Public Health Statement for Pyrethrins and Pyrethroids
Spanish: Piretrinas y Piretroides
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This Public Health Statement is the
summary chapter from the Toxicological
Profile for Pyrethrins and Pyrethroids. It is one in a
series of Public Health Statements about hazardous substances
and their health effects. A shorter version, the ToxFAQs™, is also available. This information is important because this
substance may harm you. The effects of exposure to any hazardous
substance depend on the dose, the duration, how you are exposed,
personal traits and habits, and whether other chemicals are
present. For more information, call the ATSDR Information
Center at 1-800-232-4636.
This public health statement tells you about pyrethrins and pyrethroids and the effects of exposure.
The Environmental Protection Agency (EPA)
identifies the most serious hazardous waste sites in the nation.
These sites make up the National Priorities List (NPL) and
are the sites targeted for long-term federal cleanup activities.
Pyrethrins and pyrethroids have been found in at least 5 and
2 of the 1,636 current or former NPL sites, respectively.
However, the total number of NPL sites evaluated for these
substances is not known. As more sites are evaluated, the
sites at which pyrethrins and pyrethroids are found may increase.
This information is important because exposure to these substances
may harm you and because these sites may be sources of exposure.
When a substance is released from a large
area, such as an industrial plant, or from a container, such
as a drum or bottle, it enters the environment. This release
does not always lead to exposure. You are exposed to a substance
only when you come in contact with it. You may be exposed
by breathing, eating, or drinking the substance, or by skin
If you are exposed to pyrethrins and
pyrethroids, many factors determine whether you'll be harmed.
These factors include the dose (how much), the duration (how
long), and how you come in contact with them. You must also
consider the other chemicals you're exposed to and your age,
sex, diet, family traits, lifestyle, and state of health.
What is pyrethrins and pyrethroids?
Pyrethrum is a naturally occurring mixture
of chemicals found in certain chrysanthemum flowers. Pyrethrum
was first recognized as having insecticidal properties around
1800 in Asia and was used to kill ticks and various insects
such as fleas and mosquitos. Six individual chemicals have
active insecticidal properties in the pyrethrum extract, and
these compounds are called pyrethrins. Pyrethrum looks like
a tan-colored dust as ground flowers or a syrupy liquid as
the crude extract. Pyrethrins are only slightly soluble in
water, but they dissolve in organic solvents like alcohol,
chlorinated hydrocarbons, and kerosene. Pyrethrins are often
used in household insecticides and products to control insects
on pets or livestock. Pyrethrins break down quickly in the
environment, especially when exposed to natural sunlight.
Pyrethroids are manufactured chemicals
that are very similar in structure to the pyrethrins, but
are often more toxic to insects, as well as to mammals, and
last longer in the environment than pyrethrins. More than
1,000 synthetic pyrethroids have been developed, but less
than a dozen of them are currently used in the United States.
Pyrethrins and pyrethroids are often combined commercially
with other chemicals called synergists, which enhance the
insecticidal activity of the pyrethrins and pyrethroids. The
synergists prevent some enzymes from breaking down the pyrethrins
and pyrethroids, thus increasing their toxicity.
Most commercial pyrethroids are not one
single molecule; rather, they are several molecules with the
same chemical formula that have their atoms joined together
in the same sequence, but have a different arrangement of
the atoms in space. Such compounds are called stereoisomers.
If the stereoisomers are not mirror images of one another,
they are called diastereomers and have different physical
properties like boiling point, melting point, and solubility.
If they are nonsuperimposable mirror images of each other,
they are called enantiomers and properties like boiling point,
melting point, and solubility are identical. However, both
diastereomers and enantiomers can have different insecticidal
properties and different toxicities. Some pyrethroids are
composed of as many as eight different stereoisomers.
Technical-grade (concentrated) pyrethrins
and pyrethroids are usually mixed with carriers or solvents
to produce a commercial-grade formulated product. The formulated
product contains many inert ingredients that can increase
the toxicity of the product when compared to the technical-grade
material. By law, the active ingredient must be identified
by name on the pesticide label and its percentage must be
provided. Nonactive ingredients (sometimes called inert ingredients)
do not need to be identified by name on a pesticide label,
only the percentage of nonactive ingredients must be specified,
so it is often difficult to determine what other chemicals
are included in the final formulated product.
What happens to pyrethrins and pyrethroids when it enters the environment?
