Wednesday, November 15, 2006 - 9:30 AM
305-4
Nonequilibrium Sorption and Transport of Agricultural Antibiotics in Soil.
Veterinary antibiotics can enter soil and aquatic environment via the application of animal manure to agricultural land. Land application of animal manure can change the soil chemical properties, thus affecting sorption and mobility of agricultural antibiotics in soil. The effects of soil properties on the fate and transport of chlortetracycline (CTC), tylosin (TYL), and sulfamethazine (SMT) were examined by conducting batch and column experiments. Sorption of CTC and TYL to montmorillonite and kaolinite generally decreased with increasing pH and ionic strength, implying that cation exchange is one of the major sorption processes of the antibiotics. Decreased retention of CTC and TYL to the clays and soils (surface and subsurface soil of Etowah clay loam and Captina sandy loam) was observed in the presence of Ca ion compared with Na. Weak SMT sorption to clays relative to CTC and TYL and inability of surface complexation model to adequately predict SMT sorption in the pH greater than 4 range imply hydrophobic interactions between neutral SMT species and clay surfaces. Additionally, the SMT retention by soils was strongly influenced by soil organic matter content, which is consistent with the hydrophobic character of SMT. Sorption of CTC and TYL to clays and soils decreased by adding dissolved organic carbon (DOC), while SMT sorption increased by DOC addition. Enhanced SMT sorption can be explained by co-sorption of DOC-SMT and/or alteration of surface characteristics of solid phase. Column miscible displacement experiments using surface and subsurface soil of a sandy loam showed increased CTC mass recovery in effluents and decreased retardation factors (R) in the presence of DOC. Elevated levels of DOC also resulted in decreased R of TYL and increased SMT mass recovery in effluents for surface soil column.
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