glyphosate

glyphosate
Name	Glyphosate
IUPACName	N-(phosphonomethyl)glycine
OtherNames	Roundup

glyphosate. It is a broad-spectrum systemic herbicide and crop desiccant, first brought to market by Monsanto under the trade name Roundup in 1974. As an organophosphorus compound, it is absorbed through foliage and translocates to growing points, effectively killing a wide variety of plants. Its discovery revolutionized agricultural practices, particularly with the subsequent development of genetically modified glyphosate-resistant crops, but it has also become one of the most intensely debated agrochemicals in modern history due to health and environmental concerns.

Chemical properties and synthesis

Glyphosate is a phosphonic acid derivative, specifically an aminophosphonic analogue of the natural amino acid glycine. Its molecular structure features a stable carbon-phosphorus bond, which is uncommon in biological systems and contributes to its environmental persistence under certain conditions. The compound is typically synthesized via several industrial routes, most commonly involving the reaction of phosphorous acid with formaldehyde and glycine in a Mannich reaction. It is commercially available as various salts, such as the isopropylamine, diammonium, or potassium salts, which enhance its solubility in water for practical application. In its pure form, it appears as a white crystalline powder with low volatility and is amphoteric, capable of acting as both an acid and a base.

History and development

The molecule was first synthesized in 1950 by Swiss chemist Henri Martin at the pharmaceutical company Cilag, but its herbicidal properties remained unknown. Its potential as a herbicide was discovered in 1970 by John E. Franz, a chemist working for the Monsanto Company. Franz's research, for which he received the National Medal of Technology and Innovation, identified its unique ability to inhibit a crucial plant enzyme. Monsanto patented the compound and introduced it to the market in 1974, initially marketing it as a non-selective herbicide for industrial and orchard use. The subsequent development and 1996 commercial release of genetically modified "Roundup Ready" crops, such as soybean, maize, and cotton, engineered by Monsanto to tolerate its application, led to an unprecedented surge in its global agricultural use.

Mechanism of action

Glyphosate acts by specifically inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a critical component of the shikimate pathway. This biochemical pathway, absent in animals but essential in plants, bacteria, archaea, and fungi, is responsible for the biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan. By binding competitively to the EPSPS enzyme, it blocks the conversion of shikimate-3-phosphate and phosphoenolpyruvate to 5-enolpyruvylshikimate-3-phosphate. This inhibition leads to a depletion of these essential amino acids, a subsequent shutdown of protein synthesis, and an accumulation of shikimate-3-phosphate and shikimic acid in plant tissues, ultimately causing plant death over several days.

Agricultural and non-agricultural uses

Its primary use is in agriculture, where it is applied for weed control in crops genetically engineered for resistance, a system dominant in the United States, Brazil, and Argentina. It is also used as a pre-harvest desiccant on non-resistant crops like wheat, oats, and lentils to dry the plants for easier harvesting. Beyond farming, it is widely utilized in forestry management, urban landscaping, and for controlling aquatic vegetation. Home gardeners commonly use it for weed control in driveways and garden paths. Furthermore, it has applications in areas such as railroad track maintenance, utility right-of-ways, and in programs to eradicate illicit crops like coca in regions such as Colombia.

Health and environmental controversies

The compound has been at the center of major scientific and public controversy. In 2015, the International Agency for Research on Cancer (IARC), an agency of the World Health Organization, classified it as "probably carcinogenic to humans" (Group 2A). This assessment starkly contrasts with conclusions from other regulatory bodies like the European Food Safety Authority and the United States Environmental Protection Agency, which have not classified it as a human carcinogen. Environmental concerns include potential impacts on biodiversity, the development of herbicide-resistant "superweeds," and effects on non-target organisms, including monarch butterfly populations and soil microbiome health. High-profile litigation, notably the case of Dewayne Johnson in California, has resulted in substantial jury awards alleging a link between exposure and non-Hodgkin lymphoma.

Regulation and legal status

Regulatory status varies significantly across the globe, reflecting the divergent scientific and political interpretations of its risk profile. In the European Union, its license for use was controversially renewed for a shortened period in 2023 following intense debate among member states like France and Germany. Countries including Austria and Luxembourg have enacted national bans. In the United States, the Environmental Protection Agency maintains its registration for use, though some states and municipalities have imposed restrictions. Nations such as Vietnam and Thailand have banned or severely restricted its use, while others, like Australia and Canada, continue to permit it with specific guidelines. The legal landscape continues to evolve, shaped by ongoing scientific reviews, public advocacy from groups like the Environmental Working Group, and multinational litigation.

Category:Herbicides Category:Organophosphorus compounds Category:IARC Group 2A carcinogens