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Pesticide Toxicity Profile: Synthetic Pyrethroid Pesticides1

Frederick M. Fishel2

This document provides a general overview of human toxicity, provides a listing of laboratory animal and wildlife toxicities and a cross reference of chemical and common names with their trade names of many synthetic pyrethroid pesticides registered for use in Florida.

General

Pyrethrins were originally derived from East African chrysanthemum flowers and shown to have insecticidal activity. In a natural environment, they were chemically unstable and broke down rapidly upon exposure to air and sunlight. Beginning in the 1970s, synthetic pyrethroids came into the market for agricultural purposes as they were synthesized from petroleum derivatives. They are also widely used as home and garden insecticides along with uses on pets and livestock, mosquito control, treatment of transport vehicles, and for treatment of ectoparasitic disease. Their desirable features are providing a quick knockdown of insects at low rates, relatively low mammalian toxicity and improved stability in outdoor environments, which has increased their marketability in agriculture. They are effective against a wide range of insect and mite pests and may be mixed with other pesticides for a broad spectrum of pest control. Formulations that are commercially available include aerosols, dips, emulsifiable concentrates, wettable powders, granules, and concentrates for ultra low volume applications targeting mosquitoes. Pyrethroids may be mixed with piperonyl butoxide, a synergist, which enhances the effect of the active ingredient. Their mode of action is interference with transmission of nerve impulses.

Toxicity

Pyrethroids are one of the least acutely toxic insecticides to mammals because they are quickly deactivated by metabolic processes. However, rats fed high doses (1,000 mg/kg of body weight) showed liver damage (Hayes, 1982). Toxicity by inhalation and dermal absorption is low. Sensitization sometimes occurs in some individuals after a single exposure which causes either an asthmatic condition or a skin rash or inflammation. After the initial exposure to the sensitizing agent, the sensitized individual responds to a dose smaller than the initial dose. Symptoms are more common with exposure to the pyrethroids whose structures include cyano-groups. Sensations are described as stinging, burning, itching, and tingling, progressing to numbness, with the face most commonly affected. Persons treated with permethrin for lice or flea infestations sometimes experience itching and burning at the site of application, but this is more of a reaction to the effects of the parasites themselves. Due to the inclusion of certain solvents, some formulations of fluvalinate are corrosive to the eyes. Scientists have no data from work-related, accidental poisonings, or epidemiological studies that indicate whether or not pyrethrins are likely to cause cancer in humans. There were no birth defects in pups of rabbits exposed to pyrethrins (Vettorazzi, 1979); however, rat pups born to rats fed very high doses of pyrethrins for three weeks prior to mating were of low body weights (Hayes, 1982). Pyrethrins are highly toxic to fish and tadpoles. They affect their skin touch receptors and balance organs (Tomlin, 1994). Mammalian toxicities for pyrethroid pesticides registered in Florida are shown in Table 1. Table 2 lists the toxicities to wildlife by the common name of the pyrethroid pesticide. Table 3 provides a cross listing of many of the trade names that these products are registered and sold by in Florida.

Additional Information

Table 1. Pyrethroid pesticide mammalian toxicities (mg/kg of body weight).

Common name

Rat oral LD50

Rabbit dermal LD50
Allethrin

860

11,332
Bifenthrin

375

>2,000
Cyfluthrin

869 - 1271

>5,000 (rat)
Cyhalothrin

79

632 (rat)
Cypermethrin

250

>2,000
Deltamethrin

31 - 139 (female)

>2,000
Esfenvalerate

451

2,500
Fenpropathrin


70.6 -164

>2,000
Fluvalinate

261 - 282

>20,000
Permethrin

430 - 4,000

>2,000
Resmethrin

1,244 - >2,500

>2,500
Tefluthrin

969

>2,000 (rat)
Tetramethrin

>5,000

>2,000
Tralomethrin


284

>2,000

Table 2. Pyrethroid pesticide wildlife toxicity ranges.

