Method for repairing cadmium-polluted soil by brassicaceous vegetables based on selenium-enriched soil regulation and control

Abstract

The invention provides a method for restoring cadmium-polluted soil by brassicaceous vegetables based on selenium-enriched soil regulation and control. By using selenium-rich soil and simulating a high-COconcentration environment, the enrichment capacity and tolerance of cruciferous vegetables (such as rape and pakchoi) to cadmium are improved. The antioxidant characteristic of selenium element relieves cadmium toxicity, promotes plant growth and improves biomass. Under the regulation and control of selenium-rich soil, the absorption capacity of the brassicaceous vegetables to cadmium is enhanced, and the remediation efficiency is higher in a high-COC environment. The experimental group is treated by using selenium-rich soil, the cadmium content, biomass and antioxidant enzyme activity in plant roots, stems and leaves are measured when the remediation effect is evaluated, and compared with a traditional non-selenium-rich soil remediation method, the remediation efficiency of the experimental group is improved by 35%-60% compared with that of a control group. Results show that the antioxidant enzyme activity is obviously enhanced, and the biomass and the growth stability are improved. The method is easy and convenient to operate, low in cost, environmentally friendly and suitable for remediation of the light and medium cadmium polluted soil with the cadmium concentration lower than 5.0 mg / kg.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ecological environment restoration, particularly a phytoremediation method in the remediation technology of heavy metal contaminated soil, and specifically a phytoremediation technology based on selenium-rich soil regulation. The technology combines plant physiology, soil science and environmental pollution control science, and enhances the enrichment ability and tolerance of cruciferous vegetables to cadmium (Cd) to achieve efficient remediation of cadmium-contaminated soil. The present application mainly utilizes selenium elements in selenium-rich soil to enhance the antioxidant system of plants, reduce the toxic effects of cadmium, and thus improve the absorption and enrichment efficiency of plants to cadmium.

[0002] The remediation method of the present application belongs to the phytoremediation technology in ecological restoration, and is particularly suitable for biological remediation of medium and light cadmium-contaminated soil. By utilizing the antioxidant properties of selenium elements, the bioavailability of cadmium and its toxicity to plants can be effectively reduced. This method not only has the characteristics of green environmental protection and low cost, but also can realize long-term remediation of soil heavy metal pollution, which meets the current requirements of sustainable development in the field of environmental remediation.

[0003] The remediation method of the present application is simulated under the background of future climate change, particularly the phytoremediation effect under high CO2 concentration environment, which has high innovation. This technology is particularly suitable for environmental pollution control fields such as facility agriculture, contaminated land reclamation, farmland ecological restoration and mining land reclamation, and can effectively promote soil health, reduce the harm of heavy metals to the ecological system, and provide new ideas for realizing environmental sustainable development. BACKGROUND

[0004] With the acceleration of global industrialization, the improvement of agricultural intensification level and the continuous expansion of urbanization, heavy metal pollution, especially cadmium (Cd) pollution, has become a major environmental problem that has attracted worldwide attention. Cadmium is a heavy metal element with high toxicity, easy migration and bioaccumulation, which widely exists in pollution sources such as industrial wastewater discharge, fertilizer and pesticide application, and mineral resource development. Due to its long-term retention and difficulty in degradation in soil, it is easily absorbed by plants and enters the food chain, posing a potential threat to the ecological environment and human health, and can cause kidney damage, osteoporosis and even cancer.

[0005] Among many soil remediation technologies, phytoremediation has gradually become a research hotspot and application direction for the remediation of soil heavy metal pollution due to its green environmental protection, simple operation and low cost. Phytoremediation realizes the purification of contaminated soil through the absorption, transport and accumulation of pollutants, and has good ecological adaptability and long-term treatment ability.

[0006] Cruciferous vegetables, such as Brassica rapa, Brassica chinensis, and radish, have certain cadmium enrichment potential and stress resistance, thus having good application prospects in the field of phytoremediation. Suitable cruciferous vegetables should have the following characteristics: strong root absorption capacity, high biomass output, good heavy metal tolerance, and high cadmium enrichment capacity. Compared with some specific hyperaccumulators, cruciferous vegetables are more easily promoted and accepted in actual agricultural ecosystems, and have higher practical value.

[0007] Studies have shown that selenium (Se) in soil can effectively alleviate the toxicity of cadmium to plants by regulating the antioxidant system in plants, and improve the stress resistance and growth performance of plants. Selenium can also reduce the bioavailability of cadmium and enhance the tolerance of plants to cadmium through mechanisms such as antagonistic absorption and formation of stable complexes. Therefore, selenium-rich soil as a control means has been widely concerned.

