It must be noted that the issue of a Data Sheet for a particular pesticide does not imply endorsement of the pesticide by WHO or FAO for any particular use, or exclude its use for other purposes not stated. While the information provided is believed to be accurate according to data available at the time when the sheet was compiled, neither WHO nor FAO are responsible for any errors or omissions, or any consequences therefrom.

The issue of this document does not constitute formal publication. It should not be reviewed, abstracted or quoted without the agreement of the Food and Agriculture Organization of the United Nations or of the World Health Organization.

Ce document ne constitue pas une publication. Il ne doit faire l'objet d'aucun compte rendu ou résumé ni d'aucune citation sans l'autorisation de l'Organisation des Nations Unies pour l'Alimentation et l'Agriculture ou de l'Organisation Mondiale de la Santé.

resmethrin (BSI, E-ISO, ANSI, JMAF) Resmethrine (F-ISO).

Resmethrin is a mixture of four optical isomers; the (1R, trans)- and 1R, cis)- isomers have strong insecticidal activity, whilst the (1S, trans)-and (1S, cis)-isomers do not. Relative proportions are approximately 4:1:4:1, respectively.

Benzofuroline; Benzyfuroline^R; Chryson^R; Chrysron^R; FMC-17370; FOR-SYN; NIA-17370; NRDC-104; Premgard^R; Pynosect^R; Resmetrina; SBP-1382; Synthrin^R.

Resmethrin is a pyrethroid of broad spectrum insecticidal activity. It acts as a fast acting neurotoxin with good contact action. It has low mammalian and plant toxicity and is readily decomposed by exposure to air and light. Resmethrin was introduced commercially in 1969.

Technical resmethrin consists of 20-30% cis-isomers and 80-70% trans-isomers and is an off white to tan coloured waxy solid with chrysanthemate odour. Melting point of the technical material is 43 - 48 ºC; boiling point 180 ºC at 1.33 Pa.

25 ºC; Insoluble in water (<1 mg/litre)

> 500 g/litre in methylene chloride

> 500 g/litre in acetone

80 g/litre in ethanol

70 g/litre in isopropanol

Very soluble in xylene and aromatic petroleum hydrocarbons.

Somewhat more stable than pyrethrins but is decomposed on exposure to air and light, in acids and alkalis.

< 0.01 mPa at 25ºC.

With or without other pyrethroids and pyrethrin synergists in aerosol concentrates, 0.5% water based sprays, 10% wettable powders, 2% emulsifiable concentrate, ULV concentrates.

Flying and crawling insects, including mosquitoes, cockroaches, spiders, ticks, fleas.

For use in households, greenhouses, indoor landscaping, mushroom houses, industrial storehouses. Also used in insecticidal mists and fogs, in fabric protection, pet sprays and shampoos, and for application to horses and horse stables.

Not phytotoxic when used as recommended. Toxic to fish and bees.

See 1.4 above.

See 1.4 above.

Resmethrin is rapidly, but probably incompletely absorbed from the gastro-intestinal tract. It may be absorbed by inhalation of dust and fine spray mist, or through intact skin.

Resmethrin is a neurotoxin which acts to stimulate repetitive action in the peripheral nervous system membranes by prolonging the sodium ion permeability during the excitatory phase of the action potential. When given in extreme dosages (over 1500 mg/kg) to rats and mice irritability, tremors, ataxia, respiratory depression, chromodacryorrhea and diarrhea result (T-syndrom). It is classified as a type I pyrethroid.

Except at extremely high doses, the rat excretes no unchanged resmethrin in the urine or faeces. Metabolism proceeds by hydrolysis and subsequent oxidation and/or conjugation, but the extent of metabolism varies between species, between individual isomers and depends on the magnitude of dose. Generally negligible amounts of ¹⁴CO₂ are detected following administration of any ¹⁴C labelled isomer to rats. The ratio of urinary/faecal excretion observed is, however, dependent on both the magnitude of the dose and the proportions of each isomer present in the dose. Although metabolites rapidly appear in the bile after dosing, the excretion is not particularly rapid. In cows only 50% of an oral dose of 10 mg/kg b.w. was recovered within 48 hours; in rats receiving an oral dose of 500 mg/kg b.w. 70-80% of the dose was recovered in seven days, 100% by 20 days. Differences in the rate of metabolism of four different isomers and enterohepatic re-circulation may contribute to these slow excretion rates.

