Fig. 3. The K_d of Cd in the calcareous soil as affected by organic ligands compared with estimated values at the same equilibrium pH in the absence of ligand. Values and error bars of K_d in the presence of ligands represent the mean and standard deviation of triplicate measurements. The K_d values in the absence of ligands were calculated using the five-parameter nonlinear regression derived from the data of Fig. 1 and the mean pH values measured from triplicate samples containing the ligands.