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Extension Toxicology Network

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.


Publication Date: 9/93


Some trade names include Ambush, BW-21-Z, Cellutec, Ectiban, Eksmin, Exmin, FMC-33297, Indothrin, Kafil, Kestril, NRDC 143, Pounce, PP 557, Pramiex, Qamlin and Torpedo.


All formulations labeled for agricultural use, excluding livestock and premises uses, are classified by the U.S. Environmental Protection Agency (EPA) as Restricted Use Pesticides (RUP) because of their possible adverse effects on aquatic organisms (17). This restricted classification applies to emulsifiable concentrates and ready-to-use formulations (0.05% to 38.4%). Formulations labeled for use in the control of termites through subsurface ground insertion are also restricted (18). Restricted Use Pesticides may be purchased and used only by certified applicators. Products containing permethrin must bear the signal word "Warning" or "Caution," depending on the toxicity of the particular product (23). Check with specific state regulations for local restrictions which may apply.


Permethrin is a broad spectrum insecticide, a chemical used to kill a variety of insects. Permethrin is referred to as a synthetic pyrethroid insecticide because, while manmade, it resembles naturally-occurring chemicals with insecticidal properties, called pyrethroids. Pyrethroids are found especially in chrysanthemums. Pyrethroids are one of the oldest classes of organic insecticides known (10). They work by quickly paralyzing the nervous systems of insects, producing a quick "knockdown" effect on insect pest populations. Permethrin acts as a stomach poison when it is ingested by insects or as a contact poison through direct contact with target pests. It kills adults, eggs, and larvae, and has a slight repellent effect against insects (7). The insecticidal activity of this material lasts up to 12 weeks after application (8).

Permethrin is used against a number of pests, on nut, fruit, vegetable, cotton, ornamental, mushroom, potato and cereal crops. It is used in greenhouses, home gardens and for termite control (23). It also controls animal ectoparasites, biting flies, and cockroaches (7). It may cause a mite buildup by reducing mite predator populations (16). Permethrin is available in dusts, emulsifiable concentrates, smokes, ULV (ultra low volume), and wettable powder formulations (23).



Permethrin has low mammalian toxicity. However, contact with eyes, skin, or clothing should be avoided and handlers of permethrin should wash thoroughly after handling (1). Breathing of the spray mist or vapors of permethrin by workers should be avoided.

Pyrethroids act by interfering with the transmission of nerve impulses along the neurons (22).

The amount of permethrin that is lethal to one-half (50%) of experimental animals exposed to it is referred to as the lethal dose fifty, or LD50, of this insecticide. The oral LD50 for technical permethrin in rats is 430 to 4,000 milligrams per kilogram (mg/kg). Its LD50 is over 270 mg/kg when injected into the veins.

The dermal LD50 in rats is over 4,000 mg/kg, and in rabbits is over 2,000 mg/kg (1, 8, 23). Permethrin caused mild irritation of intact or abraded skin of rabbits. It also caused conjunctivitis when it was applied to the eyes (8).

The lethal concentration fifty, or LC50, is the concentration of a chemical in air or water that kills half the experimental animals exposed to the material for a set time period. The 4-hour inhalation LC50 for rats was greater than 23.5 milligrams per liter (mg/l) of air (1).


Long-term feeding of pyrethroids resulted in an increase in liver size and excessive formation of bile duct tissue. The 90-day No-Observable Effect Level (NOEL) was 5 mg/kg/day in dogs fed permethrin (5). Dermal application for 21 days did not cause toxicity (8). Rats fed 150 mg/kg/day for 6 months, showed a slight increase in liver weights (22). Very low levels of permethrin in the diet of chickens (0.1 ppm for 3 to 6 weeks after hatching) have been reported to suppress immune system activity (22).

Reproductive Effects

The fertility of female rats was affected when they received oral doses of 250 mg/kg of permethrin during the 6th through 15th day of pregnancy (13).

Teratogenic Effects

Permethrin is not teratogenic (22). Pyrethroids, the chemical class to which permethrin belongs, have not been identified as being teratogenic (8, 11).

Mutagenic Effects

Permethrin is not mutagenic (22). Pyrethroids have not been identified as being capable of causing mutations (8, 11).

Carcinogenic Effects

Pyrethroids are not thought to be carcinogenic (11). However permethrin may be a weak tumor-former, or oncogen, in mice and rats (5). It is suspected of having carcinogenic effects (6).

Organ Toxicity

Permethrin is suspected of causing enlargement of the liver and destruction of the lining of nerve tracts (6).

