Pyrethroid
Encyclopedia
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
similar to the natural pyrethrin
Pyrethrin
The pyrethrins are a pair of natural organic compounds that have potent insecticidal activity. Pyrethrins are neurotoxins that attack the nervous systems of all insects. When present in amounts not fatal to insects, they still appear to have an insect repellent effect. Pyrethrins are gradually...
s produced by the flowers of pyrethrum
Pyrethrum
Pyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C...
s (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids now constitute a major commercial household insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s. In the concentrations used in such products, they may also have insect repellent
Insect repellent
An insect repellent is a substance applied to skin, clothing, or other surfaces which discourages insects from landing or climbing on that surface. There are also insect repellent products available based on sound production, particularly ultrasound...
properties and are generally harmless to human beings in low doses but can harm sensitive individuals. They are usually broken apart
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...
by sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
and the atmosphere in one or two days, and do not significantly affect groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
quality. Pyrethroids are however toxic to aquatic organisms.
Mechanism of action
Pyrethroids are extremely popular for insecticideInsecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
because exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
s of insects are sufficiently porous to pyrethroids. They are axonic poisons and cause paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
of an organism. The chemical causes paralysis by keeping the sodium channels open in the neuronal membranes of an organism. The sodium channel consists of a membrane protein
Membrane protein
A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. More than half of all proteins interact with membranes.-Function:...
with a hydrophilic interior; this interior is effectively a tiny hole which is shaped exactly right to strip away the partially charged water molecules from a sodium ion and create a thermodynamically favorable way for sodium ions to pass through the membrane, enter the axon, and propagate an action potential. When the toxin keeps the channels in their open state, the nerves cannot de-excite, so the organism is paralyzed.
Pyrethroids are usually combined with piperonyl butoxide
Piperonyl butoxide
Piperonyl butoxide is an organic compound used as pesticide synergist, especially for pyrethroids and rotenone. It does not by itself have pesticidal properties. However, when added to insecticide mixtures, typically pyrethrin, pyrethroid, and carbamate insecticides, their potency is increased...
, a known inhibitor of key microsomal oxidase enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s. Piperonyl butoxide prevents the insect's enzymes from clearing the pyrethroid from its body, maximizing the lethality of the pyrethroid.
Development
Pyrethroids were introduced in the late 1900s by a team of Rothamsted Research scientists following the elucidation of the structures of pyrethrin I and II by Hermann StaudingerHermann Staudinger
- External links :* Staudinger's * Staudinger's Nobel Lecture *....
and Leopold Ružička in the 1920s. The pyrethroids represented a major advancement in insecticidal activity with relatively low mammalian toxicity and usually fast biodegradation. Their development coincided with the identification of problems with DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
use. Their work consisted firstly of identifying the most active components of pyrethrum
Pyrethrum
Pyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C...
, extracted from East African chrysanthemum flowers and long known to have insecticidal properties. Pyrethrum rapidly knocks down flying insects but has a low mammalian toxicity and negligible persistence - which is good for the environment but gives poor efficacy when applied in the field. Pyrethroids are essentially chemically stabilized forms of natural pyrethrum and belong to IRAC MoA group 3 (they interfere with sodium transport in insect nerve cells).
The 1st generation pyrethroids, developed in the 1960s, include bioallethrin
Bioallethrin
Bioallethrin is an ectoparasiticide. It consists of two of the eight stereosiomers of allethrin I....
, tetramethrin
Tetramethrin
Tetramethrin is a potent synthetic insecticide in the pyrethroid family. It is a white crystalline solid with a melting point of 65-80 °C. The commercial product is a mixture of stereoisomers....
