Electronic Thesis and Dissertation Repository


Master of Science




Pharmaceutical residues can reach agricultural land through amendment with animal or human waste. Since 2010, a series of replicated plots received annual applications of ivermectin, monensin and zinc bacitracin, either singly or in a mixture, at 0.1 mg/kg and 10 mg/kg concentrations. I collected soil samples before and after the fourth annual application of pharmaceuticals and assayed them for functional changes and amoA gene abundance, a gene needed for ammonia oxidation. In 2013, I exposed the soils to 100 mg/kg in a laboratory experiment which resulted in acceleration of nitrification. Under 10 mg/kg treatments in the field the abundance of ammonia-oxidizing bacteria was suppressed, while ammonia-oxidizing archaea increased, suggesting that bacteria are more sensitive to these pharmaceuticals, and that archaea can expand to occupy the partially vacated niche. None of the pharmaceuticals at the guideline level of 0.1 mg/kg had any effect on soil function or ammonia oxidizing organisms.