Study of the Ciprofloxacin hysteresis phenomenon in soil

Antibiotics as emerging pollutants, potentially affect the environment and human health and their entry into the environment has created great concerns. To study the ciprofloxacin hysteresis phenomenon in the soil, the adsorption process was done with different concentrations of ciprofloxacin (0–1 mmol L-1) on a calcareous soil system. Then, the reversibility of the adsorption process was assessed through desorption experiments of ciprofloxacin-loaded soil samples. The concentration of ciprofloxacin was determined using high-performance liquid chromatography-tandem mass spectrometry (HPLC–MS/MS). The experimental data were analyzed using the Langmuir, Freundlich, and Redlich-Peterson isotherms. The results demonstrated the experimental data followed the Redlich-Peterson isotherm model due to the lowest value of error (SE= 0.24) and the highest value of correlation coefficient (R²=0.99). The exponent value of this equation (g) was less than one, so the adsorption surfaces are heterogeneous. Ciprofloxacin adsorption increased with increasing initial concentrations. The highest adsorption and desorption efficiency of ciprofloxacin was obtained at concentration 1 mmol L-1, 96% and 2%, respectively. The hysteresis index was 0.89 indicating low reversibility of the adsorption process or hysteresis phenomenon. The strong bind of the ciprofloxacin to the soil components leads to less degradability in soil and forms stable residues in the soil environment.