Glufosinate: Difference between revisions

{{Short description|Broad-spectrum herbicide}}

{{Distinguish|Glyphosate}}

| Watchedfields = changed

| verifiedrevid = 443837190

| ImageFile = Glufosinate.png

| ImageSize = 200px

| ImageAlt = Skeletal formula of glufosinate

| ImageFile1 = Glufosinate zwitterion 3D ball.png

| ImageAlt1 = Ball-and-stick model of the glufosinate zwitterion

| PIN = 2-Amino-4-[hydroxy(methylphosphonoyl)]butanoic acid

| OtherNames = Phosphinothricin

|Section1 = {{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| CASNo=51276-47-2

| CASNo1_Ref = {{cascite|changed|CAS}}

| CASNo1 = 77182-82-2

| CASNo1_Comment = (monoammonium salt)

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = C8W4FP6BTY

| EINECS = 257-102-5

| PubChem = 4794

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEBI = 52136

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| C=5 | H=12 | N=1 | O=4 | P=1

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|Section3 = {{Chembox Hazards

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'''Glufosinate''' (also known as '''phosphinothricin''' and often sold as an [[ammonium salt]]) is a naturally occurring broad-spectrum [[herbicide]] produced by several species of ''[[Streptomyces]]'' soil bacteria. Glufosinate is a non-selective, contact herbicide, with some systemic action.<ref>{{cite web |url=http://sitem.herts.ac.uk/aeru/ppdb/en/Reports/372.htm |title=glufosinate-ammonium |website=PPDB: Pesticide Properties DataBase |access-date= }}</ref> Plants may also metabolize [[bialaphos]] and [[phosalacine]], other naturally occurring herbicides, directly into glufosinate.<ref>{{cite journal | doi = 10.1128/AEM.70.12.7093-7102.2004 | pmid=15574905 | volume=70 | issue=12 | title=Biosynthetic Gene Cluster of the Herbicide Phosphinothricin Tripeptide from Streptomyces viridochromogenes Tu494 | journal=Applied and Environmental Microbiology | pages=7093–7102| pmc=535184 | year=2004 | last1=Schwartz | first1=D. | last2=Berger | first2=S. | last3=Heinzelmann | first3=E. | last4=Muschko | first4=K. | last5=Welzel | first5=K. | last6=Wohlleben | first6=W. | bibcode=2004ApEnM..70.7093S }}</ref> The compound irreversibly inhibits [[glutamine synthetase]], an enzyme necessary for the production of glutamine and for ammonia detoxification, giving it [[antibacterial]], [[antifungal]] and herbicidal properties. Application of glufosinate to plants leads to reduced [[glutamine]] and elevated [[ammonia]] levels in tissues, halting [[photosynthesis]] and resulting in plant death.<ref name=PAN>{{cite web |url = http://www.pan-uk.org/pestnews/Actives/glufosin.htm |title = Glufosinate ammonium fact sheet |date = December 1998 |access-date = |publisher = Pesticides News No.42 |last = Topsy Jewell for Friends of the Earth |archive-url = https://web.archive.org/web/20150701084024/http://www.pan-uk.org/pestnews/Actives/glufosin.htm |archive-date = 2015-07-01 |url-status = dead }}</ref>

==Discovery==

In the 1960s and early 1970s, scientists at [[University of Tübingen]] and at the [[Meiji Seika|Meiji Seika Kaisha Company]] independently discovered that species of ''[[Streptomyces]]'' bacteria produce a tripeptide they called [[bialaphos]] that inhibits bacteria; it consists of two [[alanine]] residues and a unique [[amino acid]] that is an analog of [[glutamate]] that they named "phosphinothricin".<ref name=Donn/>{{rp|90}} They determined that phosphinothricin irreversibly inhibits [[glutamine synthetase]].<ref name=Donn/>{{rp|90}} Phosphinothricin was first synthesized by scientists at [[Hoechst AG|Hoechst]] in the 1970s as a [[racemic]] mixture; this racemic mixture is called glufosinate and is the commercially relevant version of the chemical.<ref name=Donn>Donn, G and Köcher, H. Inhibitors of Glutamine Synthetase. Chapter 4 in Herbicide Classes in Development: Mode of Action, Targets, Genetic Engineering, Chemistry. Eds Peter Böger, Ko Wakabayashi, Kenji Hirai. Springer Science & Business Media, 2012 {{ISBN|9783642594168}}</ref>{{rp|91–92}}

