Fig. 4 shows the sorption and desorption isotherms of Cu(II) on the two soils with and without SDZ. The sorption data of Cu(II) could also be described well with the Freundlich equation
(r = 0.986–0.996, Table 2). The measured Kd values of BS and RS were 1835 and 50 L kg1, respectively, which were in the range of the values reported in literatures (Agbenin and Atin, 2003; Arias et al., 2005). Further comparison of the Kd values of Cu(II) and SDZ shows that SDZ is clearly a weaker sorbate than Cu(II). In contrast to SDZ, the Kd values of Cu(II) on BS was higher than that on RS, which might due to higher CEC and pH in BS, as compared with RS (Table S1).