United States		Prevention, Pesticides		EPA 738-F-09-001

Environmental Protection	and Toxic Substances		August 2009

Agency			(7508P)

   										     Permethrin Facts		

Pesticide Registration

	All pesticides sold or distributed in the Unites States must be
registered by the Environmental Protection Agency (EPA), based on
scientific studies showing that they can be used without posing
unreasonable risks to people or the environment.  Because of advances in
scientific knowledge, the law requires that pesticides, which were first
registered before November 1, 1984, be reregistered to ensure that they
meet today’s more stringent standards.  

	In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human
health and environmental effects of each pesticide.  To implement
provisions of the Food Quality Protection Act (FQPA) of 1996, EPA
considered the special sensitivity of infants and children to
pesticides, as well as aggregate exposure of the public to pesticide
residues from all sources, and the cumulative effects of pesticides and
other compounds with common mechanisms of toxicity.  The Agency develops
any mitigation measures or regulatory controls needed to effectively
reduce each pesticide’s risks.  EPA then registers pesticides that
meet the safety standard of the FQPA and can be used without posing
unreasonable risks to human health or the environment.  

	When a pesticide is eligible for reregistration, EPA explains the basis
for its decision in a Reregistration Eligibility Decision (RED)
document.  This fact sheet summarizes the information in the revised RED
document (May 2009) for the pesticide permethrin, case 2510.

Regulatory History

Permethrin was first registered and tolerances established in the United
States in 1979 for use on cotton (April 29, 1979 44FR 24287).  The
registration was made conditional due to the need for additional
toxicology and ecological effects data to fully evaluate carcinogenicity
and aquatic risk, respectively.  After additional toxicity data were
reviewed, EPA concluded that permethrin was a weak carcinogen.  Further,
laboratory studies indicated that permethrin was highly toxic to fish
and aquatic invertebrates; therefore, it was classified as Restricted
Use pesticide (RUP) for the cotton use.  From 1982 to 1989, an
additional 55 + crop tolerances were approved for a wide variety of
crops, including various fruits and vegetables, meat, milk and eggs.  

In 1985 a Data Call-In (DCI) for ecological effects data for permethrin
was issued.  After evaluation of this data EPA concluded that the
current RUP classification be maintained for all products for wide area
agricultural uses (except livestock and premises uses) and outdoor wide
area non-crop uses because of the possible adverse effects on aquatic
organisms from spray drift and runoff.  In 1988 a comprehensive DCI was
issued requiring additional residue chemistry, environmental fate and
toxicological data.  In 1994 the producers of products containing
permethrin for use on cotton requested voluntary cancellation of this
use.  From 1994 thru 2000 permethrin was subject to specific DCIs
requesting data to assess agricultural and residential exposure,
agricultural re-entry, and mosquito ULV products.  

The Reregistration Eligibility Decision (RED) document for Permethrin
was signed on April 5, 2006, and was revised (December 2007) based on
public comments and post-RED activities.  The 2006 RED and 2007 Revised
RED, as well as the accompanying risk assessments, benefit assessments,
and public comments can be found on the Federal Docket Management System
(FDMS), available at http://www.regulations.gov (docket #
EPA-HQ-OPP-2004-0385).  The permethrin RED was further revised (2009)
based on a submitted Estimated Dermal Penetration in Humans Based on In
Vitro and In Vivo Data, which decreased the dermal absorption factor
relied upon in the cancer portion of the occupational and residential
exposure (ORE) risk assessment from 15% to 5.7%.  The Agency has also
revised the RED document to reflect the current status of Office of
Pesticide Program initiatives, such as the cumulative risk assessment
and the Endangered Species Program, and updated the label table to
reflect updates in labeling on permethrin residential, agricultural, and
wide area public health use products.  

Uses

Permethrin is registered for use on/in numerous food/feed crops,
livestock and livestock housing, modes of transportation, structures,
buildings (including food handling establishments), Public Health
Mosquito abatement programs, and numerous residential use sites
including use in outdoor and indoor spaces, pets, and clothing
(impregnated and ready to use formulations). 

