E X T O X N E T
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
Publication Date: 9/93
TRADE OR OTHER NAMES
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
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).
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).
Permethrin is not teratogenic (22). Pyrethroids, the chemical class to
which permethrin belongs, have not been identified as being teratogenic (8, 11).
Permethrin is not mutagenic (22). Pyrethroids have not been identified
as being capable of causing mutations (8, 11).
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).
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
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).
PHYSICAL PROPERTIES AND GUIDELINES
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).
|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).
|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
Review by Basic Manufacturer:
Comments solicited: November, 1992
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