Assessment of Glucocorticoid Removal by UVA/Chlorination and Ozonation: Performance Comparison in Kinetics, Degradation Pathway, and Toxicity

Glucocorticoids (GCs) have drawn great concern due to widespread contamination in the environment and application in treating COVID-19. This work aimed to compare the performance of UVA/chlorination and ozonation on GC removal in terms of removal efficiency, degradation pathway, and toxicity change, with fluocinolone acetonide (FA), triamcinolone acetonide (TA), and clobetasol propionate (CP) as target compounds. The results showed that both UVA/chlorination and ozonation could degrade GCs. Compared with UVA/chlorination (removal efficiency of 89% for FA, 86% for TA, and 90% for CP at 7 h), ozonation (removal efficiency of 90% for FA, 96% for TA, and 98% for CP at 15 min) was more effective in GC removal. Photodegradation contributed most to GC removal during UVA/chlorination, while O3 molecules were the main functional species during ozonation. H-abstraction, dechlorination, carbon–carbon bond cleavage, and ester hydrolysis were proposed for both UVA/chlorination and ozonation based on the identification of intermediates. However, ozone tended to attack C=C double bonds, resulting in the cracked benzene ring of GCs, while chlorine was more likely to attack alcohol and ketone groups. Although most GCs were removed during ozonation and UVA/chlorination, their acute toxicities slightly declined. Compared with UVA/chlorination, ozonation was more effective in toxicity reduction.