Aqueous OH Radical Reaction Rate Constants for Organophosphorus Flame Retardants and Plasticizers: Experimental and Modeling Studies.

Abstract

Aqueous ·OH reaction rate constants ( kOH) for organophosphate esters (OPEs) are essential for assessing their environmental fate and removal potential in advanced oxidation processes (AOPs). Herein experimental and in silico approaches were adopted to obtain kOH values for a variety of OPEs. The determined kOH for 18 OPEs varies from 4.0 × 108 M-1 s-1 to 1.6 × 1010 M-1 s-1. Based on the experimental kOH values, a quantitative structure-activity relationship model that involves molecular structural information on the number of heavy atoms, content index, and the most negative charge of C atoms was developed for predicting kOH of other OPEs. Furthermore, appropriate density functional theory (DFT) and solvation models were selected, which together with transition state theory were employed to predict kOH of three representative OPEs. The deviation between the DFT calculated and the experimental kOH values ( kcal/ kexp) is within 2. Half-lives of the OPEs were estimated to be 0.5-22791.3 days in natural waters and 0.044-19.7 s in AOPs, indicating the OPEs are potentially persistent in natural waters and can be quickly eliminated by AOPs. The determined kOH values and the in silico methods offer a scientific base for assessing OPEs fate in aquatic environments.