Glyphosate

Two main approaches are used to synthesize glyphosate industrially. The first is to react iminodiacetic acid with phosphorous acid and hydrochloric acid (sometimes formed in situ by addition of phosphorus trichloride) via a modified Mannich reaction. Oxidation then leads to the desired glyphosate product. Iminodiacetic acid is usually prepared on-site by various methods depending on reagent availability.[15]

The second involves hydrophosphonylation, using dimethyl phosphite in a one-pot synthesis. Glycine and paraformaldehyde are reacted in a suitable organic solvent (typically triethylamine and methanol) to produce bishydroxymethylglycine, (HOCH₂)₂NCH₂COOH. Dimethyl phosphite is then introduced, which leads to a substitution reaction of the hydroxyl of one of the two hydroxymethyl groups. Work-up with hydrochloric acid and heat cleaves the remaining hydroxymethyl group from the nitrogen atom and hydrolyzes both phosphate ester linkages.[15]

This synthetic approach is responsible for a substantial portion of the production of glyphosate in China, with considerable work having gone into recycling the triethylamine and methanol.[15] Progress has also been made in attempting to eliminate the need for triethylamine altogether.[32]

Technical grade glyphosate is a white powder which, according to FAO specification, should contain not less than 95% glyphosate. Formaldehyde, classified as a known human carcinogen, [33] [34] and N-nitrosoglyphosate, have been identified as toxicologically relevant impurities.[35] The FAO specification limits the formaldehyde concentration to a maximum of 1.3 g/kg glyphosate. N-Nitrosoglyphosate, "belonging to a group of impurities of particular concern as they can be activated to genotoxic carcinogens",[36] should not exceed 1 ppm.[35]

Some micro-organisms have a version of 5-enolpyruvoyl-shikimate-3-phosphate synthetase (EPSPS) resistant to glyphosate inhibition. A version of the enzyme that was both resistant to glyphosate and that was still efficient enough to drive adequate plant growth was identified by Monsanto scientists after much trial and error in an Agrobacterium strain called CP4, which was found surviving in a waste-fed column at a glyphosate production facility.[59][72][73]^:56 This CP4 EPSPS gene was cloned and transfected into soybeans. In 1996, genetically modified soybeans were made commercially available.[74] Current glyphosate-resistant crops include soy, maize (corn), canola, alfalfa, sugar beets, and cotton, with wheat still under development.

In 2015, 89% of corn, 94% of soybeans, and 89% of cotton produced in the United States were from strains that were genetically modified to be herbicide-tolerant.[75]

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. However, a field test showed that lettuce, carrots, and barley contained glyphosate residues up to one year after the soil was treated with 3.71 lb of glyphosate per acre (4.15 kg per hectare).[52] The U.S. has determined the acceptable daily intake of glyphosate at 1.75 milligrams per kilogram of bodyweight per day (mg/kg/bw/day) while the European Union has set it at 0.5.[89]

Pesticide residue controls carried out by EU Member States in 2016 analysed 6,761 samples of food products for glyphosate residues. 3.6% of the samples contained quantifiable glyphosate residue levels with 19 samples (0.28%) exceeding the European maximum residue levels (MRLs), which included six samples of honey and other apicultural products (MRL = 0.05 mg/kg) and eleven samples of buckwheat and other pseudo‐cereals (MRL = 0.1 mg/kg). Glyphosate residues below the European MRLs were most frequently found in dry lentils, linseeds, soya beans, dry peas, tea, buckwheat, barley, wheat and rye.[90]

The acute oral toxicity for mammals is low,[91] but death has been reported after deliberate overdose of concentrated formulations.[92] The surfactants in glyphosate formulations can increase the relative acute toxicity of the formulation.[93][94] In a 2017 risk assessment, the European Chemicals Agency (ECHA) wrote: "There is very limited information on skin irritation in humans. Where skin irritation has been reported, it is unclear whether it is related to glyphosate or co-formulants in glyphosate-containing herbicide formulations." The ECHA concluded that available human data was insufficient to support classification for skin corrosion or irritation.[95] 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.[93]

