Toxicity
Glyphosate is the active ingredient in herbicide formulations containing it. However, in addition to glyphosate salts, commercial formulations of glyphosate contain additives such as surfactants which vary in nature and concentration. Laboratory toxicology studies have suggested that other ingredients in combination with glyphosate may have greater toxicity than glyphosate alone.[47] Toxicologists have studied glyphosate alone, additives alone, and formulations.
Glyphosate toxicity
Glyphosate has a United States Environmental Protection Agency (EPA) Toxicity Class of III (on a I to IV scale, where IV is least dangerous) for oral and inhalation exposure.[48] Nonetheless, as with other herbicides, the EPA requires that products containing glyphosate carry a label that warns against oral intake, mandates the use of protective clothing, and instructs users not to re-enter treated fields for at least 4 hours.[48][49] Glyphosate does not bioaccumulate and breaks down rapidly in the environment.[50]
Human
The EPA considers glyphosate to be noncarcinogenic and relatively low in toxicity.[48] 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.[48]
Effects on fish and amphibians
Glyphosate is generally less persistent in water than in soil, with 12 to 60 day persistence observed in Canadian pond water, yet because glyphosate binds to soil, persistence of over a year has been observed in the sediments of ponds in Michigan and Oregon.[48] In streams, maximum glyphosate concentrations were measured immediately post-treatment and dissipated rapidly.[48] Glyphosate is "practically nontoxic to slightly toxic" for amphibians and fish.[51]
Soil degradation, and effects on micro-organism and worms
Degradation pathway of glyphosate in the ground[51]
When glyphosate comes into contact with the soil, it can be rapidly bound to soil particles and be inactivated.[48][52] Unbound glyphosate can be degraded by bacteria.[53]
In soils, half-lives vary from as little as three days at a site in Texas to 141 days at a site in Iowa.[52] In addition, the glyphosate metabolite aminomethylphosphonic acid has been found in Swedish forest soils up to two years after a glyphosate application.[54] Glyphosate adsorption to soil varies depending on the kind of soil.[55]
It has been suggested that glyphosate can harm the bacterial ecology of soil and cause micronutrient deficiencies in plants,[56] including nitrogen-fixing bacteria.[57] A 2012 study found that while Roundup had toxic effects at low levels on three food microorganisms (e.g. Lactobacillus delbrueckii), "glyphosate at these levels has no significant effect".[58]
...
Human
Data from the California Environmental Protection Agency's Pesticide Illness Surveillance Program, which also tracks other agricultural chemicals, shows that glyphosate-related incidents are some of the most common.[60][61] However, incident counts alone do not take into account the number of people exposed and the severity of symptoms associated with each incident.[61] For example, if hospitalization were used as a measure of the severity of incidents, then glyphosate would be considered relatively safe; over a 13-year period in California, none of the 515 reported hospitalizations were attributed to glyphosate.[61]
Deliberate ingestion of Roundup in quantities ranging from 85 to 200 ml 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.[62] There is a reasonable correlation between the amount of Roundup ingested and the likelihood of serious systemic sequelae or death. Ingestion of >85 ml of the concentrated formulation is likely to cause significant toxicity in adults. Corrosive effects – mouth, throat and epigastric pain and dysphagia – are common. Renal and hepatic impairment are also frequent and usually reflect reduced organ perfusion. Respiratory distress, impaired consciousness, pulmonary edema, infiltration on chest x-ray, shock, arrythmias, renal failure requiring haemodialysis, metabolic acidosis, and hyperkalaemia may occur in severe cases. Bradycardia and ventricular arrhythmias often present prior to death.
Dermal exposure to ready-to-use glyphosate formulations can cause irritation, and photo-contact dermatitis has been occasionally reported. These effects are probably due to the preservative Proxel (benzisothiazolin-3-one). 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.[47]
In vitro studies on human cells
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".[63] A 2002 review by the European Union reached the same conclusion.[64]
Glyphosate causes oxidative damage to human skin cells. Antioxidants such as vitamins C and E were found by one study to provide some protection against such damage, leading the authors to recommend that these chemicals be added to glyphosate formulations.[65] Severe skin burns are very rare.[47]
Endocrine disruption
A study published in 2000 found that Roundup interfered with an enzyme involved in testosterone production in mouse cell culture.[66] A study by the Seralini lab published in 2005 found that glyphosate interferes with aromatase, an estrogen biosynthesis enzyme, in cultures of human placental cells and that the Roundup formulation of glyphosate had stronger such activity.[67] A follow up study by the Seralini lab, published in 2009, showed similar results in human liver cells.[68] A study on rats published in 2010 found that administering Roundup Transorb orally to prepubescent rats at a dose of 0.25 mL/100 g of body weight, once a day for 30 days, reduced testosterone production and affected testicle morphology, but did not affect levels of estradiol and corticosterone.[69]
Monsanto has responded, saying that (a) Roundup formulations do contain surfactants (detergents) to help the active ingredient penetrate the waxy cuticle of the plant. (b) The surfactants are indeed more toxic than the glyphosate. (c) "If you put a detergent of any sort on cells in a petri dish, the cells get sick (and will die if you get the concentration high enough or recover if you remove the detergent soon enough)"; (d) the cell types chosen in these studies and the parameters measured were selected more to score political points than to help fully describe the risks of glyphosate and surfactants; (e) the experiments are artificial and not helpful – no one is supposed to drink Roundup, and it is not ever put on naked cells (we all have skin and workers are meant to wear protective clothes).[70]
In 2007, the EPA selected glyphosate for further screening through its Endocrine Disruptor Screening Program. Selection for this program is based on a compound's prevalence of use and does not imply particular suspicion of endocrine activity.[71]
Genetic damage
A 2009 study on mice found that a single intraperitoneal injection of Roundup in concentration of 25 mg/kg caused chromosomal aberrations and induction of the micronuclei.[72]
Other mammals
A review of the ecotoxicological data on Roundup shows there are at least 58 studies of the effects of Roundup itself on a range of organisms.[51] This review concluded that "for terrestrial uses of Roundup minimal acute and chronic risk was predicted for potentially exposed non-target organisms".
