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Roundup



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Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (June 2007)
Roundup
Other names Glyphosate
Identifiers
CAS number 1071-83-6
Properties
Molecular formula C3H8NO5P
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Roundup is the brand name of a systemic, broad-spectrum herbicide produced by the U.S. company Monsanto and contains the active ingredient glyphosate. Glyphosate is the most used herbicide in the USA[1] and is the most-sold agrichemical of all time.[citation needed] In the US 5-8 million pounds are used every year on lawns and yards and 85-90 million pounds are used annually in US agriculture.[1]

Monsanto developed and patented the glyphosate molecule in the 1970s, and marketed Roundup from 1973. It retained exclusive rights in the US until its US patent expired in September, 2000, and maintained a predominant marketshare in countries where the patent expired earlier.

The active ingredient of Roundup is the isopropylamine salt of glyphosate. Glyphosate's mode of action is to inhibit an enzyme involved in the synthesis of the amino acids tyrosine, tryptophan and phenylalanine. It is absorbed through foliage and translocated to growing points. Weeds and grass will generally re-emerge within one to two months after usage. Because of this mode of action, it is only effective on actively growing plants; it is not effective as a pre-emergence herbicide. Monsanto also produces seeds which grow into plants genetically engineered to be tolerant to glyphosate which are known as Roundup Ready crops. The genes contained in these seeds are patented. Such crops allow farmers to use glyphosate as a post-emergence pesticide against both broadleaf and cereal weeds. Soy was the first Roundup Ready crop and was produced at Monsanto's Agracetus Campus located in Middleton, Wisconsin. In May 2007, a federal court decision barred new plantings of Roundup Ready alfalfa and the resale of seeds, due to the failure of regulators to complete an environmental impact statement examining the potential that genetically-modified alfalfa would contaminate non-GM alfalfa crops, encourage new weeds tolerant to herbicides and limit export markets.

Contents

Chemistry

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

Biochemistry

Glyphosate kills plants 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.[4][5] These amino acids are used as building blocks in peptides and to produce secondary metabolites such as folates, ubiquinones and naphthoquinone. X-ray crystallographic studies of Glyphosate and EPSPS shows that glyphosate functions by occupying the binding site of the phosphoenol pyruvate, mimicking an intermediate state of the ternary enzyme substrates complex.[6] The shikimate pathway is not present in animals, which 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]

Health, ecological concerns and controversy

Toxicity and ecological impact

Roundup is classed as a "moderately toxic" herbicide in EPA toxicity class II.[10] A 2000 review of the available literature concluded that "under present and expected conditions of new use, there is no potential for Roundup herbicide to pose a health risk to humans".[11] The Northwest Coalition for Alternatives to Pesticides disputes this classification.[12]

False advertising

In 1996 Monsanto was accused of false and misleading advertising of glyphosate products, prompting a law suit by the New York State attorney general.[13] More recently, Monsanto was convicted of false advertising of Roundup for aquatic applications in Europe, and it is currently appealing the verdict.[14]

Human and mammalian toxicity

Glyphosate itself is practically nontoxic by ingestion or by skin contact. The acute oral toxicity of Roundup is > 5,000 mg/kg in the rat.[15] It showed no toxic effects when fed to animals for 2 years, and only produced rare cases of reproductive effects when fed in extremely large doses to rodents and dogs. It has not demonstrated any increase in cancer rates in animal studies and is poorly absorbed in the digestive tract. Glyphosate has no significant potential to accumulate in animal tissue. [16][17]

A review of the toxicological data on Roundup shows that there are at least 58 studies of the effects of Roundup itself on a range of organisms.[18] This review concluded that "for terrestrial uses of Roundup minimal acute and chronic risk was predicted for potentially exposed nontarget organisms". It also concluded that there were some risks to aquatic organisms exposed to Roundup in shallow water. More recent research indicates glyphosate induces a variety of functional abnormalities in fetuses and pregnant rats.[19] Also in recent mammalian research, glyphosate has been found to interfere with an enzyme involved testosterone production in mouse cell culture[20] and to interfere with an estrogen biosynthesis enzyme in cultures of Human Placental cells.[21]