Common name


 Bird acute oral LD50 (mg/kg)*


 Fish LC50 (ppm)**

Bee LD50 †
Allethrin

PNT

HT

HT
Bifenthrin

ST - PNT

HT

HT
Cyfluthrin

PNT

VHT

HT
Cyhalothrin

PNT

HT

HT
Cypermethrin

PNT

VHT

HT
Deltamethrin

PNT

HT

HT
Esfenvalerate

PNT

VHT

HT
Fenpropathrin

ST

VHT

HT
Fluvalinate

PNT

VHT

MT
Permethrin

PNT

VHT

HT
Resmethrin

PNT

VHT

HT
Tefluthrin

ST - PNT

VHT

HT
Tetramethrin

PNT

HT

---
Tralomethrin

---

VHT

HT
*Bird LD50: Practically nontoxic (PNT) = >2,000; slightly toxic (ST) = 501 - 2,000; moderately toxic (MT) = 51 - 500; highly toxic (HT) = 10 - 50; very highly toxic (VHT) = <10.

**Fish LC50: PNT = >100; ST = 10 - 100; MT = 1 - 10; HT = 0.1 - 1; VHT = <0.1.

†Bee: HT = highly toxic (kills upon contact as well as residues); MT = moderately toxic (kills if applied over bees); PNT = relatively nontoxic (relatively few precautions necessary).

Table 3. Cross reference list of common, trade and chemical names of pyrethroid insecticides.

Common name*


 Trade names**


 Chemical name
Allethrin


 Many household products


 (RS)-3-allyl-2-methyl-4-oxycyclopent-2-enyl (1RS)-cis-trans chrysanthemate
Bifenthrin


 Capture®, Talstar®


 [1-alpha,3-alpha-(Z)]-(+)-(2 methyl[1,1'-biphenyl]-3yl) methyl 3-(2,chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate
Cyfluthrin


 Baythroid®, Tame®


 Cyano(4-fluoro-3-phenoxyphenyl)methyl 3-(2,2-dichloro-ethenyl)-2,2-dimethylcyclopropanecarboxylate
Cyhalothrin


 Karate®, Warrior®, Demand®, Scimitar®


 alpha-cyano-3-phenoxybenzyl 3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate
Cypermethrin


 Ammo®, Fury®, Mustang®


 (+)-alpha-cyano-3-phenoxybenzyl (+)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethycyclopropanecarboxylate
Deltamethrin


 Decis®, DeltaGard®, Demand®


 (S)-cyano(3-phenoxybenzyl) (1R,3R)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate
Esfenvalerate


 Asana®


 (S)-cyano(3-phenoxyphenyl)methyl (S)-4-chloro-alpha-(1-methylethyl)-benzeneacetate
Fenpropathrin


 Danitol®, Tame®


 RS-alpha-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate
Fluvalinate


 Mavrik®, Zoecon®


 Á-RS,2R)-fluvalinate [(RS)-alpha-cyano-3-phenoxybenzyl (R)-2-[2-chloro-4-(trifluoromethyl)anilino]-3-methyl-butanoate]
Permethrin


 Ambush®, Pounce®


 (3-phenoxyphenyl)methyl (+)-cis,trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate
Resmethrin


 Many household products


 ([5-(phenylmethyl)-3-furanyl]methyl 2,2-dimethyl-3-(2-methyl-1-proenyl)cyclopropanecarboxylate)
Tefluthrin


 Force®


 2,3,5,6-tetrafluoro-4-methylbenzyl (Z)-(1 RS, 3RS)-3-(2-chloro-3,3,3-trifluoroprop-1-ethyl) -2,2-dimethylcyclopropanecarboxylate
Tetramethrin


 Many household products


 3,4,5,6-tetrahydrophthalimidomethyl (1RS)-cis,trans-chrysanthemate
Tralomethrin


 Scout®


 (1R,3S)3[(1',2',2',2',-tetrabromoethyl)]-2,2-dimethylcyclopropanecarboxylic acid (S)-alpha-cyano-3-phenoxybenzyl ester
*Basic molecule; isomers not listed.

**Does not include manufacturers prepackaged mixtures; major agricultural brands for basic manufacturers.

Footnotes

1. This document is PI-54, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published July, 2005. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2. Frederick M. Fishel, Associate Professor, Agronomy Department, and Director, Pesticide Information Office; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.


Copyright Information

This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.