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Image:Glyphosate-2D-skeletal.png|Skeletal formula of glyphosate|thumb|right|250px]]

Glyphosate (N-(phosphonomethyl) glycine, C₃H₈NO₅P) is a non-selective systemic herbicide to kill weeds, especially perennials.

Glyphosate is the primary ingredient in Monsanto's popular herbicide, Roundup. Many crops have now been genetically engineered to be resistant to it. The chemical is only absorbed by the leaves of plants and it is not absorbed by roots from the soil. No other herbicide active ingredient compares in numbers of approved uses.

Chemistry

Glyphosate is an aminophosphonic analogue of the natural amino acid glycine and the name is a contraction of glycine, phospho-, and -ate, and has the C.A.S. number 1071-83-6. Glyphosate holds an elite position among honored technologies, it was first discovered to have herbicidal activity in 1970 by John Franz, a scientist that worked for the Monsanto company. In 1987 Franz received the National Medal of Technology for his discoveries , and in 1990 he received the Perkin Medal for Applied Chemistry . Also in 1996, Monsanto received the Presidential Green Chemistry Challenge Award for environmentally responsible systems used in the manufacture of glyphosate herbicides.In addition, Farm Chemicals magazine, in its September 1994 100th anniversary edition, called the original Roundup® herbicide one of the “Top 10 Products That Changed the Face of Agriculture.”

Biochemistry

Glyphosate kills plants by inhibiting the enzyme 5-enolpyruvoyl-shikimate-3-phosphate synthase (EPSPS), which forms the aromatic amino acids: phenylalanine, tyrosine and tryptophan. The production of Chorismate is ultimately stopped by the presence of the glyphosphate. EPSPS catalyzes the reaction of shikimate 3-phosphate (S3P) and phosphoenolpyruvate (PEP) to form ESP and phosphate. The aromatic amino acids are also used to make secondary metabolites such as folates, ubiquinones and naphthoquinones. The shikimate pathway is not present in animals.

Toxicity

Glyphosate is less toxic than a number of other herbicides and pesticides, such as those from the organochlorine family. Conservation groups have chosen glyphosate formulations because of their effectiveness against most weeds, and the fact that glyphosate has very low toxicity to wildlife.

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". 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 . Glyphosate was given an EPA Toxicity Class of III in 1993, but more recent studies suggest that IV is appropriate for oral, dermal, and inhalation. It has a rating of I (Severe) for eye irritation, however .

Outside its intended use, glysophate may be harmful. The most extreme example is intentional poisonings (i.e., suicide), with around 10% of those ingesting glysophate dying, compared to 70% of those ingesting paraquat .

Laboratory studies testing for toxicity suggest that other ingredients combined with glyphosate may be more toxic than glyphosate itself. For example, a study comparing glyphosate and Roundup found that Roundup had a greater effect on aromatase than glyphosate . Statistics from the Californian Envionmental Protection Agencies Pesticide Illness Surveillance Program program indicate that Glyphosate related incidents are one of the highest reported of all pesticides . However, incident count does not take into account the number of people exposed and the severity of symptoms assocated with each incident . If hostpitalization is used as a measure of the severity of pesticide related incidents in California then Glyphosate should be regarded as very safe since none of the 515 pesticide related hospitalizations recorded by the program over a 13 year period are attributed to glyhposate .

Greenpeace states that poor quality testing methods are responsible for results that usually show little glyphosate contamination on food products or in other systems, yet makes no statement as to the harms of minor glyphosate contamination on human foods and only as to harms on ecology.

Other species

The direct toxicity of pure glyphosate to mammals and birdsis low . It has been reported that glyphosate formulations negatively impact earthworm and beneficial insect populations .

Fish and invertebrates are more sensitive to formulations of glyphosate. As with humans, the surfactants can be responsible for much of the harm . Toxicity is increased with higher water temperatures, and pH. In Australia, there is controversy over glyphosate formulations used in or near water, most of this stems from ingredients in the formulations other than the actual glyphosate, Monsanto corporation had adjusted its formulations for Australia in the late 1990s to address this issue with its "Biactive" line of products.

Of nine herbicides tested for their toxicity to soil microorganisms, glyphosate formulations were found to be the second most toxic to a range of bacteria, fungi, actinomycetes and yeasts. However, when glyphosate comes into contact with the soil it rapidly binds to soil particles and is inactivated. Unbound glyphosate is degraded by bacteria. Low activity because of binding to soil particles suggests that glyphosate's effects on soil flora will be limited. However, some recent work shows that glyphosate can be readily released from certain types of soil particles, and therefore may leach into water or be taken up by plants . Low glyphosate concentrations can be found in many creeks and rivers in U.S. and Europe.