Pyrethrins and pyrethroids are primarily
released to air because of their use as insecticides. Sometimes
they are sprayed on crops from planes and helicopters or sprayed
from the ground by trucks, tractors, or hand-held applicators.
They are also used to control flying insects like mosquitos
and flies on livestock and pets. These compounds are also
in aerosol bombs and sprays that can be used indoors. Pyrethrins
can be released naturally from chrysanthemum flowers, but
these releases are small compared with the amounts used as
commercial insecticides. Manufacturing facilities that produce
these compounds can also release them to the environment during
the production process.
In air, all six of the pyrethrins and
many of the pyrethroids are broken down or degraded rapidly
by sunlight or other compounds found in the atmosphere. Often,
they last only 1 or 2 days before being degraded. Rain and
snow help remove the pyrethroids from air that are not rapidly
degraded. Since many of these compounds are extremely toxic
to fish, they are usually not sprayed directly onto water,
but they can enter lakes, ponds, rivers, and streams from
rainfall or runoff from agricultural fields. These compounds
bind strongly to dirt and usually are not very mobile in soil.
Pyrethrins and pyrethroids are not easily taken up by the
roots of plants and vegetation because they are strongly bound
to the soil; however, they are often sprayed directly onto
crops and plants so they may be found on leaves, fruits, and
vegetables. Because these compounds adsorb so strongly to
soil, pyrethrins and pyrethroids usually do not leach into
groundwater, do not contaminate drinking water supplies, and
volatilize from soil surfaces slowly. These compounds are
eventually degraded by the microorganisms in soil and water.
They can also be degraded by sunlight at the surfaces of water,
soil, or plants. However, some of the more recently developed
pyrethroids can persist in the environment for a few months
before they are degraded.
For more information about the fate and
movement of pyrethrins and pyrethroids in the environment,
see Chapter 6.
How might I be exposed to pyrethrins and pyrethroids?
You can be exposed to pyrethrins and
pyrethroids in several ways. Eating foods that are contaminated
with these compounds is the most likely way. You can also
breathe in air that contains these compounds. This is especially
possible soon after the insecticide has been sprayed. After
spraying, these compounds can also come in contact with your
skin and you can be exposed by dermal contact. These compounds
are contained in many household insecticides, pet sprays,
and shampoos. Some pyrethroids are also used as lice treatments
that are applied directly to the head and as mosquito repellents
that can be applied to your clothes. A common treatment for
scabies is the application of a pyrethroid to the affected
skin surface excluding the scalp. The use of these products
can lead to exposure.
The average daily intake of permethrin
(the most frequently used pyrethroid in the United States)
for a 70 kilogram adult male is estimated as about 3.2 micrograms
per day (1 microgram equals 1/1,000,000 of a gram). This value
is about 1,000 times less than the acceptable daily intake
(ADI) of permethrin derived by the United Nations' Food and
Agriculture Organization (FAO) and the World Health Organization
How can pyrethrins and pyrethroids enter and leave my body?
Pyrethrins and pyrethroids usually enter
the body when people eat foods contaminated by these chemicals.
They may also enter your body by breathing air that contains
these compounds or through dermal exposure when you use commercially
available insecticides that contain pyrethrins and pyrethroids.
These chemicals are absorbed by the body when you eat contaminated
foods and breathe contaminated air, but they are not as easily
absorbed through the skin when you touch contaminated soil,
vegetation, or insecticides containing these compounds. Some
insect repellents that are applied to the skin contain pyrethrins
or pyrethroids in addition to another chemical called DEET,
which may allow the pyrethrins or pyrethroids to enter your
body more easily. Pyrethrins and pyrethroids can enter your
body if you swallow drinking water contaminated with these
compounds, but since pyrethrins and pyrethroids are rarely
found in drinking water, this will be a minor exposure route.
Accidental exposures to pyrethrins or pyrethroids may also
occur if these pesticides are improperly used.
Pyrethrins and pyrethroids that enter
the body leave quickly, mainly in the urine, but also in feces
and breath. These compounds are also quickly broken down by
the body into other chemicals called metabolites. The concentration
of these chemicals in the urine increases as the amount of
the exposure goes up. If exposure levels are very high or
if exposure occurs over a long time, then pyrethrins and pyrethroids
can build up in fatty tissue and remain in the body for a
little longer. Certain types of pyrethroids can also be retained
for longer periods of time in the skin and hair.
