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The use of Napier grass to remediate heavy metal-contaminated soil is a new phytoremediation technique. The objective of this study was to evaluate the ability of Napier grass (Pennisetum purpureum Schumach.) to remediate Cd- and Zn-contaminated cultivated soil under nonmowing and mowing and the possibility of safe utilization of the stem and leaf after detoxification by liquid extraction. Three Napier grass varieties, P. purpureum cv. Mott (PM), P. purpureum cv. Red (PR), and P. purpureum cv. Guiminyin (PG), were planted in a field with 3.74 mg kg−1 Cd and 321.26 mg kg−1 Zn for 180 days. The maximum amounts of Cd and Zn removed by PG were 197.5 and 5023.9 g ha−1, respectively, almost equaling those of hyperaccumulators. Compared with nonmowing, mowing did not decrease the Cd and Zn contents in various tissues but increased the biomasses of PM, PR, and PG by 86.6%, 18.9%, and 26.1%, respectively. Compared with nonmowing, the amounts of Cd removed by PM, PR, and PG under mowing increased by 110.5%, 40.0%, and 107.9%, respectively, and that of Zn increased by 63.0%, 53.1%, and 71.6%. The dominant Cd and Zn chemical fractions in Napier grass were the pectate- and protein-integrated fractions. After liquid extraction, although the nutrient element (Ca, K, Mg, and Mn) contents in the stem and leaf were reduced significantly, the Cd and Zn contents decreased below the limit of the Chinese Hygienic Standard for Feeds, and the crude protein content was largely retained. Such detoxified stems and leaves can be safely used as feeds or as raw materials for energy production.

To investigate the differences in cadmium (Cd) and lead (Pb) uptake and translocation among rape cultivars and genotypes and select suitable rape cultivars for both safe production and soil remediation, a field experiment was carried out with 39 rape cultivars of three genotypes on a farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb contents in rape tissues were measured, and the amount of Cd and Pb removed was calculated. The results showed that Cd in rape plants accumulated mostly in stems, while Pb accumulated mostly in roots. The Cd accumulation in various rape tissues followed the sequence stem > root > husk > rapeseed, while the Pb accumulation followed the sequence root > stem > husk > rapeseed. The total Cd and Pb removed by planting rape were 4.50–23.6 g ha−1 and 5.85–13.7 g ha−1, respectively, and the Cd and Pb contents in rapeseeds were in the range 0.11–0.47 mg kg−1 and 0.03–0.84 mg kg−1, respectively. Only the Pb content in rapeseed of “Youyan 9” exceeded the limit of the maximum levels of contaminants in foods (GB2762-2017, Pb ≤ 0.2 mg kg−1). In this experiment, the roots of most rape cultivars showed a greater capacity for Cd transport, while the stems showed a greater capacity for Pb transport. Except for the TFstem-husk for Cd, there were no significant differences in the TFs and BAFs of 39 rape cultivars, and clear variations in Cd content were found in the stems of the three genotypes, while there was no significant difference in the Cd and Pb contents in the other tissues. In the farmland polluted with Cd and Pb, planting “Xiangzayou 695” and “Youyan 2013” not only reduced soil pollution but also allowed the production of safe rapeseed.

Nano-Fe

Nano-Fe3O4-modified biochar (BC–Fe) was prepared by the coprecipitation of nano-Fe3O4 on a rice husk biochar surface. The effects of BC-Fe on cadmium (Cd) bioavailability in soil and on Cd accumulation and translocation in rice (Oryza sativa L. cv. ‘H You 518’) were investigated in a pot experiment with 7 application rates (0.05–1.6%, w/w). BC-Fe increased the biomass of the rice plants except for the roots and affected the concentration and accumulation of Cd and Fe in the plants. The Cd concentrations of brown rice were significantly decreased by 48.9%, 35.6%, and 46.5% by the 0.05%, 0.2%, and 0.4% BC-Fe treatments, respectively. Soil cation exchange capacity (CEC) increased by 9.4%–164.1% in response to the application of BC-Fe (0.05–1.6%), while the soil Cd availability decreased by 6.81%–25.0%. However, 0.8–1.6% BC-Fe treatments promoted Cd transport to leaves, which could increase the risk of Cd accumulation in brown rice. Furthermore, BC-Fe application promoted the formation of iron plaque and enhanced the root interception of Cd. The formation of iron plaque reduced the toxicity of Cd to rice roots, but this barrier effect was limited and had an interval threshold (DCB-Fe: 22.5–27.3 g·kg−1) under BC-Fe treatments.