity potential in rats.
- An 80-week mouse feeding oncogenic study was conducted at doses of 0,
300, 3,000 and 10,000 (reduced to 7,00 at week 23). The systemic NOEL
was 300 ppm (40.0 mg/kg/day) for males and less than 10 ppm (1.4
mg/kg/day) for females. The systemic LEL was 3,000 ppm (408
mg/kg/day) for males and 10 ppm (1.7 mg/kg/day) for females. The
effects were increased mortality, body weight gain decreases,
hypoplasia of teeth, liver weight increases, chronic nephritis and
testicular degeneration/epididymal aspermia. There was an apparent
increase in hepatocellular adenomas and hepatocellular carcinomas in
both males and females at 3,000 and 10,000/7,000 ppm. Tumors were
statistically significantly higher than concurrent controls, but only
at dose levels exceeding the maximum tolerated dose (MTD).
- The Agency Peer Review Committee classified primisulfuron-methyl as a
Group D carcinogen - not classifiable as to human carcinogenicity.
Physiological and Biochemical Behavioral Characteristics
- A rat radiolabeled primisulfuron-methyl metabolism study showed that
88 to 102% of radioactive primisulfuron-methyl was excreted in feces
and urine within 9 days. Most of the radioactivity was in the form of
unchanged parent compound. There were 6 major metabolites in the
feces and urine. Hydroxylation of the pyrimidinyl ring occurs at the
S-position, and is followed by either an N- or 0- rearrangement of a
difluoromethoxy group. There appears to be little cleavage of the
sulfonylurea bridge with the S-hydroxylate primisulfuron-methyl to
form an oxidized and/or oxidized and rearranged modified pyrimi-dinyl
moiety. Some cleavage of the sulfonylurea bridge of the parent is
evident by the isolation of a sulfonyl-benzoate intermediate and its
cyclized counterpart, saccharin, and the isolation of the
bis(difluoromethyl) pyrimidinyl moiety. Similar metabolism of
primisulfuron-methyl was observed in the goat and the chicken.
Mechanism of Pesticidal Action
- Primisulfuron-methyl is a photosynthesis inhibitor. It inhibits growth
and development by inhibiting the function of chlorophyll. It
inhibits growth and development of susceptible weeds. It is applied
postemergence to corn and weed species. Its selectivity is not
completely understood. Susceptible plants become chlorotic and then
necrotic at their growing points. The herbicidal activity of
primisulfuron-methyl is influenced by temperature, moisture as
associated with optimum growth of weed species both before and after
application, weed species, weed size at time of application, rate
applied and general growing conditions. Some weeds not killed are
often stunted and are less competitive to corn. Primisulfuron-methyl
may provide some herbicidal activity as a premergence herbicide.
Certain corn hybrids may be sensitive to Primisulfuron-methyl and
respond to application with temporary injury at labeled dosages. A
list of corn hybrids having good tolerance to this herbicide is
available from CIBA-GEIGY Corporation.
Hydrolysis: Primisulfuron-methyl does not hydrolyze in neutral and
mildly alkaline solutions (pH 7 and 9), it hydrolized slowly (half-
life > 30 days) in acidic (pH 5) solutions.
Photodegradation: Primisulfuron-methyl does not photodegrate in either
water or on soil.
Aerobic Soil Metabolism: In aerobic soil maintained under controlled
laboratory conditions phenyl ring-labeled [14c] primisulfuron-methyl
degraded with a half-life of 63 days and pyrimidine ring-labeled [14c]
primisulfuron-methyl degraded with a half-life of 30 days.
Anaerobic Soil Metabolism: In anaerobic soil maintained under
controlled conditions, phenyl ring-labeled [14c] primisulfuron-methyi
degraded with a half-life of 89 days and pyrimidine ring-labeled [14c]
primisulfuron-methyl degraded with a half-life of 41 days.
Field Dissipation: Dissipation occurred more rapidly under field
conditions where primisulfuron-methyl dissipated with half-lives of 3
to 12 days (detection limits of 0.01 ppm), and total phenyl and
pyrimidine ring-labeled [14c] primisulfuron-methyl residues dissipated
with initial half-lives of 12 and 30 days respectively.
Leach, Adsorption/Desorption: [14c] Primisulfuron-methyl and its
degradates were very mobile in both laboratory and field leaching
studies, however unlabeled primisulfuron-methyl was not detected
(>0.01 ppm) below a depth of 9 inches in field studies. Detection
limits is a limiting factor in conducting such studies.
Accumulation Studies: Primisulfuron-methyl accumulates up to 0.011 ppm
in wheat, soybeans, sugar beets, corn, or lettuce that were planted
103-334 days after corn plants growing in the plots had been foliarly-
treated with primisulfuron-methyl.
