Environmental behaviour of a pesticide metabolite, the AMPA. Sequestration of Ca2+, Mg2+, Cu2+, Zn2+ and Al3+

The chelating and sequestering ability of a glyphosate metabolite, the aminomethylphosphonic acid (AMPA) towards bi- and trivalent metal cations, such as Ca2+, Mg2+, Zn2+, Cu2+ and Al3+, were investigated in aqueous solutions of NaCl, in an ionic strength range of 0.1 ≤ I/mol dm-3 ≤ 1.0 and at constant temperature of T = 298.15 ± 0.15 K. The investigations on the acid-base properties and complexing ability were performed, by means of potentiometry, in conditions of different cM:cAMPA molar ratios and pH values. The formation of insoluble species was experimentally observed in the Mn+/AMPA2- systems, and the solid phases were characterized by means of X-Ray Diffractometry (XRD), Scanning Electron Microscopy (SEM) and InfraRed Attenuated Total Reflection spectroscopy (IR-ATR). The dependence on ionic strength of the stability constants of the Mn+/AMPA2- complexes species, determined at different ionic strengths, was modelled by the Debye-Hückel type equation. The sequestering ability of AMPA toward the investigated metal cations was evaluated by pL0.5 parameter.