, resmethrin
Resmethrin
Resmethrin is a pyrethroid insecticide with many uses, including control of the adult mosquito population.The resmethrin molecule has four stereoisomers determined by cis-trans orientation around a carbon triangle and chirality. Technical resmethrin is a mixture of -, -, -, - isomers, typically in...
and bioresmethrin. They are more active than the natural pyrethrum but are unstable in sunlight. Activity of pyrethrum and 1st generation pyrethroids is often enhanced by addition of the synergist piperonyl butoxide (which is not itself biologically active). With the 91/414/EEC review, many 1st generation compounds have not been included on Annex 1, probably because the market is simply not big enough to warrant the costs of re-registration (rather than any special concerns about safety).
By 1974, the Rothamsted team had discovered a 2nd generation of more persistent compounds notably: permethrin
Permethrin
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...
, cypermethrin
Cypermethrin
Cypermethrin is a synthetic pyrethroid used as an insecticide in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It behaves as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when...
and deltamethrin
Deltamethrin
Deltamethrin is a pyrethroid ester insecticide.-Usage:Deltamethrin products are among the most popular and widely used insecticides in the world and have become very popular with pest control operators and individuals in the United States in the past five years. This material is a member of one of...
. They are substantially more resistant to degradation by light and air, thus making them suitable for use in agriculture, but they have significantly higher mammalian toxicities. Over the subsequent decades these derivatives were followed with other proprietary compounds such as fenvalerate
Fenvalerate
Fenvalerate is an insecticide. It is a mixture of four optical isomers which have different insecticidal activities. The 2-S alpha configuration is the most insecticidally active isomer. Fenvalerate consists of about 23% of this isomer....
, lambda-cyhalothrin and beta-cyfluthrin. Most patents have now expired, making these compounds cheap and therefore popular (although permethrin and fenvalerate have not been re-registered under the 91/414/EEC process). One of the less desirable characteristics, especially of 2nd generation pyrethroids is that they can be irritant
Irritation
Irritation or exacerbation, in biology and physiology, is a state of inflammation or painful reaction to allergy or cell-lining damage. A stimulus or agent which induces the state of irritation is an irritant...
to the skin and eyes, so special formulations
Pesticide formulation
The biological activity of a pesticide, be it chemical or biological in nature, is determined by its active ingredient . Pesticide products very rarely consist of pure technical material. The AI is usually formulated with other materials and this is the product as sold, but it may be further...
such as capsule suspensions (CS) have been developed.
Classes of pyrethroids
The earliest pyrethoids are related to pyrethrin I and II by changing the alcohol group of the esterEster
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
of chrysanthemic acid
Chrysanthemic acid
Chrysanthemic acid is an organic compound that is related to a variety of natural and synthetic insecticides. It is related to the pyrethrin I and II, as well as the pyrethroids...
. This relatively modest change can lead to substantially altered activities. For example the 5-benzyl-3-furanyl ester called resmethrin is only weakly toxic to mammals (LD50 (rat, oral) = 2,000 mg/kg) but is 20-50x more effective than natural pyrethrum and is also readily biodegraded. Other commercially important esters include tetramethrin, allethrin, phenothrin, barthrin, dimethrin, and bioresmethrin. Another family of pyrethroids have altered acid fragment together with altered alcohol components. These require more elaborate organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. Members of this extensive class include the dichlorovinyl and dibromovinyl derivatives. Still others are tefluthrin, fenpropathrin, and bioethanomethrin.
Types
- AllethrinAllethrinThe allethrins are a pair of related synthetic compounds used in insecticides. They are synthetic pyrethroids, a synthetic form of a chemical found naturally in the chrysanthemum flower. They were first synthesized in the United States by Milton S. Schechter in 1949...
, the first pyrethroid synthesized (active ingredient of RaidRaid (insecticide)Raid is the brand name of a line of insecticides produced by SC Johnson, first launched in 1956.The initial active ingredient was the first synthetic pyrethroid, allethrin...
) - BifenthrinBifenthrinBifenthrin is a pyrethroid insecticide that affects the nervous system of insects.It was discovered and developed by FMC Corporation. Products containing bifenthrin include Talstar, Maxxthor, Capture, Brigade, Bifenthrine, Ortho Home Defense Max, Bifen IT, Bifen L/P, and Scotts LawnPro Step...