Potential to Contaminate Groundwater: The use of primisulfuron as a
postemergence herbicide in the culture of corn, turf and in vegetation
control in low maintenance turf sites may result in low levels of
contamination in groundwater in highly vulnerable soils with high
water tables. The present analytical methodology for primisulfuron-
methyl and its degradates with detection limits of only 0.01 ppm is
not sufficiently sensitive to detect residues resulting from the uses
of this chemical as a postemergence herbicide, as registered.
Avian Studies: Primisulfuron-methyl is practically non-toxic to birds
based on the following studies:
Single Dose Oral Studies: Bobwhite quail with 94.0% ai, LC50 > 2150
mg/kg.; Mallard duck with 94.0% ai, LC50 > 2150 mg/kg.
Subacute Dietary Study: Bobwhite quail with 94.0% ai, LC50 >5000 ppm.
Avian Reproduction: Mallard duck with 95.9% ai, NOEL was 500 ppm.,
No reproductive impairment occurred at 500 ppm dietary test level.
Aquatic Organisms: The following data indicate that primisulfuron-
methyl is no more than slightly toxic to freshwater fish, aquatic
invertebrates and estuarine shrimp:
Fish cute Toxicity: Bluegill sunfish, LC50 > 48 ppm (supplementary
study). Rainbow trout, LC50 > 13 ppm (supplementary study).
Effects on Freshwater Invertebrates:
Acute Toxicity Study:
Daphnia magna, LD50 > 100.0 ppm.
Daphnia magna, NOEL of 0.41 ppm.
Effects on estuarine organisms:
Acute Toxicity Study:
Mysid shrimp, LC50 of 16 ppm.
Effects on honey bees:
Acute Contact Toxicity Study:
Apis mellifera, LC50 > 100 ug/bee, practically non-toxic.
Effects on Nontarget plants:
Aquatic species, EC50 is 0.27 to 24.0 ppb
Terrestrial species, EC25 for:
Seed germination was 3.7 to 473.0 gm/ha,
Seed emergence was 0.15 to 44.0 gm/ha,
Vegetative vigor was 0.14 to 33.4 gm/ha.
Endangered Species Hazards:
Based on available data the registered uses of primisulfuron-methyl
is unlikely to pose a hazard to endangered aquatic and avian species.
There may be some hazard to endangered plants.
A tolerance regulation has been established for residues of
primisulfuron-methyl associate with its use as a postemergence herbicide
in the culture of corn. The regulation is found under Section 180.45 in
the Code of Federal Regulations. The regulation establishes tolerances
for residues of primisulfuron-methyl in or on corn (forage) at 0.10 ppm;
corn (fodder) at 0.10 ppm; corn (grain) at 0.02 ppm; corn (sweet)
(kernels plus cobs with husks removed) at 0.10 ppm; milk at 0.02 ppm;
meat, fat, meat byproducts of cattle, goats, hogs, horses, and sheep at
0.10 ppm; poultry fat, meat and meat by-products at 0.10 ppm; and eggs
at 0.10 ppm.
4. SUMMARY OF REGULATORY POSITION AND RATIONALE
Available data provided adequate information to support the
conditional registration of Beacon Herbicide, Rifle Herbicide, and CGA-
136872 Technical, that were first registered on May 11, 1990 under
Section 3 of the Federal Insecticide, Fungicide and Rodenticide Act as
Use, formulation, manufacturing process or geographic restrictions:
Crop rotation restrictions are specified on the Beacon Herbicide
label. Aerial applications of Beacon and Rifle Herbicides are
not permitted. Beacon and Rifle Herbicides are water dispersible
granules that are in pre-measured quantities in water-soluble
5. SUMMARY OF DATA GAPS
Environmental Fate and Groundwater Data:
a. Information on the relative mobilities of primisulfuron-methyl in
soil (EPA Guideline Date 163-1) and its major phenyl and pyrimidine
ring-labeled 14c degradates must be submitted within 12 months from
the date of registration.
b. A new field dissipation study in soil (EPA Guideline Date 164-1) in
which residues at the level of 10% of the applied rate are measured
with the appropriately sensitive methodology. In lieu of a new
study, the registrant may submit data that characterize the residues
detected in the submitted soil dissipation study. This study must
be submitted within 27 months form the date of registration.
c. A small-scale prospective ground-water monitoring study that
addresses the mobility of the parent compound and its degradates must
be submitted within 30 months from the date of registration.
Ecological Effects Data:
Aquatic organism testing with a warmwater freshwater fish and a
coldwater freshwater fish (EPA Guidelines data 72-1) must be submitted 9
months from the date of registration.
6. CONTACT PERSON AT EPA
Joanne I. Miller
Acting Product Manager 23
Registration Division (KH-7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Office Location and Telephone Number
Room 237, Crystal Mall Building #2
1921 Jefferson Davis Highway
Arlington, VA 22202
DISCLAIMER: The information presented in this Pesticide Fact Sheet is
for informational purposes only and may not be used to fulfill data
requirements for pesticide registration and reregistration.