Fate of glyphosate and its degradation products AMPA, glycine and sarcosine in an agricultural soil: Implications for environmental risk assessment.

Glyphosate can be biodegraded via the aminomethylphosponic acid (AMPA) and the sarcosine/glycine pathway leading to the formation of three intermediate products AMPA, sarcosine or glycine. The fate of the three intermediate compounds of glyphosate biodegradation including nature of non-extractable residues (NERs; harmless biogenic [NERs _biogenic ] versus hazardous xenobiotic [NERs _xenobiotic ]) in soils has not been investigated yet. This information is crucial for an assessment of environmental risks related to the speciation of glyphosate-derived NERs which may stem from glyphosate intermediates. Therefore, we incubated ¹³ C- and ¹⁵ N-labeled glyphosate (2- ¹³ C, ¹⁵ N-glyphosate) and its degradation product AMPA ( ¹³ C, ¹⁵ N-AMPA), sarcosine ( ¹³ C ₃ , ¹⁵ N-sarcosine) or glycine ( ¹³ C ₂ , ¹⁵ N-glycine) in an agricultural soil separately for a period of 75 days. ¹³ C ₂ -glycine and ¹³ C ₃ -sarcosine mineralized rapidly compared to 2- ¹³ C-glyphosate and ¹³ C-AMPA. The mineralization of ¹³ C-AMPA was lowest among all four compounds due to its persistent nature. Only 0.5% of the initially added 2- ¹³ C, ¹⁵ N-glyphosate and still about 30% of the initially added ¹³ C, ¹⁵ N-AMPA was extracted from soil after 75 days. The NERs formed from ¹³ C, ¹⁵ N-AMPA were mostly NERs _xenobiotic as compared to other three compounds for which significant amounts of NERs _biogenic were determined. We noticed 2- ¹³ C, ¹⁵ N-glyphosate was biodegraded via two biodegradation pathways simultaneously; however, the sarcosine/glycine pathway with the formation of harmless NERs _biogenic presumably dominated.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Karolina Nowak reports financial support was provided by Helmholtz Centre for Environmental Research - UFZ. Karolina Nowak reports financial support was provided by German Research Foundation. Sohaib Aslam reports was provided by Alexander von Humboldt Foundation.
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