College of Resources and Environment, Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou, 350002, Fujian, China.
College of Resources and Environment, Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou, 350002, Fujian, China; Department of Soil and Environmental Science, Ghazi University, Dera Ghazi Khan, 32200, Punjab, Pakistan.
Ecotoxicol Environ Saf. 2020 Jun 15;196:110490. doi: 10.1016/j.ecoenv.2020.110490. Epub 2020 Apr 7.
Immobilization is widely used to decrease the availability of heavy metals, such as Cd and Pb, in contaminated soils. However, the spatial and temporal changes in the immobilization of soil by amendments combined with planting effects have not been studied well. In this study, unplanted and planted (with rice plants) pot experiments were used to assess the spatial and temporal changes in water-soluble Cd, Fe, Mn, and Ca. Soil properties, such as pH, redox potential (Eh), and dissolved organic carbon (DOC), were continuously recorded in both the rhizosphere and bulk soil using non-invasive rhizon samplers and a microelectrode system (Unisense). In unplanted soil, pH and Eh varied with time, but showed little radial variation from the rhizosphere to the bulk soil. The addition of hydrated lime (Ca(OH)) sharply increased the pH, DOC, and Ca content; decreased the Eh, Fe content, and Mn content; and gradually decreased the water-soluble Cd content in the soil profile. Hydroxyapatite showed no obvious effects in reducing Cd concentrations in different soil zones. The water-soluble Fe, Mn, Ca, and DOC content did not differ significantly between soil zones over time and a non-significant correlation with water-soluble Cd was shown. In planted soil, the pH increased while the Eh value decreased with an increase in the distance from the roots, regardless of the soil amendments used during the rice growth period. Hydroxyapatite gradually increased but hydrated lime decreased the water-soluble Cd in the rhizosphere. The concentration of water-soluble Cd in the rhizosphere was higher than that of the other soil zones during rice growth. These changes lead to more Cd uptake by roots and induced Cd accumulation in rice tissues. In addition, Cd and Fe concentration in iron plaque showed a significant positive correlation with Cd in rice, indicating that iron plaque promotes the uptake and accumulation of Cd in rice with soil amendments. Compared with the control, hydroxyapatite did not significantly affect the Cd content, while Ca(OH) significantly reduced the Cd content in iron plaque and rice tissues. In conclusion, the application of hydrated lime can significantly reduce the risk of Cd accumulation by rice in Cd-contaminated soils under flooding conditions.
固定化广泛用于降低污染土壤中重金属（如 Cd 和 Pb）的有效性。然而，添加物与种植相结合对土壤固定化的空间和时间变化还没有得到很好的研究。在这项研究中，采用未种植和种植（水稻植株）盆栽实验来评估水可溶性 Cd、Fe、Mn 和 Ca 的空间和时间变化。使用非侵入式 rhizon 采样器和微电极系统（Unisense）连续记录根际和原状土壤的土壤性质，如 pH 值、氧化还原电位（Eh）和溶解有机碳（DOC）。在未种植的土壤中，pH 值和 Eh 值随时间变化，但从根际到原状土壤的径向变化很小。水合石灰（Ca(OH)）的添加显著增加了 pH 值、DOC 和 Ca 含量；降低了 Eh 值、Fe 含量和 Mn 含量；并逐渐降低了土壤剖面中的水可溶性 Cd 含量。羟基磷灰石在降低不同土壤区 Cd 浓度方面没有明显效果。随着时间的推移，水可溶性 Fe、Mn、Ca 和 DOC 含量在不同土壤区之间没有显著差异，与水可溶性 Cd 之间也没有显著相关性。在种植的土壤中，无论在水稻生长期间使用何种土壤改良剂，pH 值随距离根部的增加而增加，而 Eh 值则随距离根部的增加而降低。羟基磷灰石逐渐增加，但水合石灰降低了根际水可溶性 Cd。在水稻生长期间，根际的水可溶性 Cd 浓度高于其他土壤区。这些变化导致更多的 Cd 被根系吸收，并诱导 Cd 在水稻组织中积累。此外，铁斑中 Cd 和 Fe 浓度与水稻中的 Cd 呈显著正相关，表明铁斑促进了 Cd 在添加物土壤中向水稻的吸收和积累。与对照相比，羟基磷灰石对 Cd 含量没有显著影响，而 Ca(OH)显著降低了铁斑和水稻组织中的 Cd 含量。总之，在淹水条件下，施用水合石灰可显著降低 Cd 污染土壤中水稻对 Cd 的积累风险。
