Use of Zeolite to Reduce the Bioavailability of Heavy Metals in a Contaminated Soil

Soil enrichment with heavy metals plays a significant role in soil pollution which led towards buildup/accumulation of heavy metals in edible crops. This situation causes severe threats to sustainability of ecosystem and humans health. Bioavailability of heavy metals can be restricted by the addition of immobilizing agents. Therefore, a pot experiment was carried out to evaluate the potential of zeolite i.e., ‘clinoptilolite’ as immobilizing agent to reduce the bioavailability of different heavy metals in soil. For this purpose, pots containing soil contaminated with different heavy metals (Cd, Pb, Cu and Zn) was treated with variable concentration of zeolite i.e., 1, 3, 5, 7, 9, 15, 20, 30, 40, 50 g∙kg^-1 along pots with no addition of ZL as control treatment and incubated for 30, 60 and 90 days. The effectiveness of the applied treatments was evaluated by single metal extraction method in soil using DTPA having 7.3 pH and NH₄NO₃. Results showed that soils treated with ZL exhibited significant increase in soil pH and CEC along reduction in concentration of metals (Cd, Pb, Cu and Zn) as compared to control soil. Among the different concentrations of ZL, the most promising results were achieved with ZL at 50 g∙kg^-1 after 90 days of incubation. It was observed that soil treated with zeolite at 50 g∙kg^-1 showed significantly higher contents immobilized DTPA and NH₄NO₃ concentrations of Cd, Cu, Pb and Zn after 90 days of incubation when compared with control treatment. The trend of reduction in DTPA extractable concentration of heavy metals was in order of Cd < Pb < Zn 4NO₃ was noticed as follow 16.09, 20.11, 23.83 and 38.37 % respectively but the trend of reduction was Cd < Pb < Zn < Cu. Therefore, reduction in concentration of heavy metals and their accumulation in the soil improved the soil quality. So the addition zeolites can significantly reduce the concentration of heavy metals in the soil although the reduction contents are not satisfactory for the production of food.