Glyphosate

Description

Glyphosate (N-(phosphonomethyl)glycine; 1071-83-6) is the active ingredient in several commercial herbicides for nonselective weed control. Glyphosate herbicides are among the world’s most widely used herbicides. Roundup?, containing the active ingredient glyphosate, was developed and introduced by Monsanto Company in 1974. Other formulations include WeatherMax, UltraMAX, Buccaneer, Razor Pro, Rodeo, and AquaMaster?. Some crops such as soybeans and cotton have been genetically engineered to be resistant to glyphosate (Roundup Ready), allowing farmers to use glyphosate as a postemergence herbicide. The United States Environmental Protection Agency (EPA) considers glyphosate to be relatively low in toxicity compared to organochlorine and organophosphate pesticides.

Description

Glyphosate, or?N-(phosphonomethyl)glycine, was originally developed as a corrosion inhibitor, but it has been the world’s most widely used herbicide for almost 40 years. Monsanto patented it in the early 1970s and began to sell it under the trade name Roundup. More recently, the company developed glyphosate-resistant transgenic crop seeds. But competition has hurt Roundup, and?Monsanto has announced cutbacks?associated with this business unit.

Chemical properties

Glyphosate is a broad-spectrum, non-selective systemic herbicide. It is a colorless crystal at room temperature and is soluble in acetone, ethanol, xylene, and water. Glyphosate is used for the control of annual and perennial plants, including grasses, sedges, broadleaved weeds, and woody plants. It can be used on non-cropland as well as on many varieties of crops. Glyphosate itself is an acid, but it is commonly used in salt form, most commonly isopropylamine salt. It may also be available in acidic or trimethylsulfonium salt forms. It is generally distributed as water-soluble concentrates and powders. Glyphosate is a GUP.

Chemical properties

Glyphosate, an organophosphate/carboxylic acid (substituted), is a colorless crystalline powder. Often used as a liquid in a carrier solvent which may change physical and toxicological properties.

The Uses of Glyphosate

Glyphosate is the active ingredient in several commercial herbicides. It is a broad-spectrum systemic herbicide for various types of weeds, grasses (Poaceae), and woody plants.

The Uses of Glyphosate

Nonselective, postemergence, broad spectrum herbicide used to control annual and perennial grasses, sedges, broad-leaved and emerged aquatic weeds. This herbicide is also used to control insects on fruit trees.

What are the applications of Application

Glyphosate is an herbicide

Definition

ChEBI: Glyphosate is a phosphonic acid resulting from the formal oxidative coupling of the methyl group of methylphosphonic acid with the amino group of glycine. It is one of the most commonly used herbicides worldwide, and the only one to target the enzyme 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS). It has a role as an agrochemical, an EC 2.5.1.19 (3-phosphoshikimate 1-carboxyvinyltransferase) inhibitor and a herbicide. It is a phosphonic acid and a glycine derivative. It is a conjugate acid of a glyphosate(2-) and a glyphosate(1-).

General Description

Odorless white powder. Decomposition begins at approximately 419°F (darkens). pH (1% solution in water) 2.5.

Reactivity Profile

Glyphosate may react with galvanized steel or unlined steel (except stainless steel) containers to produce hydrogen gas which may form a highly combustible or explosive gas mixture. Glyphosate can react with caustic (basic) materials to liberate heat. Glyphosate is corrosive to iron.

Health Hazard

Glyphosate is practically non-toxic if ingested, with a reported acute oral LD50 of 5600 mg/kg in the rat. The toxicities of the technical acid (glyphosate) and the formulated product (Roundup) are nearly the same. Laboratory animals, such as rats, dogs, mice, and rabbits, exposed to glyphosate for 2 years did not indicate any kind of adverse health effects.

Fire Hazard

Flash point data for Glyphosate are not available; however, Glyphosate is probably combustible.

Biochem/physiol Actions

Glyphosate?(N-[phosphonomethyl] glycine) is the herbicide form of the isopropylamine salt of glyphosate.

Pharmacology

Glyphosate is the only known inhibitor of the biosynthesis of aromatic acids that has been commercialized as a successful herbicide (1). Glyphosate acts as a competitive inhibitor of phosphoenolpyruvate, the natural substrate of the enzyme 5-enolpyruvyl-shikimate-3-phosphate (EPSP) synthase, and causes amassive accumulation of shikimate in treated plant tissue (1).
Glyphosate is a nonselective herbicide, and it has been characterized as a low-risk herbicide for the evolution of herbicide resistance. A few weed species are somewhat tolerant to glyphosate, probably due to uptake or translocation mechanisms, but no plant species has sufficient resistance to glyphosate to allow its use directly on the crop as a selective herbicide. The complicated procedure used to genetically engineer the commercialized glyphosate-tolerant crops (31) would suggest that the evolution of glyphosate-resistant weeds will be a very slow process and that the level of resistance from field selection will be relatively low.

Safety Profile

Poison by intraperitoneal route. Moderately toxic by ingestion. Human systemic effects: arrhythmias, blood pressure lowering, body temperature increase, change in heart rate, convulsions, darrhea, fibrosing alveolitis, fibrosis, hypermoultty, respiratory depression, respiratory stimulation. Used as an herbicide. When heated to decomposition it emits very toxic fumes of NOx and POx.

