Organophosphate

From Wikipedia, the free encyclopedia
Jump to: navigation, search
See also: Organophosphorus compound
General chemical structure of an organophosphate

An organophosphate (sometimes abbreviated OP) or phosphate ester is the general name for esters of phosphoric acid. Many of the most important biochemicals are organophosphates, including DNA and RNA, as well as many of the cofactors essential for life. Organophosphates are the basis of many insecticides, herbicides, and nerve agents. The United States Environmental Protection Agency lists organophosphates as very highly acutely toxic to bees, wildlife, and humans.[1] Recent studies suggest a possible link to adverse effects in the neurobehavioral development of fetuses and children, even at very low levels of exposure. Organophosphates are widely used as solvents, plasticizers, and EP additives.

Organophosphates are widely employed both in natural and synthetic applications because of the ease with which organic groups can be linked together.

OP(OH)3 + ROH → OP(OH)2(OR) + H2O
OP(OH)2(OR) + R'OH → OP(OH)(OR)(OR') + H2O
OP(OH)(OR)(OR') + R"OH → OP(OR)(OR')(OR") + H2O

The phosphate esters bearing OH groups are acidic and partially deprotonated in aqueous solution. For example, DNA and RNA are polymers of the type [PO2(OR)(OR')−]n. Polyphosphates also form esters; an important example of an ester of a polyphosphate is ATP, which is the monoester of triphosphoric acid (H5P3O10).

Alcohols can be detached from phosphate esters by hydrolysis, which is the reverse of the above reactions. For this reason, phosphate esters are common carriers of organic groups in biosynthesis.

Organophosphate pesticides[edit]

The word "organophosphates", when appearing in communications (e.g., from the press or the government), in areas such as agriculture, the environment, and human and animal health, very often refers to a group of insecticides (pesticides) that act on the enzyme acetylcholinesterase[citation needed] (see also carbamates).[citation needed] Organophosphate pesticides (OPPs), like some nerve agents, inhibit this neuromuscular enzyme, which is broadly essential for normal function in insects, but also in humans and many other animals.[2][better source needed] OPPs affect this enzyme in varied ways, a principle one being through irreversible inactivation (covalent inhibition), and so create potentials for poisoning that vary in degree.[citation needed] For instance, parathion, one of the first OPPs commercialized, is many times more potent[clarification needed] than malathion, an insecticide used in combatting the Mediterranean fruit fly (Med-fly) and West Nile Virus-transmitting mosquitoes.[citation needed] Human and animal exposure to them can be through ingestion of foods containing them, or via absorption through the skin or lungs.[2][better source needed]

The human and animal toxicity of OPPs make them a societal health and environmental concern;[2][better source needed][citation needed] the EPA banned most residential uses of organophosphates in 2001,[verification needed] but their agricultural use, as pesticides on fruits and vegetables, is still permitted, and they are as is their use in mosquito abatement in public spaces such as parks.[2][better source needed] For instance, the most commonly used OPP in the U.S., malathion,[3] sees wide application in agriculture, residential landscaping, and pest control programs (including mosquito control in public recreation areas).[4] As of 2010, forty such OPPs were registered for use in the U.S.,[5][better source needed] with at least 73 million pounds used in one time period in agricultural and residential settings.[when?][5][better source needed] Commonly used organophosphates have included:

Studies have shown that prolonged exposure to OPPs—e.g., in the case of farm workers—can lead to health problems, including increased risks for cardiovascular and respiratory disease, and cancer, and in the case of pregnant women, exposure can result in premature births.[7]

Organophosphate pesticides degrade rapidly by hydrolysis on exposure to sunlight, air, and soil, although small amounts can be detected in food and drinking water.[citation needed] Their ability to degrade made them an attractive alternative to the persistent organochloride pesticides, such as DDT, aldrin, and dieldrin.[citation needed] Although organophosphates degrade faster than the organochlorides,[citation needed] the greater acute toxicity of OPPs result in the elevated risk associated with this class of compounds (see the Toxicity section below).

