Effects of Biochars Produced from Coconut Shell and Sewage Sludge on Reducing the Uptake of Cesium by Plant from Contaminated Soil

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Immobilization using biochar is a cost-effective and environmentally friendly remediation method to inhibit the transfer of soil contaminants to the food chain. This study evaluated the effects of coconut shell–derived biochar (CSB) and sewage sludge–derived biochar (SSB) on reducing the accumulation of cesium (Cs) by plant from contaminated soil. Pot experiment was conducted by cultivating Napier grass on the soil added with different Cs concentrations (0, 25, and 50 mg kg−1) and biochar ratios (0: control, 5% and 10%). It was observed that both biochars significantly restricted the transfer of Cs to the root, leaf sheath, and leaf blade of Napier grass (p < 0.01). The possible mechanisms of Cs immobilization by biochar could be the sorption of Cs on the surface of biochar as well as the restriction of the uptake of Cs by plant due to the increased K concentration of biochar-amended soil. CSB application was more effective than SSB on reducing the transfer of Cs to plant. Compared to control, the CSB application reduced the concentration of Cs in the plant by 80.2–98.2%. Moreover, obtained results in terms of pH, organic matter content, cation exchange capacity, specific surface area, and K concentration of biochar-amended soil highlighted the remarkable efficiency of CSB to adsorb Cs and restrict Cs transfer to plant providing the key evidences for Cs immobilization. Considering these results, CSB could be a potential amendment for the immobilization of Cs-contaminated soil.