Effects of Surfactants on the Sorption of Sulfamethoxazole by Sediment

Adsorption and desorption of sulfamethoxazole (SMX) at water-sediment interfaces from Taihu Lake, China, were investigated in this study. The effects of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and an anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), on the adsorption/desorption processes were also studied. Results show that adsorption and desorption could be well described by the Freundlich isotherm model. CTAB significantly increased the SMX adsorption on sediments, while SDBS decreased the adsorption of SMX, probably because SDBS at high concentrations competed in the limited adsorption sites with SMX, and the addition of SDBS increased SMX solubility, thereby reducing the SMX adsorption on sediment. The degree of adsorption irreversibility was quantified by the Thermodynamic Index of Irreversibility (TII) values. It shows that the TII values increased with the increase of CTAB concentration, and decreased with the increase of SDBS concentration. These results imply that cationic and anionic surfactants may have contrasting impacts on the distribution and transport of SMX in the environment.