Effects of Three Inorganic Amendments on Stabilization of As and Pb in Heavy Metal Contaminated Paddy Soil

Many soil amendments are used to remediate paddy soils polluted with heavy metals, including arsenic (As) and lead (Pb). This study was conducted to assess the efficacy of three inorganic soil amendments, such as calcium carbonate (CaCO₃), calcium sulfate (CaSO₄), and ferrous sulfate (FeSO₄), on As and Pb co-contaminated paddy soils. The amendments were applied alone and/or in combinations to compare theirs efficacy for the As and Pb stabilization and the rice growth. In addition, two single extraction methods, 1 M ammonium nitrate (NH₄NO₃) and Mehlich-3, were used to assess the effects on As and Pb immobilization using amendments. The alone (CaSO₄ and FeSO₄) and combined (CaCO₃ + CaSO₄, FeSO₄ + CaCO₃, FeSO₄ + CaSO4) amendment treatments significantly decreased the extractable As concentrations in NH₄NO₃ and Mehlich-3 extraction of the treated soil. Furthermore, FeSO4 alone treatment indicated the maximum reduction of the extractable As concentration in Mehlich-3 extraction of the treated soil. The extractable Pb concentrations by FeSO₄ alone treatment were significantly increased in both extractions of the treated soil, but no significant differences were observed in CaSO₄ alone and combined amendment treatments, relative to the concentrations in the untreated soils (As and Pb co-contaminated paddy soils). Shoot dry weight (DW) of rice plants slightly decreased with the application of alone and combined amendments compared with that of the untreated soils. However, As concentrations in the leaf sheath of rice plants were reduced 21 - 41% by the alone and combined amendment treatments, but no significant difference was observed in the leaf blade relative to the untreated control. On the other hand, Pb concentration in the rice plants with FeSO₄ + CaSO₄ (1:1) treatment significantly increased in the leaf sheath and leaf blade, but no significant differences were observed in all organs with other amendments compared with the untreated control. Therefore, FeSO₄ can be applied to a feasible approach for alleviating As stress in rice plants and reducing the affect of the As accumulation of As and Pb co-contaminated paddy soils.