Chapter 3 contains more information on how pyrethrins and pyrethroids enter and leave the human body.
How can pyrethrins and pyrethroids affect my health?
Pyrethrins and pyrethroids interfere
with the way that the nerves and brain function. If you get
a large amount of pyrethrins or pyrethroids on your skin,
you may get feelings of numbness, itching, burning, stinging,
tingling, or warmth that could last for a few hours. You are
not likely to be exposed to amounts of pyrethrins or pyrethroids
by breathing air, eating food, or touching anything that would
cause enough pyrethrins or pyrethroids to enter your body
and cause other problems. But if very large amounts of these
chemicals were to enter your body, you might experience dizziness,
headache, and nausea that might last for several hours. Larger
amounts might cause muscle twitching, reduced energy, and
changes in awareness. Even larger amounts could cause convulsions
and loss of consciousness that could last for several days.
Allergic reactions have been seen in a few individuals who
used products that contain pyrethrins or pyrethroids. There
is no evidence that pyrethrins or pyrethroids cause birth
defects in humans or affect the ability of humans to produce
children. There is evidence from animal studies that pyrethrins
and pyrethroids might be capable of causing cancer in people,
but the evidence comes from animals that ate very large amounts
of pyrethrins or pyrethroids for a lifetime.
To protect the public from the harmful
effects of toxic chemicals and to find ways to treat people
who have been harmed, scientists use many tests.
One way to see if a chemical will hurt
people is to learn how the chemical is absorbed, used, and
released by the body; for some chemicals, animal testing may
be necessary. Animal testing may also be used to identify
health effects such as cancer or birth defects. Without laboratory
animals, scientists would lose a basic method to get information
needed to make wise decisions to protect public health. Scientists
have the responsibility to treat research animals with care
and compassion. Laws today protect the welfare of research
animals, and scientists must comply with strict animal care
Animal studies show effects of pyrethrins
and pyrethroids similar to those seen in people exposed to
very high amounts of these chemicals. In addition, exposure
to pyrethrins or pyrethroids might affect the ability of some
animals to reproduce and may also cause cancer.
How can pyrethrins and pyrethroids affect children?
This section discusses potential health effects from exposures during the period from conception to
maturity at 18 years of age in humans.
Children exposed to large amounts of
pyrethrins or pyrethroids would be expected to be affected
in the same manner as adults. If children were to get a large
amount of pyrethrins or pyrethroids on their skin, they might
get feelings of numbness, itching, burning, tingling, or warmth
that could last for a few hours. If very large amounts of
these chemicals were to enter a child's body, the child might
experience dizziness, headache, and nausea that might last
for several hours. Even larger amounts could cause muscle
twitches, tremors, convulsions, and loss of consciousness
that could last up to several days.
Pyrethroids might be able to penetrate
the skin of infants and young children more easily than the
skin of adults. Infants and young children are more easily
dehydrated than adults through exercise, flue, colds, and
the conditions that contribute to fluid loss. Therefore, pyrethroids
that penetrate the skin may become more concentrated in internal
tissues of the young.
There is no evidence in humans that pyrethrins
or pyrethroids cause birth defects. Some young animals showed
signs of possible damage to the body's defense system that
fights infection after their mothers were exposed to pyrethroids
while their babies were developing in the womb. There is some
indication that the developing brain of some very young animals
could be affected by pyrethroids.
How can families reduce the risk of exposure to pyrethrins and pyrethroids?
If your doctor finds that you have been
exposed to significant amounts of pyrethrins or pyrethroids,
ask whether your children might also be exposed. Your doctor
might need to ask your state health department to investigate.
Pyrethrins and pyrethroids are effective
insecticides that are often used in household sprays, aerosol
bombs, insect repellents, pet shampoos, and lice treatments.
Using products containing these compounds will expose you
to these chemicals. If you decide to use these products, carefully
follow the instructions on how to apply them properly and
how long to wait before re-entering the treated area. Do not
apply more than the recommended amount. Pesticides and household
chemicals should be stored out of reach of young children
to prevent accidental poisoning. Always store pesticides in
their original labeled containers; never store pesticides
in containers that young children would find attractive, such
as old soda bottles. If you feel sick after a pesticide has
been used in your home, call the local poison control center
or see a doctor. Keep your poison control center's number
next to the phone. If a close neighbor or someone living nearby
is applying pyrethrins or pyrethroids, you may want to remain
indoors with your children and pets in order to avoid being
accidentally exposed to these chemicals. Certain pyrethroids,
such as permethrin, phenothrin, and resmethrin, are sprayed
to control mosquitos during the spring and summer. Remaining
indoors and closing your windows while your neighborhood is
being sprayed will lessen your exposure.
