Experiments on the Interactions between a Fluoroquinolone Antibiotic and Nanometer-Size Soil Oxide Particles: Adsorption and Breakdown
Dr. Michael Seymour, Hope College
Dr. Jonathan Peterson, Hope College
Antibiotic contamination is a concern in soil-water systems because of the potential for promoting antibiotic resistance. Mobility of drugs may involve nanometer (nm)-size particles, so there is a need for data on both adsorption to nanoparticle surfaces and the fate of drugs after adsorption. To address this, batch experiments were done with ofloxacin (OFX), a common veterinary antibiotic, and nm-size particles of Al2O3, SiO2, Fe2O3, and TiO2. Sorption and breakdown were quantified and identified by HPLC and LC/MS analysis. OFX sorption to Al2O3 generates linear isotherms of mass sorbed/mass nano vs. liquid concentration (R2>.96), with a Kd of 441 L/kg (± 35).
OFX sorption to SiO2, TiO2 and Fe2O3 is logarithmic, such that: SiO2 Ln Kf=3.0 (± .52), n=.57 (± .10); TiO2. Ln Kf = 8.6 (±3.5), n= .82 (±.51); Fe2O3 Ln Kf = 5.5 (± 1.2), n=.89 (± .17). Maximum OFX sorbed was 10 mmol/kg to SiO2, 370 mmol/kg to TiO2, and 11 mmol/kg to Fe2O3. Substrates with sorbed OFX were rinsed with OFX-free solutions in desorption experiments to remove weakly-attached molecules. Results show ~ 7% of the OFX could be removed from Al2O3, 89% from SiO2, < 1% from TiO2, and 27% from Fe2O3. Smaller percentages indicate stronger adsorption mechanisms. Breakdown of zwitterionic OFX was observed in 80-hr timed mixing experiments with 25nm-TiO2. Decrease in OFX was accompanied by an increase in at least 2 product compounds. Mass spectral data suggest these breakdown reactions may involve the N-methyl, carbonyl, and carboxyl groups. Concentrations of the two products (m/z = 336-337 and m/z = 348-349) increase at a linear rate of ~ 1.5%/hr. Comparison of data from isotherm and timed experiments will quantify the amount of sorption vs. breakdown. Preliminary results from SiO2, Fe2O3 and Al2O3 timed experiments indicate less breakdown of OFX compared to the effects of TiO2.
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