Organophosphates as nerve agents[edit]

Main article: Nerve agents

History of nerve agents[edit]

Early pioneers in the field include Jean Louis Lassaigne (early 19th century) and Philippe de Clermont (1854). In 1932, German chemist Willy Lange and his graduate student, Gerde von Krueger, first described the cholinergic nervous system effects of organophosphates, noting a choking sensation and a dimming of vision after exposure. This discovery later inspired German chemist Gerhard Schrader at company IG Farben in the 1930s to experiment with these compounds as insecticides. Their potential use as chemical warfare agents soon became apparent, and the Nazi government put Schrader in charge of developing organophosphate (in the broader sense of the word) nerve gases. Schrader's laboratory discovered the G series of weapons, which included Sarin, Tabun, and Soman. The Nazis produced large quantities of these compounds, though did not use them during World War II. British scientists experimented with a cholinergic organophosphate of their own, called diisopropylfluorophosphate, during the war. The British later produced VX nerve agent, which was many times more potent than the G series, in the early 1950s, almost 20 years after the Germans had discovered the G series.

After World War II, American companies gained access to some information from Schrader's laboratory, and began synthesizing organophosphate pesticides in large quantities. Parathion was among the first marketed, followed by malathion and azinphosmethyl. The popularity of these insecticides increased after many of the organochlorine insecticides such as DDT, dieldrin, and heptachlor were banned in the 1970s.

Structural features of organophosphates[edit]

Effective organophosphates have the following structural features:

  • A terminal oxygen connected to phosphorus by a double bond, i.e. a phosphoryl group
  • Two lipophilic groups bonded to the phosphorus
  • A leaving group bonded to the phosphorus, often a halide

Terminal oxygen vs. terminal sulfur[edit]

Thiophosphoryl compounds, those bearing the P=S functionality, are much less toxic than related phosphoryl derivatives. Thiophosphoryl compounds are not active inhibitors of acetylcholinesterase in either mammals or insects; in mammals, metabolism tends to remove lipophilic side groups from the phosphorus atom, while in insects it tends to oxidize the compound, thus removing the terminal sulfur and replacing it with a terminal oxygen, which allows the compound to more efficiently act as an acetylcholinesterase inhibitor.

Fine tuning[edit]

Within these requirements, a large number of different lipophilic and leaving groups have been used. The variation of these groups is one means of fine tuning the toxicity of the compound. A good example of this chemistry are the P-thiocyanate compounds which use an aryl (or alkyl) group and an alkylamino group as the lipophilic groups. The thiocyanate is the leaving group.

One of the products of the reaction of Fc2P2S4 with dimethyl cyanamide

A German patent claimed that the reaction of 1,3,2,4-dithiadiphosphetane 2,4-disulfides with dialkyl cyanamides formed plant protection agents which contained six-membered (P-N=C-N=C-S-) rings. It has been proven in recent times by the reaction of diferrocenyl 1,3,2,4-dithiadiphosphetane 2,4-disulfide (and Lawesson's reagent) with dimethyl cyanamide that, in fact, a mixture of several different phosphorus-containing compounds is formed. Depending on the concentration of the dimethyl cyanamide in the reaction mixture, either a different six-membered ring compound (P-N=C-S-C=N-) or a nonheterocylic compound (FcP(S)(NR2)(NCS)) is formed as the major product; the other compound is formed as a minor product.

In addition, small traces of other compounds are also formed in the reaction. The ring compound (P-N=C-S-C=N-) {or its isomer} is unlikely to act as a plant protection agent, but (FcP(S)(NR2)(NCS)) compounds can act as nerve poisons in insects.

Organophosphate poisoning[edit]

Main article: Organophosphate poisoning

Many "organophosphates" are potent nerve agents, functioning by inhibiting the action of acetylcholinesterase (AChE) in nerve cells. They are one of the most common causes of poisoning worldwide, and are frequently intentionally used in suicides in agricultural areas. Organophosphosphate pesticides can be absorbed by all routes, including inhalation, ingestion, and dermal absorption. Their inhibitory effects on the acetylcholinesterase enzyme lead to a pathological excess of acetylcholine in the body. Their toxicity is not limited to the acute phase, however, and chronic effects have long been noted. Neurotransmitters such as acetylcholine (which is affected by organophosphate pesticides) are profoundly important in the brain's development, and many organophosphates have neurotoxic effects on developing organisms, even from low levels of exposure. Other organophosphates are not toxic, yet their main metabolites, such as their oxons, are. Treatment includes both a pralidoxime binder and an anticholinergic such as atropine.

