The Influence of pH on Sulfamethoxazole in Soil Systems: Migration and Degradation

Owing to their widespread use, sulfonamide antibiotics (SAs), an important class of emerging pollutants, have caused significant ecological disruption. Both acid deposition and salinization of soil may have an impact on migration and degradation of antibiotics. Sulfamethoxazole (SMX), has a migration and transformation process in the environment that is closely dependent on environmental pH. Nevertheless, scarcely any studies have been conducted on the effect of soil pH changes on the environmental behavior of sulfamethoxazole. To investigate the impact of different pH levels on the migratory mechanisms and degradation pathways of SMX within soil systems, indoor soil column leaching experiments were conducted. Ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF–MS) were used to analyse the dynamic changes in the content of SMX as well as to identify its degradation products. The results showed that acidic conditions constrained the vertical migration of antibiotics in the soil. These transformations ensued through a sequence of reaction processes, encompassing ring opening, hydroxylation, S-C bond breaking, and the oxidation of aniline groups. The study of the migration and transformation of sulfamethoxazole under different pH conditions can lay a solid theoretical foundation for the assessment of the pollution risk of sulfamethazine degradation products under acid rain and salt and alkali conditions, so as to better prevent and protect underground water resources.