[Adsorption and desorption of norfloxacin on four typical soils in China]

Batch equilibrium experiments were used to reveal norfloxacin (NOR) adsorption/desorption on four kinds of soils, namely Ustic Cambosols collected from Fengqiu of Henan, Ali-Perudic Ferrosols collected from Yingtan of Jiangxi, Gleyic-Stagnic Anthrosols collected from Changshu and Udic Argosols collected from Nanjing of Jiangsu. Results show that the experimental data are best described by the Freundlich and Langmuir model, but not fitted successfully by the linear model. Different sorption behaviors of NOR are observed in the four tested soils, with the Kf values varying greatly from 82.0 L/kg (Cambosols) and 432 L/kg (Argosols) to 5677 L/kg (Anthrosols) and 8790 L/kg (Ferrosols). The apparent sorption-desorption hysteresis is found, and the hysteresis index in Ali-Perudic Ferrosols is at least as five times as those in the other tested soils. Moreover, the Kf values are in a significantly negative correlation to soil pH but significantly positive correlated to the percentage of cationic NOR in solution. At the tested pH interval of 5-9, logarithm Kd values of NOR increased slightly and then decreased with the rise of pH in Ali-Perudic Ferrosols and Gleyic-Stagnic Anthrosols, while decreased linearly in Udic Argosols and Ustic Cambosols. It could be deduced that cation adsorptions is the predominant sorption mechanism of NOR on the four soils, and at low pH, NOR cation adsorption in Ali-Perudic Ferrosols and Gleyic-Stagnic Anthrosols is affected by the competitive adsorption of co-existing cations in soil solution.