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. 

1
�
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. 

2
�
	 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 physiologicallybased 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 (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 LongEvans 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, 

3
�
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 postapplication 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 nonoccupational 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 

4
�
	 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. 

	 The estimated cancer risks for the majority of grower scenarios were 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 postapplication 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 

5
�
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. 

o	 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: 

o	 Wettable Powders- baseline PPE (long pants, long sleeved shirt, and 

shoes), and chemical-resistant gloves for mixers, loaders, and 

applicators. 

o	 Emulsifiable Concentrations- baseline PPE and chemical-resistant 

gloves for mixers, loader, and applicators. Additional chemicalresistant apron is required for applicators performing animal dip 

applications. 

6
�
o	 Dry Flowables- baseline PPE and chemical-resistant gloves. 

o	 Dust- Double layer (coveralls over baseline PPE), chemical-resistant 

gloves, and a PF5 respirator for loaders and applicators. 

o	 RTU Formulations- Baseline PPE and chemical-resistant gloves. 

o	 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: 

o	 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: 

o	 Remove 100 foot buffer zone restriction; 

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

ai/A per year. 

o	 Specify minimum release height of 100 feet for fixed wing aircraft, 

and 75 feet for helicopter applications. 

o	 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 

7
�
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 

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) 

8
�
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 http://npic.orst.edu. 

9
�
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 

(0.4 

dormant 

only) 

10 0.65 

Cherries 0.2 As needed 1.2 0.2 10 0.6 

Peaches/Nectarines 0.3 7 1.5 0.25 10 0.75 

Artichokes 0.3 As needed 1.5 0.3 10 0.9 

Asparagus 0.1 As needed 0.4 0.1 7 0.4 

Avocados 0.2 7 1.2 0.2 7 0.8 

Broccoli 0.2 As needed 0.8 0.2 5 0.8 

Brussels Sprouts 0.2 As needed 0.8 0.1 5 0.4 

Cabbage 0.2 5 1 0.2 5 0.4 (0.8 in 

HI) 

Cauliflower 0.2 As needed 0.8 0.1 5 0.4 (0.6 in 

HI) 

Cantaloupes 0.2 7 1.6 0.2 7 0.8 (1.2 in 

HI) 

Cucumbers 0.2 As needed 1.6 0.2 7 1.2 

Pumpkins 0.2 As needed 1.6 0.2 7 1.2 

Squash (summer, 

winter) 

0.2 As needed 1.6 0.2 7 1.2 

Watermelon 0.2 As needed 1.6 0.2 7 1.2 

Eggplant 0.21 3 2 0.15 7 0.6 (1.0 in 

HI) 

Peppers, bell 0.2 As needed 1.6 0.2 5 0.8 

Tomatoes 0.2 5 1.2 0.2 7 0.6 (0.8 in 

HI) 

Celery 0.2 As needed 2 0.2 7 1.0 (1.2 in 

HI) 

Lettuce 0.2 3 2 0.2 7 0.8 (1.2 in 

HI) 

Spinach 0.2 As needed 2 0.2 3 0.6 

Collards 0.2 As needed 0.8 (0.4 in 

SC, GA, 

FL, WA) 

0.15 3 0.45 

Greens, Turnip 0.2 As needed 0.8 (0.4 in 

SC, GA, 

0.15 3 0.45 

10
�
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) 

FL, WA) 

Corn, Field 0.2 6 0.6 0.15 7 0.45 

Sweet Corn 0.25 3 1.2 0.2 3 0.8 

Garlic 0.3 As needed 2 0.2 10 0.8 

Onions 0.3 As needed 2 0.3 7 1.0 

Horseradish 0.21 As needed 0.6 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 

11
