Fig. 3. Sorption isotherms for p-nitrocyanobenzene (p-NCB) and 1,4-dinitrobenzene (1,4-DNB) by the K⁺–saturated Webster B horizon soil (WB) and soil fractions: carbonates removed (-CO₃), carbonates and soil OM removed (-CO₃–OM), and the residual sand + silt fraction remaining after removal of carbonates, SOM, free FeO_x and clay. Isotherms with different letters (a, b, c) are statistically different at p < 0.05.