OH-Initiated Heterogeneous Reactions of Novel Organophosphate Esters: Insights into Oxidation Chemistry and Atmospheric Persistence

Abstract

Novel organophosphate esters (OPEs), formed through chemical transformation of commercial antioxidants, are emerging contaminants with widespread environmental occurrence and potential health effects. Despite their widespread detection, the atmospheric reactivity, persistence, and transformation of novel OPEs remain unknown. Here, the heterogeneous OH oxidation of two surface-bound novel OPEs [tris(2,4-ditert-butylphenyl) phosphate (TDtBPP) and triisodecyl phosphate (TiDeP)] was explored by investigating the reaction kinetics and chemical mechanisms. The measured heterogeneous rate constants for TDtBPP and TiDeP were (2.81 ± 0.12) × 10–12 and (1.99 ± 0.16) × 10–12 cm3 molecules–1 s–1, respectively, equivalent to atmospheric lifetimes of up to 6.3 and 9.0 days. These lifetimes are significantly longer than previously predicted values (<1 day), suggesting that they are much more persistent in air than predicted. Based on UPLC-HRMS measurements, 22 transformation products from the heterogeneous reactions were identified for the first time. Analysis of atmospheric particle samples from two megacities in China identified four TDtBPP transformation products, demonstrating that the oxidation chemistry can occur under genuine environmental conditions. In-silico hazard screening further indicated that many transformation products may be more bioaccumulative and more toxic than the parent novel OPEs. The results not only provide new insights into the atmospheric persistence of novel OPEs but also underscore the significance of considering atmospheric transformation in the risk assessment of these emerging contaminants.