According to Agency data, approximately 2 million pounds of permethrin
are applied annually to agricultural, residential and public health uses
sites.  The majority of permethrin, over 70%, is used in
non-agricultural settings; 55% is applied by professionals, 41% is
applied by homeowners on residential areas, and 4% is applied on
mosquito abatement areas.    

Permethrin is a restricted use pesticide for crop and wide area
applications (i.e., nurseries, sod farms) due to high toxicity to
aquatic organisms, except for wide area mosquito adulticide use.  It is
a general use pesticide for residential and industrial applications.  

Permethrin also has non-FIFRA pharmaceutical uses as a pediculicide for
the treatment of head lice and scabies.  The Food and Drug
Administration (FDA) approves use of the pesticide-containing
pharmaceutical under FFDCA.  

Health Effects

	Permethrin is a member of the pyrethroid class of pesticides. 
Pyrethroids are undergoing an extensive collaborative research effort
with EPA’s Office of Research and Development’s National Health and
Environmental Effects Laboratory (NHEERL), the National Exposure
Research Laboratory, and the National Center for Computational
Toxicology (NCCT).  This research effort has focused on evaluating
whether or not pyrethroids share a common mechanism of toxicity and on
developing physiologically-based pharmacokinetic models (PBPK) and
exposure models for key pyrethroids.  Because of ongoing research, OPP
has not made a determination of a common mechanism group for the
pyrethroids.  However, significant research is now available, and a
FIFRA SAP was held June 16-19, 2009 to discuss the state of the science
on pyrethroids that may serve as a basis for determining a common
mechanism of toxicity.  All materials from the FIFRA SAP are available
on the Federal Docket Management System (  HYPERLINK
"http://www.regualtions.gov"  www.regualtions.gov ); docket number
EPA-HQ-OPP-2008-0489.

	If there is scientific consensus by the FIFRA SAP that there is
sufficient data to support a common mechanism grouping for pyrethroids,
the Agency will make revisions to the draft document, as appropriate,
and subsequently will announce the pyrethroids as a common mechanism
group in late 2009 or early 2010.  After such an announcement, the
Agency will begin work on the cumulative risk assessment for this group.
    

	Additionally, the Agency classified permethrin as “Likely to be
Carcinogenic to Humans” by the oral route.  This classification was
based on two reproducible benign tumor types (lung and liver) in the
mouse, equivocal evidence of carcinogenicity in Long-Evans rats, and
supporting structural activity relationship information.  

Risks

Dietary 

Acute, chronic non-cancer, and cancer dietary (food and drinking water)
risks from permethrin were below the Agency’s level of concern (LOC).

Residential  

All handler scenarios (cancer and non-cancer) assessed were below the
Agency’s LOC.  

The non-cancer post-application risk estimates for adults, youth aged
children, and toddlers exposed to an environment treated with permethrin
were below the Agency’s LOC.  All post-application scenarios for
adults, youth aged children, and toddlers were below the Agency’s
cancer LOC.  However, the combined oral and dermal exposure for toddlers
to indoor broadcast surface spray is below the Agency’s cancer LOC.  

The Agency considered post-application exposure to both outdoor
residential misting systems and permethrin treated clothing.  All
scenarios were below the Agency’s non-cancer and cancer LOCs. 

Aggregate Risks 

The acute aggregate risk non-cancer and cancer estimate from food and
drinking water does not exceed the Agency’s LOC.  

Aggregate short-term (1-30 days) non-cancer risk estimates, which
include the contribution of risk from chronic dietary sources (food +
drinking water) and short-term residential sources, exceeded the
Agency’s LOC for toddlers exposed to permethrin through food and
drinking water, and through post-application exposure during high
contact activities on lawns and indoor surfaces.  The risk driver for
the aggregate non-cancer risk estimate was post-application exposure to
permethrin on treated indoor surfaces (carpets). 

The aggregate cancer risk estimates exceeded the Agency’s LOC for
adults exposed to permethrin through food and drinking water, and
through post-application exposure during high contact activity on lawns
and indoor surfaces.  Similar to the non-cancer aggregate risk
assessment, post-application exposure to treated indoor carpets was the
risk driver.  

