EDTA, Water-extractable Lead and Bioavailability of Lead in Non-mined Soil, Capped and Uncapped Tailings: The Effect of Biochar Amendment

A study was undertaken to determine the effects of corn cob biochar application on Pb-water and Pb-EDTA extractable, pH and bioavailability of Pb in non-mined soil and mine tailings. Biochar was applied to soil/tailings at a rate of 0–8 t ha-1) and incubated at room temperature for 4 – 12 weeks. Lettuce (Lactuca sativa) was planted on biochar-amended soil/tailings for 12 weeks. The levels of Pb in amended soil/tailings and lettuce were monitored after 0, 4, 8 and 12 weeks from incubation. The application of biochar decreased significantly the levels of EDTA-extractable Pb by 13–14%, 7–16% and 9 – 11% in non-mined soil, capped and uncapped tailings respectively after 12 weeks biochar application. Water extractable Pb concentrations also decreased by 30 – 33% in non-mined soil, 33 – 37% in capped tailings and 13 – 18% in uncapped tailings. The concentration of Pb in lettuce cropped on biochar-amended non-mined soil (0.2 mg kg-1) and capped tailings (0.2 mg kg-1) were within the maximum limit (0.3 mg kg-1) in vegetable, while the amended uncapped tailings recorded Pb level (0.85 mg kg-1) which is well above the permissible limit.