Abiotic Degradation of Glyphosate into Aminomethylphosphonic Acid in the Presence of Metals

Abstract

Glyphosate [N-phosphono-methylglycine (PMG)] is the most used herbicide worldwide, particularly since the development of transgenic glyphosate-resistant (GR) crops. Aminomethylphosphonic acid (AMPA) is the main glyphosate metabolite, and it may be responsible for GR crop damage upon PMG application. PMG degradation into AMPA has hitherto been reckoned mainly as a biological process, produced by soil microorganisms (bacteria and fungi) and plants. In this work, we use density functional calculations to identify the vibrational bands of PMG and AMPA in surface-enhanced Raman spectroscopy (SERS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra experiments. SERS shows the presence of AMPA after glyphosate is deposited from aqueous solution on different metallic surfaces. AMPA is also detected in ATR-FTIR experiments when PMG interacts with metallic ions in aqueous solution. These results reveal an abiotic degradation process of glyphosate into AMPA, where metals play a crucial role.

Surface-enhanced Raman Spectroscopy and Density Functional Theory Study of Glyphosate and Aminomethylphosphonic acid Using Silver Capped Silicon Nanopillars

“…On the other hand, the DFT results for AMPA show three strong Raman bands at 1017 cm 1 , 928 cm 1 and 727 cm 1 , which can be attributed to symmetric stretching vibrations from C H and C O functional groups and an asymmetric stretching vibration from P C bond, respectively (Figure 2b). These values correlate well with those obtained in [26]. The Raman bands located around 865 cm 1 and 809 cm 1 are directly related to those frequencies of the OH groups around the phosphorus atom, providing potential fingerprint signals for detection of AMPA.…”

“…A significantly increased intensity of the Raman signal located at 1591 cm 1 attributed to a symmetric vibration of C O is observed. The relative intensities from the SERS signals are expected to differ significantly from those of normal Raman signals [26]. For example, the GP SERS vibrational modes observed at 1319 cm 1 , 1136 cm 1 and 705 cm 1 are likely due to the interaction between GP and silver metal (AgNPs).…”

Dynamics of Glyphosate and Aminomethylphosphonic Acid in Soil Under Conventional and Conservation Tillage

“…Glyphosate is moderately persistent in soil, with a DT50 value (time for dissipation of 50% of the initial concentration) ranging from 1 to 197 days (Giesy et al 2000;Laitinen et al 2006;Lewis et al 2016;Bento et al 2016). Glyphosate is primarily degraded by biological activity, although evidence of an abiotic pathway via metal interaction has been reported (Ascolani Yael et al 2014). Aminomethylphosphonic acid (AMPA) is the main degradation product of glyphosate (Sprankle et al 1975;Giesy et al 2000).…”

Metabolic dependency of chorismate in Plasmodium falciparum suggests an alternative source for the ubiquinone biosynthesis precursor

“…However, it is also possible that the presence of degradation products may result in different IC 50 values. In the case of glyphosate, both microbial 31 or abiotic degradation in the presence of metals 32 releases aminomethylphosphonic acid which may have antimalarial effect, but it remains to be tested. Therefore, neither inhibitor was pursued as a potential metabolic modulator due to the high concentration required.…”