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] versus hazardous xenobiotic [NERs]) 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 C- and N-labeled glyphosate (2-C,N-glyphosate) and its degradation product AMPA (C,N-AMPA), sarcosine (C,N-sarcosine) or glycine (C,N-glycine) in an agricultural soil separately for a period of 75 days. C-glycine and C-sarcosine mineralized rapidly compared to 2-C-glyphosate and C-AMPA. The mineralization of C-AMPA was lowest among all four compounds due to its persistent nature. Only 0.5% of the initially added 2-C,N-glyphosate and still about 30% of the initially added C,N-AMPA was extracted from soil after 75 days. The NERs formed from C,N-AMPA were mostly NERs as compared to other three compounds for which significant amounts of NERs were determined. We noticed 2-C,N-glyphosate was biodegraded via two biodegradation pathways simultaneously; however, the sarcosine/glycine pathway with the formation of harmless NERs presumably dominated.