[0008] However, existing phytoremediation researches mostly focus on conventional climate conditions, ignoring the influence of environmental factor changes caused by global climate change on remediation effect. Especially under the background of continuous increase of CO2 concentration in the atmosphere, the photosynthesis, water use efficiency, and nutrient absorption mechanism of plants will change, thereby affecting the enrichment process and remediation capacity of plants to heavy metals. Some studies have shown that high CO2 concentration can increase plant biomass and photosynthesis rate, which may help to improve remediation efficiency, but the related mechanisms and specific applications still need further research.

[0009] At present, there is still a lack of composite phytoremediation technology that can consider the synergistic effect of selenium-rich soil regulation and future climate scenarios (such as high CO2 concentration) at the same time. Therefore, it is necessary to develop a phytoremediation method based on selenium-rich regulation suitable for various vegetables, and evaluate its effect and mechanism under simulated future climate conditions. This will provide a more scientific, feasible and sustainable technical solution for the treatment of heavy metal pollution in agricultural soils in the future. SUMMARY

[0010] The present application provides a method for repairing cadmium-contaminated soil by cruciferous vegetables based on selenium-rich soil regulation, which aims to improve the absorption capacity of cruciferous vegetables to cadmium by selenium-rich soil, and to enhance the resistance and remediation efficiency of plants by combining high CO2 concentration to simulate future climate scenarios. This method not only can effectively reduce the pollution of cadmium in soil, but also can improve the biomass and antioxidant capacity of plants, realizing efficient, green and low-cost environmental remediation.

[0011] The present application provides a method for repairing cadmium-contaminated soil by cruciferous vegetables based on selenium-rich soil regulation, which aims to improve the absorption capacity of cruciferous vegetables to cadmium by selenium-rich soil, and to enhance the resistance and remediation efficiency of plants by combining high CO2 concentration to simulate future climate scenarios. This method not only can effectively reduce the pollution of cadmium in soil, but also can improve the biomass and antioxidant capacity of plants, realizing efficient, green and low-cost environmental remediation. 1. Soil selection and treatment The selected selenium-rich soil should come from natural selenium-rich areas, where the soil naturally contains a higher amount of selenium, ensuring sufficient selenium for plant growth and remediation research. The selection of selenium-rich soil should strictly control its effective selenium content to ensure that the soil contains ≥0.5 mg / kg of selenium to ensure sufficient supply of selenium elements during plant remediation.

[0012] 2. Vegetable seedling and transplanting Choose cruciferous vegetable seeds of the same variety, first disinfect them with 1% potassium permanganate solution, then sow them in suitable soilless substrate. Maintain a 14-hour light cycle at 20-25°C, and keep the environment moderately humid to promote seed germination. After the seedlings grow to the three-leaf-one-heart stage, thin them out and prepare for transplanting. Keep the root system intact during transplanting, and gently transplant the seedlings into selenium-rich soil to ensure that the roots are in full contact with the soil. Provide appropriate shade and irrigation in a timely manner to help them adapt to the new environment.

[0013] 3. Environmental control Simulate future climate scenarios in a greenhouse environment by controlling CO2 concentration at 800 ppm. Studies have shown that high CO2 concentration can affect plant photosynthesis efficiency, water and nutrient absorption capacity, and heavy metal absorption pathways, thereby affecting remediation efficiency. Under this setting, plant biomass increases, growth accelerates, cadmium absorption is promoted, and stress resistance is enhanced.

[0014] 4. Selenium-rich soil regulation The introduction of selenium-rich soil aims to improve the absorption efficiency of cruciferous vegetables for cadmium. Selenium, as a key antioxidant element, can activate antioxidant enzyme systems in plants, such as superoxide dismutase (SOD) and catalase (CAT), thereby effectively alleviating oxidative stress caused by cadmium, reducing plant tissue damage, improving growth quality, and enhancing remediation capacity.

[0015] 5. Remediation evaluation of cadmium-contaminated soil After the growth cycle ends, measure the cadmium and selenium content in the roots, stems, and leaves of the plants to evaluate the impact of selenium-rich soil regulation on heavy metal enrichment capacity. At the same time, analyze the interaction mechanism of selenium and cadmium in plants to further explore the action path and potential of selenium-rich regulation on heavy metal remediation.

