Heating Temperature and Oxygen Availability Alter the Role of Pyrogenic Dissolved Organic Matter in Sulfamethoxazole Photodegradation

Increasingly frequent wildfires tend to raise the levels of pyrogenic dissolved organic matter (DOM) and affect the photodegradation of organic pollutants in waterbodies within fire-prone watersheds. However, it remains unclear whether heating temperature and oxygen availability modify the DOM impact on the photodegradation of pollutants, such as sulfamethoxazole, a frequently detected antibiotic of significant concern. Here, we investigated the effects of DOM from nonheated soil and hypoxically and aerobically heated soils (250 or 400 °C) on sulfamethoxazole photodegradation and quantified the influence percentages of multiple pathways, including light screening, photosensitization, and reverse-back reduction. All DOMs inhibited sulfamethoxazole photodegradation, with lower inhibition seen for hypoxically heated soil DOMs than others. Additionally, 400 °C-heated soil DOMs exhibited more pronounced photosensitizing and reverse-back reduction pathways than 250 °C-heated soil DOMs. The relative abundances of condensed aromatics and oxygen-rich aromatics, which were higher in DOM from aerobically heated soil than from soil heated hypoxically, were significantly correlated with the influence percentages of photosensitization and the reverse-back reduction pathways. Our findings underscore the importance of wildfire prevention in mitigating the impact of pyrogenic DOM (particularly from aerobic heating) on pollutant retention by inhibiting photodegradation.