Photodegradation of Typical Antibiotics in Natural Aquatic Environment

Antibiotics are widely used in medicine, aquaculture and animal husbandry as a preventive and curative medicine for bacterial infections in humans and animals. Antibiotics that are not absorbed by organisms are discharged into the aquatic environment and are present in water bodies and sediments. Due to their antimicrobial properties, photodegradation has become an important mode of degradation of antibiotics in natural aquatic environments, including direct photolysis, self-sensitized photolysis and indirect photolysis. The photolysis of antibiotics in natural aquatic environments is affected by many environmental factors, and dissolved substances (dissolved organic matter DOM, halide ions, HCO₃^-/CO₃^2-, NO₃^-/NO₂^-, and Fe³⁺, etc.) have a dual role in their indirect photolysis: On the one hand, they may promote the indirect photolysis of antibiotics by facilitating the generation of reactive intermediates (including triple excited state solvated organic matter ³DOM^*, other reactive oxygen species ROS, etc.), and on the other hand, they may inhibit the indirect photolysis through light shielding, bursting or scavenging of ROS, and hindering electron transfer; pH affects the photodegradation of antibiotics by influencing the protonation states of the antibiotics and the steady-state concentration of ROS. Photodegradation pathways vary greatly among different types of antibiotics: hydroxylation, demethylation, dehydration (or deamination, defluorination, decarboxylation, removal of SO₂, dehydrogenation, etc.), and direct cleavage for bond breaking, rearrangement, and ring opening may occur. Finally, this paper suggests that the research on photodegradation of antibiotics in the aqueous environment should be further strengthened to study the photodegradation process of antibiotics in sediments, at environmental concentrations, and under multifactorial effects, and to develop environmentally friendly methods to treat antibiotics in the environment.