The consensus among national pesticide regulatory agencies and scientific organizations is that labeled uses of glyphosate have demonstrated no evidence of human carcinogenicity.[96] The Joint FAO/WHO Meeting on Pesticide Residues (JMPR),[97] the European Commission, the Canadian Pest Management Regulatory Agency, the Australian Pesticides and Veterinary Medicines Authority[98] and the German Federal Institute for Risk Assessment[99] have concluded that there is no evidence that glyphosate poses a carcinogenic or genotoxic risk to humans. The EPA has classified glyphosate as "not likely to be carcinogenic to humans."[100][101] One international scientific organization, the International Agency for Research on Cancer, classified glyphosate in Group 2A, "probably carcinogenic to humans" in 2015.[10][8]

There is weak evidence human cancer risk might increase as a result of occupational exposure to large amounts of glyphosate, such as agricultural work, but no good evidence of such a risk from home use, such as in domestic gardening.[102] According to a systematic review and meta-analysis published in 2016, when weak statistical associations with cancer have been found, such observations have been attributed to bias and confounding in correlational studies due to workers often being exposed to other known carcinogens.[103] The review reported that studies that show an effect between glyphosate use and non-Hodgkin lymphoma have been criticized for not assessing these factors, underlying quality of studies being reviewed, or whether the relationship is causal rather than only correlational.[103] Writing for the Natural Resources Defense Council environmental advocacy group, Jennifer Sass criticized the influence exerted by Monsanto on research about glyphosate safety, and noted that the review was funded by Monsanto.[104]

A meta-analysis published in 2019 looked at whether there was an association between an increased risk of non-Hodgkin lymphoma in humans and high cumulative exposures to glyphosate-based herbicides. The analysis used the most recent update of the Agricultural Health Study cohort published in 2018 and five case-control studies published in 2019. The research found a "compelling link" between exposures to glyphosate-based herbicides and increased risk for non-Hodgkin lymphoma.[105]

Amongst mammals, glyphosate is considered to have "low to very low toxicity". The LD₅₀ of glyphosate is 5,000 mg/kg for rats, 10,000 mg/kg in mice and 3,530 mg/kg in goats. The acute dermal LD₅₀ in rabbits is greater than 2,000 mg/kg. Indications of glyphosate toxicity in animals typically appear within 30 to 120 minutes following ingestion of a large enough dose, and include initial excitability and tachycardia, ataxia, depression, and bradycardia, although severe toxicity can develop into collapse and convulsions.[52]

A review of unpublished short-term rabbit-feeding studies reported severe toxicity effects at 150 mg/kg/day and "no observed adverse effect level" doses ranging from 50 to 200 mg/kg/day.[106] Glyphosate can have carcinogenic effects in nonhuman mammals. These include the induction of positive trends in the incidence of renal tubule carcinoma and haemangiosarcoma in male mice, and increased pancreatic islet-cell adenoma in male rats.[8] In reproductive toxicity studies performed in rats and rabbits, no adverse maternal or offspring effects were seen at doses below 175–293 mg/kg/day.[52]

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.[107]

In many freshwater invertebrates, glyphosate has a 48-hour LC₅₀ ranging from 55 to 780 ppm. The 96-hour LC₅₀ is 281 ppm for grass shrimp (Palaemonetas vulgaris) and 934 ppm for fiddler crabs (Uca pagilator). These values make glyphosate "slightly toxic to practically non-toxic".[52]

The antimicrobial activity of glyphosate has been described in the microbiology literature since its discovery in 1970 and the description of glyphosate's mechanism of action in 1972. Efficacy was described for numerous bacteria and fungi.[108] 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.[109] Inhibition can occur with some Rhizobium species important for soybean nitrogen fixation, especially under moisture stress.[110]

Degradation pathway of glyphosate in the ground[84]

When glyphosate comes into contact with the soil, it can be bound to soil particles, thereby slowing its degradation.[83][111] 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.[112] A 2016 meta-analysis concluded that at typical application rates glyphosate had no effect on soil microbial biomass or respiration.[113] A 2016 review noted that contrasting effects of glyphosate on earthworms have been found in different experiments with some species unaffected, but others losing weight or avoiding treated soil. Further research is required to determine the impact of glyphosate on earthworms in complex ecosystems.[114]

