2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 23-12
Presentation Time: 11:20 AM-11:35 AM


POWERS, Nicholas S.1, SEYMOUR, Michael D.1, and PETERSON, Jonathan W.2, (1) Department of Chemistry, Hope College, P.O. Box 9000, Holland, MI 49422-9000, nicholas.powers@hope.edu, (2) Department of Geological & Environmental Sciences, Hope College, P.O. Box 9000, Holland, MI 49422-9000

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 human and veterinary 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 pH (2.3 - 8.7). Equilibrium aqueous concentrations were determined by HPLC and removal of TC from solution was quantified by comparison to control samples.

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 with TC-SiO2 mixes show that electrostatic attractions are likely controlling the fate of TC. The relationship between the pH-dependent surface charge (point of zero charge = pzc) of SiO2 and speciation of TC yields strong attraction at pH 5 (C* ~35,000 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* ~9,000 μmol/kg. At pH 2.3, SiO2 is (+) and TC is (1+), and the attraction is comparatively low (C* ~1,700 μmol/kg). Experiments with Fe2O3 and TiO2 indicate that electrostatic interactions are not predictable, and possibly not the primary mechanism for TC removal. In mixes with Fe2O3, removal of TC was completely removed at pH 5 (substrate+/zwitterionic drug). Greater removal occurred at pH 2 (C* ~ 4400 μmol/kg) (substrate+/drug+) than at pH 8.7 (C* ~ 2900 μmol/kg) (substrate-/drug-). TiO2 removed all TC from solutions through 111 μM, at all pH conditions investigated. Solubility of TC limited higher concentration (155 – 444 μM) experiments to pH 2.3, where data were fit with Freundlich isotherms. Removal coefficients illustrate that TiO2 removed the most TC (Kr=9587 L/kg), followed by Fe2O3 (Kr =2278 L/kg) and, SiO2 (Kr =172 L/kg). Because Al2O3 increased solution pH, data were considered separately, and TC removal showed an approximate correlation with electrostatic trends. TC was completely removed at pH 5 and pH 8.7. At pH 2.3, TC removal by Al2O3 was C* ~ 6,500 µmol/kg .

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 23
Climate, Water, and Health
Minneapolis Convention Center: Room M100BC
8:00 AM-12:00 PM, Sunday, 9 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 73

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