title: Water hardness as a photochemical parameter: tetracycline photolysis as a function of calcium concentration, magnesium concentration, and pH.
abstract: The environmental photochemical kinetics of the antibiotic compound tetracycline were investigated. The aqueous speciation of tetracycline over a range of natural pH and water hardness values is dominated by association with Ca2+ and Mg2+ ions. The association constants necessary to calculate tetracycline aqueous speciation given knowledge of pH, [Ca2+], and [Mg2+] were measured by spectrophotometric titrations and matrix deconvolution of a series of UV-vis absorption spectra into individual component species. A series of photolysis experiments was performed under simulated sunlight, and quantum yields for the solar photolysis of each environmentally relevant species were calculated. The results indicate that the pseudo-first-order rate constant for tetracycline photolysis at varied Mg2+ and Ca2+ concentrations relevant to natural conditions can vary by up to an order of magnitude. A self-sensitization effect was observed and was accounted for by varying the initial tetracycline concentration under each set of photolysis conditions.
authors.affiliation: Water Resources Science Program, University of Minnesota, 1985 Buford Avenue, St. Paul, Minnesota 55108, USA.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Werner
authors.forename: William A
authors.initials: WA
authors.lastname: Arnold
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002118:Calcium / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000032:analysis*; D010777:Photochemistry; D010782:Photolysis; D013056:Spectrophotometry, Ultraviolet; D013752:Tetracycline / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D014867:Water; D013752:Tetracycline; D008274:Magnesium; D002118:Calcium