We live in a time when we are bombarded with information about harmful substances in the food we eat. In a way, it can be said that the discourse against the technification of food production has prevailed among the general public. Among these substances are the herbicides used to control weeds in crops, and one in particular stands out: the widely used but controversial glyphosate.
Gardening enthusiasts knows that any crop, whether ornamental or food, will quickly become overrun by weeds if left unchecked. The history of agriculture is also a history of weeds, unwanted species that grow invasively and vigorously because they are well adapted to their environment. But weed control is a more recent phenomenon. Before the 20th century, mechanical means or soil modification were used, together with certain salts. The first herbicides, such as 2,4-D (2,4-Dichlorophenoxyacetic acid), were developed after the Second World War for use in warfare.
Broadly speaking there are two types of herbicides: contact herbicides, which kill where they touch the plant, and systemic herbicides, which are absorbed by the plant and distributed through its tissues. They are divided into different groups according to their mechanism of action and the biochemical process they alter. There is a wide range of products on the market. Some have been banned, such as Agent Orange, a mixture of 2,4-D and 2,4,5-T used by the United States to defoliate the jungle during the Vietnam War. This second compound, 2,4,5-T, contained high levels of dioxins that are extremely toxic.
The regulation of herbicides varies from country to country, but some have been shown to be toxic. 2,4-D remains one of the most widely used herbicides in the world. The US Environmental Protection Agency states: “2,4-D is not Agent Orange.” Harmful 2,4,5-T is no longer on the market, but some of the products still in use are also in the spotlight; for example, paraquat, which is extremely toxic to humans and the environment and, according to environmental scientist Nedeljka Rosic and her colleagues at Southern Cross University, “one sip can kill you,” is banned in more than 50 countries, including the EU, the UK and China, but not the US, Australia or other nations. Similarly, atrazine, which is particularly toxic to amphibians, has been withdrawn in the EU because of groundwater contamination, but remains one of the most widely used pesticides in the US and other countries.
The glyphosate boom
But the star of all herbicides, the most widely used in the world, is glyphosate. In 1950, the Swiss chemist Henry Martin of the Cilag company synthesised a compound that was patented 14 years later as a chemical chelator, a compound that sequesters minerals from the environment. It had no practical use until 1970, when John Franz of the Monsanto Company in the US independently rediscovered the same formula while testing variations of a compound with herbicidal activity. In 1974, Monsanto brought it to the market under the name Roundup.
Glyphosate (chemical name N-(phosphonomethyl)glycine) is a systemic herbicide that is absorbed by plants mainly through their leaves. It works by inhibiting an enzyme called EPSP synthase, which is involved in the synthesis of three amino acids. But there is a downside to such a powerful, broad-spectrum herbicide: in principle, it kills all plants without distinction. Over time, however, herbicide resistance tends to develop, particularly in weeds, affecting the use of glyphosate and other compounds.
The use of this herbicide exploded after 1996, when Monsanto launched Roundup Ready, a collection of transgenic soybean, maize and cotton crops tolerant to glyphosate, allowing the herbicide to be used without damaging the harvest. Other crops such as alfalfa and sugar beet have since been added. These GM varieties account for about 56% of the world’s use of glyphosate. This herbicide was also marketed on the basis that it was apparently harmless to humans, less toxic than caffeine, vinegar or paracetamol, and more environmentally friendly because it breaks down relatively easily, so it does not permanently pollute water.
Lack of consensus
The safety of glyphosate has been extensively debated and analysed, particularly in light of its widespread use. After an exhaustive review of studies, the World Health Organisation’s International Agency for Research on Cancer (IARC) classified it as a probable human carcinogen in 2015, based on the occurrence of liver and kidney tumours in animals and possible links to non-Hodgkin’s lymphoma in humans, as well as hormone-mediated epigenetic changes. Studies show the presence of glyphosate in the urine of pregnant women living near crop fields, raising concerns about a possible link to premature birth and reduced foetal growth. An effect on the bee microbiome has also been found.
IARC’s opinion is not shared by regulators in the US and Europe, nor by many experts, but there are lawsuits by thousands of cancer patients against Bayer, the company that acquired Monsanto in 2018. In the EU, glyphosate’s approval was renewed for 10 years in 2023, although each country can adopt its own regulation. Given that the patent for glyphosate has expired and that it remains the preferred alternative, its large-scale use can be expected to continue for decades to come. There is still no absolute consensus among scientists, but research continues.
Javier Yanes
Main picture credit: Costfoto/NurPhoto via Getty Images.
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