, active ingredient of Talstar, Capture, Ortho Home Defense Max, and Bifenthrine - CyfluthrinCyfluthrinCyfluthrin is a synthetic pyrethroid derivative that is used as an insecticide in restricted use pesticide and common household pesticide. It is a complex organic compound, and the commercial product is sold as a mixture of isomers. Like most pyrethroids, it is highly toxic to fish, invertebrates,...
, an active ingredient in BaygonBaygonBaygon is a pesticide brand produced by S. C. Johnson & Son. It is an insecticide used for extermination and control of many household pests and is very effective for crickets, roaches, ants, carpenter ants, spiders, silverfish, mosquito, and others...
, dichlorovinyl derivative of pyrethrin - CypermethrinCypermethrinCypermethrin is a synthetic pyrethroid used as an insecticide in large-scale commercial agricultural applications as well as in consumer products for domestic purposes. It behaves as a fast-acting neurotoxin in insects. It is easily degraded on soil and plants but can be effective for weeks when...
, including the resolved isomer alpha-cypermethrin, dichlorovinyl derivative of pyrethrin - CyphenothrinCyphenothrinCyphenothrin is a synthetic pyrethroid insecticide. It is effective against cockroaches that have developed resistance to organophosphorous and carbamate insecticides....
, active ingredient of K2000 Insect spray sold in IsraelIsraelThe State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
and the Palestinian territoriesPalestinian territoriesThe Palestinian territories comprise the West Bank and the Gaza Strip. Since the Palestinian Declaration of Independence in 1988, the region is today recognized by three-quarters of the world's countries as the State of Palestine or simply Palestine, although this status is not recognized by the... - DeltamethrinDeltamethrinDeltamethrin is a pyrethroid ester insecticide.-Usage:Deltamethrin products are among the most popular and widely used insecticides in the world and have become very popular with pest control operators and individuals in the United States in the past five years. This material is a member of one of...
, dibromovinyl derivative of pyrethrin - Esfenvalerate
- EtofenproxEtofenproxEtofenprox is a pyrethroid derivative which is used as an insecticide....
- Fenpropathrin
- FenvalerateFenvalerateFenvalerate is an insecticide. It is a mixture of four optical isomers which have different insecticidal activities. The 2-S alpha configuration is the most insecticidally active isomer. Fenvalerate consists of about 23% of this isomer....
- Flucythrinate
- ImiprothrinImiprothrinImiprothrin is a synthetic pyrethroid insecticide. It is an ingredient in some insecticide products for indoor use. It has low acute toxicity to humans, but to insects it acts as a neurotoxin causing paralysis....
, active ingredient of RaidRaid (insecticide)Raid is the brand name of a line of insecticides produced by SC Johnson, first launched in 1956.The initial active ingredient was the first synthetic pyrethroid, allethrin...
Ant & Roach Killer, synthesized to be an extremely fast-acting toxin by Sumitomo Chemical Co. in Canada. - lambda-Cyhalothrin
- MetofluthrinMetofluthrinMetofluthrin is a pyrethroid used as an insect repellent. The vapors of metofluthrin are highly effective and capable of repelling up 97% of mosquitoes in field tests. Metofluthrin is used in a variety of consumer products, called emanators, for indoor and outdoor use...
- PermethrinPermethrinPermethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...
, dichlorovinyl derivative of pyrethrin - PrallethrinPrallethrinPrallethrin is a pyrethroid insecticide.-References:* * *...
- ResmethrinResmethrinResmethrin is a pyrethroid insecticide with many uses, including control of the adult mosquito population.The resmethrin molecule has four stereoisomers determined by cis-trans orientation around a carbon triangle and chirality. Technical resmethrin is a mixture of -, -, -, - isomers, typically in...
, active ingredient of Scourge - SilafluofenSilafluofenSilafluofen is a pyrethroid insecticide....