All residential/recreational exposures are expected to be short-term in
duration.  Therefore, no intermediate-term (1-6 months) or long-term (>6
months) aggregate risk was assessed.  

EPA believes that the appropriate way to consider the pharmaceutical use
of permethrin in its risk assessment is to examine the impact that the
additional non-occupational pesticide exposures would have to a
pharmaceutical patient exposed to a related (or, in some cases, the
same) compound.  Based on a worse case scenario assessment, EPA
estimates that the permethrin exposure a patient is expected to receive
from a typical single application of a 1% and 5% permethrin
pharmaceutical cream, respectively, is 450 to 2300 times greater than
the combined exposure from the dietary and other non-occupational
sources of permethrin.  FDA has reviewed these estimates and determined
that pesticide exposure in patients receiving treatment with a
pharmaceutical permethrin drug product would fall within the expected
range of exposure following treatment with permethrin drug product
alone, and would not present an increased safety risk.

    

Occupational

The majority of occupational handler risk estimates were below the
Agency’s non-cancer LOC at baseline personal protective equipment
(PPE) (long-sleeve shirt, long pants, no gloves, and no respirator). 
For all other scenarios where the LOC was exceeded considering just
baseline PPE, all occupational risk estimates were below the Agency’s
non-cancer LOC with additional PPE or engineering controls.  

 also within the negligible risk range (≤3 x 10-6) or less with
baseline PPE and gloves.  However, a number of scenarios result in risk
in the 10-5 to 10-6 range at this level of PPE, and either require
additional PPE before the cancer risk estimates were below the
negligible risk range, have no data available to estimate risk, or
further mitigation measures were not feasible.  

For all agricultural post-application scenarios assessed, the non-cancer
risks do not exceed the LOC (MOEs > 100) on the day of application,
approximately 12 hours following application.  Most of the
post-application cancer risk estimated for both hired hands and
commercial/migratory farm workers were in the 10-5 to  10-7 range.  The
highest risk estimates, in the 10-4 range, were for conifer seed cone
harvesting and thinning of certain fruit trees.  

All non-cancer post-application exposure scenarios for military
personnel and garment workers exposed to permethrin-impregnated battle
dress or fabric, respectively, do not exceed the Agency’s LOC. 
Further, all of the post-application cancer risk estimates for both
populations were in the 10-6 range.  

Ecological Risks 

Permethrin is highly toxic to both freshwater and estuarine aquatic
organisms.  Most agricultural, public health, and down-the-drain
scenarios modeled resulted in exceedances in the acute risk quotient
(RQ) for freshwater and estuarine fish, invertebrates, and sediment
organisms.  The agricultural and public health scenarios also showed the
potential for chronic risks to estuarine and/or freshwater organisms. 
Further, there is a potential concern for direct effects to a variety of
aquatic organisms.  

The acute and chronic RQs for terrestrial avian species are below the
Agency’s levels of concern.  The acute RQs for terrestrial mammals
were also below the Agency’s acute LOCs; however, some chronic RQs
exceeded the Agency’s LOC.  However, the Agency believes the chronic
RQs for mammals are based on a conservative estimate of toxicity, and
therefore, may represent an overestimation of risk.  

The potential for risk to terrestrial and aquatic plants from exposure
to permethrin cannot be assessed because toxicity data are not
available.  However, any toxicity to plants would occur for reasons
other than permethrin's insecticidal mode of action because permethrin
works as a neural toxin, and unlike insects, plants do not have neural
networks that could be affected.

Permethrin toxicity data show that the compound is highly toxic to
honeybees, as well as other beneficial insects.   

Risk Mitigation

	To address assessed risks of concern, the following mitigation measures
will be implemented.    

Residential Risk

Discontinue use of all directed broadcast and spot treatment sprays
(i.e., low pressure handwand, backpack sprayer, cold fogger) on all
residential indoor surfaces.  Baseboard and crack and crevice
applications are allowable via directed and RTU sprays.  

Limit concentration of indoor sprays to 0.5% ai of permethrin.  The
Agency will consider products with higher concentrations if the
registrants for these products are able to provide justification or data
to the Agency which demonstrate that little to no exposure will occur
due to the specialized use of the product.  

