## The Freundlich model allows obtaining information on the degree

Usually, the KdD measured for an HOC desorption from a geosorbent is greater than the KdS measured for sorption on the same geosorbent. This phenomenon called hysteresis was studied at constant temperature using the hysteresis index (HI) (Huang et al., 1998).equation(4)Hysteresis index(HI)=qeD-qeSqeS T,Ce.In this relation, qeS and qeD are the ML347 sorbate concentrations for the sorption and single-cycle desorption experiments, respectively. Parameters T and Ce refer to the conditions of constant temperature and constant aqueous phase concentration. The higher the value of HI is, the stronger the sediments will entrap HOCs. A zero HI value indicates that the hysteresis is insignificant.

All statistical analyses were performed using Statistica 6.0 and the original formulas (Zar, 1984) under Microssoft Excel 97. A linear regression procedure was used to fit the sorption–desorption isotherms data collected for each sediment-B8-1413 or sediment-B9-1679 systems. Differences among slopes and intercepts of linear regression lines obtained with sorption models were assessed using an analysis of covariance (ANCOVA). Differences among KdS,D values obtained for different concentrations of B8-1413 or B9-1679 were estimated using a ozone one-way analysis of variance (ANOVA). In all tests, the statistical significance was set at α = 0.05.