The information in this profile may be out-of-date.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.
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E X T O X N E T
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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
EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
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.
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.
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.
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.
- 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
. Symptoms of exposure by any route may include
incoordination, twitching, loss of bladder control, and
seizures . 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 .
- 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 . In another study over 90
days, doses of 150 mg/kg/day did not produce any adverse
effects in exposed rats . 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 . 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 . 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 .
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 . 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 . Skeletal aberrations were seen
in the offspring of rats given doses higher than 40
mg/kg/day . No teratogenic effects were observed in
mice at dose levels of 50 mg/kg/day over an unspecified
period . 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 .
- 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
- 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
- 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
. 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 .
- Effects on birds: Resmethrin is
practically nontoxic to birds. Its LD50 in California
quail is greater than 2000 mg/kg . In Japanese quail,
the five-day dietary LC50 is greater than 5000 ppm .
- 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 . The LC50 for resmethrin synergized with
piperonyl butoxide in red swamp crawfish, Procambarus
clarkii, is 0.00082 ug/L . The LC50 in bluegill
sunfish is 0.75 to 2.6 ug/L, and 0.28 to 2.4 ug/L in
rainbow trout . 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 . 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
- Effects on other organisms: Resmethrin
is highly toxic to bees, with an LD50 of 0.063 ug per bee
- 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
. 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 .
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
- 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
. The half-life in water is 36.5 days.
- Breakdown in vegetation: No information
- Appearance: Resmethrin is a waxy,
off-white to tan solid with an odor characteristic of
- Chemical Name: 5-benzyl-3-furylmethyl
- CAS Number: 10453-86-8
- Molecular Weight: 338.45
- Water Solubility: <1 mg/L at 30 C
, insoluble in water
- Solubility in Other Solvents: s. in
hexane, kerosene, xylene, methylene chloride, isopropyl
alcohol, and aromatic petroleum hydrocarbons; m.s. in
- Melting Point: 43-48 C 
- Vapor Pressure: 0.0015 mPa @ 30 C 
- Partition Coefficient: Not Available
- Adsorption Coefficient: 100,000 
- ADI: Not Available
- MCL: Not Available
- RfD: 0.03 mg/kg/day 
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
Roussel Uclaf Corp.
95 Chestnut Ridge Road
Montvale, NJ 07645
- Phone: 201-307-9700
- Emergency: Not Available
References for the information in this PIP can be found in
Reference List Number 2
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