Investigating the Molecular Interactions of Oxytetracycline in Clay and Organic Matter:  Insights on Factors Affecting Its Mobility in Soil

Abstract

The interactions of oxytetracycline with model clay adsorbents were investigated as a function of suspension pH. The clay adsorbents used were native montmorillonite (SWy-2), Na-montmorillonite (Na-SWy-2), and hexadecyl trimethylammonium-montmorillonite (HDTMA-montmorillonite). The adsorption of oxytetracycline to the clay could be described by Freundlich-type adsorption isotherms. It was observed that the adsorption of oxytetracycline in the native and sodium forms of montmorillonite decreases with increasing pH in the order pH 1.5 > 5.0 > 8.7 > 11.0. This trend is consistent with cationic exchange interactions that are dominant at lower pH values when oxytetracycline has a net positive charge. On the other hand, hydrophobic interactions when oxytetracycline is zwitterionic (at pH 5.0) are predominant over other mechanisms, as evident from the FT-IR spectrum of the HDTMA-montmorillonite and humic acid-montmorillonite adsorbed with oxytetracycline. The presence of a large amount of dissolved organic matter (DOM) was also found to decrease the sorption of oxytetracycline to clay, suggesting that DOM may increase its mobility in the natural environment. Several mechanisms of interaction of oxytetracycline in clay are proposed based on the adsorption isotherms and the results from X-ray diffraction (XRD) and Fourier transform-infrared (FT-IR) analyses.

Oxytetracycline sorption onto Iraqi montmorillonite

“…2). The rate of decrease was small in comparison with the reports of Doi and Stoskopf (2000) and Kulshrestha et al (2004), who showed that adsorption decreased rapidly over this pH range and reported a strong correlation between pH and the sorption capacity of TC. Adsorption increased slightly at pH 10.…”

Uptake of oxytetracycline and its phytotoxicity to alfalfa (Medicago sativa L.)

“…7). Thus, soil solution pH is an important factor influencing the bioavailability of OTC in soil (Kulshrestha et al, 2004;Gu, 2005;Jones et al, 2005) and the transport from soil to plant. Time-dependent uptake of OTC by alfalfa showed that there was an equilibrium status of OTC uptake after 4 h (Fig.…”

“…For example, in Denmark, concentrations of oxytetracycline ranging from 2.5 to 50 mg g À1 in soil and from 33 to 2000 mg g À1 in pig manure have been reported (Loke et al, 2002). The fate of antibiotics, including sorption and fixation, mobility and transport in soil, has been well documented (Tolls, 2001;Kulshrestha et al, 2004;Gu, 2005;Jones et al, 2005), whereas knowledge of their toxicity to plants and their uptake and transport into plants is poorly understood (Boxall et al, 2003;Thiele-Bruhn, 2003). The accumulation may or not affect the growth and development of plants; however, the uptake into plants may represent an important exposure pathway of these compounds to humans and other biota.…”

The veterinary antibiotic oxytetracycline and Cu influence functional diversity of the soil microbial community

“…Therefore, residual concentrations of pharmaceutical antibiotics can be found in soils, surface and ground water (Hamscher et al, 2002;Kolpin et al, 2002;Simon, 2005). The fate of antibiotics including sorption and fixation, mobility and transport is well documented (Tolls, 2001;Figueroa et al, 2004;Kulshrestha et al, 2004), whereas the knowledge about their ecotoxicity and the effect of antibiotics on soil microbial functioning is scarce (Thiele-Bruhn, 2003;Boxall et al, 2003).…”