Indirect Photodegradation of Sulfamethoxazole and Trimethoprim by Hydroxyl Radicals in Aquatic Environment: Mechanisms, Transformation Products and Eco-Toxicity Evaluation

The bacteriostatic antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), have frequently been found in wastewater and surface water, which raises the concerns about their ecotoxicological effects. The indirect photochemical transformation has been proven to be an efficient way to degrade SMX and TMP. In this study, the reaction mechanisms of the degradation by SMX and TMF by OH radicals were investigated by theoretical calculations. Corresponding rate constants were determined and the eco-toxicity of SMX and TMP and its degradations products were predicted using theoretical models. The results indicate that the most favorable pathways for the transformation of SMX and TMP are both •OH-addition reaction of benzene ring site with lowest Gibbs free energy barriers (6.86 and 6.21 kcal mol−1). It was found that the overall reaction rate constants of •OH-initial reaction of SMX and TMP are 1.28 × 108 M−1 s−1 and 6.21 × 108 M−1 s−1 at 298 K, respectively. When comparing the eco-toxicity of transformation products with parent SMX and TMP, it can be concluded that the acute and chronic toxicities of the degraded products are reduced, but some products remain harmful for organisms, especially for daphnid (toxic or very toxic level). This study can give greater insight into the degradation of SMX and TMP by •OH through theoretical calculations in aquatic environment

Changes in Air Quality from the COVID to the Post-COVID Era in the Beijing-Tianjin-Tangshan Region in China

This article discussed air quality changes in the Beijing-Tianjin-Tangshan (BTT) region. The air quality index (AQI) values, and the concentrations of PM2.5, PM10, SO2, CO, NO2, and O-3 in the BTT region during the COVID-19 outbreak in 2020 were, respectively, 79.4, 47.2 mu g m(-3), 73.4 mu g m(-3), 10.3 mu g m(-3), 0.87 mg m(-3), 33.6 mu g m(-3), and 90.7 mu g m(-3). However, they were, respectively, 102.7, 61.4 mu g m(-3), 121.0 mu g m(-3), 9.0 mu g m(-3), 0.88 mg m(-3), 40.1 mu g m(-3), and 84.0 mu g m(-3) during the same period in 2021, which is an increase of 29.2%, 30.1%, 64.8%, -12.9%, 1.94 %, 19.5%, and -7.4% compared with the values in 2020. The combined proportions of grade I and grade II during the COVID-19 outbreak in 2020 were 16.7% higher than those in the same period in 2021, so the air quality has deteriorated rapidly from 2020 to the post-COVID era in 2021. The possible reasons for poorer air quality are that the frequency of dusty weather and air pollutant discharge has increased, and meteorological conditions have been relatively unfavorable. The average AQI values, and concentrations of PM2.5, PM10, SO2, CO, NO2, and O-3 during the post-COVID period in 2021 respectively decreased by 14.8%, 29.0%, 14.6%, 22.5%, 37.4%, 14.8%, and 8.7%, compared with those in 2020. It is also worth noting that all the changes in air pollution during the post-COVID era have been consistent. The combined proportions of grade I and grade II during post-COVID period in 2021 were 18.4% higher than those during the same period of 2020, which indicates that the air quality during post-COVID 2021 has obviously improved compared with those in the same period of 2020. The possible reasons are a series of clean air policies and clean air actions, as well as favorable atmospheric diffusion conditions. These results indicate that clean air policies play a very important role in improving air quality