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Glyphosate is primarily used to combat weeds in agriculture, despite criticism of the risks it poses to people and nature. Compared to other active ingredients, experts see glyphosate as an advantage, but they are still calling for a rethink.
“Probably carcinogenic” – at least since this classification by the International Agency for Research on Cancer (IARC) from the World Health Organization (WHO) in 2015, no pesticide active ingredient has been discussed as heatedly as glyphosate. Over time, additional points of criticism arose, such as the negative consequences of glyphosate use for biodiversity and the detected residues in food. But what about the individual factors?
The supposed carcinogenic effects of glyphosate in particular continue to play a major role in both social and political debates. Numerous authorities come to a different assessment than the IARC, including the German Federal Institute for Risk Assessment (BfR), the European Food Safety Authority (EFSA) and the WHO’s Joint Meeting on Pesticide Residues (JMPR).
IARC includes additives in the assessment
One reason for these different opinions is that, unlike the other institutions, the IARC not only looked at the active ingredient glyphosate, but also the additives that are added to some products. Some of these have now become dangerous in the EU, such as POE tallow amines forbidden. In addition, the IARC does not take exposure – i.e. the amount at which a substance can be carcinogenic – into account. It only assesses whether a substance can generally cause cancer, regardless of the dose.
The EFSA and the BfR, which is responsible for toxicological assessment in Germany, are therefore involved other reviews. “As a result of the renewed assessment, no critical concerns were identified in the area of health risk assessment,” writes a spokesman for the BfR. The European Chemicals Agency (ECHA) concluded that classifying glyphosate as a carcinogen is not justified. This classification is shared by the EFSA and the BfR.
The toxicological reference values depend on body weight: A daily intake of 0.5 milligrams per kilogram of body weight is considered acceptable (Acceptable Daily Intake). This means that this amount can be consumed every day for a lifetime without posing a significant health risk. The acute reference dose is an estimated value of 1.5 milligrams per kilogram of body weight. This dose can therefore be taken within a short period of time without any significant damage to health being expected.
There are also the so-called Maximum residue levels, which are not health reference values. For most types of fruit and vegetables, maximum glyphosate levels have been set according to the lower analytical limit of determination (usually 0.1 mg/kg). However, there are also exceptions where the residue levels may be higher, such as potatoes (0.5 mg/kg) and soybeans (20 mg/kg). For an adult weighing 60 kilograms, this would correspond to an acceptable daily amount of 1.5 kilograms of soybeans or six kilograms of potatoes.
According to the BfR, these “are never set higher than is required according to good agricultural practice”. “If a maximum residue level is exceeded, this does not mean that there is a health risk because there is usually a large gap to the toxicological reference values,” says the BfR.
Possible consequences for the intestinal flora
“If I look at the molecular situation, then in my opinion there is no indication that glyphosate’s structure is directly involved in a carcinogenic effect,” says Christoph Schäfers, director of the Fraunhofer Institute for Molecular Biology and Applied Ecology. However, an indirect effect cannot be ruled out.
Even if glyphosate only has a direct effect on plant organisms and bacteria, it can also have effects on people and animals – especially in the intestines. “The intestinal flora also consists of bacteria that are hindered by glyphosate from producing certain amino acids.” This could result in the intestinal flora being disrupted and, for example, a person’s immune system being attacked. According to Schäfers, there is still a need for research in this area in particular.
For example, it has been proven in cattle herds that the intestinal flora was influenced by glyphosate – albeit at a very high concentration. “Just because total herbicides containing glyphosate are cheap and readily available does not mean that they should be used everywhere,” says Schäfers. This error has now been corrected.
Glyphosate sales declined sharply since 2007
Products containing the active ingredient glyphosate are now banned in private gardens and public places such as parks and sports fields, and a general ban also applies in ecologically sensitive areas such as nature reserves. The use in agriculture has also been more strictly regulated: among other things, late use before the harvest in arable farming is prohibited and, when used on large areas, a minimum time interval must be maintained before the next spraying.
Compared to the first decade of the millennium, annual glyphosate sales in Germany have declined sharply. In 2007 sales were 7,608 tons, in 2022 it was 3,915 tons. In recent years, however, sales have remained relatively stable and have not fallen significantly.
Residues not necessarily harmful to health
There is always a lot of discussion about the residues of glyphosate and glyphosate degradation products. For a while, it was claimed, among other things, that glyphosate residues could even be detected in the mother’s breast. However, according to the BfR, this is not true. Health impairments are therefore not to be expected.
“Glyphosate is more water-soluble than most other pesticides,” says Schäfers. “And in breast milk you mainly find fat-soluble substances. You’re more likely to find lipophilic insecticides than glyphosate.”
The BfR also points out that the mere detection of glyphosate in various foods does not directly pose a health risk. There was a lot of media coverage around the residues found in beer. However, according to the BfR, the quantities detected were far too small to be really dangerous. Even with the highest glyphosate residue found in beer of 30 micrograms per liter, a 60 kilo adult would have to drink 1000 liters of beer in one day to ingest a health-threatening amount of glyphosate.
“The detection of residues is always a sign that a substance is very widespread if it can be found everywhere,” says Schäfers. “And that means you have to think about whether you’re using too much.” In principle, when it comes to residues, it should always be borne in mind that the detection also depends heavily on how good the examination options are. “We are now able to detect very low concentrations.” Therefore, there is no substance in the world that cannot be detected analytically. Twenty years ago things were different.
Aminomethylphosphonic acid (AMPA) plays a major role in the detection of glyphosate residues. This is a breakdown product of glyphosate and can be detected in the environment for longer than glyphosate itself. However, AMPA can also be formed from detergent residues and water softeners. However, it is often possible to estimate what these residues are due to based on the measurement location, says Schäfers. A new study from the University of Tübingen, which has not yet been independently reviewed, comes to the conclusion that agriculture is at least not the main source of glyphosate pollution in German waters.
Lack of alternatives
Glyphosate is also often criticized because of its negative consequences for biodiversity. The fact that wild plants no longer survive in fields treated with glyphosate also reduces the food supply, especially for insects.
However, from Schäfers’ point of view, this is not a specific problem with glyphosate, but rather a structural one. “How you remove the weeds, whether with glyphosate or mechanically, plays a minor role: the biodiversity in the field is reduced in both cases.” Ultimately, this is also the goal of conventional agriculture, as it keeps yields high.
Schäfers currently does not see any better chemical alternatives to glyphosate. “The mechanisms of action of the other pesticides involve different endpoints or different metabolic pathways that are present differently in environmental organisms, including in humans. That is why they are significantly more toxic to humans and animals.” In addition, one should not make the mistake of banning substances for which one at least knows well how they work and then replacing them with other substances whose dangers are unknown.
“Consumers need to rethink”
In order to protect biodiversity, there needs to be a rethink in agriculture and among consumers, says Schäfers. On the one hand, current cultivation practices are driving species extinction, but on the other hand, the rich harvests also enable low food prices in Germany. Greater consideration for biodiversity would therefore also be accompanied by price increases.
Christoph Gornott, head of the agroecosystem analysis and modeling department at the University of Kassel and head of the Adaptation in Agricultural Systems working group at the Potsdam Institute for Climate Impact Research (PIK), had also already called for fundamental change. “We have to rebuild the entire agricultural system; this cannot be solved with old farming practices alone. We have new problems and for this we need new and holistic answers.”