[0016] 6. Data collection and analysis After the experiment ends, harvest the plants, measure the biomass, leaf area, and antioxidant enzyme activity of the plants, and sample and test the residual cadmium content in the soil. By comparing the differences between different treatment groups, comprehensively evaluate the effectiveness of this method in improving the efficiency of remediation of cadmium-contaminated soil and promoting the healthy growth of plants, and provide experimental basis for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 :Flowchart of phytoremediation technology for cadmium-contaminated soil Figure 2 :Experimental flow chart of cruciferous vegetables remediation of cadmium-contaminated soil

[0018] To verify the feasibility of this invention, the following implementation steps were conducted using mustard (Brassica juncea) as a representative cruciferous vegetable. This method is also applicable to other cruciferous vegetables with certain heavy metal accumulation and tolerance, such as rapeseed, pakchoy, and radish. The relevant parameters and steps can be adjusted based on this protocol.

[0019] The present invention will be further described below in conjunction with specific embodiments. The implementation of this method is divided into the following steps: Step 1: Determine the experimental area and sampling location, and collect soil samples Select an experimental area suitable for the study and select sampling locations according to the experimental design to collect surface samples of mustard soil. The specific sampling method is a five-point composite sampling method. First, five sampling points are selected at different locations within the study area. Each sampling point has a sampling depth of 0-20 cm. A soil sampler is used to collect samples from different directions in a cross pattern. Soil samples from the five sampling points are mixed evenly to obtain a composite sample. The sample is then aliquoted into several small aliquots, labeled with information such as the sampling location and date. After collection, the soil samples are air-dried and sieved to remove impurities. They are then sealed and stored to prevent contamination. The entire process follows the "Technical Guidelines for Soil Quality Sampling" (GB / T 36197-2018) to ensure standardized and reproducible sampling. After collection, soil samples should be immediately placed in clean, sealed bags and brought back to the laboratory for storage, protecting them from direct sunlight and humidity, which could alter their composition. This step aims to provide a reliable soil sample base for subsequent experiments.

[0020] Step 2: Determine the heavy metal content in soil under different fertilization treatments In this step, the collected soil samples will be used to determine the content of heavy metal elements. The water used should be high-purity water with a resistivity of 18.2 MΩ. The acid used should be GR grade or higher, purified by double sub-boiling distillation. Digestion should be performed using a Teflon digestion tube. All experimental equipment should be cleaned with 10% mass fraction nitric acid to ensure contamination. After soil sample digestion, the heavy metals in the soil samples are quantitatively analyzed using standardized analytical methods (such as ICP-MS). Heavy metals (such as cadmium, lead, and copper) in the soil samples were quantitatively analyzed using an ICP-MS (PerkinElmer Elan DRC-e). The ICP-MS operating conditions were: an argon gas flow rate of 0.8 L / min, a plasma power of 1550 W, and a nitrogen reagent flow rate of 4 mL / min. Soil samples were air-dried, ground, and sieved before being digested with concentrated nitric acid and hydrogen peroxide. After constant volume, they were analyzed by ICP-MS, with a detection range of 0.01 μg / L to 500 μg / L. This step aimed to understand the accumulation of heavy metals in the soil under different fertilization treatments, particularly the relationship between cadmium (Cd) and selenium (Se), providing data support for subsequent assessment of remediation effectiveness.

[0021] Step 3: Explore the effects of different fertilization treatments on the content of heavy metal elements in the soil The main purpose of this step is to study the effects of different fertilization treatments (such as selenium-enriched soil and cadmium stress treatment) on the content of heavy metal elements in the soil. By setting up different concentrations of cadmium stress treatment (such as Cd1, Cd2, Cd5) and selenium-enriched soil groups, the remediation effects of selenium-enriched soil and cadmium stress on heavy metals in the soil are analyzed. The changes in cadmium and selenium content in the soil are used to evaluate the effects of fertilization treatments on heavy metal elements and their regulatory effects. Under different treatments, the changes in plant biomass, root absorption capacity for cadmium, and antioxidant enzyme activity are analyzed to explore how selenium-enriched soil regulation can significantly improve plant absorption efficiency and tolerance to cadmium through physical and chemical mechanisms.

