Fig. 4. Sorption–desorption data and Freundlich fits for 1,4-dichlorobenzene (DCB) on (a) Pahokee peat (PP) (K_F = 91.6 ± 4.6 [g^(1–N) kg^–1 L^N]; N_sorb = 0.79 ± 0.05; R² = 0.995; standard error of estimates, SEE = 0.06; number of samples n = 40, 10 data points on which no desorption was initiated not shown); (b) Beulah-Zap lignite (BZL) (K_F = 197.0 ± 9.3 [g^(1–N) kg^–1 L^N]; N_sorb = 0.74 ± 0.05; R² = 0.985; SEE = 0.115, n = 36, 10 data points on which no desorption was initiated not shown), and (c) Amherst soil (AS) (K_F = 90.7 ± 5.2 [g^(1–N) kg^–1 L^N]; N_sorb = 0.90 ± 0.07; R² > 0.98; SEE = 0.109; n = 60, 40 data points at different particle concentrations not shown). (d) Corresponding Thermodynamic Indices of Irreversibility TII for PP (triangles), BZL (squares), and AS (circles, shown for all particle concentrations). Error bars represent standard deviations of three replicates for PP and BZL and four replicates for AS both in C^D (concentration of the desorption point) and TII. DCB was determined by scintillation counting in (a) and (b) and gas chromatography in (c). The term C is the solute concentration; q is the sorbed concentration; K_F is the Freundlich coefficient; N_sorb is the Freundlich exponent for the forward branch of the isotherm; and C^D is the solute concentration at the experimental desorption point.