Amend all liquid and wettable powder products registered for outdoor
residential use to either prohibit use in outdoor residential misting
systems, or provide specific use directions.

Efficacy data for all finished pre-treated permethrin products, and
wash-off data to support efficacy claims is required. 

To address assessed risks of concern, the following mitigation measures
will be implemented.    

Occupational Risk

Handler

Require wettable powder formulations to be packed in water soluble
packaging.  

Require all aerial applications to be in closed cab aircraft. 

Discontinue the use of high pressure handwands in mushroom houses.  

Add PPE requirement to labels as follows:

Wettable Powders- baseline PPE (long pants, long sleeved shirt, and
shoes), and chemical-resistant gloves for mixers, loaders, and
applicators.  

Emulsifiable Concentrations- baseline PPE and chemical-resistant gloves
for mixers, loader, and applicators.  Additional chemical-resistant
apron is required for applicators performing animal dip applications.  

Dry Flowables- baseline PPE and chemical-resistant gloves.

Dust- Double layer (coveralls over baseline PPE), chemical-resistant
gloves, and a PF5 respirator for loaders and applicators.      

RTU Formulations- Baseline PPE and chemical-resistant gloves.  

Applicators of liquids via cold foggers and fog mister/generators.

Require applicators to wear double layers, chemical-resistant gloves,
and PF10 respirator.

Post-Application

Amend agricultural labels to include new use patterns (rate reductions,
seasonal maximum reductions, and minimum retreatment intervals)
identified for the selected crop uses specified Appendix A.  

To address assessed risks of concern, the following mitigation measures
will be implemented.    

Ecological Risks

Include standard pyrethroid specific spray drift language, including a
25 foot aquatic buffer zone for ground applications, 100-foot for aerial
application, and 450 foot for ULV applications.  

Amend agricultural labels to include new use pattern (rate reductions,
seasonal maximum reductions, and minimum retreatment interval)
identified for the selected crop uses specified in Appendix A.  

Include the following statement in the environmental hazard section of
the end use products:

This pesticide is highly toxic to bees exposed to direct treatment on
blooming crops or weeds.  Do not apply this product or allow it to drift
to blooming crops or weeds while bees are actively visiting the
treatment area.

For all wide area mosquito abatement products:

Remove 100 foot buffer zone restriction;

Specify a maximum application rate of 0.007 lb ai/A per day or 0.18 lb
ai/A per year.  

Specify minimum release height of 100 feet for fixed wing aircraft, and
75 feet for helicopter applications. 

Require droplet size <60 microns for aerial application, and <30 microns
for ground application.

Incorporate Pesticide Registration Notice 2008-1, “Environmental
Hazard General Labeling Statements on Outdoor Residential Use
Products.”

Include the best management and good stewardship language in the
directions for use section of all products registered for outdoor use to
reduce the amount of spray drift and runoff that can occur from these
applications.

Risk/Benefit Balance Analysis

The Agency also assessed the significance of permethrin use, and
conducted a risk/benefit balancing analysis. Given the significance of
the use of permethrin and the mitigated nature of the risks of
permethrin, the Agency believes, on balance, that the benefits of
permethrin outweigh the risks.   With respect to the ecological risks,
the Agency has reduced those risks by imposing various conditions that
should reduce exposure of aquatic species to permethrin.  With respect
to the benefits, permethrin offers substantial benefits to users.  In
the agricultural area, permethrin provides a high benefit to the
agricultural industry because of its broad label and 1 day PHI. 
According to comments received from various growers, the broad spectrum
of pests that permethrin targets makes its use highly beneficial since
the agricultural industry has been losing a number of insecticides, and
the newer insecticides replacing them have chemistries that target
specific insects and are narrow in their spectrum.  Further, permethrin
has a 1 day pre-harvest interval, which allows for effective pest
control near harvest of registered crops.   Also alternatives to
permethrin, such as the fourth generation pyrethroids, may pose a
greater risk to aquatic organisms because of their persistence in the
environment. 

