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Based on extensive research, a group of leading scientists have argued that the maximum allowed residue levels of glyphosate, a commonly used pesticide, should be lowered. This reduction would lessen the damage to our gut bacteria (microbiomes) and our health.

Until recently, the effects of relatively low glyphosate levels on soil, plant, and animal microbiomes were unknown. Whilst some researchers found no negative effects, others found clear negative effects. The authors of this review article found that the results of these studies depended on the level of detail used when analysing the microbial DNA data. The most detailed analyses consistently identified that regular glyphosate concentrations affected the microbiome. For example, one study found that nitrogen fixation by bacteria in legumes was impaired. Another found that the development of the immune system was negatively affected in bees, making them more susceptible to parasites and viruses. The development of the immune and nervous systems is partly controlled by the microbiome in the intestinal tract.

In addition, this review paper confirms that low glyphosate concentrations are harmful to many beneficial bacteria. For example, recent research has shown that up to 26% of the bacteria in the human intestines are sensitive to low glyphosate levels. In addition, it was found that many disease-causing bacteria can withstand higher concentrations of glyphosate than beneficial bacteria. Thus, the microbiome composition can shift towards more pathogenic microorganisms.

Glyphosate is the most commonly used pesticide in Europe. Glyphosate residues in the environment originate from spraying crops and applying manure deriving from animals that were fed with glyphosate-resistant internationally traded feedstuffs. As a result, glyphosate has been found in the urine of about 50% of the general population in the EU and 95% in the US. Glyphosate is deadly to plants (except glyphosate-resistant crops) and many microorganisms. There are several human health risks posed by glyphosate, which we accumulate glyphosate by consuming plants that have been sprayed.

A recently published review by van Bruggen and co-authors in the journal Frontiers of Environmental Science focuses on the indirect effects of sublethal concentrations of glyphosate on plant, animal and human health due to shifts in microbial community compositions. The soil, plant roots and spaces between plant cells, the surfaces and internal cavities of animals and humans (such as the intestines) all have characteristic 'microbiomes'. These consist of bacteria, fungi, and microscopic animals which are beneficial to their hosts (e.g., humans, animals). These specialised 'microbiomes' are involved in disease resistance and development. The composition of microbiomes are dependent on eating habits, medication use and exposure to contaminants.

At present, up to 900g of active glyphosate can be applied per hectare for controlling weeds and for desiccation according to EU regulations. Research has compared residue levels against the maximum residue levels allowed; these latter values are regularly increased if the measured concentrations can no longer meet the standards due to the accumulation of glyphosate in the environment. Glyphosate concentrations were particularly high in animal feed (up to 0.53 mg/g in grass). This is because glyphosate is largely excreted in faeces and urine after partial absorption by the intestines and circulation through the blood. In addition, glyphosate accumulates in bones, liver, and kidneys, and partially remains in the intestines (tested in rats).  

The authors conclude that the maximum allowed glyphosate levels in human and animal food should be lowered to prevent or at least minimize damage to the microbiome and thus to the host.  The authors advocate that this negative effect, alongside the many others, should be seriously considered whist deciding on the future of glyphosate use.

The review paper:

Indirect effects of the herbicide glyphosate on plant, animal and human health through its effects on microbial communities

Published in: Frontiers in Environmental Science (October 2021)

by: van Bruggen, A.H.C.1*, Finckh, M.R. 2, He, M. 3, Ritsema, C.J. 4, Harkes, P. 4, Knuth, D. 4, and Geissen, V. 4

1 Emerging Pathogens Institute and Department of Plant Pathology, University of Florida, Gainesville, FL 32610, USA

2 Faculty of Organic Agricultural Sciences, Ecological Plant Protection, University of Kassel, 37213 Witzenhausen, Germany

3 Department of Life and Environment Science, Hangzhou Normal University, Zhejiang, 310036, China

4 Department of Environmental Sciences, Soil Physics and Land Management Group, Wageningen University, 6708 PB Wageningen, Netherlands

* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

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