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Pyrethroids and Pyrethrins

Current as of December 2013

This page contains information from various EPA topic pages, fact sheets, and other sources that relate to the insecticides pyrethroids and pyrethrins.

On this page you will find:

About These Pesticides

Pyrethrins and pyrethroids are insecticides included in over 3,500 registered products, many of which are used widely in and around households, including on pets, in mosquito control, and in agriculture. The use of pyrethrins and pyrethroids has increased during the past decade with the declining use of organophosphate pesticides, which are more acutely toxic to birds and mammals than the pyrethroids. This change to less acutely toxic pesticides, while generally beneficial, has introduced certain new issues. For example, residential uses of pyrethrins and pyrethroids may result in urban runoff, potentially exposing aquatic life to harmful levels in water and sediment.

Pyrethrins are botanical insecticides derived from chrysanthemum flowers most commonly found in Australia and Africa. They work by altering nerve function, which causes paralysis in target insect pests, eventually resulting in death.

Pyrethroids are synthetic chemical insecticides whose chemical structures are adapted from the chemical structures of the pyrethrins and act in a similar manner to pyrethrins. Pyrethroids are modified to increase their stability in sunlight.

Most pyrethrins and some pyrethroid products are formulated with synergists, such as piperonyl butoxide and MGK-264, to enhance the pesticidal properties of the product. These synergists have no pesticidal effects of their own but enhance the effectiveness of other chemicals.

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EPA’s Reevaluation of Pyrethrins, Pyrethroids and Synergists

Reregistration – Ten of the pyrethrins, pyrethroids and synergists were registered before November 1, 1984, and therefore were subject to reregistration. In 2008, EPA completed risk management Reregistration Eligibility Decisions (REDs) for these 10 individual pesticides:

The remaining pyrethroids, registered later, were not subject to reregistration.

Through the reregistration program, EPA reassessed the human health and ecological effects of older pesticides and required mitigation to address risks of concern. EPA’s REDs, RED fact sheets, related information, and links to FDMS dockets are available at Pesticide Reregistration Status.

Registration review is EPA’s program for systematically reviewing all registered pesticides every 15 years to make sure that every pesticide can still perform its intended function without unreasonable adverse effects on human health or the environment.

Registration Review –EPA is reevaluating all pyrethrins, pyrethroids and synergists during registration reviewstarting in fiscal year (FY) 2010 through FY 2012. Because many of the pyrethroids were registered after November 1984, they were not subject to re-evaluation under the reregistration program. Since they may be used as alternatives for one another, it makes sense to assess and manage the risks of pyrethrins, pyrethroids and synergists within a similar time frame.

The Agency moved these pesticides ahead in the registration review schedule in order to evaluate the effectiveness of recent regulatory decisions and consider new data and information about them sooner. Using this approach, EPA can ensure that risk assessment and risk management approaches are consistent within this class of pesticides.

Pyrethroids that Started Registration Review in FY 2010
First Quarter (October – December 2009):   Cyphenothrin, Esfenvalerate
Second Quarter (January – March 2010):   Allethrin stereoisomers, Deltamethrin, Tralomethrin
Third Quarter (April – June 2010):   Bifenthrin, Fenpropathrin
Fourth Quarter (July – September 2010):   Cyfluthrin,
Pyrethroids that Started Registration Review in FY 2011
First Quarter (October - December 2010):   Gamma cyhalothrin, Lambda-cyhalothrin, Piperonyl butoxide, Tau-fluvalinate
Second Quarter (January - March 2011):   Fenvalerate (cancelled)
Third Quarter (April - June 2011):   Permethrin
Fourth Quarter (July - September 2011):   Imiprothrin
Pyrethroids that Started Registration Review in FY 2012
First Quarter (October - December 2011):   Pyrethrin and derivatives, Sumithrin (Phenothrin), Tetramethrin
Second Quarter (January - March 2012):   Cypermethrin
Third Quarter (April - June 2012):   Prallethrin, Resmethrin, MGK-264
Fourth Quarter (July - September 2012):   Metofluthrin, Tefluthrin

Documents related to individual pesticides that have begun the registration review process are available in Chemical Search and in the individual pesticide dockets at www.regulations.gov.