 For the public health use, permethrin is the most widely used mosquito
adulticide in the United States because of its low cost, high efficacy,
and low incidence of pest resistance.  Although permethrin alternatives
are comparably priced and are likely to be as effective as permethrin in
many situations, they are not likely to universally substitute for all
permethrin uses because of labeling constraints or resistance concerns. 
The Agency believes that the loss of permethrin would adversely affect
the ability of mosquito abatement professionals to control mosquitoes in
some situation, such as agricultural-urban interface and areas with
known resistance to alternatives.  With regard to the treatment of
fabrics, permethrin is the only pesticide registered to pre-treat
fabrics, which the AFPMB strongly supports as a method of preventing
many diseases that might afflict military personnel in the field.  On
other uses, such as residential uses, where there may be a potential for
ecological effects due to urban runoff, the Agency intends to identify
steps which can be taken to allow a greater understanding of potential
ecological risk from urban uses of pyrethroid as a whole during
Registration Review.  

Data Requirements  tc "			1.	Generic Data Requirements " \l 2 

	The Agency has identified data necessary to confirm the reregistration
eligibility decision for permethrin.  These studies are listed below and
will be included in the generic DCI for this RED, which the Agency
intends to issue at a future date. 

Toxicology:

870.1300	Acute Inhalation Toxicity Study

Residue Chemistry:

860.1200	Directions for Use

860.1340	Enforcement Analytical Method-Animals

860.1380	Storage Stability

860.1500	Magnitude of the Residue in Crop Plants (leaf lettuce,
collards, and cabbage)

Occupational Exposure

875.1200	Dermal Exposure Indoors (ULV Cold Fogger)

875.1400	Inhalation Exposure Indoors (ULV Cold Fogger)

Environmental Toxicology

850.1735	Whole sediment acute toxicity for estuarine/marine
invertebrates

850.1740	Whole sediment acute toxicity for estuarine/marine
invertebrates

850.1000	Chronic Freshwater Sediment Testing

850.1000	Chronic Estuarine/Marine Sediment Testing

Regulatory Conclusion

	The Agency has determined that permethrin containing products are
eligible for reregistration provided that the risk mitigation measures
are adopted and labels are amended to reflect these measures.  

For More Information

	Electronic copies of the Permethrin RED and all supporting documents
are available in the public docket EPA-HQ-OPP-2004-0385 located on-line
in the Federal Docket management System (FDMC) at
http://www.regulations.gov.  

	For more information about EPA’s pesticide reregistration program,
the Permethrin RED, or reregistration of individual products containing
permethrin, please contact the Special Review and Reregistration
Division (7508P), Office of Pesticide Programs, U.S. EPA, Washington,
D.C. 20460, telephone 703-308-8000.  

	For information about the health affects of pesticides, of for
assistance in recognizing and managing pesticide poisoning symptoms,
please contact the National Pesticide Information Center (NPIC).  Call
toll-free 1-800-858-7378, from 6:30 am to 4:30 am Pacific Time, or 9:30
am to 7:30 pm Easter Standard Time, seven days a week. The NPIC internet
address is   HYPERLINK "http://npic.orst.edu"  http://npic.orst.edu .

Appendix A:

Amended Agricultural Use Patterns

	Current Labels	Mitigation Per the RED

Crop	Max. Rate per application

(lb ai/A)	Minimum

retreatment interval (days)	Seasonal Maximum  Application Rate

 (lb ai/A)	New

Maximum rate per application (lb ai/A)	New

Minimum

retreatment interval

(days)	New

Seasonal Maximum  Application Rate

 (lb ai/A)

Alfalfa	0.2	14	0.2 per cutting	0.2	30	0.2 per cutting

Almonds	0.4	3	2	0.25	10	0.75

Hazelnuts	0.4	As needed	1.6	0.25	10	0.75

Pistachios	0.4	As needed	1.6	0.3	10	0.9

Walnuts	0.4	As needed	1.6	0.25	10	0.75

Apples	0.4	As needed	0.6	0.25	10	0.5

Pears	0.4	As needed	0.8	0.25

½

¾

h

h

 h

h

h

 h

h

옍

$

0.15	10	0.45

Papaya	0.4	7	1.2	0.15	10	0.75

Potatoes	0.2	As needed	1.6	0.2	10	0.8

Soybeans	0.2	As needed	0.4	0.2	10	0.4



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