Nitrate and oxytetracycline: Agricultural residues and antibiotics at environmental interfaces studied by nonlinear optics

AGRO 40

Patrick L. Hayes, Jennifer J. Kruk, and Franz M. Geiger, f-geiger@northwestern.edu. Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113
The binding behavior of nitrate and oxytetracycline (OTC) with model environmental interfaces was investigated using the surface-specific spectroscopy technique second-harmonic generation (SHG). SHG allows us to track the interaction of nitrate or OTC with interfaces in real-time and measure surface-specific binding parameters. A nitrate adsorption isotherm at the quartz/water interface was obtained and fitted to the Langmuir model resulting in a binding constant and a free energy of adsorption that is consistent with the high mobility of nitrate in soils. For OTC, the strength of adsorption was found to depend on the organic moieties present at the functionalized quartz/water model interface, which indicates OTC mobility in the environment is dependent on the chemical composition of natural organic matter in soils. These SHG studies probe the fundamental interfacial processes that control the mobility of agricultural residues and antibiotics in soils providing insight into the threat posed by eutrophication and antibiotic resistance.