SORPTION CHARACTERISTICS OF MONENSIN, LASALOCID, AND IVERMECTIN TO SOIL CLAY MINERALS

The environmental occurrence of human and veterinary pharmaceutical residues in surface waters and agricultural soils has become a growing research topic in recent years. Many of these compounds are used globally to promote growth and/or prevent infection in livestock, domestic animals and humans. Two ionophore anticoccidials, monensin (MON) and lasalocid (LAS), and an avermectin antiparasitic, ivermectin (IVM), are commonly detected in the aquatic and terrestrial environments, typically associated with animal and human waste products (i.e. manure). Once in contact with sediments and soil, the mechanisms affecting adsorption/ desorption are not well understood. Current literature reports irreversible desorption characteristics in these matrices, possibly slowing transport, a positive aspect, and inhibiting the ultimate removal of the residues by degradation mechanisms, a negative aspect. In order to help understand the underlying adsorption and desorption mechanisms of MON, LAS, and IVM, kinetic and batch equilibrium studies were used to determine coefficients of sorption (K_ads and K_des) using the clay mineral components found in many typical soils and sediments as the base.Liquid chromatography tandem-mass spectrometry equipped with electrospray ionization (LC-ESI-MS/MS) was used for detection of the three compounds. Experimental procedures followed EPA and OECD guidelines for the testing of organic chemicals on soil and sediment. Preliminary results correlate well with the literature, showing strong sorption to the clay minerals, as expected. Using these base findings additional complexity will be added in order to identify the influence of organic matter, cations, soil solution pH and other chemical and physical properties in soils on adsorption and desorption trends.