Effect of Oxytetracycline on Molybdenum Adsorption at the Hematite–Water Interface: Insights From Macroscopic and in Situ ATR‐FTIR Study

ABSTRACT Background Veterinary antibiotic (VA) oxytetracycline (OTC) is commonly used in confined animal feeding operations to treat animal diseases, as a prophylactic and as a growth promoter. OTC can enter the environment via various routes, including runoff from stored manure stockpiles and application of manure or contaminated irrigation water to agricultural lands. Once introduced, OTC could alter the biogeochemical cycling of various coadsorbing ions, especially micronutrient oxyanions, such as molybdate (MoO 4 2− ). Iron oxide minerals, which play a major role in the soil's biogeochemical cycling of nutrient oxyanions in soil, are known to modify the plant's availability of molybdenum (Mo) via adsorption reactions. Aim In this study, we examined the impact of OTC on Mo retention on hematite under different solution properties. Methods We used macroscopic and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopic experiments to understand the interactions. Results The results from macroscopic adsorption experiments indicated no reduction in the extent of Mo adsorption in the presence of OTC at higher pH. The spectroscopic results suggested that Mo retention occurred by forming tetrahedral inner‐sphere surface species on hematite. Furthermore, the results indicated some alterations in Mo adsorption mechanisms in the presence of OTC. The effect of Mo on OTC adsorption was more prominent as suggested by in situ ATR‐FTIR results. Conclusion This study contributes to a better understanding of the biogeochemical cycling of Mo in the presence of VAs.