In 2007, the EPA selected glyphosate for further screening through its Endocrine Disruptor Screening Program (EDSP). Selection for this program is based on a compound's prevalence of use and does not imply particular suspicion of endocrine activity.[115] On June 29, 2015, the EPA released Weight of Evidence Conclusion of the EDSP Tier 1 screening for glyphosate, recommending that glyphosate not be considered for Tier 2 testing. The Weight of Evidence conclusion stated "...there was no convincing evidence of potential interaction with the estrogen, androgen or thyroid pathways."[116] A review of the evidence by the European Food Safety Authority published in September 2017 showed conclusions similar to those of the EPA report.[117]

Some studies have found causal relationships between glyphosate and increased or decreased disease resistance.[118] Exposure to glyphosate has been shown to change the species composition of endophytic bacteria in plant hosts, which is highly variable.[119]

Glyphosate-based formulations may contain a number of adjuvants, the identities of which may be proprietary.[120] Surfactants are used in herbicide formulations as wetting agents, to maximize coverage and aid penetration of the herbicide(s) through plant leaves. As agricultural spray adjuvants, surfactants may be pre-mixed into commercial formulations or they may be purchased separately and mixed on-site.[121]

Polyethoxylated tallow amine (POEA) is a surfactant used in the original Roundup formulation and was commonly used in 2015.[122] Different versions of Roundup have included different percentages of POEA. A 1997 US government report said that Roundup is 15% POEA while Roundup Pro is 14.5%.[123] Since POEA is more toxic to fish and amphibians than glyphosate alone, POEA is not allowed in aquatic formulations.[124][123][125] A 2000 review of the ecotoxicological data on Roundup shows at least 58 studies exist on the effects of Roundup on a range of organisms.[84] This review concluded that "...for terrestrial uses of Roundup minimal acute and chronic risk was predicted for potentially exposed non-target organisms".[126]

Acute toxicity and chronic toxicity are dose-related. Skin exposure to ready-to-use concentrated glyphosate formulations can cause irritation, and photocontact dermatitis has been occasionally reported. These effects are probably due to the preservative benzisothiazolin-3-one. Severe skin burns are very rare.[93] 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.[93] Death has been reported after deliberate overdose.[93][92] Ingestion of Roundup 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.[127] Adult consumption of more than 85 ml of concentrated product can lead to corrosive esophageal burns and kidney or liver damage. More severe cases cause "respiratory distress, impaired consciousness, pulmonary edema, infiltration on chest X-ray, shock, arrhythmias, renal failure requiring haemodialysis, metabolic acidosis, and hyperkalaemia" and death is often preceded by bradycardia and ventricular arrhythmias.[93] While the surfactants in formulations generally do not increase the toxicity of glyphosate itself, it is likely that they contribute to its acute toxicity.[93]

A 2000 review concluded that "under present and expected conditions of new use, there is no potential for Roundup herbicide to pose a health risk to humans".[128] A 2012 meta-analysis of epidemiological studies (seven cohort studies and fourteen case-control studies) of exposure to glyphosate formulations found no correlation with any kind of cancer.[129] The 2013 systematic review by the German Institute for Risk Assessment of epidemiological studies of workers who use pesticides, exposed to glyphosate formulations found no significant risk, stating that "the available data are contradictory and far from being convincing".[6]^{:vol. 1, 64–66} However, a 2014 meta-analysis of the same studies found a correlation between occupational exposure to glyphosate formulations and increased risk of B cell lymphoma, the most common kind of non-Hodgkin lymphoma. Workers exposed to glyphosate were about twice as likely to get B cell lymphoma.[7]

A 2016 systematic review and meta-analysis found no causal relationship between glyphosate exposure and risk of any type of lymphohematopoietic cancer including non-Hodgkin lymphoma and multiple myeloma.[103] The same review noted that the positive associations found may be due to bias and confounding.[103] The Natural Resources Defense Council has criticized that review, noting that it was funded by Monsanto.[104]

A 2015 systematic review of 10 observational studies found that except for an excess of attention deficit hyperactivity disorder among children born to glyphosate appliers, there was no evidence that glyphosate exposure among pregnant mothers caused adverse developmental outcomes in their children. Noting the limited size and scope of the review articles available, the authors noted that "these negative findings cannot be taken as definitive evidence that GLY, at current levels of occupational and environmental exposures, brings no risk for human development and reproduction."[130]

