Glyphosate
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Glyphosate
IUPAC name [(phosphonomethyl)amino]acetic acid
Identifiers
CAS number
PubChem 3496
SMILES
 
Properties
Molecular formula C3H8NO5P
Molar mass 169.07 g mol-1
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox references

Glyphosate (N-(phosphonomethyl) glycine) is a non-selective systemic herbicide, absorbed through the leaves, injected into the bole, or applied to the stump of a tree, used to kill weeds, especially perennials and broadcast or used in the cut-stump treatment as a forestry herbicide. Some crops have been genetically engineered to be resistant to it. Glyphosate was first sold by Monsanto under the tradename Roundup, but is no longer under patent. It is now also available in other formulations, e.g. Resolva 24H, which contains glyphosate and diquat.[1]

Contents

Chemistry

Glyphosate is an aminophosphonic analogue of the natural amino acid glycine and the name is a contraction of glycine, phospho-, and -ate. Glyphosate was first discovered to have herbicidal activity in 1970 by John E. Franz, while working for Monsanto.[2] Franz received the National Medal of Technology in 1987 ,[3] and the Perkin Medal for Applied Chemistry.[4] in 1990 for his discoveries.

Biochemistry

Glyphosate kills plants by interfering with the synthesis of the amino acids phenylalanine, tyrosine and tryptophan. It does this by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which catalyzes the reaction of shikimate-3-phosphate (S3P) and phosphoenolpyruvate to form 5-enolpyruvyl-shikimate-3-phosphate (ESP). ESP is subsequently dephosphorylated to chorismate, an essential precursor in plants for the aromatic amino acids: phenylalanine, tyrosine and tryptophan.[5][6] These amino acids are used as building blocks in peptides, and to produce secondary metabolites such as folates, ubiquinones and naphthoquinone. The shikimate pathway is not present in animals, which instead obtain aromatic amino acids from their diet. Glyphosate has also been shown to inhibit other plant enzymes[7][8] and also has been found to affect animal enzymes.[9]

Use

Glyphosate is effective in killing a wide variety of plants, including grasses, broadleaf, and woody plants.[10] It has a relatively small effect on some clover species[11]. By volume, it is one of the most widely used herbicides.[12] It is commonly used for agriculture, horticulture, and silviculture purposes, as well as garden maintenance (including home use).[12]

Glyphosate is supplied in several formulations for different uses:

  • Ammonium salt.
  • Isopropyl amine salt.
  • Glyphosate acid - standalone, as ammonium salt or as isopropyl salt.

Products are supplied most commonly in formulations of 120, 240, 360, 480 and 680g active ingredient per litre. The most common formulation in agriculture is 360g, either alone or with added cationic surfactants.

For 360g formulations, European regulations allow applications of up to 12 litres per hectare for control of perennial weeds such as couch grass. More commonly, rates of 3 litres per hectare are practiced for control of annual weeds between crops[13].

Genetically modified crops

Some micro-organisms have a version of 5-enolpyruvoyl-shikimate-3-phosphate synthetase (EPSPS) that is resistant to glyphosate inhibition. The version used in genetically modified crops was isolated from Agrobacterium strain CP4 (CP4 EPSPS) that was resistant to glyphosate.[14][15] This CP4 EPSPS gene was cloned and transfected into soybeans, and in 1996, genetically modified soybeans were made commercially available.[16] This greatly improved the ability to control weeds in soybean fields since glyphosate could be sprayed on fields without hurting the crop. As of 2005, 87% of U.S. soybean fields were planted with glyphosate resistant varieties.[17][18] The use of such Roundup Ready crops has changed the herbicide use profile away from atrazine, metribuzin and alachlor. This has the benefit of reducing the dangers of herbicide run off into drinking water.[19]

Other uses

Glyphosate is one of a number of herbicides used by the United States government to spray Colombian coca fields through Plan Colombia. Its health effects, effects on legal crops, and effectiveness in fighting the war on drugs have been widely disputed.[20]

Toxicity

Glyphosate is less toxic than a number of other herbicides and pesticides, such as those from the organochlorine family.[21]

Humans

A review of the literature in 2000 concluded that "under present and expected conditions of new use, there is no potential for Roundup herbicide to pose a health risk to humans".[22] This review considered the likely effects experienced by the two groups most likely to have high exposures, herbicide applicators and children aged 1-6, noting the exposure in those subpopulations was not a health concern.[22] Glyphosate has an EPA Toxicity Class of III in 1993,[23] but more recent studies suggest that IV is appropriate for oral, dermal, and inhalation exposure.[22] It has been rated as class I (Severe) for eye irritation, however.[22]

Outside its intended use, glyphosate can be lethal. For example, with intentional poisonings there is approximately a 10% mortality for those ingesting glyphosate, compared to 70% for those ingesting paraquat.[24]