The toxicity varies with the cis/trans ratio and characteristics of the carrier used; non-polar carriers may increase absorption. Acute toxicity data show that resmethrins are mildly toxic, except cismethrin, for which the acute oral toxicity in mice is moderate.

In rats following acute oral exposure, the (1R, cis)-isomer is more toxic than the (1R, trans)-isomer. Toxic symptoms observed in both rats and mice included hypersensitivity, tremors and motor ataxia. In rats these symptoms were accompanied by bloody tears and urinary incontinence. The onset of effects in mice occurred in 30-60 minutes, while in rats they occurred in 2-3 hours.

In these experiments no deaths occurred. Exposure to high concentrations elicited symptoms of hypersensitivity, urinary incontinence and ataxia. These effects were not observed in rats or mice at concentrations below 400 mg/m³.

Primary irritation:

Installation of technical bioresmethrin into the eye of rabbits (0.1 ml) did not produce irritation or corneal damage.

Sensitization: Technical grade resmethrin was found to be a slight irritant to the skin in rabbits. It did not cause sensitization and photochemical irritation in guinea-pig and New Zealand white rabbits.

Oral: When rats were fed resmethrin in the diet at levels of up to 6000 mg/kg for 14 days, mortality was observed at the highest dose level, and tremor, reduced body weight and food consumption were noted at levels of 1500 mg/kg or more.

Dermal: Resmethrin was applied twice weekly, for 3 weeks, to the skin of New Zealand white rabbits by fixing a piece of cotton cloth treated with resmethrin (0.247 mg/cm²) over skin that had been pre-treated with liquid, imitating sweat, or with resmethrin (10 g), or had not been pre-treated. No significant changes were noted in body weight and organ weight ratios on day 24 or in the clinical chemistry in any of the groups up to day 24. No significant compound-related dermal effects were observed.

Inhalation: Exposure of male and female rats or mice to 23, 47 or 210 mg/m³ as (1R, trans, cis-isomers, 4:1) for four hours a day, five days a week for four weeks, did not adversely affect food intake, behaviour, blood and clinical chemistry parameters or organ histopathology.

Rats and rabbits inhaled aerosolized resmethrin formulations for 5 h/day on 5 consecutive days at levels of 3200 mg/m³. Though clinical signs including rapid breathing and nasal discharge were observed, there was no indication of toxic effects other than irritation in any of the tests.

Intravenous: Beagle dogs injected intravenously with 25 mg/kg b.w. per day for 15 days showed no toxic effects or compound related enzyme changes.

Cumulation of compound: No published information is available on tissue residues following repeated exposure. Since the overall excretion rate is not rapid (Section 2.1.3) resmethrin or its metabolites might have the potential to accumulate following repeated exposure.

Cumulation of effects: No published information available. Review of the limited number of sub-chronic exposure studies (Section 2.1.5) does not however provide evidence of a severe cumulative toxicity.

Short-term: Tremor, decreased body weight, increased liver and kidney weight and alkaline phosphatase levels were observed in Sprague Dawley rats receiving 5000 mg/kg diet (as (1R, trans, cis)-isomers, 4:1) for 24 weeks. A no-effect level (NOEL) of 1500 mg/kg diet was established.

When rats were fed bioresmethrin in the diet at levels of up to 8000 mg/kg for 91 days, body weight was reduced at the highest level, and was accompanied by changes in blood chemistry indicating liver dysfunction.

Dogs were administered bioresmethrin at levels of up to 500 mg/kg body weight for 90 days. A no-observed-adverse-effect level was observed at 80 mg/kg body weight.

No pathological or histopathological abnormalities were seen in dogs receiving resmethrin in the diet for three months, at concentrations calculated to give a dose of 25, 80 or 250 mg/kg b.w./day.

Long-term: When resmethrin was administered to rats at dietary levels up to 5000 mg/kg for 24 weeks, tremors, decreased body weight, and increased liver and kidney weights were observed at 5000 mg/kg.

Dogs fed resmethrin for 6 months showed increased liver weights at 30 mg/kg body weight per day, but did not show any adverse effects at 10 mg/kg body weight per day.