Glyphosate products for aquatic use generally do not use surfactants, and aquatic formulations do not use POEA due to aquatic organism toxicity.[124] Due to the presence of POEA, such glyphosate formulations only allowed for terrestrial use are more toxic for amphibians and fish than glyphosate alone.[124][123][125] The half-life of POEA (21–42 days) is longer than that for glyphosate (7–14 days) in aquatic environments.[131] Aquatic organism exposure risk to terrestrial formulations with POEA is limited to drift or temporary water pockets where concentrations would be much lower than label rates.[124]

Some researchers have suggested the toxicity effects of pesticides on amphibians may be different from those of other aquatic fauna because of their lifestyle; amphibians may be more susceptible to the toxic effects of pesticides because they often prefer to breed in shallow, lentic, or ephemeral pools. These habitats do not necessarily constitute formal water-bodies and can contain higher concentrations of pesticide compared to larger water-bodies.[125][132] Studies in a variety of amphibians have shown the toxicity of GBFs containing POEA to amphibian larvae. These effects include interference with gill morphology and mortality from either the loss of osmotic stability or asphyxiation. At sub-lethal concentrations, exposure to POEA or glyphosate/POEA formulations have been associated with delayed development, accelerated development, reduced size at metamorphosis, developmental malformations of the tail, mouth, eye and head, histological indications of intersex and symptoms of oxidative stress.[125] Glyphosate-based formulations can cause oxidative stress in bullfrog tadpoles.[10]

A 2003 study of various formulations of glyphosate found, "[the] risk assessments based on estimated and measured concentrations of glyphosate that would result from its use for the control of undesirable plants in wetlands and over-water situations showed that the risk to aquatic organisms is negligible or small at application rates less than 4 kg/ha and only slightly greater at application rates of 8 kg/ha."[133]

A 2013 meta-analysis reviewed the available data related to potential impacts of glyphosate-based herbicides on amphibians. According to the authors, the use of glyphosate-based pesticides cannot be considered the major cause of amphibian decline, the bulk of which occurred prior to the widespread use of glyphosate or in pristine tropical areas with minimal glyphosate exposure. The authors recommended further study of species- and development-stage chronic toxicity, of environmental glyphosate levels, and ongoing analysis of data relevant to determining what if any role glyphosate might be playing in worldwide amphibian decline, and suggest including amphibians in standardized test batteries.[134]

Several studies have not found mutagenic effects,[135] so glyphosate has not been listed in the United States Environmental Protection Agency or the International Agency for Research on Cancer databases. Various other studies suggest glyphosate may be mutagenic. The IARC monograph noted that glyphosate-based formulations can cause DNA strand breaks in various taxa of animals in vitro.[10]

A 2013 systematic review by the German Institute for Risk Assessment (BfR) examined more than 1000[136] epidemiological studies, animal studies, and in vitro studies. It found that "no classification and labelling for carcinogenicity is warranted" and did not recommend a carcinogen classification of either 1A or 1B.[6]^{:34–37, 139} It provided the review to EFSA in January 2014 which published it in December 2014.[6][137][138] In November 2015, EFSA published its conclusion in the Renewal Assessment Report (RAR), stating it was "unlikely to pose a carcinogenic hazard to humans".[139] The EU was largely informed by this report when it made its decision on the use of glyphosate in November 2017.[140]

EFSA's decision and the BfR report were criticized in an open letter published by 96 scientists in November 2015 saying that the BfR report failed to adhere to accepted scientific principles of open and transparent procedures.[141][142] The BfR report included unpublished data, lacked authorship, omitted references, and did not disclose conflict-of-interest information.[142]

In April 2016, Dr. Vytenis Andriukaitis, European Commissioner for Health and Food Safety, wrote an open letter to the Chair of the Board of the Glyphosate Task at Monsanto Europe asking to publish the full studies provided to the EFSA.[143]

In September 2017, The Guardian reported that sections of the Renewal Assessment Report prepared by the BfR and used by Efsa were copy-pasted from a study done by Monsanto. Some sections of copy contained small changes such as using British spelling rather than American forms but others were copied word for word, including most of the peer-reviewed papers that were used in the report. The Guardian reported that a "Monsanto spokesperson said that Efsa allowed renewal reports to be written this way because of the large volume of toxicological studies submitted."[140]

In a 1993 review, the EPA, considered glyphosate to be noncarcinogenic and relatively low in dermal and oral acute toxicity.[83] The EPA considered a "worst case" dietary risk model of an individual eating a lifetime of food derived entirely from glyphosate-sprayed fields with residues at their maximum levels. This model indicated that no adverse health effects would be expected under such conditions.[83] In 2015, the EPA initiated a review of glyphosate's toxicity and in 2016 reported that glyphosate is likely not carcinogenic.[5][144]

