Ca-containing amendments to reduce the absorption and translocation of Pb in rice plants

Abstract

The influence of three Ca-containing amendments (dolomite, slaked lime, and limestone) on soil water soluble Pb (Pb-w) levels, Pb accumulation by two rice plants (TJ-8, japonica and II-3301, indica), and the factors affecting Pb-w were investigated. Pot experiment was performed under waterlogged conditions using Pb-contaminated soil collected from an agricultural field near a mine. It was found that the soil amendments significantly reduced Pb content in the rice plants in the order dolomite > slaked lime > limestone, irrespective of rice cultivar. The Pb content of brown rice with the added soil amendments was lower than that of the recommended limit (0.2 mg kg^-1, GB2762-2017) except for cultivar II-3301 with slaked lime. There was a significant positive correlation between the Pb content of the roots, stems, leaves, and grains and the soil Pb-w levels. The amendments reduced soil Eh, Fe, and Mn concentrations in the pore water and increased soil pH. The total organic carbon (TOC) in the pore water significantly decreased for II-3301 but not for TJ-8 at the ripening stage after addition of the amendments. Among soil Eh, pH, TOC, Fe, and Mn in the pore water, Fe and Mn were the most influential in lowering soil Pb-w levels. The amendments inhibited the formation of iron plaques on the root surface and reduced Pb adsorption. The Pb content of the roots was positively correlated with that in iron plaque. These findings are significant as they imply that the application of Ca-containing amendments in Pb-contaminated paddy soils near mines is an effective approach for in situ immobilization of Pb and reduction in Pb levels in the edible parts of crops.

Keywords: Dolomite; Lead; Lime; Pore water; Rice.