Fenthion is an
organothiophosphate Organothiophosphates or organophosphorothioates are a subclass of organophosphorus compounds. Many are used as pesticides, some have medical applications, and some are used as oil additives. They generally have the chemical formula (RO)3PS, RO)2P( ...
insecticide,
avicide An avicide is any substance (normally a chemical) used to kill birds.
Commonly used avicides include strychnine (also used as rodenticide and predacide), DRC-1339 (3-chloro-4-methylaniline hydrochloride, Starlicide) and CPTH (3-chloro-p-toluid ...
, and
acaricide
Acaricides are pesticides that kill members of the arachnid subclass ''Acari'', which includes ticks and mites.
Acaricides are used both in medicine and agriculture, although the desired selective toxicity differs between the two fields.
Termin ...
. Like most other
organophosphate
In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...
s, its mode of action is via
cholinesterase inhibition. Due to its relatively low toxicity towards humans and mammals, fenthion is listed as moderately toxic compound in
U.S. Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
and
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
toxicity class.
[HSDB. (2003). ''Hazardous Substance Data Bank: Fenthion''. National Library of Medicine: National Toxicology Program. Available at http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB Accessed April 29, 2009.][EXTOXNET. (2003). ''Pesticide information Profile for Fenthion''. Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Available at http://pmep.cce.cornell.edu/profiles/extoxnet/dienochlor-glyphosate/fenthion-ext.html Accessed April 25, 2009.]
Uses
Fenthion is a contact and stomach insecticide used against many biting insects. It is particularly effective against fruit flies, leaf hoppers, cereal bugs, stem borers, mosquitoes, animal parasites, mites, aphids, codling moths, and weaver birds. It has been widely used in sugar cane, rice, field corn, beets, pome and stone fruit, citrus fruits, pistachio, cotton, olives, coffee, cocoa, vegetables, and vines.
[
Based on its high toxicity on birds, fenthion has been used to control weaver birds and other pest-birds in many parts of the world. Fenthion is also used in cattle, swine, and dogs to control lice, fleas, ticks, flies, and other external parasites.][USEPA. (2001). ''Interim Reregeistration Eligibility Decision for Fenthion''. United States Environmental Protection Agency. Available at http://www.epa.gov/pesticides/reregistration/REDs/0290ired.pdf Accessed April 25, 2009.][APVMA. (2005). ''Fenthion Review - Frequently asked questions''. Australian Pesticides and Veterinary Medicines Authority. Available at http://www.apvma.gov.au/chemrev/fenthion_faq.shtml Accessed April 26, 2009.]
Amid concerns of harmful effects on environment, especially birds, Food and Drug Administration
The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
no longer approves uses of fenthion. However, fenthion has been extensively used in Florida to control adult mosquitoes. After preliminary risk assessments on human health and environment in 1998 and its revision in 1999, USEPA issued an Interim Reregistration Eligibility Decision (IRED) for fenthion in January 2001. The EPA has classified fenthion as Restricted Use Pesticide
Restricted use pesticides (RUP) are pesticides not available to the general public in the United States. Fulfilling its pesticide regulation responsibilities, the United States Environmental Protection Agency (EPA) registers all pesticides and i ...
(RUP), and warrants special handling because of its toxicity.[ASTDR. (2005). ''Toxicologic Information about Insecticides Used for Eradicating Mosquitoes (West Nile Virus Control)''. Department of Health and Human Services: Agency for Toxic Substances and Disease Registry. Available at http://www.atsdr.cdc.gov/consultations/west_nile_virus/fenthion.html Accessed April 25, 2009.]
Some common trade names for fenthion are Avigel, Avigrease, Entex, Baytex, Baycid, Dalf, DMPT, Mercaptophos, Prentox, Fenthion 4E, Queletox, and Lebaycid.[ Fenthion is available in dust, emulsifiable concentrate, granular, liquid concentrate, spray concentrate, ULV, and wettable powder formulations.