In May 2019, CNN reported that the agency had reaffirmed its position that, when used according to instructions, glyphosate is not carcinogenic. Noting company emails between Monsanto and EPA executives released in 2015 which appear to suggest that an EPA official offered to kill an agency glyphosate review,[145] CNN cited "concerns about whether Monsanto has had undue influence over regulators."[146]

In March 2015, 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 of their forthcoming monograph on glyphosate, and 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.[5][8][9][10][147] The IARC classifies substances for their carcinogenic potential, and "a few positive findings can be enough to declare a hazard, even if there are negative studies, as well." Unlike the BfR, it does not conduct a risk assessment, weighing benefits against risk.[148]

The BfR responded that IARC reviewed only a selection of what they had reviewed earlier, and argued that other studies, including a cohort study called Agricultural Health Study, do not support the classification.[149] The IARC report did not include unpublished studies, including one completed by the IARC panel leader.[150] The agency's international protocol dictates that only published studies be used in classifications of carcinogenicity,[151] since national regulatory agencies including the EPA have allowed agrochemical corporations to conduct their own unpublished research, which may be biased in support of their profit motives.[152]

Monsanto called the IARC report biased and said it wanted the report to be retracted.[153] In 2017, internal documents from Monsanto were made public by lawyers pursuing litigation against the company,[154] who used the term "Monsanto papers" to describe the documents.[155] This term was later used also by Leemon McHenry[156] and others.[157] The documents indicated Monsanto had planned a public relations effort to discredit the IARC report, and had engaged Henry Miller to write a 2015 opinion piece in Forbes Magazine challenging the report. Miller did not reveal the connection to Forbes, and according to the New York Times, when Monsanto asked him if he was interested in writing such an article, he replied "I would be if I could start from a high-quality draft" provided by the company.[158] Once this became public, Forbes removed his blog from their site.

Two journalists from Le Monde won the 2018 European Press Prize for a series of articles on the documents, also titled Monsanto Papers. Their reporting described, among other things, Monsanto's lawyers' letters demanding that IARC scientists turn over documents relating to Monograph 112, which contained the IARC finding that glyphosate was a "probable carcinogen"; several of the scientists condemned these letters as intimidating.[159]

A 2017 review done by personnel from EFSA and BfR argued that the differences between the IARC's and EFSA's conclusions regarding glyphosate and cancer were due to differences in their evaluation of the available evidence. The review concluded that "Two complementary exposure assessments ... suggests that actual exposure levels are below" the reference values identified by the EFSA "and do not represent a public concern."[160]

In contrast, a 2016 analysis concluded that in the EFSA's Renewal Assessment Report, "almost no weight is given to studies from the published literature and there is an over-reliance on non-publicly available industry-provided studies using a limited set of assays that define the minimum data necessary for the marketing of a pesticide", arguing that the IARC's evaluation of probably carcinogenic to humans "accurately reflects the results of published scientific literature on glyphosate".[161]

In October 2017, an article in The Times revealed that Christopher Portier, a scientist advising the IARC in the assessment of glyphosate and advocate for its classification as possibly carcinogenic, had received consulting contracts with two law firm associations representing alleged glyphosate cancer victims that included a payment of US$160,000 to Portier.[162][163] The IARC final report was also found to have changed compared to an interim report, through the removal of text saying certain studies had found glyphosate was not carcinogenic in that study's context, and through strengthening a conclusion of "limited evidence of animal carcinogenicity," to "sufficient evidence of animal carcinogenicity".[164]

In March 2015, the California Office of Environmental Health Hazard Assessment (OEHHA) announced plans to have glyphosate listed as a known carcinogen based on the IARC assessment. In 2016, Monsanto started a case against OEHHA and its acting director, Lauren Zeise,[165] but lost the suit in March 2017.[166]

Glyphosate was listed as "known to the State of California to cause cancer" in 2017.[167] In February 2018, as part of an ongoing case, an injunction was issued prohibiting California from enforcing carcinogenicity labeling requirements for glyphosate until the case was resolved. The injunction stated that arguments by California "[do] not change the fact that the overwhelming majority of agencies that that have examined glyphosate have determined it is not a cancer risk.".[168] In August 2019, the EPA also said it no longer allow labels claiming glyphosate is a carcinogen, as those claims would "not meet the labeling requirements of the Federal Insecticide, Fungicide, and Rodenticide Act" and misinform the public.[169]

