Evaluation of the impact of photodegradation processes on the environmental persistence of amoxicillin

Highly used antibiotics, such as amoxicillin (AMX), are frequently detected in the aquatic environment due to contaminated effluent disposal, alerting for the possible induction of antimicrobial resistance. In this study, the photodegradation of AMX under simulated solar radiation and environmental influencing factors affecting this process (pH, salinity, and presence of humic substances or reactive oxygen species scavengers) were evaluated to further understand its persistency in the aquatic environment. Photodegradation of AMX was shown to be faster at higher pH (t1/2 = 21.0 ± 0.6 h at pH 8.0; t1/2 = 8.0 ± 0.3 h at pH 9.0). On the other hand, photolysis was slower (t1/2 = 25.1 ± 0.7 h) for high salinity (NaCl). Through the use of •OH and 1O2 scavengers (propan-2-ol (20 mmol L−1) and sodium azide (5 mmol L−1), respectively), it was concluded that the main pathway for AMX photodegradation in phosphate buffer solution (PBS) is indirect photolysis via •OH. Freshwater and brackish water were also studied to evaluate matrix effects on the photodegradation, which were found to be significantly faster than in PBS (t1/2 = 12.5 ± 0.3 h in freshwater; t1/2 = 3.8 ± 0.3 h in brackish water; t1/2 = 21.0 ± 0.6 h in PBS, pH 8.0).