Revealing the mechanism, pathways and kinetics of UV sub(254nm)/H sub(2)O sub(2)-based degradation of model active sunscreen ingredient PBSA

Transformation byproducts and pathways for the degradation of 2-phenylbenzimidazole-5-sulfonic acid (PBSA), a widely used organic active sunscreen agent, by UV sub(254nm)/H sub(2)O sub(2) advanced oxidation process (AOP) were elucidated by mass spectrometry. Fourteen byproducts were identified, including environmentally hazardous benzamide (BD) and benzamidine (BZD). Beside of aromatic ring opening, desulfonation (-80 Da) and hydroxylation (+16 Da) were also two main reaction pathways. Degradation kinetics were compared with two PBSA structurally related compounds 2-phenylimidazole (2-PIZ) and benzimidazole (BZ) to estimate the application feasibility of the studied AOP. No apparent photolysis was noticed while the degradation of 1 mu M pollutants in the presence of 1 mM H sub(2)O sub(2) followed pseudo-first-order kinetics, with their observed rate constant (k sub(obs)) in the order of 2-PIZ > PBSA > BZ > BD > BZD, which is consistent with their respective second-order rate constant with hydroxyl radical. However, at high pollutant and oxidant concentrations, i.e., 50 mu M and 5 mM, respectively, light attenuation contributed significantly to the change in k sub(obs) in the following manner, 2-PIZ similar to BZ > PBSA similar to BD > BZD. SO sub(4) super(2-) and NH sub(4) super(+) were the major inorganic mineral ions monitored in this study. Release of SO sub(4) super(2-) from PBSA degradation system reached 70% at 190 min. At the same time interval, NH sub(4) super(+) were [el]50% for all pollutants studied. Ultimate mineralization of PBSA, 2-PIZ, BZ, BD and BZD in terms of %TOC at 190 min was found to be 23%, 38%, 45%, 57% and 62%, respectively. UV/H sub(2)O sub(2) was shown to be efficient for the removal of organic sunscreen agents from water, however, special care toward the formation of environmentally hazardous byproducts should be considered.