In the late 1980s scientists discovered enzymes in these ''Streptomyces'' species that selectively inactivate free phosphinothricin; the gene encoding the enzyme that was isolated from ''[[Streptomyces hygroscopicus]]'' was called the "bialaphos resistance" or "bar" gene, and the gene encoding the enzyme in ''[[Streptomyces viridochromogenes]]'' was called "[[phosphinothricin acetyltransferase]]" or "pat".<ref name=Donn/>{{rp|98}} The two genes and their proteins have 80% homology on the DNA level and 86% amino acid homology, and are each 158 amino acids long.<ref name=Donn/>{{rp|98}}

==Use==

[[File:Glufosinate USA 2018.png|thumb|Glufosinate use in the USA in 2018]]

Glufosinate is a broad-spectrum herbicide that is used to control important weeds such as [[morning glories]], hemp sesbania ([[Sesbania bispinosa]]), Pennsylvania smartweed ([[Polygonum pensylvanicum]]) and [[yellow nutsedge]] similar to [[glyphosate]]. It is applied to young plants during early development for full effectiveness.<ref name=PAN/> It is sold in formulations under brands including Basta, Rely, Finale, Challenge and Liberty.<ref name=PAN/>

Glufosinate is typically used in three situations as an herbicide:

*directed sprays for weed control, including in [[genetically modified crops]]

*use as a [[crop desiccation]] to facilitate harvesting<ref name=moneuro>{{cite web | url=http://www.monsanto.com/products/Documents/glyphosate-background-materials/Agronomic%20benefits%20of%20glyphosate%20in%20Europe.pdf | title=The agronomic benefits of glyphosate in Europe | publisher=[[Monsanto]] Europe SA | date=February 2010 | url-status=dead | archive-url=https://web.archive.org/web/20120117143642/http://www.monsanto.com/products/Documents/glyphosate-background-materials/Agronomic%20benefits%20of%20glyphosate%20in%20Europe.pdf | archive-date=2012-01-17 }}</ref>

Glufosinate also has shown to provide some protection against various plant diseases, as it also acts to kill fungi and bacteria on contact.<ref name=Duke>Duke, SO. Biotechnology: Herbicide Resistant Crops. In Encyclopedia of Agriculture and Food Systems, 2nd edition. Ed. Neal K. Van Alfen. Elsevier, 2014. {{ISBN|9780080931395}}. [https://books.google.com/books?id=Y-VfAwAAQBAJ&pg=RA1-PA97&lpg=RA1-PA97 Page 97]</ref>

===Genetically modified crops===

[[Genetically modified crops]] resistant to glufosinate were created by [[genetic engineering|genetically engineering]] the ''bar'' or ''pat'' genes from ''streptomyces'' into the relevant crop seeds.<ref name=Donn/>{{rp|98}}<ref name=Green/> In 1995 the first glufosinate-resistant crop, canola, was brought to market, and it was followed by corn in 1997, cotton in 2004, and soybeans in 2011.<ref name=Green>Green JM and Castle LA. Transitioning from Single to Multiple Herbicide-resistant Crops. Chapter 4 in Glyphosate Resistance in Crops and Weeds: History, Development, and Management. Editor, Vijay K. Nandula. John Wiley & Sons, 2010 {{ISBN|9781118043547}} [https://books.google.com/books?id=I0PfNQPct_cC&pg=PT112 Page 112]</ref>

==Mode of action==

Phosphinothricin is a [[glutamine synthetase]] [[enzyme inhibitor|inhibitor]] that binds to the [[glutamate]] site. Glufosinate-treated plants die due to a buildup of [[ammonia]] in the [[thylakoid]] lumen, leading to the uncoupling of [[photophosphorylation]].<ref name=Duke/> The uncoupling of photophosphorylation causes the production of [[reactive oxygen species]], [[lipid peroxidation]], and membrane destruction.<ref>[http://wssa.net/wp-content/uploads/HerbicideMOAClassification.pdf Summary of Herbicide Mechanism of Action], HRAC and WSSA</ref>

Elevated levels of ammonia are detectable within one hour after application of phosphinothricin.<ref name=PAN/>

==Toxicity==

===Exposure to humans in foods===

As glufosinate is often used as a pre-harvest [[desiccant]], it can be found in foods that humans ingest. Such foods include potatoes, peas, beans, corn, wheat, and barley. In addition, the chemical can be passed to humans through animals who are fed contaminated straw. Flour processed from wheat grain that contained traces of glufosinate was found to retain 10-100% of the chemicals' residues.<ref name=monograph>{{cite web|last1=Watts|first1=Meriel|title=Glufosinate Ammonium Monograph|url=http://www.pananz.net/wp-content/uploads/2013/04/Glufosinate-monograph-12-Dec-2008.pdf|publisher=[[Pesticide Action Network]] Asia and the Pacific|access-date=20 April 2015}}</ref>

