An Examination of the Adsorption Patterns of Antibiotics Onto Clay Minerals.

Antibiotic agents are used extensively in livestock production, human health, and aquaculture.  One of the main routes which antibiotics enter the environment is through field application of antibiotic-laden manure.  It is known that antibiotics sorb strongly to clay minerals. It is important to understand the interactions of antibiotics to clay minerals in order to predict the fate and transport of pharmaceutical agents in the soil and water systems. The chemical properties of the soil affect the magnitude and mechanism by which antibiotics sorb to soil constituents.  The objective of this study is to determine the effect of pH, background cation type, antibiotic loading, and antibiotic type on the adsorption and intercalation into a reference smectite and clay extract from a Tennessee soil by conducting batch equilibration adsorption tests and subsequent X-ray diffraction (XRD) analyses.  A batch adsorption study will be carried out at two fixed pH values under both a calcium- and potassium-saturated system with a 0.03 M ionic strength.  Five different initial concentrations will be employed to observe the intercalation of the antibiotics at each various adsorption level using XRD. This method will provide a direct measurement of changes in clay interlayer spacing as a function of surface loading, thus the information necessary to elucidate adsorption mechanisms.  Samples of interest will also undergo FTIR analysis to determine adsorption mechanism due to changes in the bonding strength and molecular structure. We expect the adsorption of all three antibiotics will be higher at low pH as opposed to high pH, and higher under a calcium saturated system as opposed to a potassium system, with the exception of any vermiculitic clay fraction in which potassium forms a stable structure with the interlayer resulting in a collapsed structure. We also hypothesize that all three antibiotics have the ability to intercalate both clay samples.