Studies have shown that the application of Roundup on wheat crops a week before harvesting results in higher glyphosate residue in the resulting grain and in the baked flour. [22]

The United States Environmental Protection Agency,[23] the EC Health and Consumer Protection Directorate, and the UN World Health Organization have all concluded that pure glyphosate is not carcinogenic. Opponents of glyphosate claim that Roundup has been found to cause genetic damage, citing Peluso et al.[24] The authors concluded that the damage was "not related to the active ingredient, but to another component of the herbicide mixture.

Aquatic effects

Fish and aquatic invertebrates are more sensitive to Roundup than terrestrial organisms.[18] Glyphosate is generally less persistent in water than in soil, with 12 to 60 day persistence observed in Canadian pond water, yet persistence of over a year have been observed in the sediments of ponds in Michigan and Oregon.[25]

Roundup is not registered for aquatic uses[26] and studies of its effects on amphibians indicates it is toxic to them.[27] Glyphosate formulations that are registered for aquatic use have been found to have negligible adverse effects on sensitive amphibians.[28]

Environmental degradation and effects

When glyphosate comes into contact with the soil it can be rapidly bound to soil particles and be inactivated.[25] Unbound glyphosate can be degraded by bacteria.[29] Low activity because of binding to soil particles suggests that glyphosate's effects on soil flora will be limited.[citation needed] Low glyphosate concentrations can be found in many creeks and rivers in U.S. and Europe,[citation needed] and in the US glyphosate has been called "relatively persistent" by its EPA.[25]

In soils, half lives vary from as little as 3 days at a site in Texas, 141 days at a site in Iowa, to between 1 - 3 years in Swedish forest soils.[30] It appears that more northern sites have the longest soil persistences such as in Canada and Scandinavia.

However, the binding of glyphosate to particulates can be an advantage. Treatment of industrial wastewater using immobilized bacteria showed complete conversion of glyphosate to nontoxic aminomethylphosphonic acid.[31]

A recent study concluded that certain amphibians may be at risk from glyphosate use.[32] One study has shown an effect on growth and survival of earthworms.[33] The results of this study are in conflict with other data and has been criticized on methodological grounds.[18] In other studies nitrogen fixing bacteria have been impaired, and also crop plant susceptibility to disease has been increased.[34][35][36][37][38][39] Monsanto firmly denies any negative impact on anything, including wildlife, and has many studies it has funded to back up its position. They would also be quick to point out that any possible negative impact on earthworms and nitrogen fixing bacteria, etc., would be offset by greater yields as of the elimination of weeds, and also would point to soil benefits from less mechanical cultivation of weeds by using Roundup and similar products.

Endocrine disruptor debate

An in-vitro studiy[40] has suggested glyphosate may have an effect on progesterone production in mammalian cells and affect mortality of placental cells in-vitro.[21] 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.

Glyphosate resistance in weeds and microorganisms

The first documented cases of weed resistance to glyphosate were found in Australia, involving rigid ryegrass near Orange, New South Wales.[41] Some farmers in the United States have expressed concern that weeds are now developing with glyphosate resistance, with 13 states now reporting resistance, and this poses a problem to many farmers, including cotton farmers, that are now heavily dependent on glyphosate to control weeds.[42][43] Farmers associations are now reporting 103 biotypes of weeds within 63 weed species with herbicide resistance, and this will continue to grow as a problem.[44][45]

Some microorganisms 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 resisitant to glyphosate.[46][47] The CP4 EPSPS gene was cloned and inserted into soybeans. The CP4 EPSPS gene was engineered for plant expression by fusing the 5' end of the gene to a chloroplast transit peptide derived from the petunia EPSPS. This transit peptide was used because it had shown previously an ability to deliver bacterial EPSPS to the chloroplasts of other plants. The plasmid used to move the gene into soybeans was PV-GMGTO4. It contained three bacterial genes, two PC4 EPSPS genes, and a gene encoding beta-glucuronidase (GUS) from Escherichia coli as a marker. The DNA was injected into the soybeans using the particle acceleration method. Soybean cultivar A54O3 was used for the transformation. The expression of the GUS gene was used as the initial evidence of transformation. GUS expression was detected by a staining method in which the GUS enzyme converts a substrate into a blue precipitate. Those plants that showed GUS expression were then taken and sprayed with glyphosate and their tolerance was tested over many generations.