Health effects[edit]

Chronic toxicity[edit]

Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure including the delayed symptoms. Other effects reported in workers repeatedly exposed include impaired memory and concentration, disorientation, severe depressions, irritability, confusion, headache, speech difficulties, delayed reaction times, nightmares, sleepwalking, drowsiness, or insomnia. An influenza-like condition with headache, nausea, weakness, loss of appetite, and malaise has also been reported.[8]

A recent study done by Madurai Kamaraj University in India have shown a direct correlation between usage of organophosphates and diabetes among Indian agricultural population. [9]

Low-level exposure[edit]

Even at relatively low levels, organophosphates may be hazardous to human health. The pesticides act on acetylcholinesterase,[10] an enzyme found in the brain chemicals closely related to those involved in ADHD, thus fetuses and young children, where brain development depends on a strict sequence of biological events, may be most at risk.[11][12] They can be absorbed through the lungs or skin or by eating them on food. According to a 2008 report from the U.S. Department of Agriculture, ″detectable″ traces of organophosphate were found in a representative sample of produce tested by the agency, 28% of frozen blueberries, 20% of celery, 27% of green beans, 17% of peaches, 8% of broccoli, and 25% of strawberries.[13]

The United States Environmental Protection Agency lists parathion as a possible human carcinogen.[14]

A 2007 study linked the organophosphate insecticide chlorpyrifos, which is used on some fruits and vegetables, with delays in learning rates, reduced physical coordination, and behavioral problems in children, especially ADHD.[15]

An organic diet is an effective way to reduce exposure to the organophosphorus pesticides commonly used in agricultural production.[16] Organophosphate metabolite levels rapidly drop, and for some metabolites, become undetectable in children's urine when an organic diet is consumed.[16] This is speculative based on a short study of 23 children, in which only a few organophosphate compounds were potentially reduced, no effect was shown for the majority of them that were found in the samples.

Occupational organophosphate exposure is associated with an increased risk of Alzheimer's disease.[17] Another study found that each 10-fold increase in urinary concentration of organophosphate metabolites was associated with a 55% to 72% increase in the odds of children being diagnosed with ADHD.[18][19][20] Researchers analyzed the levels of organophosphate residues in the urine of more than 1,100 children aged 8 to 15 years old, and found that those with the highest levels of dialkyl phosphates, which are the breakdown products of organophosphate pesticides, also had the highest incidence of ADHD. Overall, they found a 35% increase in the odds of developing ADHD with every 10-fold increase in urinary concentration of the pesticide residues. The effect was seen even at the low end of exposure; children who had any detectable, above-average level of pesticide metabolite in their urine were twice as likely as those with undetectable levels to record symptoms of ADHD.

Children who were exposed to organophosphate pesticides while still in their mother's womb were more likely to develop attention disorders years later. Children at ages 3.5 and 5 years were evaluated for symptoms of attention disorders and ADHD using maternal reports of child behavior, performance on standardized computer tests, and behavior ratings from examiners. Each 10-fold increase in prenatal pesticide metabolites was linked to having five times the odds of scoring high on the computerized tests at age 5, suggesting a greater likelihood of a child having ADHD. The effect appeared to be stronger for boys than for girls.[21]

Prenatal organophosphate exposure had a significant impact on birthweight and gestational age. A 10-fold increase in organophosphates concentrations in the mother was associated with a 0.5-week decrease in the infant's gestational age and a birth weight decline of 151 g (adjusted to account for changes in gestational age). "Diet and home pesticide use have been identified as important routes of exposure in non-agricultural populations," the researchers wrote, but noted that switching children from conventional to organic diets for several days reduced levels near or below the limit of detection, "suggesting that diet was the primary source of exposure in that study population."[22]

Proposal restrictions[edit]

