Glyphosate

Outline

Glyphosate, Scientific name: N-(methyl phosphonate) glycine. The pure product is non-volatile white solid with the density being 0.5 and the melting point of about 230 °C which is accompanied with decomposition. At 25 ℃, its water solubility is 1.2%. It is insoluble in common organic solvents. However, its isopropylamine salt can be completely dissolved in water. It is non-flammable, non-explosive, and is stable under room temperature. It is general being processed into amine salt water preparation. It is herbicide of low toxicity. It has systemic effect with a broad weeding spectrum. It has controlling effect on plant belongs to more than 40 families, including both monocots and dicots, annual and perennial, herbaceous plants and shrubs. It is very destructive on the underground tissue of the deep rooted perennial weeds and can reach a depth being out of the reach of general farm machinery. It is suitable to be applied to sugar cane, tea, mulberry, sisal, rubber, trees, and orchards for destructive weeding. It can be produced from raw materials such as monochloroacetic acid, ammonia, phosphorous acid, formaldehyde, and sulfuric acid. Glyphosate is a kind of organic phosphorus herbicide. It is a kind of non-selective systemic stem leaf herbicide. It was developed by the Monsanto Company in the early 1970s. It is typically used in the form of its isopropylamine salt or sodium salt. The isopropylamine salt is the active component of a famous trademark herbicide "Roundup". The proto-drug is a white or slightly yellow crystalline powder with the melting point being at 232~236 ℃ (decomposition), it is easily soluble in water, acetone, chlorobenzene, ethanol, kerosene and xylene. Glyphosate is a highly efficient, low toxicity, broad-spectrum systemic Herbicide. This product can dissolve the surface wax layer of the weed leafy shoots stem and rapidly penetrate into the plant conduction system effects, thus resulting in the death of the weeds. It can effectively control annual, biennial Gramineae, sedges and broadleaf weeds as well as perennial weeds such as sexual abuse grass, nutsedge, and bermudagrass. It is therefore widely applied to the chemical weeding in orchards, mulberry fields, tea plantations, rubber park, prairie update, forest firebreak, railways, highways wasteland and no-tillage farmland.

Mechanism

Glyphosate mainly takes effects by blocking the biosynthesis of aromatic amino acid, namely the biosynthesis of phenylalanine, tryptophan and tyrosine via shikimic acid pathway. It has inhibitory effect on the 5-enolpyruvylshikimate-3-phosphate synthase (EPSP synthase), which can catalyze the conversion between shikimate-3-phosphate and 5-enolpyruvate phosphate into 5-enolpyruvylshikimate-3-phosphate (EPSP), so glyphosate interfere with this biosynthesis of enzymatic reactions, resulting shikimic acid accumulation in vivo. [4] In addition, the glyphosate can also suppress other kinds of plant enzymes [5], [6] and the animal enzyme [7] activity. The metabolism of glyphosate in higher plants is very slow and it has been tested that its metabolite is aminomethylphosphonic acid and methyl amino acetic acid. Because of the high working performance, slow degradation, as well as high plant toxicity of glyphosate in plants body, the glyphosate is regarded as a kind of ideal controlling perennial weeds herbicides. [8] We are currently studying the culture of glyphosate resistant plants. Biochemists have isolated from microorganisms of strains with excess amount of EPSP and further introduce the gene into tobacco and soybean tissues in order to cultivate the plants resistant to glyphosate.

Usage of glyphosate pesticide

1. weeding of orchards and mulberry: annual weeds: apply 0.5-1 kg of 10% water preparation per acre; for controlling of perennial weeds, use 1-1.5 kg of water preparation per acre. Mix with 20-30 kg of water and directly spray the weed stems and leaves. 2. Farmland weeding: for weeds emerged before the reverse cropping and seeding in the farmland, the dosage can be referred to the orchard weed section. For medication during cotton growth, it requires the application directed spray with a hood. Apply 0.5-0.75 kg of 10% water preparation per acre and mixing with 20-30 kg of water. 3. Weeding of leisure place, Tanabe, roadside; during the 4-6 leaf stage of weeds, apply 0.5-1 kg of 10% water per acre, add 100 mL of diesel and mix with 20-30 kg of water and apply weed spray.

What causes the difference of glyphosate herbicide efficacy?

