Adsorption, Leaching and Degradation of Sulfadiazine in Natural Soil

Unused soil from the mountainous area at north of Taiyuan City was used to investigate sulfadiazine (SDZ) adsorption. Two SDZ concentrations (2 and 5 mg·kg^-1) were used. Adsorption by and leaching from different soil layers after different times were investigated by performing column tests. Migration of leached SDZ was assessed using the groundwater pollution index, and possible SDZ degradation products and pathways in natural soil were identified. The results indicate that the SDZ adsorption capacity of each soil layer was concentration-dependent and markedly more SDZ was adsorbed and accumulated in the upper than in the lower soil. The SDZ leaching rate gradually decreased over time and stabilized after 8-10 d of leaching. Like the adsorption capacity, the SDZ concentration in the leachate and SDZ leaching rate were markedly higher when the SDZ concentration in soil was 5 mg·kg^-1 than when it was 2 mg·kg^-1. The SDZ groundwater pollution indices (GUS) at SDZ concentrations in soil was 2.99, which was higher than the groundwater pollution index limit of 2.8, suggesting that with the increasing of SDZ concentration in soil, the chance of risks posed by SDZ entering groundwater was also increased. The leachate contained 16 SDZ degradation products, which allowed five possible SDZ degradation pathways in unused soil to be identified. The study confirms that concentration-dependent SDZ adsorption and leaching occurs in soil and SDZ degradation is identified in natural soil. The results can improve our ability to assess the ecological risks posed by SDZ.