No carcinogenic effects were seen when CD-1 mice were fed resmethrin in the diet up to 1000 mg/kg, for 85 weeks.

Resmethrin fed to Wister rats at dosage levels up to 5000 mg/kg in the diet of 112 weeks was found not to be carcinogenic.

Several studies using different animal models have been performed to test the teratogenic potential of the compound. Dose levels up to 1000 mg/kg b.w. were found not to be teratogenic in mice, rats and rabbits.

Resmethrin was not mutagenic to several strains of Salmonella typhimurium in vitro, with and without metabolic activation. Salmonella typhimurium G46 cells harvested from abdomens of mice three hours after receipt of an oral dose of 250 mg/kg b.w. (1R, trans)-isomer or (1R, cis)-isomer did not show an increased mutation rate in this host-mediated assay.

In a 3-generation reproduction study, Sprague-Dawley rats were fed resmethrin in the diet up to 1250 mg/kg. A decrease in pup weight and a slight increase in the number of pups cast dead were observed at the 500 mg/kg.

Inhibitors of esterases and microsomal oxidase enzyme systems may increase the toxicity of resmethrin in mammals and target organisms, however, the interaction is complex, and in mice the inhibition of either enzyme group alone is not sufficient to increase the toxicity of the rapidly metabolised (1R, trans)-isomer.

No published information available but resmethrin has the potential for absorption from the gastrointestinal tract, the lungs and from the skin.

No published information available.

No published information available.

No published information available.

No published information available.

No published information available.

2.3.1

No mortalities occurred following oral administration of 2000 mg/kg b.w. to lovebirds.

[For definition of categories see the "Introduction to data sheets".]

Formulations in Category 5: Should be transported and stored in clearly labelled leakproof containers. Containers should be kept out of reach of children and away from food and drink.

Formulations in Category 4: All stipulations for category 5 should be met. Additionally, storage should be under lock and key, secure from access by children and unauthorized persons.

Formulations in Category 5: Facilities as required for the handling of any chemical should be provided, including washing facilities.

Formulations in Category 4: Protective clothing should be worn when handling the compound. Adequate washing facilities should be provided at all times during handling, and should be close to the site of handling. Eating, drinking and smoking should be prohibited during handling. Hands and face should be washed prior to eating, drinking or smoking after handling compound.

All formulations: Empty containers may be decontaminated by washing three times with detergent and water. Additionally, the container should be soaked overnight in 5% sodium hydroxide. Impermeable gantlets should be worn for all decontamination procedures. A deep soakage pit should be provided for the rinsings. Decontaminated containers must not be used for storage or transport of food or drink. Containers not decontaminated should be burned or crushed and buried below topsoil. Care muse be taken to avoid contamination of water sources.

Formulations in Category 5: Warning of workers to minimize contact is essential. Workers suffering from asthma, allergies and other respiratory disorders and cardiovascular disorders should avoid contact.

Formulations in Category 4: Workers suffering from asthma, allergies and other respiratory disorders and cardiovascular disorders should be excluded from contact. Persons under medication with neuroactive drugs should avoid contact. Workers should be able to comprehend and follow instructions. Workers should be trained in techniques to avoid contact.

All formulations: Pilots and loaders should have specialized training in application methods and recognition of early warning symptoms of poisoning. Flagmen should wear protective clothing as detailed in Section 4.1.3. Additionally they should wear a broad brimmed hat and be well away from the dropping zone.

Formulations in Category 4 - Minimum Cautionary Statement:

Resmethrin is a synthetic pyrethroid pesticide, a neurotoxin, and it may be poisonous if swallowed or inhaled as a dust or mist. It may be irritating to the skin and eyes. Avoid skin and eye contact, wear protective clothing and impermeable gloves and eye protection when handling the material. Wash thoroughly with soap and water after using the product. Keep the material out of reach of children and well away from food stuffs, animal feed and food containers. If poisoning occurs, call a physician. There are no specific antidotes. Cardio-pulmonary resuscitation may be required.

Formulations in Category 5 - Minimum Cautionary Statement: This formulation contains resmethrin, and is poisonous if swallowed. Keep the material out of reach of children and well away from food stuffs, animal feed and food containers. Wash thoroughly after using this product.

