Glyphosate (IUPAC name: N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant.
An organophosphorus compound, specifically a phosphonate
It acts by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP).
It works by inhibiting an enzyme pathway (the shikimate pathway) that plants need to make certain essential amino acids.
Without these amino acids, plants can’t survive.
It’s the active ingredient in many commercial herbicides, most notably Roundup.
It’s often used in conjunction with genetically modified “Roundup Ready” crops that are engineered to be resistant to glyphosate, allowing farmers to spray fields and kill weeds without harming their crops.
Its safety for humans has been the subject of significant controversy.
Glyphosate-based herbicides are used to kill weeds, especially annual broadleaf weeds and grasses that compete with crops.
A widely used broad-spectrum herbicide and crop desiccant.
It works by inhibiting the shikimic acid pathway, a process essential for plant growth, leading to the death of targeted weeds and grasses.
Studies link glyphosate to neurotoxic effects, oxidative stress, and potential developmental issues in animals.
Regulatory agencies differ in their cancer risk assessments: the U.S. EPA deems it “not likely” carcinogenic, while IARC classifies it as “probably carcinogenic” to humans.
Glyphosate is absorbed through foliage, and minimally through roots, and from there translocated to growing points.
It inhibits EPSP synthase, a plant enzyme involved in the synthesis of three aromatic amino acids: tyrosine, tryptophan, and phenylalanine.
It is effective only on actively growing plants and is not effective as a pre-emergence herbicide.
Crops have been genetically engineered to be tolerant of glyphosate which allows farmers to use glyphosate as a post-emergence herbicide against weeds.
The WHO and FAO Joint committee on pesticide residues issued a report in 2016 stating the use of glyphosate formulations does not necessarily constitute a health risk, and giving an acceptable daily intake limit of 1 milligram per kilogram of body weight per day for chronic toxicity.
The consensus among national pesticide regulatory agencies and scientific organizations is that labeled uses of glyphosate have demonstrated no evidence of human carcinogenicity.
The World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate as probably carcinogenic in humans.
In contrast, the European Food Safety Authority concluded the substance is unlikely to be genotoxic or to pose a carcinogenic threat to humans, later clarifying that while carcinogenic glyphosate-containing formulations may exist, studies that look solely at the active substance glyphosate do not show this effect.
The European Chemicals Agency (ECHA) classified glyphosate as causing serious eye damage and as toxic to aquatic life but did not find evidence implicating it as a carcinogen, a mutagen, toxic to reproduction, nor toxic to specific organs.
Studies associate glyphosate exposure with non-alcoholic fatty liver disease, metabolic syndrome, and chronic kidney disease.
Research suggests glyphosate may disrupt hormones and impair fertility, though the EPA found no conclusive evidence of endocrine disruption.
Glyphosate may cause gut dysbiosis, potentially contributing to conditions like inflammatory bowel disease and mental health issues.
It has been shown to induce oxidative stress, neuroinflammation, and mitochondrial dysfunction, potentially affecting neuronal development.
It can irritate the respiratory system in those exposed occupationally.
Regulatory agencies like the EPA find no significant risks under proper use.
However, independent studies highlight potential long-term health effects, warranting further research and scrutiny.
Glyphosate interferes with the shikimate pathway, which produces the aromatic amino acids phenylalanine, tyrosine and tryptophan in plants and microorganisms.
This pathway does not exist in the genome of animals, including humans.
Glyphosate is absorbed through foliage and minimally through roots, meaning that it is only effective on actively growing plants and cannot prevent seeds from germinating.
Glyphosate is readily transported around the plant to growing roots and leaves and this systemic activity is important for its effectiveness.
Inhibiting the enzyme causes shikimate to accumulate in plant tissues and diverts energy and resources away from other processes, eventually killing the plant.
While growth stops within hours of application, it takes several days for the leaves to begin turning yellow.
Glyphosate also may chelate Co2+ which contributes to its mode of action.[
Glyphosate functions by occupying the binding site of the phosphoenolpyruvate, mimicking an intermediate state of the ternary enzyme–substrate complex.
Glyphosate inhibits the EPSPS enzymes of diverse species of plants and microbes, although rates vary.
Glyphosate is effective in killing a wide variety of plants, including grasses and broadleaf and woody plants.
By volume, it is one of the most widely used herbicides.
It is commonly used for agriculture, horticulture, viticulture, and silviculture purposes, as well as garden maintenance including home use
It has a relatively small effect on some clover species and morning glory.
Glyphosate often used in invasive species eradication and habitat restoration, especially to enhance native plants.
In many cities, glyphosate is sprayed along the sidewalks and streets, as well as crevices in between pavement where weeds often grow.
Up to 24% of glyphosate applied to hard surfaces can be run off by water.
Glyphosate contamination of surface water is attributed to urban and agricultural use.
Glyphosate is systemic, excess residue levels can persist in plants due to incorrect application and this may render the crop unfit for sale.
Current glyphosate-resistant crops include soy, maize, canola, alfalfa, sugar beets, and cotton, with wheat still under development.
