Hydrolysis rate constant (kH) is a key parameter for assessing the environmental persistence of chemicals. However, the kH values are lacking for most chemicals of high production volume. It is not realistic to experimentally measure the kH values for their environmental persistence assessment, due to the high time cost and unavailability of some chemical standards. Therefore, it is necessary to develop methods for predicting the kH values. In this study, phthalate esters (PAEs) and parabens were selected as model compounds. Quantum chemical calculation were employed to unveil hydrolysis pathways of PAEs and parabens. Furthermore, hydrolysis kinetic parameters were calculated, and quantitative structure-activity relationship models for predicting kH values were developed.
Many PAEs are chemicals of high production volume and of toxicological concern. In this study, results indicate that hydrolysis of PAEs follows the order: PAEs with cyclic side chains > PAEs with linear alkyl side chains > PAEs with branched alkyl side chains. The calculated hydrolysis half-lives (t1/2) vary from 0.001 hours to 558 years (pH = 7 ~ 9, 25 ℃), which solves the problem in evaluating the environmental persistence of PAEs due to lack of hydrolysis kinetic parameters.
Parabens for which the molecules contain hydrolysable and ionizable groups, are emerging pollutants because of their ubiquity in the environment. Parabens in the aquatic environments have different dissociation forms, which influence their base-catalyzed hydrolysis kinetics. In this study, the t1/2 values of parabens range from 6 hours to 1.52 × 106 years (pH = 7 ~ 9, 25 ℃), which efficiently fills the data gaps of parabens. The study provides a theoretical foundation and data support for evaluating the environmental persistence of PAEs and parabens.