Tetracycline (TC) antibiotics are commonly prescribed for human and veterinary health. These pharmaceuticals are not completely metabolized in the human body and, as a result, have been detected in wastewater treatment plants at concentrations up to 4 μg L-1. TCs exhibit complex acid-base dissociation reactions, which influence interactions with dissolved organic matter (DOM) and divalent cations, such as Ca2+ and Mg2+. In this study, we investigated the individual and combined effects of these parameters on the photochemical properties of TCs, specifically doxycycline, meclocycline, and methacycline. In particular, UV-visible absorbance spectra at 200-600 nm were generated after a 24-h equilibration time in the dark for the following solutions: (i) 250 µM TC; (ii) 250 µM Ca2+ or Mg2+; (iii) 20 mgC L-1 DOM; (iv) 250 µM TC with 250 µM Ca2+ or Mg2+; (v) 250 µM TC with 20 mgC L-1 DOM; (vi) 250 µM Ca2+ or Mg2+ with 20 mgC L-1 DOM; and, (vii) 250 µM TC with 20 mgC L-1 DOM and 250 µM Ca2+ or Mg2+. All solutions were tested at pH 2, 3, 5, 7, 9, and 10, although at 254 nm, solution pH had a minimal effect on TC absorbance, in the absence of DOM and divalent cations. For example, species-specific molar extinctions for doxycycline were 1.57×104 M-1 cm-1 (ε0,254), 1.20×104 M-1 cm-1 (ε1,254), 1.13×104 M-1 cm-1 (ε2,254), and 1.52×104 M-1 cm-1 (ε3,254). Solutions containing 5 μM TC, 5 μM Ca2+ or Mg2+, 10 mgC L-1, and 5 mM phosphate buffer were irradiated at 254 nm using a merry-go-round Rayonet reactor. The species-specific, fluence-based rate constants for doxycycline, DC were 1.68×10-4 cm2 mJ-1(k’p,0,254), 4.68×10-5 cm2 mJ-1(k’p,1,254), 7.44×10-4 cm2 mJ-1 (k’p,2,254) and 1.21×10-3 cm2 mJ-1(k’p,3,254), for the cation, zwitterion, monovalent anion, and divalent anion, respectively. Impacts of DOM and divalent cations were determined relative to these direct photolysis rate constants. Experimental results indicated that environmental factors, such as pH, DOM, and divalent cations, influenced the photodegradation of TCs in engineered processes.

Combined effects of dissolved organic matter, pH, and divalent cations on UV-254 phototransformation of tetracycline antibiotics

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.