Glyphosate, a chelating agent.

Glyphosate, a chelating agent.

The review of available data indicates that, in addition to the competitive inhibition of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), leading to interference with the shikimic acid pathway in plants (and many microorganisms) and known as the main mode of action of the declared active ingredient glyphosate, other properties of this herbicide may be important too. Glyphosate is a chelating agent and as such binds macro- and micronutrients and can impact their uptake and availability in plants treated with glyphosate-based herbicides, be they genetically modified to resist the application of glyphosate or not. In particular, availability of micronutrients such as iron, manganese, zinc, copper, and nickel may be affected. As macro- and micronutrients are essential for many plant processes and also for pathogen resistance, their undersupply can contribute to the reported toxic effects of glyphosate on plants and lower resistance to pathogens. By this mechanism, plant–microorganism interactions, e.g., nitrogen fixation of leguminous plants, can be influenced too. GBH-treated plants and their products very often contain residues of glyphosate and its main metabolite AMPA, in some cases exceeding the maximum residue levels. Animals and humans consuming these products may thus be affected by residues of glyphosate (and formulants), whose potential toxicity is subject of an ongoing debate. Whether the toxic effects of GBH on non-plant life, described in many papers, could also be linked to the chelating property, has not been extensively studied. The chelating agent glyphosate might also impact soil life by metals that are bound to soil particles. While the compiled data indicate that the occurrence of natural chelators with considerably higher chelating potentials and the high concentrations of potential counterions make a general additional impact by glyphosate for most metals less likely, this may depend on soil characteristics, e.g., on micronutrient supply, on amounts of glyphosate applied, and on the resolution and scale of the analytical approaches. Therefore, research should be undertaken to elucidate the role of glyphosate as a chelating agent, also considering formulants, in particular, as chelation is a nonspecific property potentially affecting many organisms and processes and as glyphosate-based herbicides are the most often applied herbicides worldwide.