Pyrethrin

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Chemical structure of some pyrethrins: pyrethrin I (R=CH3), pyrethrin II (R=CO2CH3) Pyrethrin.svg
Chemical structure of some pyrethrins: pyrethrin I (R=CH3), pyrethrin II (R=CO2CH3)

The pyrethrins are a class of organic compounds normally derived from Chrysanthemum cinerariifolium that have potent insecticidal activity by targeting the nervous systems of insects. Pyrethrin naturally occurs in chrysanthemum flowers and is often considered an organic insecticide when it is not combined with piperonyl butoxide or other synthetic adjuvants. [1] Their insecticidal and insect-repellent properties have been known and used for thousands of years.

Contents

Pyrethrins are gradually replacing organophosphates and organochlorides as the pesticides of choice as the latter compounds have been shown to have significant and persistent toxic effects to humans.They first appeared on markets in the 1900's and have been continually used since then in products such as bug bombs, building insect sprays, and even to spray animals so that they do not get infectious diseases. [2]

Chemistry

Physical and chemical properties of some pyrethrins.
GroupPyrethrin IPyrethrin II
Chemical compoundPyrethrin I [3] [4] Cinerin I [5] [4] Jasmolin I [6] Pyrethrin II [7] [4] Cinerin II [8] [4] Jasmolin II [9]
Chemical structure Pyrethrin-I-2D-skeletal.svg Cinerin-I-2D-skeletal.svg Jasmolin-I-2D-skeletal.svg Pyrethrin-II-2D-skeletal.svg Cinerin-II-2D-skeletal.svg Jasmolin-II-2D-skeletal.svg
Chemical formulaC21H28O3C20H28O3C21H30O3C22H28O5C21H28O5C22H30O5
Molecular mass (g/mol)328.4316.4330.5372.5360.4374.5
Boiling point (°C)170137?200183?
Vapor pressure at 25 °C (mmHg)2.03×10−51.13×10−6?3.98×10−74.59×10−7?
Solubility in water (mg/L)0.20.085?9.00.03?

History

The pyrethrins occur in the seed cases of the perennial plant pyrethrum ( Chrysanthemum cinerariaefolium), which has long been grown commercially to supply the insecticide. Pyrethrins have been used as an insecticide for thousands of years. It is believed that the Chinese crushed chrysanthemum plants and used the powder as an insecticide as early as 1000 BC. It was widely known that the Zhou Dynasty in China widely used pyrethrin for its insecticide properties. [10] For centuries, crushed Chrysanthemum flowers have been used in Iran to produce Persian Powder, an insecticide for household use. Pyrethrins were identified as the potent chemical in the Chrysanthemum plants responsible for the insecticidal properties in the crushed flowers around 1800 in Asia. In the Napoleonic Wars, French soldiers used the flowers to keep away fleas and body lice. [10] [ dubious – discuss ]

Biosynthesis

Cyclopropanation reaction producing chrysanthemyl diphosphate, an intermediate in the biosynthesis of chrysanthemic acid CCPaseRxn'.png
Cyclopropanation reaction producing chrysanthemyl diphosphate, an intermediate in the biosynthesis of chrysanthemic acid

Well after their use as insecticides began, their chemical structures were determined by Hermann Staudinger and Lavoslav Ružička in 1924. [11] Pyrethrin I (CnH28O3) and pyrethrin II (CnH28O5) are structurally related esters with a cyclopropane core. Pyrethrin I is a derivative of (+)-trans-chrysanthemic acid. [12] [13] Pyrethrin II is closely related, but one methyl group is oxidized to a carboxymethyl group, the resulting core being called pyrethric acid. Knowledge of their structures opened the way for the production of synthetic analogues, which are called pyrethroids. Pyrethrins are classified as terpenoids. The key step in the biosynthesis of the naturally occurring pyrethrins involves two molecules of dimethylallyl pyrophosphate, which join to form a cyclopropane ring by the action of the enzyme chrysanthemyl diphosphate synthase. [14]

Production

Tanacetum cinerariifolium also called the Dalmatian chrysanthemum Tanacetum cinerariifolium1.jpg
Tanacetum cinerariifolium also called the Dalmatian chrysanthemum

Commercial pyrethrin production mainly takes place in mountainous equatorial zones. The commercial cultivation of the Dalmatian chrysanthemum (C. cinerariifolium) takes place at an altitude of 1600 to 3000 meters [15] above sea level. [16] This is done because pyrethrin concentration has been shown to increase as elevation increases to this level. Growing these plants does not require much water because semiarid conditions and a cool winter deliver optimal pyrethrin production. The Persian chrysanthemum C. coccineum also produces pyrethrins but at a much lower level. Both may be planted in low-altitude zones in dry soil, but the pyrethrin level is lower. [15]