Mammalian research indicates glyphosate induces a variety of functional abnormalities in fetuses and pregnant rats.Also in recent mammalian research glyphosate has been found to cause interference in reproductive chemistry specifically interfering in male testosterone production.. There are currently few studies into the toxicity of glyphosate formulations, and Greenpeace's cautious 10 year old statement that glyphosate is not at all toxic to mammals came before the more recent research, on the reproductive effects of the commonly used glyphosate formulations, and on pure glyphosate toxicity to male reproductive cells.

Health concerns

There are concerns about the effects of glyphosate (and Roundup) on non-plant species even including on possible human reproductive dysfunction. For more information, see the Roundup article.

Endocrine disruptor debate

In-vitro studies (Walsh, et al 2000) have shown glyphosate to have an effect on progesterone production in mammalian cells and can affect mortality of placental cells in-vitro (Richard, et al 2005). Whether these studies classify glyphosate as an endocrine disruptor is a matter of debate, with others stating that studies of even pure glyphosate on Leydig cells to demonstrate conclusively that it is an endocrine disruptor.

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. Many current toxicological studies supportive of non.endocrine activity were mainly provided by Monsantos own studies of pure glyphosate and not the chemical formulations of glyphosate that are actually used (EU 2002).

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.

Glyphosate resistance

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. 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 soybeans were available commercially(). This greatly improved the ability to control weeds in soybean fields since glyphosate could be sprayed on fields without hurting the crop. As of 2004, glyphosate was used on 80% of U.S. soybean fields to eliminate weeds.

Tradenames

It was first sold by Monsanto under the tradename Roundup but is no longer under patent so is now marketed under various names (for example TOP UP48 in Thailand).

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.

References

1. ^ 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.
2. Nagami et al. (2005). Hospital-based survey of pesticide poisoning in Japan, 1998--2002. Int J Occup Environ Health, 11(2):180-4.PMID 15875894
3. Richard S, Moslemi S, Sipahutar H, Benachour N, Seralini GE. (2005) Differential effects of glyphosate and roundup on human placental cells and aromatase, Environmental Health Perspectives, 113 (6): 716-720. PMID 15929894
4. Goldstein DA et al An analysis of glyphosate data from the California Environmental Protection Agency Pesticide Illness Surveillance Program J Toxicol Clin Toxicol. 2002 40:885-92
5. ^ California EPA 1996, California Pesticide Illness Serveillance Program Report HS-1733
6. Northwest Coalition for Alternatives to Pesticides. 2004. Herbicide Factsheet: Glyphosate (Roundup). Journal of Pesticide Reform, VOL. 24, NO. 4

• EU (2002). Review report for the active substance glyphosate. Retrieved October 28, 2005.
• U.S. EPA ReRegistration Decision Fact Sheet for Glyphosate. http://www.epa.gov/oppsrrd1/REDs/factsheets/0178fact.pdf]. Retrieved Nov 13, 2005.
• Walsh; et al. (2000). "Roundup inhibits steroidogenesis by disrupting steroidogenic acute regulatory (stAR) protein expression". Environmental Health Perspectives. 108-N8: 769–776. {{cite journal}}: Explicit use of et al. in: |author= (help)
• Sophie Richard, Safa Moslemi, Herbert Sipahutar, Nora Benachour, Gilles-Eric Seralini (2005). "Differential effects of glyphosate and Roundup on human placental cells and aromatase". Environmental Health Perspectives. 113-N6: 716–720.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• JP Giesy, KR Solomon, S Dobson (2000). "Ecotoxicological Risk Assessment for Roundup Herbicide". Reviews of Environmental Contamination and Toxicology. 167: 35–120.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• KR Solomon, DG Thompson (2003). "Ecological risk assessment for aquatic organisms from over-water uses of glyphosate". Journal of Toxicology and Environmental Health. 6: 289–324.
• World Health Organization. (1994) Environmental Health Criteria 159: Glyphosate.
• Monsanto History of Glyphosate.

External links

• Monsanto Website - Background Information about Glyphosate and Roundup
• US weighs costs of Plan Colombia
• Effect of Glyphosate on human placental cells in culture
• Website of the SynBioC research group, working on different types of aminophosphonates

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• Herbicides
• Organic compounds
• Phosphorus compounds