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Pyrethroids and Pyrethrins
Current as of June 19, 2009
This page contains information from various EPA topic pages, fact sheets, and other sources that relate to the insecticides pyrethroids and pyrethrins.
- About These Pesticides
- EPA’s Reevaluation of Pyrethrins, Pyrethroids and Synergists
- Related Issues/Topics
- Ecological Risk Mitigation
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.
- Pyrethrins, a single pesticide active ingredient, contain six components that have insecticidal activity:
pyrethrin 1, pyrethrin 2, cinerin 1, cinerin 2, jasmolin 1, and jasmolin 2 - Pyrethroids include:
Allethrin stereoisomers, Bifenthrin, Beta-Cyfluthrin, Cyfluthrin, Cypermethrin, Cyphenothrin, Deltamethrin, Esfenvalerate, Fenpropathrin, Tau-Fluvalinate, Lambda-Cyhalothrin, Gamma Cyhalothrin, Imiprothrin, 1RS cis-Permethrin, Permethrin, Prallethrin, Resmethrin, Sumithrin (d-phenothrin), Tefluthrin, Tetramethrin, Tralomethrin, and Zeta-Cypermethrin - Synergists include:
MGK-264 and Piperonyl butoxide
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:
- Pyrethrins
- Pyrethroids
- Synergists
-
allethrins, cypermethrin, tau-fluvalinate, permethrin, resmethrin, sumithrin (d-phenothrin), tetramethrin
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 will be reevaluating all pyrethrins, pyrethroids and synergists during registration review starting in 2010. 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.
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 is considering whether some or all of the pyrethroid pesticides share a common mechanism of toxicity and, therefore, need a cumulative risk assessment. 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 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.
Related Issues/Topics
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.
- Review of the Relationship between Pyrethrins, Pyrethroid Exposure and Asthma and Allergies (28 pp, 398k, About PDF)
- Fact Sheet - June 19, 2009
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 Web fact sheet.
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 Non-agricultural Outdoor Products – To reduce exposure from residential uses of pyrethroids, EPA is requiring revised Environmental Hazard Statements and general Directions for Use for pyrethroid 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 will 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.