Genetically modified crops

In 1996, genetically modified Roundup Ready soybeans resistant to Roundup became commercially available, followed by Roundup Ready corn in 1998[48]. Current Roundup Ready crops include soy, maize (corn), sorghum, canola, alfalfa, and cotton, with wheat still under development. These cultivars greatly improved conventional farmers' ability to control weeds since glyphosate could be sprayed on fields without hurting the crop. As of 2005, 87% of U.S. soybean fields were planted to glyphosate resistant varieties.[49][50]

Tradenames

The Roundup trademark is registered with the US Patent Office and still extant. However, the chemical formulation is no longer under patent, so similar products using glyphosate as the active ingredient are available from other maufacturers and marketed under many names,[51] including Buccanner, Razor Pro, (41%), Roundup Pro Concentrate (50.2 %), Rodeo (51.2%), Aquaneat (53.8%), and Aquamaster (53.5%)[52]

Other uses

Glyphosate is one of a number of herbicides used by the United States government to spray Colombian coca fields through Plan Colombia. There are reports that widespread application of glyphosate in attempts to destroy coca crops in South America have resulted in the development of glyphosate-resistant strains of coca which have been selectively bred to be both "Roundup ready" and also larger and higher yielding than the original strains of the plant. [27][53] However, there are no reports of glyphosate-resistant coca in the peer-reviewed literature.[54]