Most of the world's supply of pyrethrin and C. cinerariaefolium comes from Kenya, which produces the most potent flowers. Other countries include Croatia (in Dalmatia) and Japan. The flower was first introduced into Kenya and the highlands of Eastern Africa during the late 1920s. Since the 2000s, Kenya has produced about 70% of the world's supply of pyrethrum. [17] A substantial amount of the flowers are cultivated by small-scale farmers who depend on it as a source of income. It is a major source of export income for Kenya and source of over 3,500 additional jobs. About 23,000 tons were harvested in 1975. The active ingredients are extracted with organic solvents to give a concentrate containing the six types of pyrethrins: pyrethrin I, pyrethrin II, cinerin I, cinerin II, jasmolin I, and jasmolin II. [18]

Processing the flowers to cultivate the pyrethrin is often a lengthy process, and one that varies from area to area. For instance, in Japan, the flowers are hung upside down to dry which increases pyrethrin concentration slightly. [15] To process pyrethrin, the flowers must be crushed. The degree to which the flower is crushed has an effect on both the longevity of the pyrethrin usage and the quality. The finer powder produced is better suited for use as an insecticide than the more coarsely crushed flowers. However, the more coarsely crushed flowers have a longer shelf life and deteriorate less. [15]

Use as an insecticide

Pyrethrin is most commonly used as an insecticide and has been used for this purpose since the 1900s. [18] In the 1800s, it was known as "Persian powder", "Persian pellitory", and "zacherlin". Pyrethrins delay the closure of voltage-gated sodium channels in the nerve cells of insects, resulting in repeated and extended nerve firings. This hyperexcitation causes the death of the insect due to loss of motor coordination and paralysis. [19] Resistance to pyrethrin has been bypassed by pairing the insecticide with synthetic synergists such as piperonyl butoxide. Together, these two compounds prevent detoxification in the insect, ensuring insect death. [20] Synergists make pyrethrin more effective, allowing lower doses to be effective. Pyrethrins are effective insecticides because they selectively target insects rather than mammals due to higher insect nerve sensitivity, smaller insect body size, lower mammalian skin absorption, and more efficient mammalian hepatic metabolism. [21] Also, mammals are able to process pyrethrin quickly and have higher body temperatures which prevent pyrethrin from working effectively [22]

Although pyrethrin is a potent insecticide, it also functions as an insect repellent at lower concentrations. Observations in food establishments demonstrate that flies are not immediately killed, but are found more often on windowsills or near doorways. This suggests, due to the low dosage applied, that insects are driven to leave the area before dying. [23] Because of their insecticide and insect repellent effect, pyrethrins have been very successful in reducing insect pest populations that affect humans, crops, livestock, and pets, such as ants, spiders, and lice, as well as potentially disease-carrying mosquitoes, fleas, and ticks.

As pyrethrins and pyrethroids are increasingly being used as insecticides, the number of illnesses and injuries associated with exposure to these chemicals is also increasing. [24] However, few cases leading to serious health effects or mortality in humans have occurred, which is why pyrethroids are labeled "low-toxicity" chemicals and are ubiquitous in home-care products. [21] Pyrethrins are widely regarded as better for the environment, and can be harmless if used only in the field with localized sprays, as UV exposure breaks them down into harmless compounds. Additionally, they have little lasting effect on plants, degrading naturally or being degraded by the cooking process. [25]

Specific pest species that have been successfully controlled by pyrethrum include: potato, beet, grape, and six-spotted leafhopper, cabbage looper, celery leaf tier, Say's stink bug, twelve-spotted cucumber beetle, lygus bugs on peaches, grape and flower thrips, and cranberry fruitworm. [26]

Toxicity

Pyrethrins are among the safest insecticides on the market due to their rapid degradation in the environment.

