NANOPARTICLE-ENHANCED DEGRADATION OF PENICILLIN ANTIBIOTIC IN WATER: IMPLICATIONS FOR FATE AND TRANSPORT OF PHARMACEUTICALS IN GROUNDWATER

Extensive use of pharmaceuticals in human and animal medicine has resulted in antibiotic contamination of natural waters. Nanoparticles (10^-9 m) are found in natural soil-water environments and have the ability to adsorb contaminants due to the large surface to volume ratio. Though adsorption to nanosurfaces likely plays a significant role in reducing aqueous concentrations of drugs, nanoparticle-mediated degradation of organic compounds may also be a significant mechanism. This was investigated by exposing ampicillin (AMP), a common penicillin antibiotic, to nanoparticles of Fe₂O₃, TiO₂, Al₂O₃, and SiO₂ in separate timed batch experiments. AMP adsorption and degradation were measured by HPLC analysis of solutions and breakdown products were identified by LC/MS analysis.

Degradation of zwitterionic AMP (pKa₁ = 2.5, pKa₂ = 7.3) was observed in timed mixing experiments with 25nm- TiO₂ (anatase) at pH 6.2 over 48 hours. TiO₂ has a net positive surface charge at pH < 7.2 (pzc). Significant degradation of AMP (m/z = 350) was measured in mixed samples relative to controls, with initial parent AMP of 553 μmol/L dropping to 1 μmol/L within 48 hours. Decrease in AMP concentration was accompanied by an increase in the concentrations of two products, isomers of penicilloic acid (P1 and P2, at m/z = 368-369), likely formed by the hydrolysis of the beta-lactam ring of AMP. Formation of the P2 penicilloic acid isomer can be described by a logarithmic function of ln [P2] = 0.965 (ln(time)) + 5.02 (R² > 0.98). Comparison of adsorption isotherm and timed experiment data are in progress to quantify the actual extent of, and relationships between adsorption and degradation mechanisms. Similar trends were observed in experiments with nano-Fe₂O₃ and Al₂O₃, but no significant enhancement was observed in SiO₂ data experiments.