Since these compounds frequently are
used on crops, they are often detected in fruits and vegetables.
Make sure you wash fruits and vegetables thoroughly before
eating them. Trim the fat from meat and poultry because pesticides
often concentrate in fat. These compounds are often detected
in soils, especially in agricultural areas. Some children
eat a lot of dirt. You should discourage your children from
eating dirt. Make sure they wash their hands frequently and
before eating. Discourage your children from putting their
hands in their mouths or any other hand-to-mouth activity.
Is there a medical test to determine whether I have been exposed to pyrethrins and pyrethroids?
Methods exist that can detect pyrethrins
and pyrethroids in blood and urine. Because these compounds
are broken down in the body quickly, there are also ways to
measure the metabolites of these chemicals in human blood
and urine. These methods are not available in a doctor's office
because special equipment is required. However, a sample taken
in a doctor's office can be shipped to a special medical laboratory,
if necessary. These laboratories are usually located at research
universities or affiliated with government agencies such as
the Centers for Disease Control and Prevention (CDC). Your
doctor may need to contact the county health department for
a list of laboratories that can perform these tests. Because
pyrethrins and pyrethroids break down in the body rapidly,
these methods are useful only if exposure has occurred within
the last few days. At this time, these methods can tell only
if you have been exposed to pyrethrins or pyrethroids and
cannot tell if you will have any adverse health effects. Methods
also exist that can measure the concentration of pyrethrins
and pyrethroids in air, water, soil, and foods.
For pesticide emergencies, the National
Pesticide Information Center (NPIC) (formerly called the National
Pesticide Telecommunications Network [NPTN]) located at Oregon
State University, is also available. The NPIC (telephone number:
1-800-858-7378 for the general public and 1-800-858-7377 for
medical profession/government agencies) provides information
about pesticides to anyone in the United States.
Chapter 7 contains more information regarding
the measurement of pyrethrins and pyrethroids in humans and
What recommendations has the federal government made to protect human health?
The federal government develops regulations
and recommendations to protect public health. Regulations
can be enforced by law. Federal agencies that develop regulations
for toxic substances include the Environmental Protection
Agency (EPA), the Occupational Safety and Health Administration
(OSHA), and the Food and Drug Administration (FDA). Recommendations
provide valuable guidelines to protect public health but cannot
be enforced by law. Federal organizations that develop recommendations
for toxic substances include the Agency for Toxic Substances
and Disease Registry (ATSDR) and the National Institute for
Occupational Safety and Health (NIOSH).
Regulations and recommendations can be expressed in not-to-exceed levels in air, water, soil, or food that are usually based on levels that affect animals; then they are adjusted to help protect people. Sometimes these not-to-exceed levels differ among federal organizations because of different exposure times (an 8-hour workday or a 24-hour day), the use of different animal studies, or other factors.
Recommendations and regulations are also periodically updated as more information becomes available. For the most current information, check with the federal agency or organization that provides it. Some regulations and recommendations for pyrethrins and pyrethroids include the following:
The WHO has recommended that the level of permethrin in drinking water not exceed 20 micrograms per liter (µg/L). OSHA regulates the level of pyrethrins in workplace air. The occupational exposure limits for an 8-hour workday, 40-hour workweek are 5 mg per cubic meter (mg/m3). The EPA has recommended daily oral exposure limits for 10 different pyrethroids. These limits range from 0.005 to 0.05 mg/kg/day.
In September of 1997, the EPA issued a request to pesticide formulators to voluntarily change the term "inert ingredients" to "other ingredients" on pesticide labels because the general public often believed that inert ingredients meant harmless ingredients. Since federal law does not define inert ingredients on the basis of toxicity or hazard to humans, it should not be assumed that all inert ingredients are nontoxic. The EPA publishes a list of all inert ingredients used in currently registered pesticides, but it does not specify which ingredients are contained in any specific formulated product.
For more information on regulations and guidelines, see Chapter 8.
Agency for Toxic Substances and Disease Registry (ATSDR). 2003. Toxicological profile for Pyrethrins and Pyrethroids. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.