Fate in Humans and Animals

Pyrethrins are efficiently metabolized by mammalian livers (11). Breakdown products, or 'metabolites,' of permethrin are quickly excreted and do not persist significantly in body tissues (8). There are no methods for identifying metabolites in the urine (11). When permethrin is administered orally to rats, it is rapidly metabolized and almost completely eliminated from the body in a few days. Only three to six percent of the original dose was excreted unchanged in the feces of experimental animals (14). Permethrin may persist in fatty tissues, with half-lives of 4 to 5 days in brain and body fat (22). Pyrethroids do not block, or inhibit, cholinesterase enzymes (11).


Effects on Birds

Permethrin is practically non-toxic to birds (2, 23). The oral LD50 for the permethrin formulation, Pramex is >9,900 mg/kg in mallard ducks, in pheasants is >13,500 mg/kg, and >15,500 mg/kg in Japanese quail (14).

Effects on Aquatic Organisms

Permethrin is toxic to fish and should be kept out of all bodies of water (1). It was highly toxic to fish in laboratory tests, but showed low toxicity in field tests (23). Aquatic ecosystems are particularly vulnerable to the impact of permethrin. A fragile balance exists between the quality and quantity of insects and other invertebrates that serve as fish food (2).

The LC50 for rainbow trout is 12.5 micrograms per liter (ug/l) for 24 hours, and 5.4 ug/l for 48 hours (7). The LC50 for 48 hours in bluegill sunfish and salmon is 1.8 ug/l (2). As a group, synthetic pyrethroids were toxic to all estuarine species tested. They had a 96-hour LC50 of less than or equal to 7.8 ug/l (15).

Effects on Other Animals (Nontarget species)

Permethrin is extremely toxic to bees. Severe losses may be expected if bees are present at treatment time, or within a day thereafter (7, 12). Permethrin is also toxic to wildlife (9). It should not be applied, or allowed to drift, to crops or weeds in which active foraging takes place (4).


Breakdown of Chemical in Soil and Groundwater

Because permethrin binds very strongly to soil particles and it is nearly insoluble in water, it is not expected to leach or to contaminate groundwater (24). The binding, or adsorption, of permethrin in soil may be limited to organic matter. Very little leaching of permethrin has been reported (21). It is not very mobile in a wide range of soil types (14).

Permethrin is readily broken down, or degraded, in most soils except organic types. Soil micro-organisms play a large role in the degradation of permethrin in the soil. Permethrin was found to persist for 28 days in organic soils, decreasing slowly throughout the season. It has a half-life of from three to six weeks (10). The addition of nutrients to soil may increase the degradation of permethrin. It has been observed that the availability of sodium and phosphorous decreases when permethrin is added to the soil.

Breakdown of Chemical in Water

The results of one study indicate that synthetic pyrethroids can present a significant threat if they are used near estuarine areas. They tend to bioconcentrate in these environments. In this study, permethrin had a half- life of less than 2.5 days. When exposed to sunlight, the half-life was 4.6 days (15). Permethrin should be kept out of lakes, streams, or ponds. Do not contaminate water by cleaning equipment or by disposing of wastes near a body of water. Permethrin may not be applied when weather conditions favor drift from treated areas (1). Permethrin degrades rapidly in water, although it can persist in sediments (7, 21). There is a gradual loss of toxicity after permethrin ages for 48 hours in sunlight at 50 parts per billion (ppb) in water (14).

Breakdown of Chemical in Vegetation

Permethrin is not phytotoxic, or poisonous to most plants, when it is used as directed. Some injury has occurred on certain ornamental plants (16). No incompatibility has been observed with permethrin on cultivated plants. Treated apples, grapes, and cereal grains contain less than one mg/kg of permethrin at harvest time (7).


Permethrin is an odorless, colorless crystalline solid or a viscous liquid that is white to pale yellow. It is stable in light and air (9, 21, 23). It should not be stored near food, feed, heat, or open flame (1). Permethrin keeps for a year or longer when stored under cool, dry conditions. It does not corrode aluminum (7). No incompatibility has been observed between permethrin and common insecticides and fungicides. Mixing permethrin with calcium nitrate is not recommended, however (7).

Avoid contact with eyes, skin or clothing. Avoid breathing vapor or spray mist (23).

Exposure Guidelines:

NOEL: 5.0 mg/kg/day or 100 ppm/day (two-year chronic feeding/oncogenicity study) (3).
MPI (Maximum Permitted Intake): for a 60-kg human is calculated to be 3.0 mg/day (3).
ADI: 0.05 mg/kg of body weight (bw)/day, based on a two-year rat chronic feeding/oncogenicity study with a NOEL of 5.0 mg/kg/day with a 100-fold safety factor (25).

