DL-Phosphinothricin

From Wikipedia, the free encyclopedia
Jump to: navigation, search
DL-Phosphinothricin
DL-Phosphinotricin.png
Names
IUPAC name
(±)-Ammonium 2-amino-4-(methylphosphinato)butanoate
Other names
Glufosinate ammonium; 2-Amino-4-(hydroxymethylposphinyl)butanoic acid monoammonium salt; Phosphinothricin
Identifiers
77182-82-2 N
Jmol-3D images Image
PubChem 53597
Properties
C5H15N2O4P
Molar mass 198.16 g·mol−1
Appearance white crystalline powder
Melting point 205 °C (401 °F; 478 K)
Boiling point Decomp 245–305 °C
Hazards
GHS pictograms GHS-pictogram-exclam.svgGHS-pictogram-silhouette.svg[1]
H302, H312, H332, H360, H361, H373[1]
P260, P280, P281[1]
R-phrases R23/24/25
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N verify (what isYesY/N?)
Infobox references

DL-Phosphinothricin also known as glufosinate ammonium, is a broad-spectrum systemic herbicidal ammonium salt (a derivative of glufosinate) with the chemical formula C5H15N2O4P.[2] DL-Phosphinothricin irreversibly inhibits glutamine synthetase, an enzyme necessary for the production of glutamine and for ammonia detoxification. Application of DL-phosphinothricin to plants leads to reduced glutamine and elevated ammonia levels in tissues, halting photosynthesis, resulting in plant death.[3] It is found in many non-selective systemic herbicides.[2]

History[edit]

The discovery of the herbicidal properties of DL-phosphinothricin in the 1970s led to its use in many different commercial herbicides. The non-selective herbicidal effects made it ideal for controlling a variety of weeds in horticulture, farming and agricultural applications.

DL-phosphinothricin is typically used in three situations as an herbicide:

  • directed sprays for weed control
  • use as a crop desiccant to facilitate the harvest
  • use in genetically modified DL-phosphinothricin-resistant crops

Most DL-phosphinothricin used within the United States is with genetically modified crops.[4]

A crop sprayer

Glufosinate also has shown to provide some protection against various plant diseases, as it also acts to kill fungi and bacteria on contact.[5]

History and use of phosphinothricin-resistant crops[edit]

Glufosinate-resistance was first commercialized in canola in 1995 and has since been commercialized in other crops such as corn (1997), cotton (2004) and soybeans (2011). Utilizing the bar gene from Streptomyces hygroscopicus or the pat gene from Streptomyces viridochromeogenes, crops are transformed to resist the herbicidal properties of the chemical. The two genes encode highly homogenous phosphinothricin acetyltransferases that catalyze N-acetylation of glufosinate, converting it into a compound that does not inhibit glutamine synthetase.[4] Use of the bar or pat genes produces a very high level of resistance to the herbicide throughout the plant's life.[citation needed]

Production[edit]

Properties and chemistry[edit]

DL-Phosphinothricin is a broad-spectrum herbicide. It is used to control important weeds such as morning glories, hemp sesbania (Sesbania bispinosa), Pennsylvania smartweed (Polygonum pensylvanicum) and yellow nutsedge similar to a formerly used broad-spectrum herbicide, glyphosate. DL-Phosphinothricin is applied to young plants during early development for full effectiveness.[3] It is found in many nonselective systemic herbicides such as Basta, Rely, Finale, Challenge and Liberty. [3]

Biochemistry[edit]

Phosphinothricin is produced by various species of actinomycetes as a component of non-ribosomally synthesized peptides, for example, the tripeptide bialaphos from Streptomyces viridochromeogenes. Bialaphos is hydrolyzed to L-phosphinothricin which directly acts as the irreversible inhibitor of glutamine synthetase (GS). Inhibition of this enzyme causes a buildup of ammonia (NH3), one of its substrates. In chloroplasts, the resulting elevated level of ammonia has a toxic effect.[5] Elevated levels of ammonia are detectable within one hour after application of Phosphinothricin.[3]

Human exposure sources[edit]

Exposure to humans in foods[edit]

As DL-phosphinothricin is often used as a pre-harvest desiccant, residues can also 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 DL-phosphinothricin was found to retain 10-100% of the chemicals' residues.[6]

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.[3] 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.[3] 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. [6]The EPA classifies the chemical as 'persistent' and 'mobile' based on its lack of degradation and ease of transport through soil.

Exposure limits[edit]

There are no exposure limits established by the Occupational Safety & Health Administration or the American Conference of Governmental Industrial Hygienists.[1] The WHO/FAO recommended acceptable daily intake (ADI) for glufosinate is 0.02 mg/kg.[6] The European Food Safety Authority has set an ADI of 0.021 mg/kg. The Acute reference dose (ARfD) for child-bearing women is 0.021 mg/kg. [6]

US regulation[edit]

Glufosinate ammonium is a United States Environmental Protection Agency EPA registered chemical. It is also a California registered chemical. It is not banned in any country and it is not a PIC pesticide.[clarification needed] There are no exposure limits established by OSHA or the American Conference of Governmental Industrial Hygienists.[1]

References[edit]

  1. ^ a b c d e "Chemical Identification and Company Information : DL-Phosphinothricin, Monoammonium Salt" (PDF). Phytotechlab.com. Retrieved 2015-04-25. 
  2. ^ a b Caspi, R. (August 2009). "MetaCyc Compound Class: phosphinothricin". "MetaCyc" Compound Class: phosphinothricin. SRI International Pathway Tools version 19.0. Retrieved March 2015. 
  3. ^ a b c d e f Topsy Jewell for Friends of the Earth (December 1998). "Glufosinate ammonium fact sheet". Pesticides News No.42. Retrieved March 2015. 
  4. ^ a b Nandula, Vijay K (December 2010). "Glyphosate Resistance in Crops and Weeds: History, Development, and Management". John Wiley & Sons. Retrieved March 2015. 
  5. ^ a b "Encyclopedia of Agriculture and Food Systems: 5-volume set - Google Books". Books.google.com. 2014-07-29. Retrieved 2015-04-25. 
  6. ^ a b c d Watts, Meriel. "Glufosinate Ammonium Monograph" (PDF). Pesticide Action Network Asia and the Pacific. Retrieved 20 April 2015. 

Further reading[edit]