]
Synthesis
Fenthion can be synthesized by condensation of 4-methylmercapto-m-cresol and dimethyl phosphorochloridothionate
Dimethyl chlorothiophosphate is a chemical that is used as an intermediate in the manufacture of pesticides and plasticisers. It is an organophosphate with sulfur and chlorine also bonded to the central phosphorus atom.
In 1985 American Cyanamid ...
.[
]
Health effects
Fenthion exposure to general population is quite limited based on its bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. ...
. Common form of fenthion exposure is occupation related, and occurs through dermal contact or inhalation of dust and sprays.[ Another likely means of contamination is through ingestion of food, especially, if it has been applied quite recently with fenthion. So far, ingestion is the most likely severe poisoning case on humans and animals.][ To avoid this, crops applied with fenthion should be allowed enough degradation time before harvesting. Normally, two to four weeks time is enough depending upon the type of crop.
Fenthion poisoning is consistent with symptoms of other organophosphate effects on human health. Primarily, the effect is cholinesterase inhibition.
]
Acute toxicity
Acute poisoning of fenthion results in miosis (pinpoint pupils), headache, nausea/vomiting, dizziness, muscle weakness, drowsiness, lethargy, agitation, or anxiety. If the poisoning is moderate or severe, it results in chest tightness, breathing difficulty, hypertension, abdominal pain, diarrhea, heavy salivation, profuse sweating, or fasciculation.[
]
Chronic toxicity
Chronic effect of fenthion has not been reported.[
]
Environmental effects
Despite short half-life in the environment, fenthion toxicity is highly significant to birds and estuarine/marine invertebrates.[ Even though some parts of the world use fenthion to control pest birds, such as ]weaver bird
Ploceidae is a family of small passerine birds, many of which are called weavers, weaverbirds, weaver finches and bishops. These names come from the nests of intricately woven vegetation created by birds in this family. In most recent classifi ...
, many non-targeted wild birds are victim of fenthion poisoning. Acute symptoms of fenthion poisoning in birds include tearing of the eyes, foamy salivation, lack of movement, tremors, congestion of the windpipe, lack of coordination in walking, and an abnormally rapid rate of breathing or difficult breathing. Fenthion has been found toxic to fishes and other aquatic invertebrates. Bees are also found to be greatly affected by fenthion contamination.[
]
Degradation in nature
Photodegradation Photodegradation is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of sunlight and air, which cause oxidation and hydrolysis. Often photodegradation is intentionally avoided, since it destroy ...
and biodegradation
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrad ...
are common mechanisms of fenthion degradation in the environment. In the atmosphere, vapor phase fenthion reacts rapidly with photochemically produced hydroxyl radicals, and its half-life is about 5 hours. In soil and water, photodegradation is again predominant mechanism if there is enough presence of sunlight.
Under normal aquatic environment, half-life of fenthion in water is 2.9 to 21.1 days.[ It may be photodynamically, chemically or biologically degraded. The degradation mechanisms can be hydrolysis, oxidation, and/or alkylation-dealkylation, which are dependent on the presence of light, temperature, alkali, or enzymatic activity.][
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Regulation
India
Fenthion was used in India for more than 30 years as a larvicide for control of mosquito larvae. The compound was on the review list of Central Insecticide Board in India and they decided to ban the product due to high toxicity for usage. The product cannot be manufactured in India after January 2017. The government of India has released the Gazzetta notification with that effect of banning many toxic insecticides such as fenthion and DDVP.
Australia
Fenthion and dimethoate were widely used to combat the Queensland fruit fly (Bactrocera tryoni), a species that has caused more than $28.5 million a year in damage to Australian fruit crops. However, it was banned in 2011 due to safety concerns.
References
External links
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{{Acetylcholine metabolism and transport modulators
Acetylcholinesterase inhibitors
Organophosphate insecticides
Thioethers
Organothiophosphate esters