Glyphosate [(N-phosphonomethyl)glycine] is the main active molecule of the most used worldwide herbicide for weed and vegetation control. Its importance recently exploded after the introduction of transgenic glyphosate-resistant (GR) crops in 1996. In Québec only, over 1 million hectares of croplands are sprayed with glyphosate annually, while in Brazil, glyphosate consumption more than doubled over the past 10 years. Although glyphosate has been characterized as slightly mobile and rapidly biodegradable, a fraction of glyphosate and its by-products, especially the aminomethylphosphonic acid (AMPA), invariably and ubiquitously ends up in waterways draining agricultural fields.
Consequently, glyphosate and AMPA are often detected in wastewater treatment plants (WWTP) effluent and in streams. Glyphosate exerts low acute toxicity to animals because its biochemical mode of action affects the shikimic acid pathway, which is essential to plant metabolism but does not exist in animals. However, various studies in the last decade have shown possible toxicological effects linked to its use. Because of these concerns, glyphosate, as well as AMPA were included in the Annex III of the European Union 2008/105/EC Directive as a “…substance subject to review for possible identification as priority substance or priority hazard substance”.
On the other hand, the origin of AMPA is still actually under debate, as it can result from the degradation of molecules other than glyphosate. Phosphoric acids in detergents, ethylene diamine tetramethylene phosphonate (EDTMP) or the diethylenetriamine-penta-methylene phosphonic acid (DTPMP) can also be degraded into AMPA. It is therefore essential to incorporate efficient control of glyphosate (and AMPA) into the existing organic pollutant monitoring schemes of water supplies, especially when considering the universal and fast growing use of this compound around the world.
Today, the management of surface/groundwater quality with respect to diffuse contamination is almost exclusively based on monitoring micropollutant concentration levels in a selection of sites and samples through time. However, there is now ample evidence that this concentration approach does not allow to establish unambiguously the different sources and their respective contributions to water pollution.
We recently developed a new analytical protocol that allows us to precisely analyse the stable carbon isotope compositions of Glyphosate at AMPA at very low concentrations. Our most recent studies focused on the abiotic degradation pathways of both compounds, especially focusing on UV-oxidation and ozonation.