Effects of adsorption onto silica sand particles on the hydrolysis of tetracycline antibiotics

Abstract

Due to high usage of tetracycline antibiotics, concerns have been raised about their environmental fate. In this study, potential changes in the pseudo-first-order hydrolysis rate constants for three tetracyclines, tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC), were evaluated by measuring the rate constants in batch and column leaching experiments. The first-order hydrolysis rate constants were measured at pH 5, 7, and 9 using batch tests. The values were highest at pH 7 for all three tetracyclines (0.0030 ± 0.0004, 0.0042 ± 0.0001, and 0.0323 ± 0.0003 h(-1) for TC, OTC, and CTC, respectively), indicating relatively short environmental half-lives of tetracyclines. Interestingly, it was found that the rates of degradation of the parent tetracyclines were much faster when silica sand was present in a batch solution or when the solution was passed through a silica column. For example, the ratios of the first-order degradation rate constants obtained in the column experiments to those in batch experiments were 13.2, 2.1, and 2.0 for TC, OTC, and CTC at a volumetric flow rate of 0.08 mL h(-1), with an observed tendency for this ratio to increase with an increased flow rate. This indicates that the silica surface may serve as a catalyst for hydrolysis and that the actual environmental half-lives of tetracycline antibiotics could be shorter than those estimated from laboratory hydrolysis rate constants using the standard batch protocol. Furthermore, the toxicity of the column effluent containing hydrolysis metabolites was assessed using bioluminescence inhibition in Vibrio fischeri. It was estimated that the toxicity of the metabolites of CTC was lower than that of their parent compound, whereas the toxicity of metabolites of TC and OTC was as high as or higher than that of their parent compounds.

Direct photolysis of oxytetracycline: Influence of initial concentration, pH and temperature

“…The main elimination pathways for TCs in surface waters are adsorption [9,10], hydrolysis [11,12], and photochemical transformation [13][14][15][16], while biological processes seem not to be effective to degrade TCs [1,16]. Table S1 (Supplementary material, SM) reviews hydrolysis and photolysis rates of OTC from previous studies.…”

Gastroretentive montmorillonite-tetracycline nanoclay for the treatment of Helicobacter pylori infection

“…With regard to TC biological activity, its adsorption onto MM without compromising the bactericidal activity was demonstrated (Parolo et al, 2010). Moreover, considering TC degradation in aqueous solutions (Kang et al, 2012;Loftin et al, 2008;Pena et al, 1998) although the high half-life estimated by other Authors in more than 300h (Sah, 2006), a greater chemical stabilization might be provided by the adsorption process onto MM (Chang et al, 2009;Sah, 2006).…”

Assessment of the physical properties and stability of mixtures of tetracycline hydrochloride ointment and acyclovir cream

“…However, under the current storage conditions, mixtures were stored away from direct sunlight, so light was not a factor. In addition, TC is known to undergo hydrolysis (Kang et al, 2012). Thus, attention was focused on the water content in each ACV-cr.…”