Physical Properties:

CAS #: 52645-53-1
Specific gravity: 1.190-1.272 at 20 degrees C (23)
H20 solubility: nearly insoluble; approximately 0.2 mg/l at 20 degrees C (7)
Solubility in other solvents: freely soluble in most organic solvents except ethylene glycol (23).
Melting Point: 34-39 degrees C (22)
Boiling point: 220 degrees C at 0.05 mm Hg (23)
Vapor pressure: less than 10 Torr at 50 degrees C (1)
4.5 x 10 to the minus 7 mbar at 25 degrees C (7)
Kow: log Kow = 2.88 (20)
753; 3981000 (19)
Koc: 86,000 g/ml (24)
Degradation Rate Constant (days-1): 0.0396 (20)
Chemical Class/Use: Synthetic pyrethroid insecticide


Zeneca Ag Products
Wilmington, DE 19897
Telephone: 800-759-4500

Review by Basic Manufacturer:

Comments solicited: November, 1992
Comments received:


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  2. DeBoo, R. F. 1980 (Aug.). Experimental aerial applications of permethrin for control of choristoneura fumiferana in Quebec, 1976-1977. Environment Canada. Canadian Forestry Service Forest Pest Management Institute.
  3. US Environmental Protection Agency. Federal Register 51: 12885. April 16, 1986. U.S. Government Printing Office. Washington, DC.
  4. FMC Corporation. 1984 (June). Specimen label for Pounce, 3.2 EC. Philadelphia, PA.
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  9. ICI Americas, Inc. 1985 (Nov). Material safety data sheet: Permethrin. Wilmington, DE.
  10. Kaufman, D. D., et al. 1977. Permethrin degradation in soil and microbial cultures. Reprinted from ACS Symposium Series No. 42. Synthetic Pyrethroids. Michael Elliot, ed.
  11. Morgan, D. P. 1982 (Jan.). Recognition and management of pesticide poisonings. Third edition . U.S. Environmental Protection Agency. Washington, DC: U. S. Government Printing Office.
  12. Morse, R. A. 1987. Bee poisoning. 1988 New York State pesticide recommendations. Forty-ninth annual pest control conference (Nov. 9, 10, 11). Cornell University. Ithaca, NY.
  13. National Institute for Safety and Health (NIOSH). 1986. Registry of toxic effects of chemical substances (RTECS). Cincinnati, OH: NIOSH.
  14. Penick Corporation. 1979 (June). Technical information sheet: Pramex (permethrin) synthetic pyrethroid insecticide. Lyndhurst, NJ.
  15. Schimmel, S. C., et al. 1983 (Jan.-Feb.). Acute toxicity, bioconcentration, and persistence of AC 222,705, benthiocarb, chlorpyrifos, fenvalerate, methyl parathion, and permethrin in the estuarine environment. In the Journal of Agricultural and Food Chemistry. The American Chemical Society.
  16. Thomson, W. T. 1985. Insecticides. Agricultural Chemicals, Book I. Fresno, CA: Thomson Publications.
  17. US Environmental Protection Agency. 1987. (Oct. 23). Subject: Active ingredients subject to restricted use classification. Office of Pesticide Programs, Registration Division, US EPA, Washington, DC.
  18. _____. 1986. Memorandum from Ferial S. Bishop. List of federally restricted products. Registration Support and Emergency Response Branch (TS- 767). Washington, DC.
  19. _____. 1986. (Jan.). Estimating pesticide sorption coefficients for soils and sediments. Richard E. Green and Samuel W. Karickhoff. Environmental Research Laboratory. Office of Research and Development. Athens, GA.
  20. _____. 1984. Users manual for the pest root zone model (PRZM). Release 1. Athens, GA: Environmental Research Laboratory.
  21. Wagenet, L. P., et al. 1985. A review of physical-chemical parameters related to the soil and groundwater fate of selected pesticides in N.Y. State. Cornell University Agricultural Experiment Station, N.Y. State College of Agriculture and Life Sciences. Ithaca, NY. #30. ISSN 0362-2754.
  22. Hayes, W.J. and E.R. Laws (ed.). 1990. Handbook of Pesticide Toxicology, Vol. 3, Classes of Pesticides. Academic Press, Inc., NY.
  23. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  24. U.S. Department of Agriculture, Soil Conservation Service. 1990 (Nov.). SCS/ARS/CES Pesticide Properties Database: Version 2.0 (Summary). USDA - Soil Conservation Service, Syracuse, NY.
  25. US Environmental Protection Agency. 1988 (Oct. 5). Pesticide tolerance for permethrin. Federal Register 53 (193): 39109-10.