Similarities between the chemistry of pyrethrins and synthetic pyrethroids include a similar mode of action and almost identical toxicity to insects (i.e., both pyrethrins and pyrethroids induce a toxic effect within the insect by acting on sodium channels). [27]

Some differences in the chemistry between pyrethrins and synthetic pyrethroids have the result that synthetic pyrethroids have relatively longer environmental persistence than do pyrethrins. Pyrethrins have shorter environmental persistence than synthetic pyrethroids because their chemical structure is more susceptible to the presence of UV light and changes in pH.[ citation needed ]

The use of pyrethrin in products such as natural insecticides and pet shampoo, for its ability to kill fleas, increases the likelihood of toxicity in mammals that are exposed. Medical cases have emerged showing fatalities from the use of pyrethrin, prompting many organic farmers to cease use. One fatal case of an 11-year-old girl with a known asthmatic condition and who used shampoo containing only a small amount (0.2% pyrethrin) to wash her dog was documented. [28]

Chronic pyrethrin toxicity in humans

Chronic toxicity in humans occurs most quickly through respiration into the lungs, or more slowly through absorption through the skin. [29] Allergic reactions may occur after exposure, leading to itching and irritated skin as well as burning sensations. [30] These types of reactions are rare because the allergenic component of pyrethrin in semi-synthetic pyrethroids has been removed. [31] The metabolite compounds of pyrethrin are less toxic to mammals than their originators, and compounds are either broken down in the liver or gastrointestinal tract, or excreted through feces; no evidence of storage in tissues has been found [ citation needed ].

Pyrethrum toxicity

Exposure to pyrethrum, the crude form of pyrethrin, [31] causes harmful health effects for mammals. Pyrethrum also has an allergenic effect that commercial pyrethroids don't have. [31] In mammals, toxic exposure to pyrethrum can lead to tongue and lip numbness, drooling, lethargy, muscle tremors, respiratory failure, vomiting, diarrhea, seizures, paralysis, and death. [29] Exposure to pyrethrum in high levels in humans may cause symptoms such as asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, loss of coordination, tremors, convulsions, facial flushing, and swelling. [32] [ unreliable source? ] A possibility of damage to the immune system exists that leads to a worsening of allergies following toxicity. [29] Infants are unable to resourcefully break down pyrethrum due to the ease of skin penetration, causing similar symptoms as adults, but with an increased risk of death. [33]

Environmental effects

Aquatic habitats

In aquatic settings, toxicity of pyrethrin fluctuates, increasing with rising temperatures, water, and acidity. Run-off after application has become a concern for sediment-dwelling aquatic organisms because pyrethroids can accumulate in these areas. [34] Aquatic life is extremely susceptible to pyrethrin toxicity, and has been documented in species such as the lake trout. Although pyrethrins are quickly metabolized by birds and most mammals, fish and aquatic invertebrates lack the ability to metabolize these compounds, leading to a toxic accumulation of byproducts. [29] To combat the accumulation of pyrethroids in bodies of water, the Environmental Protection Agency (EPA) has introduced two labeling initiatives. The Environmental Hazard and General Labeling for Pyrethroid and Synergized Pyrethrins Non-Agricultural Outdoor Products was revised in 2013 to reduce runoff into bodies of water after use in residential, commercial, institutional, and industrial areas. [35] The Pyrethroid Spray Drift Initiative updated language for labeling all pyrethroid products to be used on agricultural crops. [35] Because of its high toxicity to fish and aquatic invertebrates even at low doses, the EPA recommends alternatives such as pesticide-free methods or alternative chemicals that are less harmful to the surrounding aquatic environment. [36]

Terrestrial Habitats

Pyrethrin is mainly used on land and can also have impacts in the places that it is used. For instance pyrethrin has the ability to be persistent in the fields that it is sprayed on. This persistence in crops can lead to negative effects for meat production. [37]

Bees

Pyrethrins are applied broadly as nonspecific insecticides. Bees have been shown to be particularly sensitive to pyrethrin, with fatal doses as small as 0.02 micrograms. [1] Due to this sensitivity and pollinator decline, pyrethrins are recommended to be applied at night to avoid typical pollinating hours, and in liquid rather than dust form. [38]

Related Research Articles

<span class="mw-page-title-main">Pesticide</span> Substance used to destroy pests

Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampricide. The most common of these are herbicides, which account for approximately 50% of all pesticide use globally. Most pesticides are intended to serve as plant protection products, which in general, protect plants from weeds, fungi, or insects. In general, a pesticide is a chemical or biological agent that deters, incapacitates, kills, or otherwise discourages pests. Target pests can include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, cause nuisance, or spread disease, or are disease vectors. Along with these benefits, pesticides also have drawbacks, such as potential toxicity to humans and other species.

<span class="mw-page-title-main">Insecticide</span> Pesticide used against insects

Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to be a major factor behind the increase in the 20th-century's agricultural productivity. Nearly all insecticides can significantly alter ecosystems; many are toxic to humans and/or animals; some become concentrated as they spread along the food chain.

