clethodim (Select) Herbicide Profile 1/92
EPA Pesticide Fact Sheet
Name of Chemical: CLETHODIM
Reason for Issuance: NEW CHEMICAL
Date Issued: January 28, 1992
Fact Sheet Number: 230
1. DESCRIPTION OF CHEMICAL
- Chemical Name: (E)-(+)-2-[1-[[(3-Chloro-2-Propenyl)oxy]imino]propyl-5-[2-
- Common and Other Names: Clethodim
- Trade Name: Select
- EPA Shaughnessy Codes: 121011
- Chemical Abstracts Service (CAS) No.: 99129-21-2
- Year of Initial Registration: 1991
- Pesticide Type: Herbicide
- Chemical Family: Cyclohexanedione
- U.S. and Foreign Producers: Valent U.S.A. Corporation
2. USE PATTERNS AND FORMULATIONS
- Application Sites: Postemergent treatment on soybeans and cotton for
control of grasses
- Types and Methods of Application: Foliar application by ground equipment
- Application Rates: 0.094 - 0.25 lb ai/acre
- Types of Formulations: 25% emulsifiable concentrate (EC)
- Usual Carriers: Mix with water
3. SCIENCE FINDINGS
Summary Science Statement
Review of the product chemistry, environmental fate, toxicology,
ecological effects and residue chemistry data have been completed. The
available data support conditional registration of Select for control of
annual and perennial grasses in soybeans and cotton. Results of acute
toxicity studies indicate Toxicity Category III (Caution). Chronic studies
present no evidence of unacceptable health hazards resulting from the proposed
uses Ecological effects data indicate that the proposed use on cotton and
soybeans will result in minimal risk to avian, aquatic and mammalian species.
Clethodim and degradates do not show persistence in field dissipation
studies. No significant bioaccumulation occurs in fish. Since it is easily
degraded both by photolysis and aerobic microbial action, clethodim does not
seem likely to threaten surface water. Under present use patterns and under
most circumstances, clethodim does not appear likely to threaten groundwater.
- Physical State: Viscous liquid
- Molecular Weight: 359.92
- Molecular Formula: C17 H26 CINO3 S
- Color: Clear amber
- Melting Point N/A
- Boiling Point N/A
- Density 1.395 g/cu.cm 20 C
- *Solubility Limit, g/100 mL solvent at 25 C
- Vapor pressure: 1 x 10 to the minus 7 torr
- Dissociation PK2 = 4.47
partition coefficient: Kow = 1.5 x 10 to the 4th power
- pH 4.1 in a stirred solution or 4.2 in a standing
solution 4.9 (5% aqueous solution.
- Flammability: Flashpoint 110 degrees C
- Explodability: N/A
- Storage Stability: < 1% and < 3% degradation in glass containers and
aluminum containers, respectively, after one
year of storage at 21 C
- Viscosity: 100 cps at 20 degrees C
- Miscibility: N/A
- Characteristics: N/A
- Dielectric Breakdown
- Corrosiveness N/A
Acute toxicology results:
(Technical (T) 83.3% & 96.ai:)
- Acute oral toxicity-(rats): 98.6% LD50(female) greater than 1.4 gm/kg
- Acute oral toxicology-(rat): 83.3% LD50(F) = 1.36 gm/kg, Toxicity
Category III, LD50(M) 1.63%g/kg
- Acute oral LD50(mice): 83.3% LD50(M)=2.57 g/kg, LD50(F) = 2.43g/kg
Toxicity Category III
- Acute Dermal LD50(rabbit): 83.3% LD50(M&F) greater than 5 g/kg Toxicity
- Acute inhalation LD50 (rat): 83.3% LC50 greater than 3.9/L(M&F)
Toxicity Category III
- Primary eye irritation(rabbit): 83.3% Toxicity Category III
- Primary dermal irritation(rabbit): Toxicity Category IV
- Acute Toxicity (Select Herbicide): 26.1 and 26.0% ai
- Acute oral toxicology-(rat): 26.1% LD50(F) 2.92g/kg, LD50(M) 3-61%g/kg
Toxicology Category III
- Acute oral LD50(rat): 26.1% LD50(M)=3.61 g/kg, Toxicity III
- Acute Dermal LD50(rabbit): 26.0% LD50(M&F) greater than 5 g/kg
Toxicity Category IV
- Acute inhalation LC50(rat): 26.1% LC50 greater than 5.4 mg/L(M&F)
- Primary eye irritation(rabbit): 26.1% Toxicity Category II
- Primary Dermal irritation(rabbit): 26.0% Toxicity Category III
- Dermal sensitization: Nonsensitizer
21-Day Dermal (rat)- The systemic NOEL is 50 mg/kg/day. The LOEL for
skin is 10 mg/kg/day (26.3%).