References

  1. ^ a b US EPA 2000-2001 Pesticide Market Estimates Agriculture, Home and Garden
  2. ^ Technology Administration Agency, US Department of Commerce [1]
  3. ^ Colby Stong, The Scientist 1990, 4(10):28 [2]
  4. ^ Purdue University, Department of Horticulture and Landscape Architecture, Metabolic Plant Physiology Lecture notes, Aromatic amino acid biosynthesis, The shikimate pathway - synthesis of chorismate.[3]
  5. ^ Saccharomyces Genome Database - S. cerevisiae Pathway: chorismate biosynthesis [4]
  6. ^ E. Schönbrunn et al, Interaction of the herbicide glyphosate with its target enzyme 5-enolpyruvylshikimate 3-phosphate synthase in atomic detail, PNAS 2001,98:1376-1380 [5]
  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. ^ Glyphosate Roadside Vegetation Management Herbicide Fact Sheet
  11. ^ Williams GM, Kroes R, Munro IC. (2000) Safety evaluation and risk assessment of the herbicide Roundup and its active ingredient, glyphosate, for humans. Regulatory Toxicology and Pharmacology, 31 (2): 117-165. PMID 10854122.
  12. ^ Carolyn Cox, Northwest Coalition for Alternatives to Pesticides[6]
  13. ^ [7]
  14. ^ http://www.organicconsumers.org/articles/article_4114.cfm]
  15. ^ Roundup PRO® Herbicide MSDS
  16. ^ http://extoxnet.orst.edu/pips/glyphosa.htm
  17. ^ http://npic.orst.edu/factsheets/glyphogen.pdf
  18. ^ a b c JP Giesy, KR Solomon, S Dobson (2000). "Ecotoxicological Risk Assessment for Roundup Herbicide". Reviews of Environmental Contamination and Toxicology 167: 35-120
  19. ^ [8]
  20. ^ Walsh et al Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (StAR) protein expression. Environ Health Perspect. 2000 108: 769–776.[9]
  21. ^ a b Richard et al, Differential Effects of Glyphosate and Roundup on Human Placental Cells and Aromatase, Environmental Health Perspectives Vol. 113, No.6, 716-720[10]
  22. ^ WHO Environmental health criteria # 159 http://www.inchem.org/documents/ehc/ehc/ehc159.htm#PartNumber:1]
  23. ^ US EPA Reregistration Eligibility Decision - Glyphosate[11]
  24. ^ Peluso M, Munnia A, Bolognesi C, Parodi S. Environ Mol Mutagen. 1998 31:55-9 PMID 9464316
  25. ^ a b c US EPA Reregistration Eligibility Decision - Glyphosate - (EPA-738-F-93-011) 1993 [12]
  26. ^ Monsanto Backgrounder 2005 Response to "The impact of insecticides and herbicides on the biodiversity and productivity of aquatic communities" [13]
  27. ^ Rick A. Relyea 2005 The impact of insecticides and herbicides on the biodiversity and productivity of aquatic communities Ecological Applications 15:618–627
  28. ^ Wojtaszek et al Effects of vision herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands Environmental Toxicology and Chemistry 23:832–842 2004 [14]
  29. ^ Balthazor, Terry M and Laurence Hallas (1986) Glyphosate-degrading microorganisms in industrial waste treatment biosystems. Appl. Environ. Microbiol. 51:432-34.[15]
  30. ^ [16]
  31. ^ Adams, William, Laurence Hallas, and Michael Heitkamp. 1994. Microbes and their use to degrade N-phosphonomethylglycine in waste streams. United States Patent 5288635 [17]
  32. ^ Bette Hileman. (2005) Common herbicide kills tadpoles. Chemical & Engineering News. Washington 83(15):11.
  33. ^ (Springett & Gray 1992, Soil Biol. Biochem. 24 (12):1739-1744) [18]
  34. ^ (Santos & Flores 1995, Lett. Appl. Microbiol. 20:349-352)
  35. ^ (Brammel & Higgins 1988, Can. J. Bot 66:1547-1555)
  36. ^ (Johal & Rahe 1988, Molec. Plant Pathol. 32:267-281)
  37. ^ (Mekwatanakarn & Sivassithamparam 1987, Biol. Fertil. Soils 5:175-180)
  38. ^ (Kawate et al. 1997, Weed Sci. 45:739-743)
  39. ^ (Bergvinson & Borden 1992, Can J. For. Res. 22:206-209)
  40. ^ Walsh LP et al. Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (StAR) protein expression. Environ Health Perspect. 2000 Aug;108(8):769-76.
  41. ^ [19]
  42. ^ [20]
  43. ^ [21]
  44. ^ [22]
  45. ^ [23]
  46. ^ Development and Characterization of a CP4 EPSPS-Based, Glyphosate-Tolerant Corn Event,G. R. Heck et al Crop Sci. 45:329-339 (2005).[24]
  47. ^ Molecular basis for the herbicide resistance of Roundup Ready crops, T. Funke et al, PNAS 2006 103:13010-13015 [25]
  48. ^ Monsanto Company History
  49. ^ 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[26]
  50. ^ National Agriculture Statistics Service (2005) in Acreage eds. Johanns, M. & Wiyatt, S. D. 6 30, (U.S. Dept. of Agriculture, Washington, DC). +
  51. ^ [California Product/Label Database]
  52. ^ [Glyphosate Roadside Vegetation Management Herbicide Fact Sheet]
  53. ^ New Super Strain of Coca Plant Stuns Anti-Drug Officials. Jeremy McDermott. The Scotsman (Scotland) 27 August 2004
  54. ^ [USDA National Agricultural Library, accessed 1 Nov 2007]
  • Baccara, Mariagiovanna, et al. Monsanto's Roundup, NYU Stern School of Business: August 2001, Revised July 14, 2003.
  • Pease W S et al. (1993) Preventing pesticide-related illness in California agriculture: Strategies and priorities. Environmental Health Policy Program Report. Berkeley, CA: University of California. School of Public Health. California Policy Seminar.
  • Wang Y, Jaw C and Chen Y (1994) Accumulation of 2,4-D and glyphosate in fish and water hyacinth. Water Air Soil Pollute. 74:397-403
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Roundup". A list of authors is available in Wikipedia.
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