Inhibition mechanisms of biochar-derived dissolved organic matter to triclosan photodegradation: A remarkable role of aliphatics

Endocrine disrupting chemicals like triclosan (TCS) have been thought to be an emergent environmental pollutant. The ubiquitous dissolved organic matter (DOM) is able to interrelate with TCS and hamper its phototransformation. However, how the components in DOM can inhibit the photodegradation of DOM/TCS complex is largely unknown. Herein, we discovered that TCS photodegradation with biochar-derived DOM (BDOM) was interfered by both binding affinity and reactive oxygen species (ROS) productivity. BDOM can not only stimulate TCS photodegradation by producing ROS, but also inhibit the removal of TCS through the interactions between BDOMs and TCS. The quantification of BDOM's impact on TCS photodegradation revealed that BDOM hampered TCS removal with the proportion of-7.95 to-11.24% at pH 8.5, but strengthened it to 13.20% at pH 7.0. Binding process was more easily to inhibit TCS photodegradation in molecular form, while anionic TCS photodegradation was dominated by ROS productivity. Different inhibition mechanisms were involved in TCS photodegradation depending on the components of BDOMs. The hydroxyls and aromatic carbonyls might have hindered the attack of ROS on the phenolic hydroxyl of TCS via hydrogen bond interaction or 7C-7C electron donor -acceptor interaction. Through hydrophobic interaction, the mobile aliphatics could greatly shield TCS to prevent ROS attack by wrapping or twining TCS, playing a significant role in inhibiting TCS removal. Results from this present study can afford a new viewpoint in elucidating the function of BDOMs in the phototransformation of organics and decrease the spread of antibiotic resistance genes.