Monsanto's glyphosate-based herbicide Roundup was first developed in the 1970s. Between 1985 and 1996, Monsanto reduced the price of Roundup by 50%. Between 1990 and 1996 sales of Roundup have increased by around 20% per year. As of 2015 it is used in over 160 countries. Roundup is used most heavily on corn, soy and cotton crops that have been genetically modified to withstand the chemical, but in 2012 glyphosate was used in California to treat other crops like almond, peach, cantaloupe, onion, cherry, sweet corn and citrus.
Monsanto is the largest producer of glyphosate-based herbicides, but formulations from other manufacturers are available that use different inert ingredients. Other glyphosate-based formulations include Bronco, Glifonox, KleenUp, Ranger Pro, Rodeo, and Weedoff. As of 2010, more than 750 glyphosate products were on the market.
In 2014, the EPA approved Enlist Duo which was developed by Dow AgroSciences, despite widespread opposition. This herbicide combined two active ingredients: 2,4-D and glyphosate. Enlist Duo is intended for use with genetically modified crops that have also been developed by the Dow Chemical subsidiary. The initial approval was limited to the states of Illinois, Indiana, Iowa, Ohio, South Dakota and Wisconsin. However, in 2015, during the course of litigation the EPA found out that Dow had told the United States Patent and Trademark Office that Enlist Duo offers "synergistic herbicidal weed control." The EPA requested additional clarification about the "synergistic effects" and sought to reverse its approval pending a full review of the new information provided by Dow. In 2016, the 9th Circuit rejected the EPA's petition to vacate its approval of the herbicide.
Surfactants, solvents and preservatives are inert ingredients that are commonly added to glyphosate-based herbicide formulations.Polyethoxylated tallow amine (POEA) is a surfactant added to Roundup and other herbicides that helps the glyphosate penetrate the plant surface. Some surfactants that are added to herbicide formulations may increase glyphosate's toxicity.
The names of inert ingredients used in glyphosate formulations are usually not listed on the product labels. In 1997 the USDA listed the contents of the following formulations: Accord (45.5% glyphosate and 58.5% water), Rodeo (53.5% glyphosate and 46.5% water), Roundup (41.0% glyphosate, 1.5% related organic acids of glyphosate, .5% isopropylamine, 15.4% POEA, and 41.6% water) and Roundup Pro (41% glyphosate, 14.5% phosphate ester neutralized ethoxylated tallow amine and 44.5% water).
The lethal dose of different glyphosate-based formulations varies, especially with respect to the surfactants used. Formulations that include the surfactant POEA are more toxic than other formulations, especially for aquatic species. Due to the variety in available formulations, including five different glyphosate salts and different combinations of inert ingredients, it is difficult to determine how much surfactants contribute to the overall toxicity of each formulation.
The acute oral toxicity for mammals is low, but death has been reported after deliberate overdose. The surfactants in glyphosate formulations generally do not increase the toxicity of glyphosate itself towards humans, but probably do increase the acute toxicity of the formulation. 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. Consumption of over 85 ml of concentrated product are likely to cause serious symptoms in adults including burns due to corrosive effects as well as kidney and 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.
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.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.
Glyphosate formulations with POEA are generally more toxic to aquatic animals then terrestrial animals. Glyphosate formulations that include the surfactants POEA and MON 0818 (75% POEA) may have negative impacts on various aquatic organisms like protozoa, mussels, crustaceans, frogs and fish.