Sorption of Monensin and Oxytetracycline On Broiler Litter-Amended Pasture Soil.

Oxytetracycline and monensin are widely used antibiotics in broiler production for treating and preventing diseases and may persist in broiler litter waste. Routine application of broiler litter to agricultural fields could release monensin and oxytetracycline to surface or ground waters. The mobility of litter-derived monensin and oxytetracycline depends not only on their chemical composition, but also on their interactions with litter-amended soil, and other relevant surfaces. We examined the sorption behavior of monensin and oxytetracycline to pasture soils in Georgia where the broiler industry is among the largest in the world. Our preliminary results suggest broiler amendments decreased sorption of monensin to soil. Monensin sorption isotherm on broiler litter-amended soil showed an S-curve whereas that of the control soil showed an L-curve. When the sorption matrix was changed to NaCl, greater monensin appears to sorb to the broiler litter-amended soil than when the matrix was CaCl₂ under low monensin concentrations. In the case of oxytetracycline, this compound was found to sorb similarly to both the control and the broiler litter amended soils. Oxytetracycline sorption isotherms on both soils are linear. Between the two antibiotics, monensin appears to be more of an environmental threat to streams possibly through surface runoff.