Glyphosate

Glyphosate (IUPAC name: N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase. It is used to kill weeds, especially annual broadleaf weeds and grasses that compete with crops. It was discovered to be an herbicide by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market for agricultural use in 1974 under the trade name Roundup. Monsanto's last commercially relevant United States patent expired in 2000. Farmers quickly adopted glyphosate for agricultural weed control, especially after Monsanto introduced glyphosate-resistant Roundup Ready crops, enabling farmers to kill weeds without killing their crops. In 2007, glyphosate was the most used herbicide in the United States' agricultural sector and the second-most used (after 2,4-D) in home and garden, government and industry, and commercial applications. From the late 1970s to 2016, there was a 100-fold increase in the frequency and volume of application of glyphosate-based herbicides (GBHs) worldwide, with further increases expected in the future, partly in response to the global emergence and spread of glyphosate-resistant weeds,:1 requiring greater application to maintain effectiveness. The development of glyphosate resistance in weed species is emerging as a costly problem. Glyphosate is absorbed through foliage, and minimally through roots, and transported to growing points. It inhibits a plant enzyme involved in the synthesis of three aromatic amino acids: tyrosine, tryptophan, and phenylalanine. It is therefore effective only on actively growing plants and is not effective as a pre-emergence herbicide. An increasing number of crops have been genetically engineered to be tolerant of glyphosate (e.g. Roundup Ready soybean, the first Roundup Ready crop, also created by Monsanto), which allows farmers to use glyphosate as a post-emergence herbicide against weeds. While glyphosate and formulations such as Roundup have been approved by regulatory bodies worldwide, concerns about their effects on humans and the environment persist, and have grown as the global usage of glyphosate increases. A number of regulatory and scholarly reviews have evaluated the relative toxicity of glyphosate as an herbicide. The German Federal Institute for Risk Assessment toxicology review in 2013 found that 'the available data is contradictory and far from being convincing' with regard to correlations between exposure to glyphosate formulations and risk of various cancers, including non-Hodgkin lymphoma (NHL). A meta-analysis published in 2014 identified an increased risk of NHL in workers exposed to glyphosate formulations. In March 2015, the World Health Organization's International Agency for Research on Cancer (IARC) classified glyphosate as 'probably carcinogenic in humans' (category 2A) based on epidemiological studies, animal studies, and in vitro studies. In contrast, the European Food Safety Authority concluded in November 2015 that 'the substance is unlikely to be genotoxic (i.e. damaging to DNA) 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 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 admissible daily maximum intake limits (one milligram/kg of body weight per day) for chronic toxicity. The European Chemicals Agency (ECHA) classified glyphosate as causing serious eye damage and toxic to aquatic life, but did not find evidence implicating it as a carcinogen, a mutagen, toxic to reproduction, nor toxic to specific organs. Glyphosate was first synthesized in 1950 by Swiss chemist Henry Martin, who worked for the Swiss company Cilag. The work was never published.:1 Stauffer Chemical patented the agent as a chemical chelator in 1964 as it binds and removes minerals such as calcium, magnesium, manganese, copper, and zinc. Somewhat later, glyphosate was independently discovered in the United States at Monsanto in 1970. Monsanto chemists had synthesized about 100 derivatives of aminomethylphosphonic acid as potential water-softening agents. Two were found to have weak herbicidal activity, and John E. Franz, a chemist at Monsanto, was asked to try to make analogs with stronger herbicidal activity. Glyphosate was the third analog he made.:1–2 Franz received the National Medal of Technology of the United States in 1987 and the Perkin Medal for Applied Chemistry in 1990 for his discoveries. Monsanto developed and patented the use of glyphosate to kill weeds in the early 1970s and first brought it to market in 1974, under the Roundup brandname. While its initial patent expired in 1991, Monsanto retained exclusive rights in the United States until its patent on the isopropylamine salt expired in September 2000.