- Sumithrin, active ingredient of AnvilAnvil (insecticide)Anvil is an insecticide widely employed to combat West Nile Virus, a mosquito-borne disease identified in approximately 10,000 residents of the United States from 1999-2006. It is sprayed in Chicago and many other cities...
- tau-Fluvalinate
- TefluthrinTefluthrinTefluthrin is a pyrethroid insecticide. It was designed to be effective against soil pests....
- TetramethrinTetramethrinTetramethrin is a potent synthetic insecticide in the pyrethroid family. It is a white crystalline solid with a melting point of 65-80 °C. The commercial product is a mixture of stereoisomers....
- TralomethrinTralomethrinTralomethrin is a pyrethroid insecticide.Tralomethrin has potent insecticidal properties; it kills by modifying the gating kinetics of the sodium channels in neurons, increasing the length of time the channel remains open after a stimulus, thereby depolarizing the neuron for a longer period of...
- TransfluthrinTransfluthrinTransfluthrin is a fast-acting pyrethroid insecticide with low persistency. It has the molecular formula C15H12Cl2F4O2.Transfluthrin can be used in the indoor environment against flies, mosquitoes and cockroaches. It is a relatively volatile substance and acts as a contact and inhalation agent....
, active ingredient in BaygonBaygonBaygon is a pesticide brand produced by S. C. Johnson & Son. It is an insecticide used for extermination and control of many household pests and is very effective for crickets, roaches, ants, carpenter ants, spiders, silverfish, mosquito, and others...
Environmental effects
Aside from the fact that they are also toxic to beneficial insects such as beeBee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s and dragonflies, pyrethroids are toxic to fish and other aquatic organisms. At extremely small levels, such as 2 parts per trillion, pyrethroids are lethal to mayflies, gadflies
Horse-fly
Insects in the order Diptera, family Tabanidae, are commonly called horse flies. Often considered pests for the bites that many inflict, they are among the world's largest true flies. They are known to be extremely noisy during flight. They are also important pollinators of flowers, especially in...
, and invertebrates that constitute the base of many aquatic and terrestrial food webs.
Pyrethroids have been found to be unaffected by secondary treatment systems at municipal wastewater treatment facilities in California. They appear in the effluent, usually at levels lethal to invertebrates.
Safety and effectiveness
Pyrethroids are considered safe because most vertebrates have sufficient enzymes required for rapid breakdown. Toxicity for vertebrates, including humans, occur at extremely high concentrations, but repeated exposure may increase health risks at lower concentration. AnaphylaxisAnaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...
has been reported after pyrethrum
Pyrethrum
Pyrethrum refers to several Old World plants of the genus Chrysanthemum which are cultivated as ornamentals for their showy flower heads. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of C. cinerariifolium and C...
exposure, but allergic reaction to pyrethroids has not been documented. Increased sensitivity occurs following repeated exposure to cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
, which is found in pyrethroids like beta-cyfluthrin (Multiple Chemical Sensitivity Awareness, J. Edward Hill, MD, President & Executive Committee Member, AMA).
A possible correlation has been noted between exposure to pyrethrins and autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
, although no causal link was established.
Resistance
BedbugBedbug
Cimicidae are small parasitic insects. The most common type is Cimex lectularius. The term usually refers to species that prefer to feed on human blood...
s have been a problem for humans for thousands of years. Up until the 1950s, they were almost completely wiped out due to the use of DDT. After DDT was banned, pyrethroids became more commonly used against bed bugs. As of 2010 a super strain of bedbugs has evolved nerve cell mutations impervious to pyrethroids. This has caused a bed bug pandemic due to ineffective treatment methods.
External links
- Pyrethrins and pyrethroids on the EXTOXNET
- Multiple Chemical Sensitivity Awareness, J. Edward Hill, MD, President & Executive Committee Member, AMA
- Environmental Health Perspectives Journal Estrogenic Potential of Certain Pyrethroid Compounds...