On March 15, 2017 the European Chemicals Agency (ECHA) announced recommendations proceeding from a risk assessment of glyphosate performed by ECHA's Committee for Risk Assessment (RAC). Their recommendations maintained the current classification of glyphosate as a substance causing serious eye damage and as a substance toxic to aquatic life. However, the RAC did not find evidence implicating glyphosate to be a carcinogen, a mutagen, toxic to reproduction, nor toxic to specific organs.[170]

In the 1990s, no glyphosate-resistant weeds were known to exist.[171] By 2014, glyphosate-resistant weeds dominated herbicide-resistance research. At that time, 23 glyphosate-resistant species were found in 18 countries.[172] "Resistance evolves after a weed population has been subjected to intense selection pressure in the form of repeated use of a single herbicide."[171][173]

According to Ian Heap, a weed specialist, who completed his PhD on resistance to multiple herbicides in annual ryegrass (Lolium rigidum) in 1988[174] – the first case of an herbicide-resistant weed in Australia[175] – by 2014 the Lolium rigidum was the "world’s worst herbicide-resistant weed with instances in "12 countries, 11 sites of action, 9 cropping regimens" and affecting over 2 million hectares.[172] Annual ryegrass was known to be resistant to herbicides since 1982. The first documented case of glyphosate-resistant L. rigidum was reported in Australia in 1996 near Orange, New South Wales.[176][177][178] In 2006, farmers associations were reporting 107 biotypes of weeds within 63 weed species with herbicide resistance.[179] In 2009, Canada identified its first resistant weed, giant ragweed, and at that time 15 weed species had been confirmed as resistant to glyphosate.[173][180] As of 2010, in the United States 7 to 10 million acres (2.8 to 4.0 million hectares) of soil were afflicted by herbicide-resistant weeds, or about 5% of the 170 million acres planted with corn, soybeans, and cotton, the crops most affected, in 22 states.[181] In 2012, Charles Benbrook reported that the Weed Science Society of America listed 22 herbicide-resistant in the U.S., with over 5.7×10^⁶ ha (14×10^⁶ acres) infested by GR weeds and that Dow AgroSciences had carried out a survey and reported a figure of around 40×10^⁶ ha (100×10^⁶ acres).[182] The International Survey of Herbicide Resistant Weeds database lists species that are resistant to glyphosate.[183]

In response to resistant weeds, farmers are hand-weeding, using tractors to turn over soil between crops, and using other herbicides in addition to glyphosate.

Monsanto scientists have found that some resistant weeds have as many as 160 extra copies of a gene called EPSPS, the enzyme glyphosate disrupts.[184]

Palmer amaranth (Amaranthus palmeri)

In 2004, a glyphosate-resistant variation of Palmer amaranth was found in the U.S. state of Georgia and confirmed by a 2005 study.[185] In 2005, resistance was also found in North Carolina.[186] The species can quickly become resistant to multiple herbicides and has developed multiple mechanisms for glyphosate resistance due to selection pressure.[187][186] The glyphosate-resistant weed variant is now widespread in the southeastern United States.[185][188] Cases have also been reported in Texas[188] and Virginia.[189]

Horseweed (Conyza canadensis)

Conyza bonariensis (also known as hairy fleabane and buva) and Conyza canadensis (known as horseweed or marestail) are other weed species that have lately developed glyphosate resistance.[190][191][192] A 2008 study on the current situation of glyphosate resistance in South America concluded "resistance evolution followed intense glyphosate use" and the use of glyphosate-resistant soybean crops is a factor encouraging increases in glyphosate use.[193] In the 2015 growing season, glyphosate-resistant marestail proved to be especially problematic to control in Nebraska production fields.[194]

Ryegrass (Lolium perenne)

Glyphosate-resistant ryegrass (Lolium) has occurred in most of the Australian agricultural areas and other areas of the world. All cases of evolution of resistance to glyphosate in Australia were characterized by intensive use of the herbicide while no other effective weed control practices were used. Studies indicate the resistant ryegrass does not compete well against nonresistant plants and their numbers decrease when not grown under conditions of glyphosate application.[195]

