Fig. 4. Effect of immobilization treatments on Pb extractability in Blackwell (BW), Henryetta (H12), and Bartlesville (B4) contaminated soils as determined by the PBASE sequential extraction. Immobilization treatment abbreviations are the same as listed in Fig. 2. Pb x 100 designation indicates the E1 values have been multiplied by 100. Treatments with the same letter are not different at P < 0.05 within each soil–extract combination.