A method for controlling agricultural heavy metal pollution based on passivation agent

Abstract

The invention discloses a method for controlling agricultural heavy metal pollution based on a passivator, and relates to the field of heavy metal pollution control, including selecting an initial passivator and a target plant; collecting target soil, and using the initial passivator to prepare potted soil; planting the target plant according to the potted soil and collecting, obtaining a soil sample group and a plant sample group; detecting the soil sample group and the plant sample group respectively, obtaining the effective cadmium content of the soil sample group and the cadmium content of the roots and stems and leaves in the plant sample group, and then obtaining the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency, and analyzing and obtaining the analysis effect; selecting the target passivator according to the analysis effect, and spraying the heavy metal contaminated soil in the target area, to achieve agricultural heavy metal pollution control based on the passivator. The invention avoids soil compaction caused by the addition of materials, has less negative impact on the soil, improves the agricultural product safety index, and improves the overall environment of the farmland.

Description

Technical Field

[0001] The invention belongs to the field of heavy metal pollution control, and particularly relates to a passivator-based agricultural heavy metal pollution control method. Background Art

[0002] Existing methods for controlling soil heavy metal pollution based on passivators have the following disadvantages and shortcomings: (1) Cost issues: The cost of high-efficiency passivators may be high, especially when applied on a large scale, which challenges their economic feasibility. (2) Environmental conditions: Lime-based passivators fix heavy metals by increasing soil pH, but if soil pH changes due to environmental factors, heavy metals may be released again. In addition, soil temperature, humidity, microbial activity, etc. will also affect the efficiency of the passivator. (3) Limited scope of application: Although chemical passivation remediation technology has good application prospects for the remediation of large areas of medium and low-level polluted soils due to its advantages such as low investment, high efficiency, rapid remediation, and simple operation, its actual scope of application is still relatively limited. (4) Lack of specificity: Different passivators have different passivation effects on different heavy metals, and the same passivator may also have different effects on different soil types and pollution levels. At present, research on the passivation effects of different passivators on different heavy metals and their influencing factors is still insufficient, which limits the efficiency improvement of passivation remediation technology.

[0003] Therefore, there is an urgent need for a passivator-based agricultural heavy metal pollution control method to address the deficiencies in the prior art. Summary of the invention

[0004] The purpose of the present invention is to propose a method for controlling agricultural heavy metal pollution based on a passivator, which not only ensures the production function of farmland without affecting the output of crops, but also effectively improves the efficiency of passivation control technology in treating polluted farmland and reduces the solubility, migration ability and biological effectiveness of heavy metals in the soil.

[0005] To achieve the above object, the present invention provides a method for controlling agricultural heavy metal pollution based on a passivator, comprising the following steps:

[0006] S1. Selecting an initial passivation agent and a target plant, wherein the initial passivation agent includes calcium magnesium phosphate fertilizer, thiol-modified clay and cadmium passivation agent No. 1;

[0007] S2. Collecting target soil and using the initial passivator to prepare potted soil, wherein the target soil includes test base soil and blended soil, the test base soil is soil with high concentration of heavy metal cadmium contamination, and the blended soil is unpolluted clean soil;

[0008] S3, planting the target plant according to the potting soil and collecting the plant to obtain a soil sample group and a plant sample group;

[0009] S4, respectively testing the soil sample group and the plant sample group, obtaining the effective cadmium content of the soil sample group and the cadmium content of the roots and stems and leaves of the plant sample group, and then obtaining the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency, wherein the plant cadmium passivation efficiency includes the cadmium passivation efficiency in the roots and the cadmium passivation efficiency in the stems and leaves;

[0010] S5. Analyze the effective cadmium content of the soil sample group, the cadmium content of the roots and stems and leaves of the plant sample group, the soil effective cadmium passivation efficiency, and the plant cadmium passivation efficiency to obtain analysis results;

[0011] S6. Select a target passivator according to the analysis results, and spray it on the heavy metal contaminated soil in the target area, thereby achieving agricultural heavy metal pollution control based on the passivator.

[0012] Optionally, the initial passivating agent is selected to include:

[0013] Through the core collection database, agricultural heavy metal pollution passivation and remediation materials are collected, wherein the agricultural heavy metal pollution passivation and remediation materials include calcium silicon materials, clay minerals, phosphorus-containing materials, biochar materials, metal oxides, organic materials, agricultural waste and new materials;

[0014] The physical and chemical properties of the soil in the target area are obtained, and the agricultural heavy metal pollution passivation and remediation materials are preliminarily screened through expert opinions to select the initial passivating agent.

[0015] Optionally, collecting the target soil and using the initial passivator to prepare potting soil comprises:

[0016] The test base soil and the blended soil are collected and blended to obtain a mixed soil, wherein the average concentration of heavy metal cadmium pollution in the test base soil is 4.5 mg / kg, and the average concentration of heavy metal cadmium pollution in the blended soil is 0.2 mg / kg;

[0017] Testing the mixed soil after mixing until obtaining low-concentration mixed soil and medium-concentration mixed soil, and calculating the mixing ratio;

[0018] Mixing the test base soil according to the mixing ratio to obtain test soil;

[0019] According to the characteristics of the initial passivating agent, obtaining a plurality of initial passivating agents of different dosages;

[0020] Several initial passivators of different dosages are added to the test soil respectively, stirred evenly and placed in a planting pot, and deionized water is added to balance for one week for aging, thereby obtaining the potting soil.

[0021] Optionally, before collecting the test base soil and the blended soil and blending them, the process also includes: airing, hammering, grinding, sieving, and stirring the base soil and the blended soil to produce uniform and fine granular soil.