[0022] Step 4: Mustard growth and restoration effect evaluation After the soil treatment was completed, the mustard seedlings were transplanted into the soil of the different fertilization treatment groups and cultivated to simulate future climate scenarios. The experiment set the CO2 concentration in the greenhouse to 800 ppm, the temperature was controlled at 25±2℃, the humidity was maintained at 60%-70%, and the photoperiod was 14 hours to simulate the impact of future climate change. The growth of the plants, including growth indicators such as leaf area, plant height, and root-to-stem ratio, were recorded regularly to evaluate the effects of different fertilization treatments on the growth of mustard. At the same time, mustard samples were harvested and the cadmium and selenium contents in their roots, stems, and leaves were measured.

[0023] Repair effect data: Comparison of cadmium content: The cadmium content in the mustard roots of the experimental group (selenium-rich soil and high CO2 treatment group) decreased by 56%, while that of the control group only decreased by 20%.

[0024] Biomass comparison: The dry weight of the experimental group was 30% higher than that of the control group. The experimental group had a well-developed root system, and the above- and below-ground biomass increased by 30%.

[0025] Comparison of antioxidant enzyme activities: The SOD and CAT activities of the experimental group were 45% and 38% higher than those of the control group, respectively.

[0026] Remediation evaluation concluded: The experimental group showed significant increases in cadmium content, biomass, and antioxidant enzyme activity, with remediation efficiency increasing by 35%-60%. These results suggest that the combined application of selenium-enriched soil and a high CO2 environment has a significant synergistic effect on the remediation of cadmium-contaminated soil.

[0027] 1. Regulatory role of selenium-rich soil Selenium-enriched soil significantly improves the cadmium absorption capacity and resistance of cruciferous vegetables through physical and chemical mechanisms. Selenium reduces the bioavailability of cadmium in plants by competitive adsorption with cadmium, forming insoluble complexes, and mitigating cadmium's toxic effects through antioxidant mechanisms. Furthermore, selenium activates antioxidant enzyme systems such as superoxide dismutase (SOD) and catalase (CAT), effectively scavenging cadmium-induced reactive oxygen species (ROS), reducing lipid peroxidation, maintaining cell membrane integrity, and enhancing overall antioxidant defenses in plants. Furthermore, selenium-enriched soil improves soil structure and enhances root water and nutrient absorption, thereby promoting plant growth and biomass. In summary, selenium-enriched soil not only improves cadmium absorption efficiency but also enhances plant growth stability and stress resistance, effectively mitigating the toxic effects of cadmium and promoting improved remediation efforts.

[0028] 2. Simulating future climate scenarios This study used a CO2 concentration of 800 ppm to simulate future climate scenarios. The results showed that high CO2 concentrations significantly boosted the photosynthetic efficiency of cruciferous vegetables and significantly increased their biomass. This provides a new theoretical basis for phytoremediation technology in the context of future climate change.

[0029] 3. The synergistic effect of selenium and high CO2 is not disclosed in the prior art The "synergistic effect of selenium and high CO2" proposed in this invention is significantly innovative in remediating cadmium-contaminated soils, and this combined application has not yet been disclosed in the prior art. Existing technologies primarily focus on the effects of single factors, such as the mechanism by which selenium mitigates cadmium toxicity (through its antioxidant effects) or the effect of CO2 on plant growth. However, the present invention combines the antioxidant properties of selenium with the growth-promoting effects of plants in high CO2 environments, significantly improving the cadmium accumulation capacity and tolerance of vegetables through synergistic gains. This combined application can simultaneously achieve the combined benefits of two independent effects under the same experimental conditions, greatly improving remediation efficiency.

[0030] 4. Existing technologies mostly focus on a single factor and do not involve combined applications Currently, relevant research has mostly focused on the effects of either selenium or CO2 alone on plant remediation capacity, lacking exploration of the combined effects of the two. The innovation of this invention lies in the first proposal and verification of the synergistic application of selenium-rich soils and high CO2 environments, and the experimental data demonstrating the advantages of this combination in cadmium pollution remediation. Through this synergistic effect, the present invention not only improves plant stress resistance but also significantly enhances its cadmium absorption capacity, further improving the efficiency of soil remediation.

[0031] 5. Green and low-cost restoration technology This method does not require expensive chemicals or complex equipment, is simple to operate, and is suitable for large-scale application. The use of selenium-enriched soil not only reduces costs but also reduces secondary pollution, meeting the current demand for environmentally friendly remediation technologies.

[0032] The technical highlights of the present invention are: Innovatively combining selenium-rich soil with a high CO2 environment to simulate phytoremediation scenarios under future climate conditions; The economically available cruciferous vegetables are used as the restoration carrier, which has promotion value; Does not rely on exogenous cadmium or chemical additives, safe and environmentally friendly; It can be expanded to multiple scenarios such as greenhouse agriculture and mine reclamation.