In a 2001, three groups of pregnant rats were fed, respectively, a regular diet with clean water, a regular diet with 0.2 ml glyphosate/ml drinking water; and a regular diet with 0.4 ml glyphosate/ml drinking water. Glyphosate induces a variety of functional abnormalities in fetuses and pregnant rats.[73] Also in recent mammalian research, glyphosate has been found to interfere with an enzyme involved testosterone production in mouse cell culture.[66]
Glyphosate is low in toxicity to rats when ingested by rats. The acute oral LD50 in rats is greater than 4320 mg/kg. Rats and mice were fed a diet containing 0, 3125, 6250, 12,500, 25,000, or 50,000 ppm of 99% pure glyphosate for 13 weeks. The two highest dose groups of male rats had a significant reduction in sperm concentrations, although concentrations were still within the historical range for that rat strain. The highest dose group of female rats had a slightly longer estrus cycle than the control group. The Reference Dose for glyphosate set by the EPA is 1.75 mg/kg/day and the maximum contaminant level set by the EPA is 0.7 mg/L[21][74]
The EPA,[75] the EC Health and Consumer Protection Directorate, and the UN World Health Organization have all concluded pure glyphosate is not carcinogenic. Opponents of glyphosate claim Roundup has been found to cause genetic damage, citing Peluso et al.[76] The authors concluded the damage was "not related to the active ingredient, but to another component of the herbicide mixture".
Mammal research indicates oral intake of 1% glyphosate induces changes in liver enzyme activities in pregnant rats and their fetuses.[77]
Laboratory studies have shown teratogenic effects of Roundup in animals.[78][79] These reports have proposed that the teratogenic effects are caused by impaired retinoic acid signaling.[80] News reports have supposed that regulators have been aware of these studies since 1980.[81]
Effects on fish and amphibians
A study of various formulations of glyphosate found that "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.".[82]
Glyphosate formulations are much more toxic for amphibians and fish than glyphosate alone.[51][83][84] "Aquaculture, freshwater and marine fisheries supply about 10% of world human calorie intake."[85] A study published in 2010 proposed commercial glyphosate can cause neural defects and craniofacial malformations in African clawed frogs (Xenopus laevis). The experiments used frog embryos that were incubated with 1:5000 dilutions of a commercial glyphosate solution. The frog embryos suffered diminution of body size, alterations of brain morphology, reduction of the eyes, alterations of the branchial arches and otic placodes, alterations of the neural plate, and other abnormalities of the nervous system. The authors suggested glyphosate itself was responsible for the observed results because injection of pure glyphosate produced similar results in a chicken model.[80]
Because of this known toxicity, only some formulations of glyphosate are registered for use in aquatic applications.[86][87] Monsanto and other companies produce glyphosate products with alternative surfactants that are specifically formulated for aquatic use, for example "Biactive" and "AquaMaster".[88] The glyphosate formulations registered for aquatic use have been found to have negligible adverse effects on sensitive amphibians.[89]
Soil degradation and effects on micro-organism and worms
A laboratory study published in 1992 indicated that glyphosate formulations could harm earthworms[90] and beneficial insects.[91] However, the reported effect of glyphosate on earthworms has been criticized.[51] The results conflict with results from field studies where no effects were noted for the number of nematodes, mites, or springtails after treatment with Roundup at 2 kilograms active ingredient per hectare.[92]
A 2009 study using a RoundUp formulation has concluded that absorption into plants delays subsequent soil-degradation, and can increase glyphosate persistence in soil from two to six times.[93]
Effect on plant health
A study published in 2005 found a correlation between an increase in the infection rate of wheat by fusarium head blight and the application of glyphosate, but the authors wrote: "because of the nature of this study, we could not determine if the association between previous GF (glyphosate formulation) use and FHB development was a cause-effect relationship".[94] Other studies have found causal relationships between glyphosate and decreased disease resistance.[95]