The herbicide is also persistent; it has been found to be prevalent in spinach, radishes, wheat and carrots that were planted 120 days after the treatment of the herbicide.<ref name=PAN/> Its persistent nature can also be observed by its [[half-life]] which varies from 3 to 70 days depending on the soil type and organic matter content.<ref name=PAN/> Residues can remain in frozen food for up to two years and the chemical is not easily destroyed by cooking the food item in boiling water.<ref name=monograph /> The EPA classifies the chemical as 'persistent' and 'mobile' based on its lack of degradation and ease of transport through soil.

A study revealed the presence of circulating PAGMF in women with and without pregnancy, paving the way for a new field in reproductive toxicology including nutrition and utero-placental toxicities<ref>{{cite journal | doi=10.1016/j.reprotox.2011.02.004 | title=Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada | year=2011 | last1=Aris | first1=Aziz | last2=Leblanc | first2=Samuel | journal=Reproductive Toxicology | volume=31 | issue=4 | pages=528–533 | pmid=21338670 | s2cid=16144327 }}</ref>

===Exposure limits===

There are no exposure limits established by the [[Occupational Safety & Health Administration]] or the [[American Conference of Governmental Industrial Hygienists]].<ref name="phytotechlab.com">{{cite web|url=http://phytotechlab.com/media/downloads/7382/P679MSDS.pdf |title=Chemical Identification and Company Information : DL-Phosphinothricin, Monoammonium Salt |publisher=Phytotechlab.com |access-date=2015-04-25 | url-status=dead | archive-url=https://web.archive.org/web/20160304093237/http://phytotechlab.com/media/downloads/7382/P679MSDS.pdf | archive-date=2016-03-04}}</ref> The WHO/FAO recommended acceptable daily intake (ADI) for glufosinate is 0.02&nbsp;mg/kg.<ref name=monograph /> The European Food Safety Authority has set an ADI of 0.021&nbsp;mg/kg. The Acute reference dose (ARfD) for child-bearing women is 0.021&nbsp;mg/kg.<ref name=monograph />

==Regulation==

Glufosinate is a [[United States Environmental Protection Agency]] EPA registered chemical. It is also a California registered chemical. It is not banned in the country and it is not a [[Rotterdam Convention|PIC pesticide]].<ref>{{Cite web |url=https://croplife.org/crop-protection/regulatory/product-management/prior-informed-consent/ |title=The Rotterdam Convention on Prior Informed Consent (PIC) |access-date=2015-08-07 |archive-date=2021-09-24 |archive-url=https://web.archive.org/web/20210924070647/https://croplife.org/crop-protection/regulatory/product-management/prior-informed-consent/ |url-status=dead }}</ref> There are no exposure limits established by OSHA or the American Conference of Governmental Industrial Hygienists.<ref name="phytotechlab.com"/>

Glufosinate is not approved for use as an herbicide in Europe; it was last reviewed in 2007 and that registration expired in 2018.<ref>European Commission. [https://ec.europa.eu/food/plant/pesticides/eu-pesticides-database/start/screen/active-substances/details/79 Glufosinate in EU Pesticides Database] Page accessed August 7, 2015</ref> It has been withdrawn from the French market since October 24, 2017 by the [[Agence nationale de sécurité sanitaire de l'alimentation, de l'environnement et du travail]] due to its classification as a possible [[reprotoxic]] chemical (R1b).<ref>Anses. [https://www.anses.fr/fr/content/l%E2%80%99anses-proc%C3%A8de-au-retrait-de-l%E2%80%99autorisation-de-mise-sur-le-march%C3%A9-du-basta-f1-un-produit L’Anses procède au retrait de l’autorisation de mise sur le marché du Basta F1, un produit phytopharmaceutique à base de glufosinate] Page accessed October 26, 2017</ref>

==References==

*[http://www.libertylinkhybrids.com/ 's site of LibertyLink crops]

*http://www.bayercropscience.com.au/resources//TechGuide/.pdf Basta technical guide

* {{PPDB|1540|Name=Glufosinate}}

* {{PPDB|372|Name=Glufosinate-ammonium}}

* {{PPDB|1667|Name=Glufosinate-P}}

{{Glutamate metabolism and transport modulators}}

[[Category:Ammonium compounds]]

[[Category:Alpha-Amino acids]]

[[Category:Glutamine synthetase inhibitors]]

[[Category:Eukaryotic selection compounds]]