Laboratory toxicology studies suggest that other ingredients combined with glyphosate may have greater toxicity than glyphosate alone. For example, a study comparing glyphosate and Roundup found that Roundup had a greater effect on aromatase than glyphosate alone.[25]

Statistics from the Californian Environmental Protection Agencies Pesticide Illness Surveillance Program indicate that glyphosate related incidents are one of the highest reported of all pesticides.[26] However, incident count does not take into account the number of people exposed and the severity of symptoms associated with each incident.[27] For example if hospitalization is used as a measure of the severity of pesticide related incidents, then Glyphosate would be considered relatively safe, since over a 13 year period in California none of the 515 pesticide related hospitalizations recorded were attributed to glyphosate.[27]

Greenpeace states that "the acute toxicity of glyphosate is very low", but note that, as mentioned above, other added chemicals (particularly surfactants, e.g. polyoxy-ethyleneamine, POEA) can be more toxic than glyphosate itself.[10]

Other species

The direct toxicity of pure glyphosate to mammals and birds is low.[28] In vitro studies indicate glyphosate formulations could harm earthworms[29] and beneficial insects.[30] However, these results conflict with results from field studies where no effects were noted for the number of nematodes, mites, or springtails after treatment with Roundup at 2 kilograms active ingredient per hectare.[31]

Certain surfactants used in some glyphosate formulations have higher toxicity to fish and invertebrates resulting in some formulations of glyphosate not being registered for use in aquatic applications.[32] Monsanto produces glyphosate products with alternative surfactants that are specifically formulated for aquatic use, for example "Biactive" and "AquaMaster".[33] According to Monsanto, "Conservation groups have chosen glyphosate formulations because of their effectiveness against most weeds as glyphosate has very low toxicity to wildlife".[34]

When glyphosate comes into contact with the soil, it rapidly binds to soil particles and is inactivated.[35][36] Unbound glyphosate is degraded by bacteria. Low activity because of binding to soil particles suggests that glyphosate's effects on soil flora are limited. Low glyphosate concentrations can be found in many creeks and rivers in U.S. and Europe.citation needed

Mammal research indicates oral intake of 1% glyphosate induces changes in liver enzyme activities in pregnant rats and their fetuses.[37]

Endocrine disruptor debate

In vitro studies have shown glyphosate affects progesterone production in mammalian cells[38] and can increase the mortality of placental cells.[25] Whether these studies classify glyphosate as an endocrine disruptor is a matter of debate.

Some feel that in vitro studies are insufficient, and are waiting to see if animal studies show a change in endocrine activity, since a change in a single cell line may not occur in an entire organism. Additionally, current in vitro studies expose cell lines to concentrations orders of magnitude greater than would be found in real conditions, and through pathways that would not be experienced in real organism.

Others feel that in vitro studies, particularly ones identifying not only an effect, but a chemical pathway, are sufficient evidence to classify glyphosate as an endocrine disruptor, on the basis that even small changes in endocrine activity can have lasting effects on an entire organism that may be difficult to detect through whole organism studies alone. Further research on the topic has been planned, and should shed more light on the debate.