According to the nongovernmental organisation Pesticide Action Network, parathion is one of the most dangerous pesticides.[23] In the US alone, more than 650 agricultural workers have been poisoned since 1966, of which 100 died. In underdeveloped countries, many more people have suffered fatal and nonfatal intoxications. The World Health Organization, PAN, and numerous environmental organisations propose a general and global ban. Its use is banned or restricted in 23 countries and its import is illegal in a total of 50 countries.[24] Its use was banned in the U.S. in 2000 and it has not been used since 2003.[24]

Other than for agricultural use, the organophosphate diazinon has been banned in the U.S. More than one million pounds of diazinon were used in California to control agricultural pests in 2000. The areas and crops on which diazinon are most heavily applied are structural pest control, almonds, head lettuce, leaf lettuce, and prunes.[25]

In May 2006, the Environmental Protection Agency (EPA) reviewed the use of dichlorvos and proposed its continued sale, despite concerns over its safety and considerable evidence suggesting it is carcinogenic and harmful to the brain and nervous system, especially in children. Environmentalists charge that the latest decision was the product of backroom deals with industry and political interference.[26]

In 2001, the EPA placed new restrictions on the use of the organophosphates phosmet and azinphos-methyl to increase protection of agricultural workers. The crop uses reported at that time as being phased out in four years included those for almonds, tart cherries, cotton, cranberries, peaches, pistachios, and walnuts. The crops with time-limited registration included apples/crab apples, blueberries, sweet cherries, pears, pine seed orchards, brussels sprouts, cane berries, and the use of azinphos-methyl by nurseries for quarantine requirements.[27] The labeled uses of phosmet include alfalfa, orchard crops (e.g. almonds, walnuts, apples, cherries), blueberries, citrus, grapes, ornamental trees (not for use in residential, park, or recreational areas) and nonbearing fruit trees, Christmas trees and conifers (tree farms), potatoes, and peas.[28] Azinphos-methyl has been banned in Europe since 2006.[29]

See also[edit]

References[edit]

