Influence of goethite on the fate of antibiotic (tetracycline) in the aqueous environment: Effect of cationic and anionic surfactants.

Over the last decades, the release and occurrence of organic pollutants in aquatic systems have become a major global concern due to their bioaccumulation, toxicity, and adverse effects on the ecosystem. Tetracycline (TC), a widely used antibiotic, is often found at high concentrations in the aqueous environment and tends to bind with the natural colloids. Post-COVID-19 pandemic, the release of surfactants in the environment has increased due to the excessive use of washing and cleaning products. This study systematically investigated the interaction of goethite with TC in the absence and presence of anionic (sodium dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) surfactants. The impact of various environmental parameters like pH, ionic strength, temperature, and organic matter was also studied. It was observed that SDS has drastically increased TC sorption onto goethite from 11 mg/g to 19 mg/g, while CTAB had the opposite effect. To delineate the goethite-TC interaction mechanisms, FTIR with two-dimensional correlation analysis (2D-COS) was performed. The pH of the solution was crucial in the presence of SDS, while ionic strength did not affect the interaction process. The sorption process was endothermic, as evidenced by the increase in sorption capacity with the rise in the temperature. The presence of organic matter hinders the sorption of TC onto goethite, which is also observed in river water where the organic content is very high. Overall, our study helps to predict the fate of organic pollutants like antibiotics in aqueous environments in the coexistence of surfactants and iron oxyhydroxides.