Aqueous multivariate phototransformation kinetics of dissociated tetracycline : implications for the photochemical fate in surface waters

• Antibiotics are ubiquitous pollutants in aquatic systems and can exist as different dissociated species depending on the water pH. New knowledge of their multivariate photochemical behavior (i.e., the photobehavior of different ionized forms) is needed to improve our understanding on the fate and possible remediation of these pharmaceuticals in surface and waste waters. In this study, the photochemical degradation of aqueous tetracycline (TC) and its dissociated forms (TCH20, TCH-, and TC2-) was investigated. Simulated sunlight experiments and matrix calculations indicated that the three dissociated species had dissimilar photolytic kinetics and photo-oxidation reactivities. TC2- photo-degraded the fastest due to apparent photolysis with a kinetic constant of 0.938 +/- 0.021 min(-1), followed by TCH- (0.020 +/- 0.005 min(-1)) and TCH20 (0.012 +/- 0.001 min(-1)), whereas Tar was found to be the most highly reactive toward center dot OH (105.78 +/- 3.40 M(-1 )s(-1)), and TC2- reacted the fastest with O-1(2) (344.96 +/- 45.07 M-1 s(-1)). Water with relatively high pH (e.g., similar to 8-9) favors the dissociated forms of TCH- and TC2- which are most susceptible to photochemical loss processes compared to neutral TC. The calculated corresponding environmental half-lives (t(1/2,E) ) in sunlit surface waters ranged from 0.05 h for pH = 9 in midsummer to 3.68 h for pH = 6 in midwinter at 45 degrees N latitude. The moms was dominated by apparent photolysis (especially in summer, 62-91%), followed by O-1(2) and center dot OH oxidation. Adjusting the pH to slightly alkaline conditions prior to UV or solar UV light treatment may be an effective way of enhancing the photochemical removal of TC from contaminated water.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Tetracycline

Dissociation

Apparent photolysis

Hydroxyl radical

Singlet oxygen

Environmental half-lives

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