In the 18-month carcinogenicity study, mice administered clethodim
(83.3%) at dosages of 0, 20, 200, 1000, or 3000 ppm resulted in a systemic
NOEL and LOEL of 200 and 1000 ppm (HDT) for male and female mice,
In a 1-year feeding study, dogs were treated with clethodim (83.3%) at
dose levels of 0, 1, 75, or 300 mg/kg/day. The systemic LOEL for both sexes
is 75 mg/kg/day based on increased absolute and relative liver weights and
alterations in hematology and clinical chemistry. The NOEL is 1 mg/kg/day.
Chronic toxicity/Carcinogenicity - (Rats)
A 2-year chronic toxicity/carcinogenicity study with rats fed clethodim
(83%) at dosages of 0, 5, 20, 500, and 2500 ppm. Liver weights were not
affected at study termination nor were there any compound-related histological
changes noted (HDT). The systemic NOEL is 500 ppm (19 mg/kg/day), based upon
the liver weights were not effected at the study termination nor were there
any compound-related histological changes noted. The systemic LOEL is 2500
ppm (100 mg/kg/day).
A rat teratology study was conducted with clethodim (82.6%) using doses
of 0, 10, 100, 350, and 700 mg/kg/day. Based upon reductions in body weight
gain and clinical signs of toxicity, the NOEL and LOEL for maternal toxicity
are 100 and 350 mg/kg/day respectively. Based on reductions in fetal body
weight and increases in skeletal anomalies the NOEL and LOEL for developmental
toxicity are 100 and 350 mg/kg/day, respectively.
A rabbit teratology study was conducted using doses of 0, 25, 100, and
300 mg/kg/day (clethodim 82.6%). Maternal toxicity was manifested by clinical
signs of toxicity, reduced weight gain and food consumption during treatment.
The NOEL and LOEL are 25 and 100 mg/kg/day, respectively. Developmental
toxicity was not observed. The NOEL for this endpoint is 300 mg/kg/day.
A rat teratology study was conducted using doses of 0, 10, 100, and 700
mg/kg/day (clethodim 98.6%). The maternal NOEL and LOEL are 10 and 100
mg/kg/day, respectively. Based upon significant reductions in fetal body
weight and litter size significantly increased litter and fetal incidence of
cervical rib at 700 mg/kg/day, the NOEL and LOEL for developmental toxicity
are 100 and 700 mg/kg/day, respectively.
In a reproductive toxicity study, rats were fed doses of 0, 5, 20, 500,
or 2500 ppm. The NOEL and LOEL for systemic toxicity are 500 ppm (51 mg/
kg/day) and 2500 ppm (263 mg/kg/day), respectively, based on reductions in
body weight, particularly in males, and decreased food consumption in both
generations. No effects on fertility, length of gestation, or growth and
development of offspring were observed. The NOEL for reproductive toxicity is
2500 ppm (HDT) (83.3%).
Technical material was not mutagenic in the Ames assay.
Metabolism - Rats
The requirement for a metabolism study in rats has been satisfied. Five
groups of rats, 5 males and 5 females, were dosed in various sequences with
either 4.5 or 450 mg/kg [14C] clethodim orally.
Clethodim is readily absorbed and eliminated with essentially all of the
[14C] dose recovered from urine. Several days after the compound was
administered, smaller amounts were recovered from feces (9-17%) and expired
air. Gastrointestinal absorption was estimated at 89-96%. There was no
evidence of bioconcentration following multiple exposures; the adrenal dosing
had the highest concentration of radiolabel (0.07 to 0.22 ppm for low and
repeated doses; 5.4 to 13 ppm for high-dose rats). Clethodim was extensively
metabolized with < 1 percent eliminated as the unchanged parent compound. The
predominant metabolite recovered was clethodim sulfoxide (48 to 63% of
administered label after 48 hours).
Hydrolysis: Propyl [14C]-clethodim degraded with half-lives of 26 days
(pH 5) and approximately 300 days (pH 7 and 9). Allyl-labeled clethodim
degraded with half-lives of 42 days(pH 5) and 360 days (pH 7). The degrades
were clethodim, oxazole, and l-chloropropen-3-ol.
Aerobic Soil Metabolism- Under aerobic soil conditions, clethodim
degrades with a half-life of 1 to 2.6 days.
Anaerobic Aquatic Metabolism- Results of the anaerobic aquatic
metabolism study indicate that clethodim has a half-life of 128 days in the
aqueous phase and 214 days in the sediment. The degradates formed are
metabolized as rapidly as they are formed, and do not appear to accumulate.
