---

The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

---

E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

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 Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Clomazone

Trade and Other Names: Trade names include Command, Commence, Gamit, Magister, and Merit.

Regulatory Status: Clomazone is a General Use Pesticide (GUP). It is classified toxicity class III - slightly toxic. Products containing clomazone bear the Signal Word CAUTION on the labels.

Chemical Class: Not Available

Introduction: Clomazone is a broad-spectrum herbicide used for control of annual grasses and broadleaf weeds in cotton, peas, pumpkins, soybeans, sweet potatoes, tobacco, winter squash, and fallow wheat fields. It can be applied early preplant, pre-emergent or preplant-incorporated, depending on the crop, geographical area, and timing.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Clomazone is a slightly toxic material by ingestion, inhalation, and dermal exposure. The oral LD50 for technical clomazone is 1369 mg/kg in female rats and 2077 mg/kg in male rats [8,58]. The oral LD50 for Command 4EC is slightly higher: 1406 mg/kg in female rats and 2343 in male rats [58]. The dermal LD50 in rabbits is greater than 2000 mg/kg [8]. The inhalation LC50 for technical clomazone is 4.23 mg/L in female rats and 6.52 mg/L in male rats [58]. The inhalation LC50 for Command 4EC in rats is 4.5 to 4.7 mg/L [58].
• Chronic toxicity: In 2-year feeding studies with rats and mice, and a 1-year feeding study with dogs, no long-term adverse effects from Command [58]. In a 1-year feeding study with dogs, increased liver weight occurred at the 2.5 mg/kg/day dose [58]. In 2-year feeding studies, rats fed more than 4.3 mg/kg/day exhibited elevated cholesterol levels, increased liver weights, and enlarged liver cells. Mice given doses above 15 mg/kg/day had elevated white blood cell counts [78].
• Reproductive effects: In a two-generation study with rats, each generation was fed clomazone at 5, 50, 100, or 200 mg/kg/day for 11 weeks in between weaning and mating. There was no effect on reproductive performance [79]. These data suggest that it does not cause reproductive effects.
• Teratogenic effects: Clomazone does not appear to be teratogenic [79]. No birth defects were seen in the offspring of rats given 600 mg/kg/day, the highest dose tested, nor in the offspring of rabbits given 700 mg/kg/day [78].
• Mutagenic effects: Clomazone is not mutagenic. The results of several tests, including a DNA synthesis test, reverse mutation tests, and a chromosomal aberration test, were all negative [78].
• Carcinogenic effects: Clomazone does not appear to be carcinogenic [80]. No tumor formation occurred in mice or rats given dietary doses as high as 100 mg/kg for 2 years [58,78].
• Organ toxicity: Animal studies have shown that clomazone affects the liver.

• Fate in humans and animals: Metabolism studies show that 90 to 99% of the product Command administered to rats was excreted within 72 hours and there was no significant retention of the herbicide in rat tissues [79].

Ecological Effects:

• Effects on birds: Clomazone is practically nontoxic to birds. The oral LD50 for technical clomazone in bobwhite quail and mallard ducks is greater than 2510 mg/kg. The 8-day dietary LC50 in bobwhites and mallards is 5620 ppm [58].
• Effects on aquatic organisms: Clomazone is moderately toxic to fish and aquatic invertebrates. The LC50 (96-hour) for technical clomazone is 19 mg/L in rainbow trout, 34 mg/L in bluegill sunfish, 6.26 mg/L in Atlantic silversides, 40.6 mg/L in sheepshead minnows, 0.566 mg/L in mysid shrimp, 5.3 mg/L in eastern oysters, and 5.2 mg/L in Daphnia magna [58]. The bioconcentration factor in bluegill sunfish is 40, indicating that there is only a small potential for this compound to accumulate in aquatic organisms [80].
• Effects on other organisms: No data are currently available.

Environmental Fate:

• Breakdown in soil and groundwater: Clomazone is moderately persistent in soil. Microbial degradation of Command is promoted by high soil moisture, warm temperature, and by increasing the pH to 6.5. Degradation was faster in a sandy loam than in silt or clay loams. In field studies, the half-life of clomazone was 28 to 84 days, depending on soil type and the organic matter content [58]. Clomazone is highly soluble in water, but it has a moderate tendency to adsorb to soil particles. It therefore has a low to moderate potential to contaminate groundwater [11]. The product Command has low mobility in sandy loam, silt loam, and clay loam soils. It is moderately mobile in fine sand [58].
• Breakdown in water: Under laboratory conditions, clomazone was not readily hydrolyzed in sterile water [81]. However, clomazone is subject to photodegradation in water with a half life of 1.5 to 7 days reported for clomazone in solutions containing acetone, a photochemical sensitizer [82].
• Breakdown in vegetation: Clomazone inhibits synthesis of chlorophyll and carotenoids in plants. It is absorbed by plants through the roots from the soil and by shoots. It is then translocated in the xylem and diffuses within leaves. It does not move downward in plants or from leaf to leaf. There is no foliar absorption of clomazone. Clomazone is metabolized by plants [58].

Physical Properties:

• Appearance: Clomazone is a colorless to light brown, viscous liquid above room temperature. When cooled, it forms a white crystalline solid [1].
• Chemical Name: 2-(2-chlorobenzyl)-4,4-dimethyl-1,2-oxazolidin-3-one [1]
• CAS Number: 81777-89-1
• Molecular Weight: 239.70
• Water Solubility: 1100 mg/L [1]
• Solubility in Other Solvents: acetone v.s.; chloroform v.s.; cyclohexanone and methanol v.s.; toluene s. [10]
• Melting Point: 25 C [1]
• Vapor Pressure: 19.2 mPa @ 25 C [1]
• Partition Coefficient: 2.5441 [1]
• Adsorption Coefficient: 300 [11]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

FMC Corporation
Agricultural Chemicals Group
1735 Market Street
Philadelphia, PA 19103

• Phone: 215-299-6661
• Emergency: 800-331-3148
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The 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 product labeling.