Pyrethrum was a genus of several Old World plants now classified as Chrysanthemum or Tanacetum which are cultivated as ornamentals for their showy flower heads. Pyrethrum continues to be used as a common name for plants formerly included in the genus Pyrethrum. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of Chrysanthemum cinerariifolium and Chrysanthemum coccineum. The insecticidal compounds present in these species are pyrethrins.

<span class="mw-page-title-main">Piperonyl butoxide</span> Chemical compound

Piperonyl butoxide (PBO) is a pale yellow to light brown liquid organic compound used as a synergist component of pesticide formulations. That is, despite having no pesticidal activity of its own, it enhances the potency of certain pesticides such as carbamates, pyrethrins, pyrethroids, and rotenone. It is a semisynthetic derivative of safrole.

<span class="mw-page-title-main">Bifenthrin</span> Chemical compound

Bifenthrin is a pyrethroid insecticide. It is widely used against ant infestations.

<span class="mw-page-title-main">Pyrethroid</span> Class of insecticides

A pyrethroid is an organic compound similar to the natural pyrethrins, which are produced by the flowers of pyrethrums. Pyrethroids are used as commercial and household insecticides.

<span class="mw-page-title-main">Permethrin</span> Medication and insecticide

Permethrin is a medication and an insecticide. As a medication, it is used to treat scabies and lice. It is applied to the skin as a cream or lotion. As an insecticide, it can be sprayed onto outer clothing or mosquito nets to kill the insects that touch them.

Persian powder is an insecticide powder. It is also known as Persian pellitory and insect powder.

<span class="mw-page-title-main">Allethrins</span> Class of synthetic chemicals used as insecticides

The allethrins are a group of related synthetic compounds used in insecticides. They are classified as pyrethroids, i.e. synthetic versions of pyrethrin, a chemical with insecticidal properties found naturally in Chrysanthemum flowers. They were first synthesized in the United States by Milton S. Schechter in 1949. Allethrin was the first pyrethroid.

<span class="mw-page-title-main">Phenothrin</span> Chemical compound

Phenothrin, also called sumithrin and d-phenothrin, is a synthetic pyrethroid that kills adult fleas and ticks. It has also been used to kill head lice in humans. d-Phenothrin is used as a component of aerosol insecticides for domestic use. It is often used with methoprene, an insect growth regulator that interrupts the insect's biological lifecycle by killing the eggs.

<span class="mw-page-title-main">Chrysanthemic acid</span> Chemical compound

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. One of the four stereoisomers, (1R,3R)- or (+)-trans-chrysanthemic acid (pictured), is the acid part of the ester pyrethrin I, which occurs naturally in the seed cases of Chrysanthemum cinerariaefolium. Many synthetic pyrethroids, for example the allethrins, are esters of all four stereoisomers. Staudinger and Ružička named chrysanthemic acid in 1924.

<span class="mw-page-title-main">Cyhalothrin</span> Synthetic pyrethroid used as insecticide

Cyhalothrin is the ISO common name for an organic compound that, in specific isomeric forms, is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as cyhalothrin are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables.

A fogger is any device that creates a fog, typically containing an insecticide for killing insects and other arthropods. Foggers are often used by consumers as a low cost alternative to professional pest control services. The number of foggers needed for pest control depends on the size of the space to be treated, as stated for safety reasons on the instructions supplied with the devices. The fog may contain flammable gases, leading to a danger of explosion if a fogger is used in a building with a pilot light or other naked flame.

<span class="mw-page-title-main">Cyfluthrin</span> Chemical compound

Cyfluthrin is a pyrethroid insecticide 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 and invertebrates, but it is far less toxic to humans. It is generally supplied as a 10–25% liquid concentrate for commercial use and is diluted prior to spraying onto agricultural crops and outbuildings.

<span class="mw-page-title-main">Mosquito coil</span> Incense coil designed to repel mosquitoes

A mosquito coil is a mosquito-repelling incense, usually made into a spiral, and typically made using dried paste of pyrethrum powder. The coil is usually held at the center of the spiral, suspending it in the air, or wedged by two pieces of fireproof netting to allow continuous smoldering. Burning usually begins at the outer end of the spiral and progresses slowly toward the center of the spiral, producing a mosquito-repellent smoke. A typical mosquito coil measures around 15 centimetres (6 in) in diameter and lasts around seven to twelve hours. Mosquito coils are widely used in Asia, Africa, South America, Canada, Mexico and Australia.