[0033] The technology of this invention can be widely applied to the remediation of cadmium-contaminated soils, and is particularly suitable for ecological restoration in areas such as farmland, agricultural facilities, and mine reclamation. As global climate change increasingly impacts the ecological environment, phytoremediation methods using selenium-enriched soils will not only help improve the remediation efficiency of heavy metal-contaminated soils, but also provide more precise solutions for remediation work under future climate conditions.

Claims

1. A method for repairing cadmium-contaminated soil with cruciferous vegetables based on selenium-enriched soil regulation, wherein the cruciferous vegetables are rapeseed, Chinese cabbage, radish or mustard, used as the repair plants. The steps include: (1) Selenium-rich soil with an effective selenium content of 0.5-2.0 mg / kg was selected as the remediation matrix, and non-selenium-rich soil with an effective selenium content of ≤ 0.1 mg / kg was set as the control; (2) Select cruciferous vegetable seeds with cadmium accumulation and tolerance for seedling cultivation, and transplant them into selenium-enriched soil after the seedlings reach the three-leaf and one-heart stage; (3) Cultivated in a greenhouse environment with a controlled CO2 concentration of 800 ± 20 ppm, a temperature of 25 ± 2 °C, a photoperiod of 14 h / day, and a relative humidity of 60%–70%; (4) By adding selenium-enriched soil (effective selenium content of 0.5-2.0 mg / kg), the selenium content in the soil is adjusted at a ratio of 10% to 40% of the soil volume to enhance the ability of vegetables to accumulate cadmium in the soil. This ratio is dynamically adjusted according to the degree of cadmium contamination in the soil. A higher ratio of selenium-enriched soil is used for soils with higher cadmium contamination. (5) The restoration effect was evaluated by combining plant growth indicators (such as plant height, leaf area, and root length), biomass (such as dry weight of aboveground and underground parts), and antioxidant enzyme activity (such as superoxide dismutase (SOD) and catalase (CAT) activity). Antioxidant enzyme activity was determined by colorimetric assay using the corresponding kits and measuring the absorbance change using a microplate reader to calculate the enzyme activity.

2. The method according to claim 1, wherein the selenium-rich soil is collected from naturally selenium-rich areas where the soil has a high selenium content. To ensure that the effective selenium content of the soil is within the range of 0.5 to 2.0 mg / kg, samples are collected from multiple sampling points and mixed to ensure representative soil samples. During the experiment, the selenium content in the soil samples was quantitatively analyzed using ICP-MS (inductively coupled plasma mass spectrometry) to ensure that it met the standard of 0.5 to 2.0 mg / kg.

3. The method according to claim 1, wherein the application amount of the selenium-rich soil can be dynamically adjusted according to the degree of soil pollution, and its proportion is 10%-40% of the volume of the soil for growing cruciferous vegetables.

4. The method according to claim 1, wherein the cruciferous vegetable is selected from rapeseed, pakchoi, radish or mustard, and has a growth period of 45-60 days.

5. The method of claim 1 , wherein the CO2 concentration is maintained at 800 ± 20 ppm by a CO2 injection system. A CO2 monitor (ABH105) is used to monitor gas concentration in real time, and an automatic regulation system (OMS-100A) is used to maintain the concentration within a set range to ensure stable CO2 concentration in the experimental environment and simulate future climate scenarios.

6. The method according to claim 1, wherein evaluating the repair effect comprises: — Growth indicators such as plant leaf area, plant height, and root-to-stem ratio; — Antioxidant / oxidative stress indicators such as superoxide dismutase (SOD), catalase (CAT) activities and lipid peroxidation levels in plants.

7. The method according to claim 1, wherein the "cadmium ion (Cd²⁺) selenium-enriched treatment group" refers to soil treated with selenium-enriched soil (effective selenium content of 0.5-2.0 mg / kg), whose cadmium ion (Cd²⁺) concentration is within the specified range to achieve a cadmium remediation effect.

8. The method according to claim 1, wherein the method is applicable to farmland, facility agriculture areas, mine reclamation areas and other ecological restoration sites with light to moderate cadmium pollution, wherein "light to moderate cadmium pollution" refers to a cadmium concentration in the soil between 0.5 and 5.0 mg / kg.

9. The method according to claim 1, wherein the interaction mechanism between cadmium and selenium in plants is studied by simulating high CO2 concentration.

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