Aqueous Photolysis- Clethodim degrades with half-lives of 1.5-9.3
days, at pH 5 and 9, respectively.
Mobility- Leaching and absorption/desorption. Clethodim and its
sulfoxide, sulfone, and oxazole sulfone degradates are weakly absorbed into
two sandy loam soils, clay loam, sandy clay loam, and sandy soil
Soil Photolysis- Photolysis of clethodim on soil will not be a major
pathway of degradation, since metabolism is rapid. After 7 days, less than
6.8% of parent compound remained. Little or no volatile material, organic or
CO2 was produced. The single major product was clethodim sulfoxide.
Metabolism is the primary mechanism of degradation.
Terrestrial Field Dissipation- No vertical movement of the residues
was observed as all measurable residues were confined to the top 20 cm of the
Accumulation - In Confined Rotational Crop and in Fish- In rotational
crops, some uptake and concentration were detected at an exaggerated rate of
4X the maximum single application. Closely-related metabolites accounted for
around 1/3 of the total radioactivity observed in the plants. No significant
bioaccumulation occurred in fish.
Available fish and wildlife data indicate that the proposed uses on
cotton and soybeans will result in minimal hazard to nontarget and endangered
beneficial insect, avian, freshwater fish and mammalian species.
Clethodim is slightly to practically non-toxic to birds. The avian acute
oral LD50 was greater than 2000 mg/kg for the bobwhite quail and the avian
dietary LC50s were > 4270 ppm for the bobwhite quail and > 3978 ppm for the
mallard duck. The mallard and avian reproduction study is acceptable and
fulfills the waterfowl guideline requirement. An NOEL of 1000 ppm was
Clethodim technical is slightly toxic to cold-and warm-water fish
species. The fish LC50 for the rainbow trout is 18.0 ppm and 13.0 ppm for the
bluegill sunfish. Select EC is slightly toxic to Daphnia magna. The 48 hour
LC50 value for Daphnia magna is 20.2 mg/L; and the NOEL is 5.5 mg/L. The
formulated product was tested because of a high level of a certain inert
ingredient in the formulation.
Clethodim technical and Select 2 EC are practically non-toxic to
honeybees, with an LD50 of greater than 100 ug/bee. Select 2 EC was evaluated
to assess the toxicity of formulation inerts.
Tier I and II non-target plant phytotoxicity data using technical
clethodim were submitted. The data demonstrate that Select 2 EC is extremely
selective in its mode of action. Only grass species are at risk from off-
target movement. Endangered grass in or around Select-treated fields is at
risk from ground or aerial applications. Thus, Select is prohibited from use
in the counties listed under "Summary of Regulatory Positions."
Tolerance Assessment- A tolerance with an expiration date is established for
residue of the herbicide clethodim (ANSI), (E)-(+)-2-[1[[(3-chloro-2-propenyl)
its metabolites containing the 2-cyclohexen-l-one moiety in/on soybeans at 10
ppm; cottonseed at 1 ppm; meat, fat, and meat byproducts of cattle, goats,
hogs, horses, poultry, and sheep at 0.2 ppm; milk at 0.05 ppm; eggs at 0.2
ppm; soybean soapstock at 15 ppm; and cottonseed meal at 2 ppm.
4. SUMMARY OF REGULATORY POSITIONS
Use, formulation, manufacturing process or geographical restriction: "Do
not apply directly to water," "Do not apply where runoff is likely to occur."
"Do not apply where weather conditions favor drift from areas treated. Do not
allow Select to come in contact with desirable grass crops such as corn, rice,
sorghum, small grains, or turf as these other grass crops will be injured or
killed." "Minor leaf spotting may occur on soybeans and cotton under certain
environmental conditions. New foliage is not affected." "Do not apply a
broadleaf (herbicide) within one day following application. Do not apply by
"Select 2 EC is prohibited from use in the following counties to avoid
non-target injury to the endangered grass species listed: (1) Solano grass-
Colusa, Contra, Costa, Fresno, Glenn, Madera, Merced, San Joaquin, Solano,
Stanislaus and Tehama Counties in California, and (2) Texas wild rice - Hays
county in Texas."
5. SUMMARY OF MAJOR DATA GAPS
Revise analytical method and have a successful independent laboratory
validation conducted on the revised method.
6. CONTACT PERSON AT EPA
Joanne I. Miller
Product Manager (23)
Registration Division (H7505C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street SW.
Washington, DC 20460
Office location and telephone number:
Rm. 245, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 22202
Disclaimer: The information in this Pesticide Fact Sheet is a summary
only and is not to be used to satisfy data requirements for pesticide
registration and reregistration. The complete Registration Standard for the
pesticide may be obtained from the contact person listed above.