Use of zeolite to reduce the bioavailability of heavy metals in a contaminated soil

Abstract

Soil enrichment with heavy metals plays a significant role in soil pollution, which leads towards buildup/accumulation of heavy metals in edible crops. This situation causes severe threats to the sustainability of ecosystem and human health. The 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, the pots containing soil contaminated with different heavy metals (Cd, Pb, Cu and Zn) were treated with variable concentration of zeolite i.e., 1, 3, 5, 7, 9, 15, 20, 30, 40, 50 g·kg-1, as well as the 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. The results showed that the soils treated with ZL exhibited significant increases in soil pH and cation exchange capacity as well as a reduction in the concentration of metals (Cd, Pb, Cu and Zn) as compared to the 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 the soil treated with zeolite at 50 g·kg-1 showed significantly higher contents of immobilized DTPA and NH4NO3 concentrations of Cd, Cu, Pb and Zn after 90 days of incubation when compared with the control treatment. The trend of reduction in DTPA extractable concentration of heavy metals was in order of Cd < Pb < Zn < Pb < Zn < Cu. Therefore, reduction in concentration of heavy metals and their accumulation in the soil improved the soil quality. Hence, the addition of zeolites can significantly reduce the concentration of heavy metals in the soil although the reduction contents are not satisfactory for the production of food.