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

Abstract

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 in termediate compounds of glyphosate biodegradation including nature of non-extractable residues (NERs; harmless biogenic [NERsbiogenic] versus hazardous xenobiotic [NERsxenobiotic]) 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 13C- and 15N-labeled glyphosate (2-13C,15N-glyphosate) and its degradation product AMPA ( 13C,15N-AMPA), sarcosine ( 13C3, 15N sarcosine) or glycine ( 13C2, 15N-glycine) in an agricultural soil separately for a period of 75 days. 13C2-glycine and 13C3-sarcosine mineralized rapidly compared to 2-13C-glyphosate and 13C-AMPA. The mineralization of 13C AMPA was lowest among all four compounds due to its persistent nature. Only 0.5% of the initially added 2-13C,15N-glyphosate and still about 30% of the initially added 13C,15N-AMPA was extracted from soil after 75 days. The NERs formed from 13C,15N-AMPA were mostly NERsxenobiotic as compared to other three compounds for which significant amounts of NERsbiogenic were determined. We noticed 2-13C,15N-glyphosate was biodegraded via two biodegradation pathways simultaneously; however, the sarcosine/glycine pathway with the formation of harmless NERsbiogenic presumably dominated.