Two Pathways Compete in the Mn(II)-Catalyzed Oxidation of Aminotrismethylene Phosphonate (ATMP)

Abstract

Mn(II)-catalyzed oxidation by molecular oxygen is considered a relevant process for the environmental fate of aminopolyphosphonate chelating agents such as aminotrismethylene phosphonate (ATMP). However, the potential roles of Mn(III)ATMP-species in the underlying transformation mechanisms are not fully understood. We combined kinetic studies, compound-specific stable carbon isotope analysis, and equilibrium speciation modeling to shed light on the significance of such Mn− ATMP species for the overall ATMP oxidation by molecular oxygen. The fraction of ATMP complexed with Mn(II) inversely correlated with both (i) the Mn(II)-normalized transformation rate constants of ATMP and (ii) the observed carbon isotope enrichment factors (ε c -values). These findings provide evidence for two parallel ATMP transformation pathways exhibiting distinctly different reaction kinetics and carbon isotope fractionation: (i) oxidation of ATMP present in Mn(III)ATMP complexes (ε c ≈ −10 ‰) and (ii) oxidation of free ATMP by such Mn(III)ATMP species (ε c ≈ −1 ‰) in a catalytic cycle. The higher reaction rate of the latter pathway implies that aminopolyphosphonates can be trapped in catalytic Mn-complexes before being transformed and suggests that Mn(III)ATMP might be a potent oxidant also for other reducible solutes in aqueous environments.

Glyphosate contamination in European rivers not from herbicide application?

“…10,16 As mentioned, AMPA is a known transformation product also of aminopolyphosphonates, which are intensely used in Europe as antiscalants, bleach stabilizers, and corrosion inhibitors mainly in laundry products, in the textile and paper industries, and in cooling circles. 37,38,51,52,53 AMPA formation from aminopolyphosphonates in WWTPs was discussed by Wang et al 54 We may thus assume that aminopolyphosphonates are the dominant source for AMPA. Then, the impressive differences between U.S. and European river contamination patterns and residues in WWTPs can easily be explained for AMPA: Opposite to Europe, the most popular U.S. laundry detergent brands do not contain aminopolyphosphonates (web search 6/2023).…”