Sorption properties and mechanisms of erythromycin and ampicillin in loess soil: Roles of pH, ionic strength, and temperature

• Sorption of erythromycin and ampicillin were strongly related to pH, temperature, coexisting ions. • Chemical structure and properties of erythromycin and ampicillin will greatly affect its sorption. • Erythromycin is highly mobile in loess soil and may contaminate water. • Ampicillin drugs sorbs strongly onto loess soil. • Clay mineral play an important role on the sorption of erythromycin and ampicillin. The concern over veterinary antibiotic (VA) pollution has significantly increased. To understand the sorption properties and mechanisms of macrolides and β-lactam antibiotics in loess soil, batch equilibrium experiment was adopted to explore the sorption kinetics, sorption thermodynamics, and factors that influence erythromycin (ERY) and ampicillin (AMP) in loess soil. The equilibrium time of ERY and AMP sorption by loess soil was about 9 h and 2 h, respectively, and the sorption process was in line with a pseudo-second-order model. A linear sorption model can well describe the sorption of ERY in loess soil, while AMP was more consistent with the Freundlich model. The sorption affinity (K d ) of AMP on loess soil was 95.3–276.6L/kg and the K d of ERY was only 8.3–9.7L/kg. The sorption capacity (C s ) of ERY first increased and then decreased, whereas the C s of AMP gradually decreased with an increase in temperatures. A weak acid condition was favorable for the sorption of ERY, whereas an alkaline condition was favorable for the sorption of AMP. With the enhance of ionic concentration, the C s of target pollutants was more effective, but ionic strengths too high inhibited the sorption of ERY. The C s of the two pollutants increased with an increase in initial concentration. The results indicated that ERY is mainly adsorbed to loess soil by electrostatic sorption and cation exchange, whereas AMP depended on complexation, cationic bridging, and hydrogen bonding. Overall, AMP indicated the higher sorption expected in loess, whereas ERY displayed a high migration potential. Data presented in this study reveal aspects of the transport of macrolide and β-lactam antibiotics in soil–aqueous systems.