Documents related to EPA's registration review of this class of pesticides are available in the Special Docket for Pyrethroids, Pyrethrins, and Synergists, EPA-HQ-OPP-2008-0331 at regulations.gov.

Cumulative Risk Assessment –EPA's October 2011 Pyrethrins/Pyrethroid Cumulative Risk Assessment indicates that exposures from the many current uses of pyrethrins and pyrethroid insecticides do not pose risk concerns for children or adults. Further, the cumulative assessment supports consideration of registering additional new uses of these pesticides. EPA issued the final pyrethrins/pyrethroids risk assessment on November 9, 2011, and requests comment, including information that may be used to further refine the risk assessment. For further information, please also visit Assessing Pesticide Cumulative Risk/ Common Mechanism Groups.

The FIFRA Scientific Advisory Panel (SAP) met on June 16 - 18, 2009, to consider and review an evaluation of the common mechanism of action of pyrethroid pesticides. The FIFRA SAP met on July 20 - 22, 2010 to consider and review a set of scientific issues related to SHEDS-Multimedia version 4, Peer consult on PBPK Modeling, and a SHEDS-PBPK Permethrin study. Meeting information and minutes are posted on those Web pages.

The Food Quality Protection Act (FQPA) requires EPA to assess the cumulative risks of pesticides that share a common mechanism of toxicity (i.e., act the same way in the body). Establishing a common mechanism group is the first stage toward developing a cumulative risk assessment.

Data Requirement Modification - EPA has determined that developmental toxicity studies (DNTs) previously required for pyrethroid insecticides do not adequately characterize potential susceptibility of the young. In a September 4, 2009 letter, EPA stated that registrants who have not fulfilled requirements for the DNT may instead cite six previously submitted pyrethroid DNT studies, rather than conducting a full new study. The Agency noted that other data may be needed to fully address the potential for increased susceptibility of young organisms to the pyrethroids, focusing on pyrethroid-specific effects related to the mode of action and pharmacokinetic characteristics of this class of compounds.

In a February 16, 2010 letter to the registrant and stakeholder community, EPA asked companies and other interested parties to voluntarily submit study protocols designed to better understand the potential susceptibility associated with pyrethroids. Proposals submitted were reviewed by the Agency and presented to the FIFRA SAP for comment at their July 23, 2010 meeting on Comparative Adult and Juvenile Sensitivity Toxicity Protocols for Pyrethroids. Meeting information and minutes are posted on that Web page.

EPA has developed a science paper, that discusses the DNT study and related data issues.

These documents are also available in pyrethroid docket EPA-HQ-OPP-2008-0331 at regulations.gov.

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Related Issues/Topics

Treated Clothing - EPA requires pesticide registration for clothing treated with insect repellents. This fact sheet describes the regulation and safety of these products.

Mosquito Control – Pyrethroids such as permethrin, resmethrin, and sumithrin are commonly used in products that control adult mosquito populations. Most pyrethroid mosquito control products can be applied only by public health officials and trained personnel of mosquito control districts.

Outdoor Residential Misting Systems - An increasing number of households have purchased timed-release outdoor residential misting systems to control mosquitoes and other insects around the home. This Web fact sheet provides information to help consumers determine if such a system would be appropriate for their situation, as well as safety precautions for using misters, other ways to control mosquitoes, and information about EPA's role in regulating misting systems.

Pets - Some pyrethroids and pyrethrins products are registered to treat household pets for fleas and ticks.  Reading and carefully following product label directions and understanding the precautions will protect your pets from both pests and potential pesticide risks.