Glyphosate-resistant Johnson grass (Sorghum halepense) has been found in Argentina as well as Arkansas, Louisiana, and Mississippi.[196]

Use of 2-4 D and other herbicides like glyphosate to clear milkweed along roads and fields may have contributed to a decline in monarch butterfly populations in the Midwestern United States.[197] Along with deforestation and adverse weather conditions,[198] the decrease in milkweed contributed to an 81% decline in monarchs.[199][200] The Natural Resources Defense Council (NRDC) filed a suit against the EPA in 2015, in which it argued that the agency ignored warnings about the potentially dangerous impacts of glyphosate usage on monarchs.[201]

In April 2014, the legislature of the Netherlands passed legislation prohibiting sale of glyphosate to individuals for use at home; commercial sales were not affected.[203]

In June 2015, the French Ecology Minister asked nurseries and garden centers to halt over-the-counter sales of glyphosate in the form of Monsanto's Roundup. This was a nonbinding request and all sales of glyphosate remain legal in France until 2022, when it was planned to ban the substance for home gardening.[204] However, more recently the French parliament decided to not to impose a definitive date for such a ban.[205] In January 2019, "the sale, distribution, and use of Roundup 360 [wa]s banned" in France. Exemptions for many farmers were later implemented, and a curb of its use by 80% for 2021 is projected.[206][207]

A vote on the relicensing of glyphosate in the EU stalled in March 2016. Member states France, Sweden, and the Netherlands objected to the renewal.[208] A vote to reauthorize on a temporary basis failed in June 2016[209] but at the last-minute the license was extended for 18 months until the end of 2017.[210]

On 27 November 2017, a majority of eighteen EU member states voted in favor of permitting the use of herbicide glyphosate for five more years. A qualified majority of sixteen states representing 65% of EU citizens was required.[211] The German Minister of Agriculture, Christian Schmidt, unexpectedly voted in favor while the German coalition government was internally divided on the issue which usually results in Germany abstaining.[212]

In December 2018, attempts were made to reopen the decision to license the weed-killer. These were condemned by Conservative MEPs, who said the proposal was politically motivated and flew in the face of scientific evidence.[213]

In March 2019, the European Court of Justice (ECJ) ordered the European Food Safety Authority (EFSA) to release all carcinogenicity and toxicity pesticide industry studies on glyphosate to the general public.[214]

In March 2019, the Austrian state of Carinthia outlawed the private use of glyphosate in residential areas while the commercial application of the herbicide is still permitted for farmers. The use of glyphosate by public authorities and road maintenance crews was already halted a number of years prior to the current ban by local authorities.[215]

In June 2019, Deutsche Bahn and Swiss Federal Railways announced that glyphosate and other commonly used herbicides for weed eradication along railway tracks will be phased out by 2025, while more environmentally sound methods for vegetation control are implemented.[216][217]

In July 2019, the Austrian parliament voted to forbid glyphosate in Austria.[218]

In September 2019, the German Environment Ministry announced that the use of glyphosate will be banned from the end of 2023. The use of glyphosate-based herbicides will be reduced from 2020.[219]

The assessment process for an approval of glyphosate in the European Union will begin in December 2019. France, Hungary, the Netherlands and Sweden will jointly assess the application dossiers of the producers. The draft report of the assessment group will then be peer-reviewed by the ESFA before the current approval expires in December 2022.[220]

In September 2013, the Legislative Assembly of El Salvador approved legislation to ban 53 agrochemicals, including glyphosate; the ban on glyphosate was set to begin in 2015.[221][222][223]

In May 2015, the President of Sri Lanka banned the use and import of glyphosate, effective immediately.[224][225] However, in May 2018 the Sri Lankan government decided to re-authorize its use in the plantation sector.[226]

In May 2015, Bermuda blocked importation on all new orders of glyphosate-based herbicides for a temporary suspension awaiting outcomes of research.[227]

In May 2015, Colombia announced that it would stop using glyphosate by October 2015 in the destruction of illegal plantations of coca, the raw ingredient for cocaine. Farmers have complained that the aerial fumigation has destroyed entire fields of coffee and other legal produce.[64]

In April 2019, Vietnam's Ministry of Agriculture and Rural Development banned the use of glyphosate throughout the country. [228]

