Oyster shell amendment reduces cadmium and lead availability and uptake by rice in contaminated paddy soil

Contamination with cadmium (Cd) and lead (Pb) in rice and paddy soil threatens food safety and human health. This study determined the effects of oyster shell amendment (0, 6, and 12 g kg^-1) on the mobility and uptake of Cd and Pb by two rice plants (ZY18, japonica and DL5, indica) in contaminated paddy soil. Oyster shell amendment significantly increased the pH of soil and pore water, and decreased the DTPA-extractable Cd concentration in soil, but not the Cd concentration in pore water. Furthermore, the DTPA-extractable Pb concentration in rhizosphere soil was not significantly influenced by oyster shell addition. Application of oyster shell reduced the Pb concentration in pore water and Pb uptake by both cultivars, but excessive application (12 g kg^-1) resulted in Cd accumulation in tissues for ZY18. Furthermore, oyster shell addition significantly increased the dissolved organic carbon, calcium, and magnesium concentrations in soil pore water, and decreased glutathione and phytochelatin levels in roots, all of which alleviated heavy metal toxicity and improved rice growth. These results demonstrate that amendment with the appropriate amount of oyster shell, combined with rice cultivar type, could simultaneously reduce Cd and Pb accumulation in rice grown in heavy metal-contaminated soil.