Allergy and Asthma Assessment – In response to concerns expressed in a July 2008 Center for Public Integrity (CPI) journal article, EPA expedited its most recent review of available animal and human studies and human incident data to determine whether a clear association exists between exposure to pyrethrins and pyrethroid products and asthma and allergy effects.  Agency scientists have concluded that there does not appear to be a clear relationship between pyrethrins/pyrethroid exposure and asthma/allergies. The Agency will continue to evaluate new data on this issue as it becomes available.

Total Release Foggers –Total release foggers, also known as "bug bombs," are pesticide products containing aerosol propellants that release their contents at once to fumigate an area. Pyrethrins, pyrethroids and synergists are often the active ingredients in these products.

Total release foggers are consumer products primarily marketed for use in homes and apartments for control of pests such as roaches or fleas. The risks and appropriate precautions for use of this type of product are described in the Agency’s Total Release Foggers fact sheet.

Fogger Labeling Changes to Improve Residential Safety

Fogger Fact Sheet

EPA required the following labeling changes for indoor total release fogger products distributed or sold by the registrant after September 30, 2012.

The Agency has created a list of approved pictograms available for use by all total release fogger registrants.

EPA sent a letter notifying pyrethrin and pyrethroid registrants of these labeling changes (5 pp, 347.84K, about PDF) on March 23, 2010. The Agency sent a second letter notifying pyrethrin and pyrethroid registrants of the list of approved pictograms (5 pp, 347.84K, about PDF) on July 6, 2011.

The Agency’s 2010 total release fogger labeling improvements are consistent with recommendations from Washington state (18 pp, 226.90K, about PDF)) and a 2008 Center for Disease Control report entitled Illnesses and Injuries Related to Total Release Foggers, and are expected to address concerns raised by a 2009 petition from the New York City Department of Health (14 pp, 808.42K, about PDF) to reclassify TRFs as restricted use pesticides. EPA’s response to the petition (15 pp, 334.46K, about PDF) explains the Agency’s careful analysis of the petition and incident reports (1 pp, 124K, about PDF) going back to the 1990s. The Agency concluded that reclassification is inappropriate and would unnecessarily remove these cost effective pest control tools from the residential market.


Records of Fogger Meetings

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Ecological Risk Mitigation

Pyrethroids are highly toxic to aquatic organisms. Because the pyrethroids can accumulate in sediments, risk to sediment-dwelling organisms is an area of particular concern. Recent water quality monitoring efforts in California have identified pyrethroids in sediments of water bodies adjacent to residential/urban areas. These monitoring data, coupled with additional pyrethroid-specific data submitted to the Agency, highlight existing concerns regarding residential uses of pyrethroid pesticide products and movement into non-target areas through runoff or spray drift that may occur during applications.

To reduce exposure to water bodies from non-agricultural and agricultural uses of pyrethroids, the Agency deployed the following labeling initiatives.

Environmental Hazard and General Labeling for Pyrethroid and Synergized Pyrethrins Non-agricultural Outdoor Products – Revised February 2013 – To reduce exposure from residential uses of pyrethroids and pyrethrins products, EPA implemented a 2009 labeling initiative, with minor revisions in 2013, requiring revised Environmental Hazard Statements and general Directions for Use for pyrethroid and pyrethrins pesticide products used in non-agricultural outdoor settings. The label statements spell out good stewardship and best-management practices and clarify how these types of products are intended to be used.

These label statements serve to reduce the potential for runoff and drift to water bodies that can result from applications of pyrethroid end-use products in residential, commercial, institutional, and industrial areas, applied by both professional pesticide control operators and residential consumers.

Pyrethroid Spray Drift Initiative – In the reregistration process for permethrin and cypermethrin, the Agency determined that the existing spray drift language for pyrethroid agricultural products needed to be updated to comply with FIFRA. Because of similarities in use patterns, and concern for exposure to aquatic resources, the Agency believes that this updated label language is necessary for all pyrethroid products used on agricultural crops. In a letter from the Agency (PDF) (6 pp, 75k, About PDF) dated February 21, 2008, registrants were instructed to incorporate the revised spray drift language onto their agricultural labels, and submit the amended labels to the Agency.

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