First, different of tillage method can lead to different efficacy of glyphosate. It is better to apply glyphosate herbicide for no-till sowing. Apply it at 1-3 days before the sowing of the crop. In order to keep pace with the seeding season, it can also be sprayed after sowing. Applying it before sowing will not affect the seed germination and seedling growth of the crops due to the absence of direct contact between glyphosate with the seeds, thus being able to give a better weeding and weed suppression effects are than plowing. As no-tillage doesn’t turn the weed seeds of the inner layer of soil into topsoil layer, it is difficult for weed seeds to get germinated. Once the crops have grown and get closing, the weed seeds and seedlings are not able to get germinated and grow due to the absence of the sunshine. Therefore, the herbicidal effect of glyphosate will be better when being used at no-tillage land than being used in plowing land. Second, administration of drugs during the different growth stage of weeds can also cause difference in the drug efficacy. Glyphosate is a kind of systemic herbicide and thus should be administrated during the most vigorous growth stage of weed. For time, it is generally from March to October. From the botanical characteristics, the best time for administration should be before flowering period. General, the height of annual weed is about 15 cm while the height of perennial weeds is about 30 cm. Spray of 6-8 leaves is the most suitable. If you don’t take the growth stages of weeds into consideration, and blindly apply the glyphosate for weeding until the aging stage of weed, of course you will not receive an ideal control effect. For weeding between rows of crops, if there is certain height gap between higher crop plants and weeds, the treatment effect is good and safe. At this time when using glyphosate as herbicide, due to the aging of the lower leaves, the weed has low sensitivity to the drug and also has poor conduction property so that the drug has little effect on crops. For weeding between the rows of corn, shelved beans as well as between rows of melons, you can all use this method. Third, there will be differences in the efficacy upon spraying different concentration. According to the survey, upon the application of glyphosate, farmers don’t have strict rule on the drug concentration which is unlike other pesticides. Farmers mostly apply it in a large arbitrary form with either increasing the dose or reducing the dose occurring. For determining the drug concentration, we must consider the type of weeds. Common weeds is sensitive to glyphosate and can be killed by low doses of the drug solution while we should increase the concentration upon controlling broadleaf weeds; For some perennial rhizome reproduction worst weed, you need to apply higher concentrations. The longer the foliar age, the higher the resistance will be, and thus the dosage should also be increased. For example, upon controlling weeds in orchards, for annual grass weeds, we can apply 500 to 700 grams of 10% Glyphosate with water of 30-40 kg; For example, to control the annual broadleaf weeds, the liquid dosage should be increased to 750-1000 grams; for controlling perennial weed, the dosage should be increased to 1250-1500 grams. But upon overdose, it will quickly kill the conducting tissues of the plant which is not good for the drug liquid absorption so that the efficacy will be reduced, and therefore for economic medication, you should first use a lower concentration to kill the young grass, and then after about 10 days, we should apply corresponding concentration for directional spraying weed.

How to fully exert the herbicidal effect of glyphosate

First, the drug liquid of glyphosate will be transferred to a large number of weed rhizome tissues before playing the herbicidal effect. This requires that the weed contain a lot of leaves. Prior to use, if the usage area of weed is small with low photosynthesis, then the stored nutrient in roots will be conducted from the bottom to up. At this time, due to the small amount of drug delivered down into roots, it can’t play enough herbicide effect. In contrast, during the late stage of weed growth, due to the high photosynthesis intensity, the photosynthetic products will be delivered from top to bottom, which can yield the best drug efficacy. Therefore, one of the most important basic principles for using glyphosate is to select the best treatment period. For example, for the use of glyphosate for weed control in Maize field, it is preferably to administer drug when corn has a height of 1.5 meters with 2-3 tablets old leafs in low place and grass height has reached 10 cm. The second is to pay attention to the environmental conditions. At the range of 24-25 °C, with the increasing temperature, the absorption amount of weeds on the glyphosate can be doubled. Therefore, higher atmospheric temperature can give a better performance of the drug than lower temperature. High air relative humidity can extend the wetting time of the drug liquid in the plant surfaces which is good for conducting the drug. The drought soil and low water content is not good for the metabolism of plants as well as for the conductivity of plants inside the plant body, and thus leading to a low drug efficacy. Again on the combination and mixing between herbicide glyphosate and other kinds of herbicide, since some farmers would like kill a variety of grass, in order to save labor, they may arbitrarily add other kinds of glyphosate herbicide, but the results may not good because some herbicides can’t be mixed with glyphosate such as MCPA, Gramoxone and other fast-acting herbicides in order to avoid that the aboveground part of being subject to premature death, causing the loss of its ability for systemic conductivity of glyphosate and reducing the effects of glyphosate on killing underground rhizomes of weeds. But adding some plant growth regulator and adjuvant to the glyphosate can further improve the control effect. The fourth is to select the best method of application. The medication method selection is very important for the weed control of glyphosate weed control because in a certain range of concentrations, the higher the concentration is, the finer the sprayer droplet will be, this is good for the absorption of the weeds. At the same concentration, higher amount will give better herbicidal effect. Addition of 0.1% detergent to the glyphosate, or adding 30 g of diesel per acre could enhance drug distribution, penetration and adhesion and also improve the control efficiency.

Security issues when being used on crops

Glyphosate is a kind of destructive herbicide and therefore may pose security risk to the crops if used improperly. Some farmers use glyphosate for ridge weeding. However, due to the drift of glyphosate, it causes toxicity to crops aside. There are also cases that farmers don’t wash the sprayer in accordance with the requirements, and therefore, the residue glyphosate cause toxicity to other drugs when they spraying other pesticides. In case of injury in rice, in mild case, there may be leaf chlorosis with severe growth retardation; in severe cases, early death, non-heading or deformed spike may occur, causing loss of rice production.

