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The information in this profile may be out-of-date.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.

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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

Pendimethalin

Trade and Other Names: Trade names include AC 92553, Accotab, Go-Go-San, Herbadox, Penoxalin, Prowl, Sipaxol, Sovereign, Stomp and Way-Up.

Regulatory Status: Pendimethalin is a slightly toxic compound in EPA toxicity class III. Products containing pendimethalin must bear the Signal Word CAUTION or WARNING, depending on the formulation. Pendimethalin is a General Use Pesticide (GUP).

Chemical Class: Not Available

Introduction: Pendimethalin is a selective herbicide used to control most annual grasses and certain broadleaf weeds in field corn, potatoes, rice, cotton, soybeans, tobacco, peanuts, and sunflowers. It is used both pre-emergence, that is before weed seeds have sprouted, and early post-emergence. Incorporation into the soil by cultivation or irrigation is recommended within 7 days following application. Pendimethalin is available in emulsifiable concentrate, wettable powder, or dispersible granule formulations.

Formulation: Pendimethalin is available in emulsifiable concentrate, wettable powder, or dispersible granule formulations.

Toxicological Effects:

• Acute toxicity: Pendimethalin is slightly to practically nontoxic by ingestion, with reported oral LD50 values of 1050 mg/kg to greater than 5000 mg/kg in rats [1,58]. It is slightly to practically nontoxic by skin exposure, with reported dermal LD50 values of greater than 2000 mg/kg [1,58]. It is not a skin irritant or sensitizer in rabbits or guinea pigs, but it causes mild eye irritation in rabbits [58]. The inhalation 4-hour LC50 for technical pendimethalin in rats is 320 mg/L, indicating practically no toxicity via this route [58]. Some formulated products (e.g., Prowl) may show slight toxicity by inhalation, and may have a greater capacity to cause skin irritation [58]. Inhalation of dusts or fumes may be mildly to moderately irritating to the linings of the mouth, nose, throat, and lungs [115].
• Chronic toxicity: Increases in alkaline phosphatase level and liver weight were produced in dogs fed 50 mg/kg/day for 2 years, but not at a dose of 12.5 mg/kg/day [58,116]. In a 90-day feeding study of rats, no effects were observed at doses of 40 mg/kg/day [116].
• Reproductive effects: In a three-generation reproductive study of rats tested at levels up to 250 mg/kg/day, there were slightly fewer offspring and they showed decreased weight gain from weaning to maturity [116]. No effects were observed at 30 mg/kg/day [58,116]. This evidence suggests that pendimethalin is unlikely to cause reproductive effects in humans under normal circumstances.
• Teratogenic effects: No birth defects and no toxic effects on fetuses occurred when pregnant rats were given 500 mg/kg/day, the highest dose tested. No fetotoxic or teratogenic effects were seen at the highest dose tested (60 mg/kg/day) in a teratology study with rabbits, although maternal toxicity was seen at 30 mg/kg/day [116]. It does not appear that pendimethalin is teratogenic.
• Mutagenic effects: Several mutagenicity studies, including tests on live animals and mammalian and bacterial cell cultures, have all indicated that pendimethalin has no mutagenic activity [116].
• Carcinogenic effects: Pendimethalin did not increase tumor formation in mice given dietary doses of 75 mg/kg/day over an 18-month period [58]. This evidence suggests that pendimethalin is not carcinogenic.
• Organ toxicity: Chronic exposure to pendimethalin has resulted in increased liver weights in test animals.

• Fate in humans and animals: Pendimethalin is largely unabsorbed from the gastrointestinal tract, and excreted unchanged in the feces [117]. Pendimethalin, which does become absorbed into the bloodstream from the gastrointestinal tract, is rapidly metabolized in the kidneys and liver and is then excreted as metabolites via urine [117]. One day after administration to rats, 90% of a 37 mg/kg dose was recovered in feces and urine. After 4 days this figure was 96% [117]. Lower doses resulted in almost 100% excretion within 4 days. Tissue burdens of the compound were on the order of 0.3 mg/kg, with slightly higher concentrations in the body fat [117].

Ecological Effects:

• Effects on birds: Pendimethalin is slightly toxic to birds, with an acute oral LD50 of 1421 mg/kg in mallard duck and 8-day dietary LC50 values of greater than 3149 mg/kg in bobwhite quail, and greater than 10,900 mg/kg in mallard duck [58,115].
• Effects on aquatic organisms: Pendimethalin is highly toxic to fish and aquatic invertebrates. The reported 96-hour LC50 for pendimethalin in bluegill sunfish is 199 ug/L, in rainbow trout is 138 ug/L, and in channel catfish is 420 ug/L [58]. The 48-hour LC50 in Daphnia magna, a small freshwater crustacean, is 280 ug/L [58,115]. The bioconcentration factor for this compound in whole fish is 5100, indicating a moderate potential to acumulate in aquatic organisms [115].
• Effects on other organisms: Pendimethalin is nontoxic to bees [1].

Environmental Fate:

• Breakdown in soil and groundwater: Pendimethalin is moderately persistent, with a field half-life of approximately 40 days [11,58]. It does not undergo rapid microbial degradation except under anaerobic conditions [58]. Slight losses of pendimethalin can result from photodecomposition and volatilization. Pendimethalin is strongly adsorbed by most soils [58,11]. Increasing soil organic matter and clay is associated with increased soil binding capacity. It is practically insoluble in water, and thus will not leach appreciably in most soils, and should present a minimal risk of groundwater contamination [11,58].
• Breakdown in water: Pendimethalin is stable to hydrolysis, but may be degraded by sunlight in aquatic systems [58]. Pendimethalin may also be removed from the water column by binding to suspended sediment and organic matter [11,58]. It is rapidly degraded under anaerobic conditions once precipitated to sediment [58].
• Breakdown in vegetation: Pendimethalin is absorbed by plant roots and shoots, and inhibits cell division and cell elongation [58]. Once absorbed into plant tissues, translocation is limited and pendimethalin breaks down via oxidation [58]. Pendimethalin is not absorbed by the leaves of grasses, and only very small amounts are taken up by plants from the soil. Residues on crops at harvest are usually below detectable levels (0.05 ppm) [58].

Physical Properties:

• Appearance: Pendimethalin is an orange-yellow crystalline solid with a faint nutty or fruit-like odor [1].
• Chemical Name: N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine [1]
• CAS Number: 40487-42-1
• Molecular Weight: 281.31
• Water Solubility: 0.3 mg/L @ 20 C [1]
• Solubility in Other Solvents: v.s. in most organic solvents such as acetone and xylene; s. in corn oil, isopropanol, heptane, benzene, toluene, chloroform, and dichloromethane; s.s. in petroleum ether and petrol [1]
• Melting Point: 54-58 C [1]
• Vapor Pressure: 4 mPa @ 25 C [1]
• Partition Coefficient: 5.1818 [1]
• Adsorption Coefficient: 5000 [11]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.04 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

American Cyanamid
One Cyanamid Plaza
Wayne, NJ 07470-8426

• Phone: 201-831-2000
• Emergency:201-835-3100
  

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.