Tetracycline and Metal Oxide Nanoparticles in Aqueous Solutions: Implications for Pharmaceutical Transport in Natural Waters

Faculty Mentor(s)

Dr. Jonathan Peterson, Hope College
Dr. Michael Seymour, Hope College

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Widespread use of pharmaceuticals and their subsequent detection in natural waters is a growing concern. The fate and transport of drug contaminants likely involves nanometer-size (10-9 m) oxides. This study investigated the interaction of tetracycline (TC), a common polyprotic antibiotic, with several metal oxide nanoparticles (NPs). Batch experiments were performed using 25-50 mg of four NPs (Al2O3, Fe2O3, SiO2, and TiO2) and varying concentrations of TC solutions (0.44 - 444 μM) over a range of pHs (2.3 - 8.7). Data indicate that the amount of TC removed from solution (C* = μmol TC removed/mass of NP) is due to adsorption and/or NP-facilitated transformation. Experiments indicate that electrostatic interactions are not predictable. The relationship between the pH-dependent surface charge (point of zero charge = pzc) of SiO2 and speciation of TC yields low attraction at pH 5 (C* ~4,000 μmol/kg) (all C* values reported are for initial TC concentrations of 111 μM), where the drug is zwitterionic and the substrate surface is (-). At pH 8.7 TC is (1-) and SiO2 is (-), and C* ~42,000 μmol/kg. At pH 2.3, SiO2 is (+) and TC is (1+), and the attraction is moderately low (C* ~7,000 μmol/kg). In mixes with Fe2O3, TC was completely removed at pH 5 (substrate+/zwitterionic drug). Greater removal occurred at pH 2 (C* ~ 30,000 μmol/kg) than at pH 8.7 (C* ~ 13,000 μmol/kg). TiO2 removed all TC from solutions through 111 μM, at all pH conditions investigated. Solubility of TC limited higher concentration experiments to pH 2.3, where data were fit with Freundlich isotherms. Removal coefficients illustrate that TiO2 removed the most TC (Kr=40738 L/kg), followed by Fe2O3 (Kr =8,709 L/kg) and SiO2 (Kr =407 L/kg). Because Al2O3 increased solution pH, data were considered separately, and TC removal showed an approximate correlation with electrostatic trends.

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