Li Hongbing,Zhang Xinying,Liu Xiaoyan,Hu Xing,Wang Qian,Hou Yunyun,Chen Xueping,Chen Xiao
Rhizodeposition is considered as a main strategy for plants to regulate its rhizospheric microorganisms. However, effect of rhizodeposition on degradation of polycyclic aromatic hydrocarbons (PAHs), and the alterations of soil structure and microbial community are still unclear, especially in metal–PAHs co-contaminated soils. The study focused on illustrating the microcosm changed by rhizodeposition to find out the dominating factors for the dissipation of pyrene. The analysis results with Fourier transform infrared spectroscopy (FT-IR) showed that the relative abundance of some functional groups in humic acids was amplified by rhizodeposition effect. A result was observed that soluble fraction of lead was rapidly transformed into other fractions by the rhizodeposits. It was found that the rhizodeposition effect exhibited considerable improvement in the degradation of pyrene especially in the lead–pyrene co-contaminated soils. Phospholipid fatty acid analysis (PLFA) showed substantial differences in microbial communities between incubation time and rhizodeposition effect. The studied results further revealed the removal mechanism of pyrene in pyrene–lead co-contaminated soils.
Cadmium pollution in the soil induces significant hazards to agricultural growth and public health. Therefore, new routes are needed to develop low-cost soil amendments that can effectively stabilize cadmium and improve soil fertility. This study introduces modified illite (MIT) with the enhanced ability to stabilize heavy metal Cd through the mixing of illite with calcium carbonate, silicate and sulfate in specific proportions by using the well-known calcination-hydrothermal process. The characterization findings revealed that the modified MIT is predominantly composed of gehlenite and akermanite, with greatly improved specific surface area, pore structure and cation exchange capacity. The main purpose of the present study is to unravel a plausible mechanism on how MIT can stabilize Cd(II) in the soil and to investigate the effect of MIT on the fertility of the contaminated soil. Experiments on soil remediation revealed that MIT has a more profound stabilizing impact on Cd(II) compared to natural illite, resulting in a 22.84% reduction in acid-soluble Cd of the soil when MIT was dosed at 0.5%. The potential mechanism of Cd(II) immobilization by MIT involves the ionic exchange of Cd2+with the exchangeable Ca2+and Mg2+. In addition, the hydrolysis products of gehlenite and akermanite are prone to form silicate precipitates with free Cd, leading to soil pH increment. The pot experiments showed that MIT significantly reduces the cadmium content of soil and improves the growth of water spinach organs. Meanwhile, enhancement of the indicators in rhizosphere soil further proved that MIT effectively increases the nutrient content, improves the soil structure and promotes microorganism growth.Keywords:modified illite;clay mineral;heavy metal;immobilization;soil fertility
This study investigated the application of a specific soil washing method to remove Cu and Pb from contaminated agricultural soil. To develop an efficient leaching agent of heavy metal compounds for use in farmland soil, a mixed chelator (MC) was prepared using potassium fulvic acid (PFA, 3.2%) and citric acid (CIT, 0.16 M) in a volume ratio of 4:1 (PFA:CIT = 4:1); the optimal solid-liquid ratio (S/L = 1:20), initial pH value (4.51) and contact time (360 min) were also explored. Under optimal conditions, the removal efficiencies of MC for Cu and Pb were 42.92% and 50.46%, respectively, both of which performed better than PFA (27.86% of Cu and 17.91% of Pb) and CIT (42.04% of Cu and 41.46% of Pb). The effective states, bioavailability and relative mobilities of Cu and Pb in soil were also efficiently reduced by MC, which also increased the stability of these elements, thereby lowering the risk to soil health. More importantly, MC not only had little effect on the soil physicochemical properties (e.g., pH, organic matter (OM), cation exchange capacity (CEC), ammonium nitrogen (AN), available phosphorus (AP) and rapidly available potassium (AK)), but also improved the restored soil. Furthermore, soil structure, surface elements and the enzyme activity did not exhibit significantly loss. Therefore, MC has great potential for remediating agricultural soil.
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