Water hardness as a photochemical parameter: Tetracycline photolysis as a function of calcium concentration, magnesium concentration, and pH

Jeffrey J. Werner, William A. Arnold, Kristopher Mcneill

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163 Scopus citations

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, [Ca 2+], 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.

Original languageEnglish (US)
Pages (from-to)7236-7241
Number of pages6
JournalEnvironmental Science and Technology
Volume40
Issue number23
DOIs
StatePublished - Dec 1 2006

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