An Overlooked Chemical Conversion Pathway of Glyphosate: Ferrous-AMPA Complex-Mediated Oxygen Activation

The widespread use of glyphosate (PMG), the most abundant herbicide globally, poses substantial ecological risks owing to the persistence of both PMG and its toxic metabolite, aminomethylphosphonic acid (AMPA). While ubiquitous transition-metal ions strongly influence PMG transformation in water systems, their specific role in the conversion of PMG and AMPA remains insufficiently understood. Here, we reveal that ferrous ions (Fe2+) mediate the sequential transformation and ultimate mineralization of PMG and AMPA by activating molecular oxygen through a dual-chelation mechanism. Initially, Fe2+ chelates the phosphonate group of PMG to form an Fe(II)-PMG complex that activates O2, generating superoxide (O2•–) and oxidizing to Fe(III)-PMG. The resulting O2•– then attacks the C(2)–N of PMG to yield AMPA. Critically, the AMPA intermediate subsequently chelates Fe2+ to form a distinct Fe(II)-AMPA complex that exhibits enhanced O2 activation to O2•– and substantially lowers the energy barrier for C(3)-P cleavage by 0.78 eV. This sustained cycle of complexation and radical generation drives the complete mineralization of PMG to inorganic end products. Our findings elucidate an overlooked pathway─continuous complexation-activated conversion of intermediates─providing new insight into the environmental fate of PMG.