Analysis of physicochemical factors regulating transport behaviors of sulfonamide antibiotics in saturated porous media

Sulfonamide antibiotics (SAs) are commonly used antibiotic classes in livestock worldwide. SAs are discharged to the environment and then may accumulate in rivers and aquifers, thereby diminishing water quality and the overall health of the ecosystem. While the occurrence and distribution of SAs in water environments have been the subject of numerous investigations, the fate and transport of SAs in aquifers have been less understood. In the present work, four of the most used SAs, including sulfadiazine (SDZ), sulfathiazole (STZ), sulfamethazine (SM2), and sulfamethoxazole (SMX), were selected for laboratory experiments and modeling analysis. The experiments were conducted in saturated columns filled with two common porous media, quartz sands and limestone grains. Results showed that the SAs had mobility changing on the order (from high to low) of SMX > SM2 > SDZ > STZ in the column, with SMX being the least absorbed SA by quartz sand or limestone grains. Moreover, calcium ions inhibited the transport of SAs more strongly than that of sodium ions, while the inhibitory effect was slightly enhanced with an increasing Na+ concentration from 0 to 10 mM. In contrast, the presence of humic acid facilitated the transport of SAs. Although the four SAs have similar molecular structures, their adsorption and transport characteristics were shown to be quite different. The dynamics of the adsorption and transport of SAs in groundwater can be effectively described by a two-site adsorption model coupled with advection and dispersion. This study sheds new light on the transport of SAs, contributing to a better understanding of how to control the presence and migration of antibiotics as new emerging contaminants in groundwater.