References

  1. ^ http://www.resolva-weeds.com/index.php Resolva Weeds
  2. ^ Alibhai, M. F. (2001). "Closing down on glyphosate inhibition---with a new structure for drug discovery". Proceedings of the National Academy of Sciences 98: 2944. doi:10.1073/pnas.061025898. PMID 11248008. 
  3. ^ Technology Administration: National Medal of Technology RECIPIENTS
  4. ^ People: Monsanto Scientist John E. Franz Wins 1990 Perkin Medal For Applied Chemistry, The Scientist 1990, 4(10):28 John Franz's Perkin Medal
  5. ^ The shikimate pathway - synthesis of chorismate
  6. ^ S. cerevisiae Pathway: chorismate biosynthesis
  7. ^ (Su , L.Y. et al. 1992. The relationship of glyphosate treatment to sugar metabolism in sugarcane: New physiological insights. J. Plant Physiol. 140:168-173.)
  8. ^ (Lamb, D.C. et al. 1998. Glyphosate is an inhibitor of plant cytochrome P450: Functional expression of Thlaspi arvensae cytochrome P45071B1/ reductase fusion protein in Escherichia coli. Biochem. Biophys. Res. Comm. 244:110114.)
  9. ^ (Hietanen, E., K. Linnainmaa, and H. Vainio. 1983. Effects of phenoxy herbicides and glyphosate on the hepatic and intestinal biotransformation activities in the rat. Acta Pharma. et Toxicol. 53:103-112.)
  10. ^ a b Greenpeace. (1997). Weed Killing Crops: Glyphosate and Your Food.[1]
  11. ^ Integrated Pest Management
  12. ^ a b U.S. Environmental Protection Agency. (2006). Technical Factsheet on: GLYPHOSATE [2]
  13. ^ e-phy: Le catalogue des produits phytopharmaceutiques et de leurs usages des matières fertilisantes et des supports de culture homologués en France
  14. ^ G. R. Heck, et al (2005). "Development and Characterization of a CP4 EPSPS-Based, Glyphosate-Tolerant Corn Event" (Free full text). Crop Sci. 45: 329–339. 
  15. ^ T. Funke et al (2006). "Molecular basis for the herbicide resistance of Roundup Ready crops" (Free full text). PNAS 103: 13010–13015. doi:10.1073/pnas.0603638103. PMID 16916934. 
  16. ^ Monsanto Company History - Monsanto Web Site - monsanto.com[3]
  17. ^ USDA/APHIS Environmental Assessment - In response to Monsanto Petition 06-178-01p seeking a Determination of Non-regulated Status for Roundup RReady2Yield Soybean MON 89788, OECD Unique Identifier MON-89788-1, U.S. Department of Agriculture Animal and Plant Health Inspection Service Biotechnology Regulatory Services, page 13 [4]
  18. ^ National Agriculture Statistics Service (2005) in Acreage eds. Johanns, M. & Wiyatt, S. D. 6 30, (U.S. Dept. of Agriculture, Washington, DC).
  19. ^ Shipitalo MJ, Malone RW, Owens LB (2008). "Impact of glyphosate-tolerant soybean and glufosinate-tolerant corn production on herbicide losses in surface runoff". J. Environ. Qual. 37 (2): 401–8. doi:10.2134/jeq2006.0540. PMID 18268303. 
  20. ^ IRC Americas Program Commentary (2005): Plan Colombia’s Drug Eradication Program Misses the Mark
  21. ^ Raspberry IPM Manual -Pesticide Selection
  22. ^ a b c d GM Williams, R Kroes, JC Munro (2000). "Safety evaluation and risk assessment of the herbicide Roundup and its active ingredient, glyphosate, for humans". Regulatory Toxicology and Pharmacology 31-N2: 117–165. PMID 10854122. 
  23. ^ U.S. EPA ReRegistration Decision Fact Sheet for Glyphosate (EPA-738-F-93-011) 1993. [5]
  24. ^ Nagami H, Nishigaki Y, Matsushima S, et al (2005). "Hospital-based survey of pesticide poisoning in Japan, 1998--2002". Int J Occup Environ Health 11 (2): 180–4. PMID 15875894. 
  25. ^ a b Richard S, Moslemi S, Sipahutar H, Benachour N, Seralini GE (June 2005). "Differential effects of glyphosate and roundup on human placental cells and aromatase" (Free full text). Environ. Health Perspect. 113 (6): 716–20. PMID 15929894. PMC:1257596. 
  26. ^ GGoldstein DA, Acquavella JF, Mannion RM, Farmer DR (2002). "An analysis of glyphosate data from the California Environmental Protection Agency Pesticide Illness Surveillance Program". J. Toxicol. Clin. Toxicol. 40 (7): 885–92. PMID 12507058. 
  27. ^ a b California EPA 1996, California Pesticide Illness Serveillance Program Report HS-1733 [6]
  28. ^ "pest control from ipmofalaska.com".
  29. ^ JA Springett and RAJ Gray (1992). "Effect of repeated low doses of biocides on the earthworm Aporrectodea caliginosa in laboratory culture". Soil Biol and Biochem 24 (12): 1739–1744. doi:10.1016/0038-0717(92)90180-6. 
  30. ^ Hassan, S. A. (1991). "Results of the fifth joint pesticide testing programme carried out by the IOBC/WPRS-Working Group “Pesticides and beneficial organisms”". Entomophaga 36: 55. doi:10.1007/BF02374636. 
  31. ^ CM Preston and J.A. Trofymow. 1989. Effects of glyphosate (Roundup) on biological activity of forest soils. In: Proceedings of Carnation Creek Workshop, ed. P. Reynolds. Namaimo 7-10 December 1987. Forest Canada/British Columbia ministry of forests, 122-140.
  32. ^ Response to "The impact of insecticides and herbicides on the biodiversity and productivity of aquatic communities", Monsanto Corporation Backgrounder [7]
  33. ^ Aquatic Use of Glyphosate Herbicides in Australia, Monsanto Corporation Backgrounder[8]
  34. ^ [9]
  35. ^ US EPA Reregistration Eligibility Decision - Glyphosate[10]
  36. ^ M.M. de Andréa, et al (2003 2003). "Influence of repeated applications of glyphosate on its persistence and soil bioactivity". Pesq. agropec. bras. 38 (11): 1329–1335. 
  37. ^ Daruich J, Zirulnik F, Gimenez MS (March 2001). "Effect of the herbicide glyphosate on enzymatic activity in pregnant rats and their fetuses". Environ. Res. 85 (3): 226–31. doi:10.1006/enrs.2000.4229. PMID 11237511. 
  38. ^ Walsh LP, McCormick C, Martin C, Stocco DM (August 2000). "Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (StAR) protein expression". Environ. Health Perspect. 108 (8): 769–76. PMID 10964798. 

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