Effects of Aqueous Environments and the Water Molecule on the Degradation Mechanism of Methylglyoxal Initiated by OH Radicals: A Theoretical Study

Carbonyl compounds are ubiquitous in the multiphase system of the atmosphere and have a significant influence on the environment. In order to explore the effects of different environments on the degradation process of pollutants, the reaction mechanisms of methylglyoxal (MGL) and OH radicals in the gas phase and aqueous phase and with/without H₂O were investigated by a theoretical calculation. At 298.15 K, the total rate constants (in units of cm³ molecule^–1 s^–1) of MGL + OH are 6.18 × 10^–11 and 1.73 × 10^–11 in the gas phase and aqueous phase, respectively. Our analysis shows that the initial pathways of the title reaction included two kinds: OH-addition and H-abstraction. The addition pathways are the most favorable, but the contribution of the aldehyde hydrogen abstraction pathways cannot be ignored due to the proportion of H-abstraction pathways could account for 42.85% at 298.15 K in the gas phase, which is just slightly less than 57.15% of OH-addition pathways. In addition, H₂O and aqueous environments inhibited the title reaction. We also evaluated the acute and chronic toxicity of MGL and its reaction products to aquatic organisms at three different trophic levels using the Ecological Structure–Activity Relationships (ECOSAR) program. This research is helpful to reveal the reaction mechanism of MGL in different environments and to assess the risk in aquatic environments.