In 2023, 91% of corn, 95% of soybeans, and 94% of cotton produced in the United States were from strains that were genetically modified to be tolerant to multiple herbicides, including dicamba, glufosinate, and glyphosate.
It is a zwitterion in aqueous solutions and is expected to exist almost entirely in zwitterionic forms in the environment.
The half-life of glyphosate in soil ranges between 2 and 197 days; a typical field half-life of 47 days has been suggested.
Soil and climate conditions affect glyphosate’s persistence in soil.
The median half-life of glyphosate in water varies from a few to 91 days.
Glyphosate is generally less persistent in water than in soil.
According to the National Pesticide Information Center fact sheet, glyphosate is not included in compounds tested for by the Food and Drug Administration’s Pesticide Residue Monitoring Program, nor in the United States Department of Agriculture’s Pesticide Data Program.
The U.S. has determined the acceptable daily intake of glyphosate at 1.75 milligrams per kilogram of body weight per day (mg/kg/bw/day) while the European Union has set it at 0.5.
The acute oral toxicity for mammals is low, but death has been reported after deliberate overdose of concentrated formulations.
The surfactants in glyphosate formulations can increase the relative acute toxicity of the formulation.
Glyphosate is less toxic than 94% of herbicides, and is also less toxic than household chemicals such as table salt or vinegar.
There is very limited information on skin irritation in humans.
Inhalation is a minor route of exposure, but spray mist may cause oral or nasal discomfort, an unpleasant taste in the mouth, or tingling and irritation in the throat.
Eye exposure may lead to mild conjunctivitis.
Superficial corneal injury is possible if irrigation is delayed or inadequate.
The consensus among national pesticide regulatory agencies and scientific organizations is that labeled uses of glyphosate have demonstrated no evidence of human carcinogenicity.
Evidence for long-term exposure to glyphosate increasing the risk of human cancer remains inconclusive.
There is weak evidence human cancer risk might increase as a result of occupational exposure to large amounts of glyphosate, such as in agricultural work, but no good evidence of such a risk from home use, such as in domestic gardening.
Some small studies have suggested an association between glyphosate and non-hodgkin lymphoma, subsequent work confirmed the likelihood this work suffered from bias, and the association could not be demonstrated in more robust studies.
Glyphosate can have carcinogenic effects in nonhuman mammals: trends in the incidence of renal tubule carcinoma and hemangiosarcoma in male mice, and increased pancreatic islet-cell adenoma in male rats.
Large quantities of glyphosate-based herbicides may cause life-threatening arrhythmias in mammals.
Evidence also shows that such herbicides cause direct electrophysiological changes in the cardiovascular systems of rats and rabbits.
Glyphosate can control the growth of apicomplexan parasites, such as Toxoplasma gondii, Plasmodium falciparum (malaria), and Cryptosporidium parvum, and has been considered an antimicrobial agent in mammals.
When glyphosate comes into contact with the soil, it can be bound to soil particles, thereby slowing its degradation.
Glyphosate and its degradation product, aminomethylphosphonic acid are considered to be much more benign toxicologically and environmentally than most of the herbicides replaced by glyphosate.
At typical application rates glyphosate had no effect on soil microbial biomass or respiration.
There is was no convincing evidence of potential interaction with the estrogen, androgen or thyroid pathways.
Overall, there is no conclusive evidence on glyphosate’s effect on human health.
Acute toxicity and chronic toxicity are dose-related.
Skin exposure to concentrated glyphosate formulations can cause irritation, and photocontact dermatitis has been occasionally reported.
Inhalation is a minor route of exposure, but spray mist may cause oral or nasal discomfort, an unpleasant taste, or tingling and irritation in the throat.
Eye exposure may lead to mild conjunctivitis, superficial corneal injury is possible if irrigation is delayed or inadequate.
Death has been reported after deliberate overdose, with Ingestion of ranging from 85 to 200 ml (of 41% solution) has resulted in death within hours of ingestion, although it has also been ingested in quantities as large as 500 ml with only mild or moderate symptoms.
Consumption of more than 85 ml of concentrated product can lead to corrosive esophageal burns and kidney or liver damage.
More severe overdose cases can cause respiratory distress, impaired consciousness, pulmonary edema, infiltration on chest X-ray, shock, arrhythmias, renal failure requiring haemodialysis, metabolic acidosis, and hyperkalemia, and death is often preceded by bradycardia and ventricular arrhythmias.
The International Agency for Research on Cancer (IARC), an intergovernmental agency forming part of the World Health Organization of the United Nations, published a summary that classified glyphosate as “probably carcinogenic in humans” (category 2A) based on epidemiological studies, animal studies, and in vitro studies.
It noted that there was “limited evidence” of carcinogenicity in humans for non-Hodgkin lymphoma.
The IARC report did not include unpublished studies, including one completed by the IARC panel leader.
The EPA, considered glyphosate to be noncarcinogenic and relatively low in dermal and oral acute toxicity.
In the 1990s, no glyphosate-resistant weeds were known to exist, and now resistance is common.