Toxicity

Acute oral-rat LD50 is 4320mg/kg, acute percutaneous-rabbit LD50> 5000mg/kg (7940mg/kg); it has mild stimulus on skin and eyes of rabbits. Using a dose 2000 mg/kg for feeding rats for 90d causes no abnormal symptoms. Animal tests exhibit no teratogenic, carcinogenic, mutagenic effect. Trout-LC50> 1000mg/L, Daphnia 780mg/L. It has low toxicity to bees and birds.

Production method

Dialkyl phosphite ester method Take glycine, dialkyl phosphite, and paraformaldehyde as raw material and go through addition, condensation, hydrolysis reaction to obtain the product with the purity of 95% and total yield 80% as well as a relative low cost. Chloromethyl phosphoric acid method Preparation of chloromethyl phosphoric acid The phosphorus trichloride and paraformaldehyde were reacted in 200~250 ℃ (corresponding pressure 2.5~3.0 MPa) for 3~5h to obtain the chloromethyl phosphonyl dichloride. It was reported that the ratio is that phosphorus trichloride: polyoxymethylene (1.2~1.5): 1 (mol). In the absence of a catalyst, the yield is 67%. This can be increased to 80% to 89% based on using Lewis acid as the catalyst. The domestic research has not yet reached the level of literature. Hydrolysis can be obtained chloromethyl phosphoric acid. Cl2P (O) CH2Cl + H2O → (HO) 2P (O) CH2Cl + HCl The synthesis of glyphosate: use equal mole of chloromethyl phosphonic acid and glycine, in the aqueous sodium hydroxide (pH> 10), the reaction was refluxed for 10~20h with further acidification to obtain the hydrochloric acid and glyphosate. If being acidified to a pH 4, that’s monosodium salt; the pH value is 8.5 for disodium salt. If glyphosate was added with equal molar of dimethylamine, giving glyphosate dimethylamine salt. Iminodiacetic acid method Preparation of the iminodiacetic acid; the chloroacetic acid, in the presence of calcium hydroxide, is reacted with aqueous ammonia, and undergo acidification, and then sodium hydroxide neutralization to get a yield of 85%. Or take hydrocyanic acid as raw materials, have it reacted with formaldehyde and ammonia to obtain a yield of 90%. Preparation of PMIDA The iminodiacetic acid and formaldehyde, phosphorous acid are subject to heating reaction in the presence of sulfuric acid to get PMIDA with the yield being 90%. Synthesis of glyphosate: PMIDA is mixed with water, with an excess of hydrogen peroxide in the presence of equal molar of sulfuric acid, etc., for heating reaction to obtain glyphosate with a yield of 90% to 95%. There are many ways for PMIDA oxidation, in addition to hydrogen peroxide; we can also use concentrated sulfuric acid, precious metals (palladium, rhodium, etc.) oxide, and activated carbon air oxidation or electrolysis method. For example, 10 parts of PMIDA, 170 parts of water and 0.6 parts of 5% palladium-charcoal catalyst were placed in an autoclave, put through oxygen to 2.07X105Pa, reacted at 90~100 °C to obtain it with the yield of 96% and purity of 97%. There are two methods of production from sub-categories, namely, method 1 using iminodiacetic acid (IDA) as raw material and method 2 using glycine-dialkyl phosphite as raw materials, wherein the glycine-dialkyl phosphite method has a largest production capacity, the largest number of production companies, about 80% of the total production of glyphosate production accounts reached 70,000 t; Production capacity of IDA law is nearly 30,000 t. There are four methods in subdivision: 1) homemade (by chloroacetic acid method) IDA, thought the method of PMIDA being subject to oxidation of concentrated sulfuric acid has gained some progress since the 1980s, owing to the large amount of strong calcium chloride acidic wastewater, causing a low yield (IDA yield of about 70%), and can only be made into water preparation with the highest annual output of 2000t (10% water). Upon entering into the 1990s, the amount of the produced company gradually reduced with lower yields. 2) Company of self-production of trimethyl phosphite for the production of glyphosate; this method apply water instead of methanol as solvent, with sodium hydroxide instead of triethylamine as the catalyst which reduces the post-treatment with a yield of 65%. However, owing to the higher price of trimethyl than dimethyl, only companies of self-production of trimethyl can have the cost being with certain market competitiveness. 3) There are many enterprises for applying dimethyl phosphite for glyphosate production; it has large-scale production plant. With optimized production process, advanced equipment and automatic systems, this method has made certain technical progress with the product quality indicators reaching the international market requirements, and therefore China mainly uses this process. 4) Homemade (use diethanolamine for dehydrogenation oxidation) IDA or outsourcing IDA, the use of hydrogen peroxide oxidation of PMIDA for preparation of glyphosate. Fixed material consumption: paraformaldehyde 500 kg/t, methanol 500kg/t, glycine 700 kg/t, triethylamine 50 kg t, dimethyl phosphite 1000 kg/t, hydrochloric acid 3000 kg/t

Flammability and hazard characteristics

combustion produces toxic gases of nitrogen oxides and phosphorus oxides

Storage characteristics

Treasury: ventilation, low-temperature and drying; store separately from food raw material

Extinguishing agent

Dry powder, foam, sand

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 0.028Plant. 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.

General Description

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