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The information in this profile may be out-of-date.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

Resmethrin

Trade and Other Names: Trade manes include Chryson, Crossfire, Derringer, FMC 17370, Isathrine, NRDC 104, Pynosect, Raid Flying Insect Killer, Respond, Scourge, Sun-Bugger #4, SPB-1382, Synthrin, Syntox, Vectrin, and Whitmire PT-110.

Regulatory Status: Resmethrin is a slightly toxic to practically non-toxic compound in EPA toxicity class III. Products containing resmethrin must bear the Signal Word CAUTION on the label. All products containing resmethrin for pest control at or near aquatic sites are classified as Restricted Use Pesticides (RUP) by the EPA because of potential fish toxicity. RUPs may be purchased and used only by certified applicators.

Chemical Class: pyrethroid

Introduction: 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. It is also used for fabric protection, pet sprays and shampoos, and it is applied to horses or in horse stables. Technical resmethrin is a mixture of its two main isomers (molecules with the same chemical formula but slightly different configurations); a typical blend is 20 to 30% of the (1RS)-cis-isomer and 70 to 80% of the (1RS)-trans-isomer.

Formulation: Technical resmethrin is a mixture of its two main isomers (molecules with the same chemical formula but slightly different configurations); a typical blend is 20 to 30% of the (1RS)-cis-isomer and 70 to 80% of the (1RS)-trans-isomer.

Toxicological Effects:

• Acute toxicity: Resmethrin is slightly to practically non-toxic by ingestion. The oral LD50 for technical resmethrin in rats is variously reported as greater than 2500 mg/kg or 1244 mg/kg [3,12]. Resmethrin is only slightly toxic through the dermal route as well. The reported dermal LD50s for technical resmethrin are: greater than 3000 mg/kg in rats, greater than 2500 mg/kg in rabbits, and greater than 5000 mg/kg in mice [3,12]. It is slightly toxic via inhalation, with a 4-hour inhalation LC50 for resmethrin of greater than 9.49 mg/L [3]. Symptoms of exposure by any route may include incoordination, twitching, loss of bladder control, and seizures [12]. Dermal exposure may lead to local numbness, itching, burning, and tingling sensations near the site of exposure. Resmethrin is reported to be nonirritating to the skin and eyes of test animals and not to cause skin sensitization in guinea pigs [3].
• Chronic toxicity: In a chronic feeding study with rats, 25 mg/kg/day (the lowest dose tested) caused liver enlargement. At 125 mg/kg/day, there were pathological liver changes in addition to increased liver weights. Doses of 250 mg/kg/day caused increased thyroid weight and thyroid cysts [3]. In another study over 90 days, doses of 150 mg/kg/day did not produce any adverse effects in exposed rats [12]. Increased liver weights occurred in dogs fed 30 mg/kg/day for 180 days. No effects were observed in dogs in this study at dose rates of 10 mg/kg/day [3]. 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 body weights and increased serum urea levels in females [3]. Resmethrin was not neurotoxic to rats at doses of 62.5 mg/kg/day for 32 weeks, 250 mg/kg/day for 30 days, or 632 mg/kg/day for 7 days [4]. It is unlikely that chronic effects will be seen in humans under normal circumstances.
• Reproductive effects: A three-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 [4]. Since these doses are much higher than expected human exposures, it is unlikely such effects will occur in humans.
• Teratogenic effects: No birth defects were observed in the offspring of rabbits given doses as high as 100 mg/kg/day [4]. Skeletal aberrations were seen in the offspring of rats given doses higher than 40 mg/kg/day [3]. No teratogenic effects were observed in mice at dose levels of 50 mg/kg/day over an unspecified period [12]. It is unlikely that teratogenic effects will be seen in humans under normal circumstances.
• Mutagenic effects: Resmethrin was not mutagenic in a test performed with the bacterium, Salmonella typhimurium [6].
• 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 [3,4].
• 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 [12].

• Fate in humans and animals: Resmethrin is quickly eliminated by chickens. When oral doses of 10 mg/kg resmethrin were given to laying hens, 90% of the dose was eliminated in urine and feces within 24 hours [46]. In another study with hens given the same treatment, residues were low in hens sacrificed 12 hours after the treatment, with the highest levels found in the liver and kidneys. Low levels were found in the hens' eggs, with levels peaking 1 day after treatment in the whites and 4 to 5 days after treatment in the yolks [47].

Ecological Effects:

• Effects on birds: Resmethrin is practically nontoxic to birds. Its LD50 in California quail is greater than 2000 mg/kg [3]. In Japanese quail, the five-day dietary LC50 is greater than 5000 ppm [48].
• Effects on aquatic organisms: Resmethrin is very highly toxic to fish with 96-hour LC50 values generally at or below 1 ug/L (0.001 mg/L) for most species tested. The LC50 for resmethrin in mosquito fish is 7 ug/L [49]. The LC50 for resmethrin synergized with piperonyl butoxide in red swamp crawfish, Procambarus clarkii, is 0.00082 ug/L [48]. The LC50 in bluegill sunfish is 0.75 to 2.6 ug/L, and 0.28 to 2.4 ug/L in rainbow trout [3]. Other reported 96-hour LC50s are 1.8 ug/L in coho salmon, 1.7 ug/L in lake trout, 3.0 ug/L in fathead minnow, 16.6 ug/L in channel catfish and 1.7 ug/L in bluegill sunfish [50]. 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 [20].
• Effects on other organisms: Resmethrin is highly toxic to bees, with an LD50 of 0.063 ug per bee [3].

Environmental Fate:

• Breakdown in soil and groundwater: Resmethrin is of low to moderate persistence in the soil environment. Its half-life has been estimated at 30 days [51]. Observed half-lives will depend on many site-specific variables. In aerobic Kentucky loamy sand, the compund showed a half-life of nearly 200 days. Degradation end-products reported for resmethrin are chrysanthemic acid, benzaldehyde, benzyl alcohol, benzoic acid, phenylacetic acid, and various esters [52]. Resmethrin is tightly bound to soil and would not be expected to be mobile or to contaminate groundwater, especially in light of its extremely low solubility in water [51].
• Breakdown in water: Resmethrin may enter surface waters through particulate run-off or misapplication. 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 [22]. The half-life in water is 36.5 days.
• Breakdown in vegetation: No information was found.

Physical Properties:

• Appearance: Resmethrin is a waxy, off-white to tan solid with an odor characteristic of chrysanthemums [12].
• Chemical Name: 5-benzyl-3-furylmethyl (1RS)-cis,trans-2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylate [12]
• CAS Number: 10453-86-8
• Molecular Weight: 338.45
• Water Solubility: <1 mg/L at 30 C [12], insoluble in water
• Solubility in Other Solvents: s. in hexane, kerosene, xylene, methylene chloride, isopropyl alcohol, and aromatic petroleum hydrocarbons; m.s. in methanol [12]
• Melting Point: 43-48 C [12]
• Vapor Pressure: 0.0015 mPa @ 30 C [12]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 100,000 [51]

Exposure Guidelines:

• ADI: Not Available
• MCL: Not Available
• RfD: 0.03 mg/kg/day [30]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Roussel Uclaf Corp.
95 Chestnut Ridge Road
Montvale, NJ 07645

• Phone: 201-307-9700
• Emergency: Not Available
  

References:

References for the information in this PIP can be found in Reference List Number 2

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.