Exchange Selectivity of Tylosin on Vermiculitic Soil.

Agricultural antibiotics are used extensively in livestock production. Because antibiotics are slowly absorbed by animals, a large amount (> 80 %) is excreted in urine and feces, potentially impacting soil and other aquatic systems. One such antibiotic is tylosin (TYL). Tylosin is used heavily as a feed additive in swine production and can be found in swine manure leachates, with concentrations as high as 4.0 mg L⁻¹. The soil adsorption of TYL is influenced by pH, background electrolyte, and ionic strength, suggesting that an important component of the retention process is ion exchange. However, few studies have explicitly examined the exchange of antibiotics with common soil cations. Thus, the objectives of this study were to examine the exchange of TYL with Na and Ca in a vermiculitic soil and reference clay minerals. Binary exchange studies were performed and exchange isotherms were developed to establish preference. The results of Na-TYL and Ca-TYL exchange on the Bt horizons of a Grenada soil will be presented.