Evaluation of the Effects of Lime-bassanite-charcoal Amendment on the Immobilization of Cadmium in Contaminated Soil

Impacts of a Compound Amendment on Cd Immobilization, Enzyme Activities and Crop Uptake in Acidic Cd-Contaminated Paddy Soils

This study assessed the effectiveness of limestone-montmorillonite-rapeseed residue-Si fertilizer compound amendment on the bioavailability and crop uptake of cadmium (Cd) and enzyme activities in acidic paddy soils. Applying the compound amendment at ratios of 1%-3% increased soil pH by 0.1-1.9 units, decreased leaching ratios of soil Cd 4.0%-22%, and decreased exchangeable and carbonated Cd 42%-55% and 27%-49%, respectively. Organic matter-bound Cd increased 47%-62% (p < 0.05). Cadmium concentrations decreased in the roots, culms, leaves, and grains of rice grown in the Cd-contaminated soils by 37%-81%, 18%-73%, 29%-64% and 27%-63%, respectively, (p < 0.05). Catalase and urease activities increased 2.5%-63% and 3.9%-36%, (p < 0.05), respectively. Applying this compound amendment may significantly mitigate soil acidification and decrease the bioavailability and crop uptake of Cd in acidic Cd-contaminated paddy soils.

Combined Amendments of Nano-hydroxyapatite Immobilized Cadmium in Contaminated Soil-Potato (Solanum tuberosum L.) System

The toxicity of cadmium (Cd) has posed major public health concern in crops grown in the Cd-contaminated soils. The effects of five amendments, nano-hydroxyapatite (n-HA) and it combined with lime, zeolite, bone mill and fly ash on Cd immobilization in soils and uptake in potatoes, were investigated in a contaminated soil by pot experiments. The result showed that the applications of combined amendments significantly decreased the bioavailable Cd concentrations extracted by TCLP, DTPA-TEA and MgCl₂ in the contaminated soils, and changed the soluble and exchangeable and specifically sorbed fractions to oxide-bound and organic-bound fractions. Compared to the control group, the concentrations of Cd in the potato tubers grown in n-HA, n-HA + Fly ash, n-HA + Lime, n-HA + Bone mill and n-HA + Zeolite soil were reduced 17.4%, 20.7%, 15.2%, 32.6% and 39.1%, respectively. Nano-hydroxyapatite combined amendments was more effective in reducing bioavailable Cd concentrations and Cd accumulations in potatoes, especially for n-HA + Z.

Knockout of OsNramp5 using the CRISPR/Cas9 system produces low Cd-accumulating indica rice without compromising yield

Rice grain with excessive cadmium (Cd) is a major source of dietary Cd intake and a serious threat to health for people who consume rice as a staple food. The development of elite rice cultivars with consistently low Cd content is challenging for conventional breeding approaches, and new strategies urgently need to be developed. Here, we report the development of new indica rice lines with low Cd accumulation and no transgenes by knocking out the metal transporter gene OsNramp5 using CRISPR/Cas9 system. Hydroponic culture showed that Cd concentrations in shoots and roots of osnramp5 mutants were dramatically decreased, resulting in rescue of impaired growth in high Cd condition. Cd-contaminated paddy field trials demonstrated that Cd concentration in osnramp5 grains was consistently less than 0.05 mg/kg, in contrast to high Cd concentrations from 0.33 mg/kg to 2.90 mg/kg in grains of Huazhan (the wild-type indica rice). In particular, the plant yield was not significantly affected in osnramp5 mutants. Furthermore, we developed promising hybrid rice lines with extremely low Cd content in grains. Our work supplies a practical approach to developing Cd pollution-safe indica rice cultivars that minimizes Cd contamination risk in grains.