Potential Exposure

A potential danger to those involved in the manufacture, formulation, and application of this nonselective and nonresidual pre-emergence organophos phate herbicide. Has wide residential use in the United States for the control of weeds.

Environmental Fate

Soil. Degrades microbially in soil releasing phosphoric acid, N-nitrosoglyphosate (Newton et al., 1984), ammonia (Cremlyn, 1991), N,N-dimethylphosphinic acid, N-methylphosphinic acid, aminoacetic acid (glycine), N-methylaminoacetic acid (sarcosine), hydroxymethylphosphonic acid (Duke et al., 1991), aminomethylphosphonic acid (Normura and Hilton, 1977; Rueppel et al., 1977; Hoagland, 1980; Duke et al., 1991; Muir, 1991) and carbon dioxide (Sprankle et al., 1975; Cremlyn, 1991). N-Nitrosoglyphosate also formed from the nitrosation of glyphosate in soil solutions containing nitrite ions (Young and Kahn, 1978).
The reported half-life of glyphosate in soil is <60 days (Hartley and Kidd, 1987). In the laboratory, experimentally determined dissipation rates of glyphosate in a Lintonia sandy loam, Drummer silty clay, Norfolk sandy loam and Raye silty loam were 0.028
Plant. In a forest brush field ecosystem, the half-life of glyphosate in foliage and litter ranged from 10.4 to 26.6 days, respectively (Newton et al., 1984).
Photolytic. When an aqueous solution of glyphosate (1 ppm) was exposed to outdoor sunlight for 9 weeks (from August 12 through October 15, 1983), aminomethylphosphonic acid and ammonia formed as major and minor photoproducts, respectively (Lund-H?ie and Friestad, 1986). More than 90% degradation was observed after only 4 weeks of exposure. Photodegradation was also observed when an aqueous solution was exposedindoors to UV light (λ = 254 nm). The reported half-lives of this reaction at starting concentrations of 1.0 and 2,000 ppm were 4 days and 3–4 weeks, respectively. When aqueous solutions were exposed indoors to sodium light (λ = 550–650 nm) and mercury light (λ = 400–600 nm), no photo-degradation occurred (Lund-H?ie and Friestad, 1986).
Chemical/Physical. Under laboratory conditions, the half-life of glyphosate in natural waters was 7–10 weeks (Muir, 1991). A 1% aqueous solution has a pH of 2.5 (Keith and Walters, 1992). This suggests glyphosate will react with alkalies and amin

Metabolic pathway

The photolytic degradation of glyphosate results in the formation of glycine, (aminomethyl)phosphonic acid (AMPA), and NH3. Glyphosate undergoes nitrogen ? carbon cleavage on reaction with m- chloroperoxybenzoic acid, leading ultimately to many of the same products formed on their metabolism and environmental degradation. It is suggested that insoluble complexes of glyphosate with iron(III), copper(II), calcium, and magnesium ions are formed at near-neutral pH, a mechanism of which is the inactivation of glyphosate in contaminated groundwater.268 The bacterium degrades high levels of glyphosate, primarily by converting to AMPA. Appreciable uptake of glyphosate is observed with seedlings and leaves and to a lesser extent with culture cells in the form of non-metabolized glyphosate, with AMPA as the only detectable metabolite.

Metabolism

In soils, glyphosate is rapidly mineralized within 1 to 2 weeks, and degradation occurs under aerobic and anaerobic conditions (79). The C?P bond is relatively resistant to chemical degradation, but several bacteria, e.g., Arthrobacter (80), Pseudomonas (81), various members of the Rhizobiaceae family (82), and certain fungi (83), have been shown to metabolize glyphosate.

Shipping

UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous haz ardous material, Technical Name Required.

Toxicity evaluation

Glyphosate’s herbicidal action works by disrupting 5-enolpyruvylshikimate- 3-phosphate (EPSP) synthase, a plant enzyme involved in the production of the amino acids such as phenylalanine, tyrosine, and tryptophan. EPSP synthase is not present in humans or animals and is the reason why glyphosate has relatively low mammalian toxicity. Additional mechanisms of action such as uncoupling of oxidative phosphorylation have been proposed. Glyphosate-based formulations have been shown to disrupt aromatase activity and mRNA levels and interact with the active site of the purified enzyme in human placental cells. As a result, some researchers consider formulations like Roundup? to be a potential endocrine disruptor. Adjuvants present in many commercial preparations may facilitate the observed effect. In contrast to organophosphate insecticides, glyphosate is not an inhibitor of acetylcholinesterase.

Incompatibilities

Organophosphates are susceptible to for mation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides. Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines) releasing substantial heat, water, and a salt that may be harmful. Incompatible with arsenic compounds (releases hydrogen cyanide gas), diazo compounds, dithio carbamates, isocyanates, mercaptans, nitrides, sulfides (releasing heat, toxic, and possibly flammable gases), thio sulfates, and dithionites (releasing hydrogen sulfate and oxides of sulfur). Solutions are corrosive to iron, unlined steel, and galvanized steel, forming a highly combustible or explosive gas mixture. Do not store glyphosate in contain ers made from these materials.