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

Aqueous ·OH reaction rate constants ( k_OH) 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 k_OH values for a variety of OPEs. The determined k_OH for 18 OPEs varies from 4.0 × 10⁸ M^-1 s^-1 to 1.6 × 10¹⁰ M^-1 s^-1. Based on the experimental k_OH 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 k_OH of other OPEs. Furthermore, appropriate density functional theory (DFT) and solvation models were selected, which together with transition state theory were employed to predict k_OH of three representative OPEs. The deviation between the DFT calculated and the experimental k_OH values ( k_cal/ k_exp) 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 k_OH values and the in silico methods offer a scientific base for assessing OPEs fate in aquatic environments.