Oxytetracycline, an antibacterial medication, can enter the agricultural system inadvertantly via human or animal waste in the form of manure, biosolids, and crop irrigation with reclaimed water. Overexposure to the medication and functionally similar metabolites can increase bacterial resistance. Thus, it is important to understand the processes that control the fate and transport of antibacterials in agroecosystems. Birnessite, a naturally occuring manganese oxide mineral, is a strong oxidant. Previous studies have shown that birnessite is capable of oxidizing oxytetracycline, but failed to study this reaction over a period longer than two days. It was also previously believed that the resulting reductive dissolution had negligible effects on the mineral’s oxidative ability. Liquid chromatography high resolution mass spectrometry (LC-HRMS) is typically used to study metabolites in solution, but cannot be used to study the mineral surface. X-ray photoelectron spectroscopy (XPS) fills this gap in knowledge as a surface sensitive technique as will be discussed in this talk. By combining results of these two methods, Karpov et al. (2018) suggest that previously defined oxidized metabolites of oxytetracyline oxidize further through interactions with the birnessite surface, and that the resulting reductive dissolution of the mineral increases its oxidative ability. By applying the knowledge gained in this study, we can better understand the fate and transport of oxytetracycline within agroecosystems. Future studies should focus on elucidating how birnessite may oxidize oxytetracycline and other phamaceuticals under natural conditions to account for variation in soil pH, and impact of competing reactions.
Karpov, M.; Seiwert, B.; Mordehay, V.; Reemtsma, T.; Polubesova, T.; Chefetz, B. Transformation of Oxytetracycline by Redox-Active Fe(III)- and Mn(IV)-Containing Minerals: Processes and Mechanisms. Water Res. 2018, 145, 136–145. https://doi.org/10.1016/j.watres.2018.08.015.