Thailand's National Hazardous Substances Committee decided to ban the use of glyphosate in October 2019[229] but reversed the decision in November 2019.[230]

In June 2018, Dewayne Johnson, a 46-year-old former California school groundskeeper who is dying of non-Hodgkin lymphoma, took Monsanto (which had been acquired by Bayer earlier that month) to trial in San Francisco County superior court, alleging that it has spent decades hiding the cancer-causing dangers of its Roundup herbicides. The judge ordered that jurors be allowed to consider both scientific evidence related to the cause of Johnson's cancer and allegations that Monsanto suppressed evidence of the risks, with possible punitive damages.[231][232] In August 2018, the jury awarded Johnson US$289 million in damages. Monsanto said they would appeal,[233] saying they were confident that glyphosate does not cause cancer when used appropriately.[234] In November 2018, the award was reduced to $78 million on appeal.[235]

In August 2018, the potential for additional cases was estimated at up to 4,000.[236] Bayer announced in April 2019 that over 13,000 lawsuits related to Roundup had been launched in the US.

In March 2019, a man was awarded $80 million in a lawsuit claiming Roundup was a substantial factor in his cancer,[237][238] resulting in Costco stores discontinuing sales.[239] In July 2019, U.S. District Judge Vince Chhabria reduced the settlement to $26 million.[240] Chhabria stated that a punitive award was appropriate because the evidence "easily supported a conclusion that Monsanto was more concerned with tamping down safety inquiries and manipulating public opinion than it was with ensuring its product is safe." Chhabria stated that there is evidence is on both sides concerning whether glyphosate causes cancer and that the behavior of Monsanto showed "a lack of concern about the risk that its product might be carcinogenic."[240]

On 13 May 2019 a jury in California ordered Bayer to pay a couple $2 billion in damages after finding that the company had failed to adequately inform consumers of the possible carcinogenicity of Roundup.[241] On July 26, 2019, an Alameda County judge cut the settlement to $86.7 million, stating that the judgement by the jury exceeded legal precedent.[242]

Using litigation discovery emails it was later revealed that in 2015 when Monsanto was discussing papers they wanted to see published to counter the expected IARC glyphosate results they wrote in an email, "An option would be to add Greim and Kier or Kirkland to have their names on the publication, but we would be keeping the cost down by us doing the writing and they would just edit & sign their names so to speak. Recall that is how we handled Williams Kroes & Munro, 2000."[243]

In June 2020 Bayer, which acquired Monsanto in 2018, agreed to a $10 billion settlement as a result of a number of class-action lawsuits alleging that Roundup had caused cancer.[244]

The New York Times reported that in 1996, "Dennis C. Vacco, the Attorney General of New York, ordered the company Monsanto to pull ads that said Roundup was "safer than table salt" and "practically nontoxic" to mammals, birds and fish. The company withdrew the spots, but also said that the phrase in question was permissible under E.P.A. guidelines."[245]

In 2001, French environmental and consumer rights campaigners brought a case against Monsanto for misleading the public about the environmental impact of its herbicide Roundup, on the basis that glyphosate, Roundup's main component, is classed as "dangerous for the environment" and "toxic for aquatic organisms" by the European Union. Monsanto's advertising for Roundup had presented it as biodegradable and as leaving the soil clean after use. In 2007, Monsanto was convicted of false advertising and was fined 15,000 euros. Monsanto's French distributor Scotts France was also fined 15,000 euros. Both defendants were ordered to pay damages of 5,000 euros to the Brittany Water and Rivers Association and 3,000 euros to the Consommation Logement Cadre de vie, one of the two main general consumer associations in France.[246] Monsanto appealed and the court upheld the verdict; Monsanto appealed again to the French Supreme Court, and in 2009 it also upheld the verdict.[247]

In 2016, a lawsuit was filed against Quaker Oats in the Federal district courts of both New York and California after trace amounts of glyphosate were found in oatmeal. The lawsuit alleged that the claim of "100% natural" was false advertising.[248] That same year General Mills dropped the label "Made with 100% Natural Whole Grain Oats" from their Nature Valley granola bars after a lawsuit was filed that claimed the oats contained trace amounts of glyphosate.[249]

United States companies have cited trade issues with glyphosate being dumped into the western world market areas by Chinese companies and a formal dispute was filed in 2010.[250][251]