Binding and Degradation of Monensin by Soil Minerals.

Concentrated animal feeding operations (CAFOs) are facilities containing a large number of agricultural animals. Antibiotics are often administered subtherapeutically to the animals in order to prevent disease spread, due to the high density of animals in the facility, and also to promote growth. Up to 90% of the administered antibiotics are not metabolized by the body, however, and are excreted from the body in the waste. It is common for manure from CAFOs to be land applied as a fertilizer, transporting antibiotics and introducing them into the environment. There is insufficient knowledge on the subsequent transport and fate of these antibiotics within the environment, although they have been shown to cause the development of harmful antibiotic resistant bacteria, and some are directly toxic to biota. To increase understanding of the behavior of antibiotics in soils, batch experiments with monensin, a common veterinary antibiotic, and a range of pure mineral phases have been performed. Sorption of monensin by the clay mineral kaolinite and mineral (hydr)oxides such as gibbsite, goethite, and birnessite have been studied. An LC-IT/MS was utilized for quantitation and investigating possible chemical transformation of monensin. Preliminary results indicate limited sorption of monensin by kaolinite or gibbsite at environmentally relevant pH levels, and moderate sorption to birnessite. Experiments with goethite reveal high amounts of sorption in a short amount of time, with sorption decreasing as ionic strength increases.