Maximum residue limits (MRLs) or acceptable daily intake (ADI) for resmethrin have not yet been determined by the Joint FAO/WHO Meeting on Pesticide Residues.

Resmethrin is a synthetic pyrethroid; a neurotoxic agent of low acute toxicity to mammals. It may be absorbed from the gastrointestinal tract, by inhalation of dust and spray mist, or through the intact skin. The health hazard is diminished by the low concentrations of the active ingredient in all current formulations.

TLV: 0.2 mg/m³. Closed systems and forced ventilation are required to reduce, as much as possible, the exposure to workers to the chemical.

When opening a container and when mixing, boots, clean overalls, gloves, face shield and face mask should be worn. Mixing, if not mechanical, should always be carried out with a paddle of appropriate length. Avoid contact with mouth, skin and eyes. Before eating, drinking or smoking, hands and other exposed skin should be thoroughly washed with soap and water.

Persons exposed to resmethrin and associated with its application should observe the precautions described above in 4.1.3.

With good agricultural practice, subject to 4.2 below, other populations should not be exposed to hazardous amounts of resmethrin.

The instability of resmethrin in moist air and in light, combined with low application rates ensure low residue levels. Unprotected persons should be kept out of treated area until the applied formulation has dried.

Residues in containers should be emptied in a diluted form into a deep pit taking care to avoid contamination of groundwaters. The empty containers may be decontaminated by rinsing two or three times with water and detergent and scrubbing the sides. Impermeable gauntlets should be worn during this work. Empty, decontaminated containers should be buried or burned (Section 3.4). Spillages should be washed away with large volumes of water and detergent.

These may include nausea and vomiting; fine or coarse tremors, hypersensitivity to external stimuli and general weakness and prostration.

The person should stop work immediately, remove contaminated clothing and thoroughly wash the affected area with water and soap. For eye contamination, wash with copious amounts of water. If the material was swallowed and signs of toxicity are severe, induce vomiting if person is conscious and if aspiration of vomit can be avoided. In the event of collapse, apply artificial respiration. Keep the person calm and comfortable and obtain medical help as soon as possible.

Resmethrin is a synthetic pyrethroid pesticide of low toxicity to mammals. It may be absorbed from the gastrointestinal tract, by inhalation of dust and spray mist, or through the intact skin. The hydrolysis and oxidation products of metabolism are fairly rapidly excreted in the urine and faeces.

Little information is available on the acute toxic effects of resmethrin in humans. Based upon animal studies, high doses may cause repetitive activity in sensory and motor nerves. Early signs of poisoning may include nausea and vomiting, dyspnoea and hyperpnoea, fine or coarse tremors, hypersensitivity to stimuli and a feeling of general weakness and prostration.

There are no established, practical methods for determining resmethrin in body fluids. Urinary levels of metabolites may be an index of exposure.

There are no specific antidotes, treatment must be symptomatic. Wash contaminated skin with soap and water. Wash contaminated eyes with copious amounts of water.

Following ingestion of larger quantities of resmethrin vomiting should be induced if the patient is fully conscious. Subsequent administration of activated charcoal may limit absorption of resmethrin remaining in the gut. Care must be taken to avoid pulmonary complications when ingested formulations contain petroleum solvents. Diazepam may be given orally or by slow intravenous administration to control nervousness and tremors, should these be apparent following severe poisoning.

There have been no reports of overt symptoms resulting from poisoning of man by resmethrin; the prognosis therefore is not known. However, by analogy with laboratory animals it may be assumed that if the acute toxic effect is survived the chances of complete recovery are good.

No published information available.

None.

Papadopoulou-Mourikidou E, Iwata Y and Gunther FA (1980), J Agric Food Chem 28(6): 1043-1049.

Zehner JM and Simonaitis RA (1976), J Assoc Off Anal Chem 59: 1101.

None.

The Pesticide Manual, A World Compendium (10th Edition 1994), Tomlin, C., ed., British Crop Protection Council, 20 Bridport Road, Thornton Heath, CR4 7QG, U.K.

WHO (1989), Environmental Health Criteria 92, Resmethrins - Resmethrin, Bioresmethrin, Cisresmethrin. UNEP/ILO/WHO Geneva, 79 pp.

    See Also:
       Toxicological Abbreviations
       Resmethrin (ICSC)