<i>Tanacetum cinerariifolium</i> Species of flowering plant

Tanacetum cinerariifolium is a species of flowering plant in the aster family, Asteraceae, and formerly part of the genus Pyrethrum, but now placed in the genus Chrysanthemum, or the genus Tanacetum by some biologists. It is called the Dalmatian chrysanthemum or Dalmatian pyrethrum, denoting its origin in that region of Europe (Dalmatia). It looks more like the common daisy than other pyrethrums do. Its flowers, typically white with yellow centers, grow from numerous fairly rigid stems. Plants have blue-green leaves and grow to 45 to 100 cm in height.

<span class="mw-page-title-main">Howard Garrett</span>

Howard Garrett, known as "the Dirt Doctor" is a radio talk show host and a leader of the Organic movement. He is a health activist, arborist, newspaper columnist and organic activist living in Dallas, Texas. He received his Bachelor of Science degree in Park Administration and Landscape Architecture from Texas Tech University in 1969. After serving in the U.S. Marine Corps Reserve, Garrett worked at Club Corporation of America, where he was a laborer and assistant golf course superintendent.

<span class="mw-page-title-main">Tefluthrin</span> Synthetic pyrethroid used as insecticide

Tefluthrin is the ISO common name for an organic compound that is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as tefluthrin are often preferred as active ingredients in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. It is effective against soil pests because it can move as a vapour without irreversibly binding to soil particles: in this respect it differs from most other pyrethroids.

<span class="mw-page-title-main">Antifeedant</span>

Antifeedants are organic compounds produced by plants to repel herbivores through distaste or toxicity. These chemical compounds are typically classified as secondary metabolites in that they are not essential for the metabolism of the plant, but instead confer longevity. Antifeedants exhibit a wide range of activities and chemical structures as biopesticides. Examples include rosin, which inhibits attack on trees, and many alkaloids, which are highly toxic to specific insect species. Such as quassinoids against the diamondback moth. Samadera indica also has quassinoids used for insect antifeedant uses.

<span class="mw-page-title-main">Fenpropathrin</span> Chemical compound

Fenpropathrin, or fenopropathrin, is a widely used pyrethroid insecticide in agriculture and household. Fenpropathrin is an ingestion and contact synthetic pyrethroid. Its mode of action is similar to other natural (pyrethrum) and synthetic pyrethroids where in they interfere with the kinetics of voltage gated sodium channels causing paralysis and death of the pest. Fenpropathrin was the first of the light-stable synthetic pyrethroids to be synthesized in 1971, but it was not commercialized until 1980. Like other pyrethroids with an α-cyano group, fenpropathrin also belongs to the termed type II pyrethroids. Type II pyrethroids are a more potent toxicant than type I in depolarizing insect nerves. Application rates of fenpropathrin in agriculture according to US environmental protection agency (EPA) varies by crop but is not to exceed 0.4 lb ai/acre.

References

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  35. 1 2 "Environmental Hazard and General Labeling for Pyrethroid Non-Agricultural Outdoor Products". EPA. Feb 2013.
  36. ↑ "Pyrethroids and Pyrethrins." EPA. Environmental Protection Agency, Dec. 2013. Web. 26 Apr. 2015. <http://www.epa.gov/oppsrrd1/reevaluation/pyrethroids-pyrethrins.html#eco>
  37. ↑ Farag, Mayada R.; Alagawany, Mahmoud; Bilal, Rana M.; Gewida, Ahmed G. A.; Dhama, Kuldeep; Abdel-Latif, Hany M. R.; Amer, Mahmoud S.; Rivero-Perez, Nallely; Zaragoza-Bastida, Adrian; Binnaser, Yaser S.; Batiha, Gaber El-Saber; Naiel, Mohammed A. E. (2021-06-25). "An Overview on the Potential Hazards of Pyrethroid Insecticides in Fish, with Special Emphasis on Cypermethrin Toxicity". Animals. 11 (7): 1880. doi: 10.3390/ani11071880 . ISSN   2076-2615. PMC   8300353 . PMID   34201914.
  38. ↑ Hooven, L., R. Sagili, and E. Johansen. "How to Reduce Bee Poisoning from Pesticides." (n.d.): n. pag. Oregon State University, Dec. 2006. Web. 23 Mar. 2015. <http://www.ipm.ucdavis.edu/PDF/PMG/pnw591.pdf>
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