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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 Chrysron, Crossfire, Pynosect, Raid Flying Insect Killer, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin and Whitmire PT-110.


Pesticides containing resmethrin must bear the signal word "Caution" on the product label (1). All products containing resmethrin for mosquito or other pest control at aquatic sites are classified as Restricted Use Pesticides (RUP) by the EPA because resmethrin is toxic to fish (11). Restricted Use Pesticides may be purchased and used only by certified applicators.


Resmethrin is a synthetic pyrethroid used for control of flying and crawling insects in homes, greenhouses, indoor landscapes, mushroom houses, industrial sites, stored product insects and for mosquito control (1). It is also used for fabric protection, pet sprays and shampoos, and it is applied to horses or in horse stables (11).



Resmethrin is moderately toxic by ingestion and slightly toxic through the skin (2). Dermal exposure may lead to numbness, itching, burning, tingling sensations. Symptoms of exposure by any route may include incoordination, twitching, loss of bladder control, and seizures (2). Resmethrin may cause eye irritation (2). It failed to cause allergic skin reactions in guinea pigs (1), but may cause skin irritation (11). The amount of a chemical that is lethal to one-half (50%) of experimental animals fed the material is referred to as its acute oral lethal dose fifty, or LD50. The oral LD50 for technical resmethrin in rats is > 2,500 mg/kg (1) or 1,244 mg/kg (2). Its oral LD50 in mice is 300 mg/kg (2). The dermal LD50 for technical resmethrin on rats is > 3,000 mg/kg (1), on rabbits is > 2,500 mg/kg, and on mice is > 5,000 mg/kg (2). The lethal concentration fifty, or LC50, is that concentration of a chemical in air or water that kills half of the experimental animals exposed to it for a set time period. The 4-hour inhalation LC50 for resmethrin is > 9.49 mg/l (11).


In a chronic feeding study with rats, the lowest dose tested (500 ppm or 25 mg/kg/day) caused liver enlargement. At 2,500 ppm (125 mg/kg/day), there were pathological liver changes in addition to increased liver weights. Doses of 5,000 ppm (250 mg/kg/day) caused increased thyroid weight and thyroid cysts (11). The NOEL in a chronic feeding study with dogs was 10 mg/kg/day (11). In a 90-day inhalation study with rats, 0.1 mg/l, the lowest dose tested, produced behavioral changes, decreased blood glucose levels in males, and decreased boy weights and increased serum urea levels in females (11).

Reproductive Effects

A 3-generation study with rats showed a slight increase in premature stillbirths and a decrease in pup weight at 25 mg/kg, the lowest dose tested (5).

Teratogenic Effects

No birth defects were observed in the offspring of rabbits given doses as high as 100 mg/kg (5). Skeletal aberrations were seen in the offspring of rats given doses higher than 40 mg/kg/day (11).

Mutagenic Effects

Resmethrin was not mutagenic in a test performed with the bacterium, Salmonella typhimurium (8).

Carcinogenic Effects

No evidence of tumor formation was observed in a 2-year rat feeding study with doses as high as 250 mg/kg/day, nor in an 85-week study with mice given doses as high as 50 mg/kg/day (5, 11).

Organ Toxicity

Pyrethroids may cause adverse effects on the central nervous system. Long-term feeding studies have shown increased liver and kidney weights and adverse changes in liver tissues in test animals (2). However, EPA reports that resmethrin was not neurotoxic to rats at doses of 62.5 mg/kg for 32 weeks, 250 mg/kg for 30 days, or 632 mg/kg for 7 days (5). In a 2-year feeding study with rats fed up to 250 mg/kg of resmethrin, increases in liver weight and liver lesions occurred at 125 mg/kg (5). Increased liver weights occurred in dogs fed 30 mg/kg/day for 180 days. The NOEL in this study was 10 mg/kg/day (5).

Fate in Humans and Animals

When oral doses of 10 mg/kg radio-labeled resmethrin were given to laying hens, 90% of the dose was eliminated in urine and feces within 24 hours (7). In another study with hens given the same treatment, radioactive residues were low in hens sacrificed 12 hours after the treatment, with the highest levels found in the liver and kidneys. Low levels of radioactivity were found in the hens' eggs, with levels peaking on 1 day after treatment in the whites and 4 to 5 days after treatment in the yolks (10).


Effects on Birds

Resmethrin is slightly toxic to birds. Its LD50 in California quail is > 2,000 mg/kg (11).

Effects on Aquatic Organisms

Resmethrin is highly toxic to fish. The LC50 for resmethrin in mosquito fish is 0.007 ppm (6). The LC50 for resmethrin synergized with piperonyl butoxide in red swamp crawfish, Procambarus clarkii, is 0.00082 ppm (9). The LC50 in bluegill sunfish is 0.75 to 2.6 ug/l, and 0.28 to 2.4 ug/l in rainbow trout (11). The pyrethroid insecticides are extremely toxic to fish with 96-hour LC50 values generally below 10 ug/l. Corresponding LD50 values in mammals and birds are in the range of several hundred to several thousand mg/kg. Fish sensitivity to the pyrethroids may be explained by their relatively slow metabolism and elimination of these compounds. The half-lives for elimination of several pyrethroids by trout are all greater than 48 hours, while elimination half-lives for birds and mammals range from 6 to 12 hours (13). Generally, the lethality of pyrethroids to fish increases with increasing octanol/water partition coefficients (14).

