Influence of Soil and Solvent Type on the Adsorption of Selected Antibiotics.

Large quantities of antibiotics are used in food animals to enhance growth, prevent diseases, and increase feeding efficiency. To make them more effective all antibiotics are usually prescribed at high doses. Literature search has revealed that 50 to 90 percent of all antibiotics consumed as medications are excreted from the body. Consequently, significant quantities of antibiotics are finding their ways into surface waters. Rivers that receive water treatment plant effluents from urban areas and those that receive runoff from confined animal operations are especially loaded with high levels of different antibiotics. Runoffs from agricultural fields that receive manure as supplemental fertilizers also contribute to the antibiotic dilemma. This research examined the adsorption of four commonly prescribed antibiotics on four soils that varied in physicochemical properties. A factorial design was used for the experiment consisting of four antibiotics (amoxyciline, oxy-tetracycline, tetracycline, and tylosin), three extraction solvents (acetonitrile, ethyl acetate, and water), four soils (Bojac, Cullen, Bourne, and Levy), and three replications. Results obtained thus far show that adsorption of antibiotics varied with soil and solvent type. Bojac adsorbed poorly especially at low concentrations (100 ppm) while Cullen and Levy showed maximum adsorption. At high concentrations (> 300 ppm), from 30 to 60% of all antibiotics were released from Bojac while the other soils retained >90% of added antibiotics. Water was a poor solvent for extraction of targeted antibiotics from soils.