  1. ^ "Basic Information". Clothianidin – Registration Status and Related Information. U.S. EPA. 27 July 2012. 
  2. ^ a b c d Goodman, Brenda (21 Apr 2011). "Pesticide Exposure in Womb Linked to Lower IQ". Health & Pregnancy. WebMD. [better source needed]
  3. ^ a b Bonner MR, Coble J, Blair A, et al. (2007). "Malathion Exposure and the Incidence of Cancer in the Agricultural Health Study". American Journal of Epidemiology. 166 (9): 1023–34. doi:10.1093/aje/kwm182. PMID 17720683. 
  4. ^ a b https://web.archive.org/web/20110307234024/http://www.epa.gov/opp00001/health/mosquitoes/malathion4mosquitoes.htm#malathion
  5. ^ a b Maugh II, Thomas H. (16 May 2010). "Study links pesticide to ADHD in children". Los Angeles Times. [better source needed]
  6. ^ "Fenitrothion". Pesticide Information Profiles. Extension Toxicology Network. Sep 1995. 
  7. ^ Morello-Frosch, Rachel; Zuk, Miriam; Jerrett, Michael; Shamasunder, Bhavna; Kyle, Amy D. (May 2011). "Understanding the Cumulative Impacts of Inequalities in Environmental Health: Implications for Policy". Health Affairs. 30 (5): 881. doi:10.1377/hlthaff.2011.0153. 
  8. ^ "PARATHION". Pesticide Information Profiles. Extension Toxicology Network. Sep 1993. 
  9. ^ "Gut microbial degradation of organophosphate insecticides-induces glucose intolerance via gluconeogenesis". 
  10. ^ "Organophosphates FAQs". Centers for Disease Control and Prevention. DHHS Department of Health and Human Services. Retrieved 6 February 2016. 
  11. ^ Jurewicz, Joanna; Hanke, Wojciech (9 Jul 2008). "Prenatal and Childhood Exposure to Pesticides and Neurobehavioral Development: Review of Epidemiological Studies". International Journal of Occupational Medicine and Environmental Health. Versita, Warsaw. 21 (2): 121–132. doi:10.2478/v10001-008-0014-z. ISSN 1896-494X. PMID 18614459. 
  12. ^ metaanalysis and inconclusive.  Missing or empty |title= (help);
  13. ^ "Study: ADHD linked to pesticide exposure". CNN. 17 May 2010. 
  14. ^ "Parathion (CASRN 56-38-2)". IRIS Summaries. U.S. EPA. 9 Aug 2012. 
  15. ^ Study Links Organophosphate Insecticide Used on Corn With ADHD. Beyond Pesticides. 5 January 2007.
  16. ^ a b Lu, Chensheng; Toepel, Kathryn; Irish, Rene; Fenske, Richard A.; Barr, Dana B.; Bravo, Roberto (2006). "Organic Diets Significantly Lower Children's Dietary Exposure to Organophosphorus Pesticides". Environmental Health Perspectives. 114 (2): 260–3. doi:10.1289/ehp.8418. PMC 1367841Freely accessible. PMID 16451864. 
  17. ^ Hayden, K.; Norton, M.; Darcey, D.; Ostbye, T.; Zandi, P.; Breitner, J. , E. A. ; Welsh-Bohmer, K. A.; For the Cache County Study Investigators (2010). "Occupational exposure to pesticides increases the risk of incident AD: the Cache County study". Neurology. 74 (19): 1524–1530. doi:10.1212/WNL.0b013e3181dd4423. PMC 2875926Freely accessible. PMID 20458069. 
  18. ^ Bouchard, Maryse F.; Bellinger, David C.; Wright, Robert O.; Weisskopf, Marc G. (17 May 2010). "Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides" (PDF). Pediatrics. American Academy of Pediatrics. 125 (6): e1270–e1277. doi:10.1542/peds.2009-3058. ISSN 1098-4275. PMC 3706632Freely accessible. PMID 20478945. 
  19. ^ Megan, Brooks (17 May 2010). "Organophosphate Pesticides Linked to ADHD". Environmental AirTechs. 
  20. ^ Klein, Sarah. Study: ADHD linked to pesticide exposure. CNN. 17 May 2010.
  21. ^ Marks, Amy R.; Harley, Kim; Bradman, Asa; Kogut, Katherine; Boyd Barr, Dana; Johnson, Caroline; et al. (19 Aug 2012). "Organophosphate Pesticide Exposure and Attention in Young Mexican-American Children: The CHAMACOS Study". Environmental Health Perspectives. 118 (12): 1768–1774. doi:10.1289/ehp.1002056. PMC 3002198Freely accessible. PMID 21126939. 
  22. ^ Rauch, SA; Braun, JM; Barr, DB; Calafat, AM; Khoury, J; Montesano, AM; et al. (20 Mar 2012). "Associations of prenatal exposure to organophosphate pesticide metabolites with gestational age and birth weight.". Environ Health Perspect. 120 (7): 1055–60. doi:10.1289/ehp.1104615. PMC 3404666Freely accessible. PMID 22476135. 
  23. ^ S. Kegley; B. Hill; S. Orme. "Parathion - Identification, toxicity, use, water pollution potential, ecological toxicity and regulatory information". Pesticide Action Network. 
  24. ^ a b "Parathion (Ethyl) - Remaining Use Canceled 9/00". Pesticide Active Ingredient Information. Cornell University. 13 Oct 2000. 
  25. ^ "Diazinon". Agrochemicals. Great Vista Chemicals. 
  26. ^ Raeburn, Paul (14 Aug 2006). "Slow-Acting". Scientific American. 
  27. ^ Hess, Glenn (1 Nov 2011). "US EPA restricts pesticides azinphos-methyl, phosmet". ICIS.com. 
  28. ^ Peck, Chuck; Aubee, Catherine (29 Mar 2010). "Risks of Phosmet Use to the Federally Threatened and Endangered California Tiger Salamander (Ambystoma californiense)" (PDF). Pesticide Effects Determinations. Environmental Fate and Effects Division, Office of Pesticide Programs. 
  29. ^ Scott, Alex (4 Aug 2008). "Europe Rejects Appeal for Use of Azinphos-methyl Pesticide". IHS Chemical Week. 

External links[edit]

Retrieved from "https://en.wikipedia.org/w/index.php?title=Organophosphate&oldid=775721770"