Effects on Other Animals (Nontarget species)

Resmethrin is highly toxic to bees, with an LD50 of 0.063 ug/bee (11).


Resmethrin breaks down in the presence of light and humidity. Its half-life in the environment is 15 minutes (3). Degradation end-products reported for resmethrin are chrysanthemic acid, benzaldehyde, benzyl alcohol, benzoic acid, phenylacetic acid, and various esters (4).

Breakdown of Chemical in Soil and Groundwater

No information was found.

Breakdown of Chemical in Surface Water

In pond waters and in laboratory degradation studies, pyrethroid concentrations decrease rapidly due to sorption to sediment, suspended particles and plants. Microbial and photodegradation also occur (12).

Breakdown of Chemical in Vegetation

No information was found.


Resmethrin is a waxy, off-white to tan solid with an odor characteristic of chrysanthemums (1). It is stable under normal temperatures and pressures, but decomposes in the presence of alkalis and light. It poses a fire and explosion hazard in the presence of strong oxidizers and a slight fire hazard if exposed to heat or flame. It may burn, but does not readily ignite. Thermal decomposition may release toxic oxides of carbon (2). Resmethrin dust-air mixtures may ignite or explode. Contact with strong oxidizers, excessive heat, sparks and open flame should be avoided (2). Protect formulations containing resmethrin from exposure to air or light. Containers should be kept tightly closed (2). Workers handling resmethrin should wear protective clothing to prevent contact with the skin (1).

Exposure Guidelines:

No occupational exposure limits have been established for resmethrin by OSHA, NIOSH or ACGIH (2).

ADI: 0.1250 mg/kg/day based on chronic feeding and 3-generation reproduction studies with rats and a 200-fold safety factor (5).
MPI: 7.50 mg/day for a 60 kg person (5)

Physical Properties:

CAS #: 10453-86-8
Chemical Name: ([5-(phenylmethyl)-3-furanyl] methyl 2,2-dimethyl-3-(2-methyl-1-propenyl(cyclopropanecarboxylate) or 5-benzyl-3-furylmethyl (1RS)-cis,trans-chrysanthemate
Chemical Class/Use: Synthetic pyrethroid insecticide
Specific gravity: 1.044 (technical) (4)
Density: 8.70 pounds/gal (11)
H20 solubility: insoluble in water (1); < 1 ppm at 30 degrees C (2)
Solubility in other solvents: 10% in kerosene; soluble in hexane, xylene, methylene chloride, isopropyl alcohol and aromatic petroleum hydrocarbons; moderately soluble in methanol (1, 2).
Melting point: 109-118 degrees F (43-48 degrees C) (2)
Boiling point: 345 degrees F (174 degrees C) at 0.0008 mm Hg (2); 180 degrees C at 0.1 mm Hg (3, 4)
Flashpoint: > 200 (technical) (4).
Vapor pressure: negligible; 2.58 mm Hg at 200 degrees C (11)


Fairfield American Corp.
201 Route 17 N.
Rutherford, NJ 07070
Emergency: 201-669-3696

Review by Basic Manufacturer:

Comments solicited: April, 1993
Comments received:


  1. Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister Publishing Company, Willoughby, OH.
  2. Occupational Health Services, Inc. 1993 (Nov. 17). MSDS for Resmethrin. OHS Inc., Secaucus, NJ.
  3. National Coalition Against the Misuse of Pesticides. Resmethrin. Pesticides and You, Dec. 1987: page 6. NCAMP, Washington, DC.
  4. Penick Corp. 1976. Technical Information Sheet: SBP-1382* (Resmethrin) Pesticide Technology Dept., Penick Corp., Orange, NJ.
  5. U.S. Environmental Protection Agency. August 10, 1983. Tolerances for pesticides in food administered by EPA; Resmethrin. Federal Register 48 (155): 36246-7.
  6. Tietze N.S., et al. 1991. Acute toxicity of mosquitocidal compounds to young mosquitofish, Gambusia affinis. J. of the American Mosquito Control Assoc. 7 (2): 290-293.
  7. Christopher, R.J., et al. 1989. Metabolism of cis- and trans- resmethrin in laying hens. J. Agric. Food Chem. 37 (3): 800-808.
  8. Herrera, A. and E. Laborda. 1988. Mutagenic activity in synthetic pyrethroids in Salmonella typhimurium. Mutagenesis 3 (6): 509-514.
  9. Holck, A.R. and C.L. Meek. 1987. Dose-mortality responses of crawfish and mosquitoes to selected pesticides. J. of the American Mosquito Control Assoc. 3 (3): 407-411.
  10. Christopher, R.J., et al. 1985. Distribution and depletion of carbon-14 resmethrin isomers administered orally to laying hens. Pesticide Science 16 (4): 378-382.
  11. U.S. Environmental Protection Agency. Dec. !988. Pesticide Fact Sheet Number 193: Resmethrin. US EPA, Office of Pesticide Programs, Registration Div., Washington, DC.
  12. Muir, D.C.G., et al. 1985. Bioconcentration of cypermethrin, deltamethrin, fenvalerate and permethrin by Chironomus tentans larvae in sediment and water. Environmental Toxicology and Chemistry 4: 51-61.
  13. Bradbury, S.P. and J.R. Coats. 1989. Toxicokinetics and toxicodynamics of pyrethroid insecticides in fish. Environmental Toxicology and Chemistry 8: 373-380.
  14. Haya, K. 1989. Toxicity of pyrethroid insecticides to fish. Environmental Toxicology and Chemistry 8: 381-391.