[0022] Optionally, several different doses of passivators include: 0.5% calcium magnesium phosphate, 1.5% calcium magnesium phosphate, 3% calcium magnesium phosphate, 0.05% thiol-modified clay, 0.1% thiol-modified clay, 0.2% thiol-modified clay, 0.05% cadmium passivator No. 1, 0.1% cadmium passivator No. 1 and 0.2% cadmium passivator No. 1.

[0023] Optionally, obtain a soil sample set and a plant sample set, including:

[0024] The potted soil before the target plant is planted and the potted soil after the target plant is mature are collected by the quartering method, and air-dried, ground and sun-dried to obtain the soil sample group, wherein the soil sample group includes soil samples and soil blank samples;

[0025] Perform routine maintenance on the target planting plants, obtain mature target planting plants, wash, bake and divide them, and then obtain the plant sample group, wherein the plant sample group includes plant samples and plant blank samples.

[0026] Optionally, testing the soil sample group to obtain the effective cadmium content of the soil sample group, and then obtaining the soil effective cadmium passivation efficiency, includes:

[0027] Weighing the target mass of the soil sample and the soil blank sample respectively, adding diethylenetriaminepentaacetic acid solution into centrifuge tubes respectively for shaking, and then filtering through dry filter paper to obtain the extract of the soil sample and the extract of the soil blank sample;

[0028] Using an inductively coupled plasma mass spectrometer to measure the extract of the soil sample and the extract of the soil blank sample respectively, to obtain the effective cadmium concentration of the soil sample and the effective cadmium concentration of the soil blank sample;

[0029] Based on the target mass, calculating the effective cadmium content of the soil sample and the effective cadmium content of the soil blank sample according to the effective cadmium concentration of the soil sample and the effective cadmium concentration of the soil blank sample, respectively;

[0030] The effective cadmium content of the soil sample is compared with the effective cadmium content of the soil blank sample to obtain the passivation efficiency of the effective cadmium in the soil.

[0031] Optionally, the plant sample group is tested to obtain the cadmium content in the roots, stems and leaves of the plant sample group, and then the plant cadmium passivation efficiency is obtained, including:

[0032] Grinding the plant sample and the plant blank sample respectively to obtain a ground plant sample and a ground plant blank sample;

[0033] The ground plant sample and the ground plant blank sample are digested and boiled by digestion solution, and the cadmium content is measured by an absorption meter to determine the cadmium content of the roots and stems and leaves in the plant sample and the cadmium content of the roots and stems and leaves in the plant blank sample;

[0034] The cadmium contents in the roots and stems and leaves of the plant sample are compared with the cadmium contents in the roots and stems and leaves of the plant blank sample, respectively, to obtain the cadmium passivation efficiency in the roots and the cadmium passivation efficiency in the stems and leaves.

[0035] Optionally, the soil sample group and the plant sample group are tested respectively to obtain the effective cadmium content of the soil sample group and the cadmium content of the roots, stems and leaves of the plant sample group, and then to obtain the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency, which further includes:

[0036] The target number of soil samples and plant samples are respectively extracted for parallel double sample analysis, the parallel double sample measurement values ​​are obtained, and the relative deviation is calculated, wherein the relative deviation is:

[0037]

[0038] In the formula, A and B are the values ​​of parallel double samples, and RD is the relative deviation;

[0039] Determine the relative deviation. If the relative deviation is within the target range, the precision control of the parallel double samples is qualified, and then calculate the qualified rate of the parallel double sample analysis test and make a judgment;

[0040] If the parallel double sample analysis test pass rate is greater than the target threshold, proceed to S5, otherwise take corrective and preventive measures, and increase the parallel double sample analysis ratio to re-analyze and test the unqualified results until the parallel double sample analysis test pass rate is reached;

[0041] If the relative deviation is not within the target range, the precision control of the parallel duplicate samples is unqualified, and the process returns to S1 until the relative deviation is within the target range.

[0042] Optionally, the analysis result is that the passivation and control effect of the thiol-modified clay is greater than the passivation and control effect of the cadmium passivation agent No. 1, which is greater than the passivation and control effect of the calcium magnesium phosphate fertilizer, and within a certain dosage range, the higher the dosage of the same passivator, the better the passivation and control effect on the effective cadmium in the soil.

[0043] The present invention has the following beneficial effects:

[0044] The agricultural heavy metal pollution prevention and control technology adopted by the present invention is fast and efficient, the passivating agent has a wide range of materials and can realize the comprehensive utilization of wastes. In practical applications, it can improve the soil structure, avoid soil compaction caused by added materials, increase soil fertility, have less negative impact on the soil, improve the agricultural product safety index, and improve the overall environment of farmland. The present invention controls agricultural heavy metal pollution in soils with high, medium and low concentrations of cadmium pollution through three passivating agents, namely, mercapto-modified clay, cadmium passivating agent No. 1 and calcium magnesium phosphate fertilizer, and it is concluded that mercapto-modified clay has the best passivation effect on effective cadmium in the soil, and within a certain dosage range, the higher the dosage, the better the passivation effect. The farmland heavy metal pollution passivation prevention and control technology not only ensures the normal rotation of farmland, but also ensures the food safety of crops produced in heavy metal polluted farmland on the basis of realizing the source control of pollutants, and is a green, environmentally friendly and sustainable development technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A flow chart of a method for controlling agricultural heavy metal pollution based on a passivator provided in an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of a flower pot with different dosages of passivating agent added to slightly contaminated soil according to an embodiment of the present invention;

[0048] Figure 3 A schematic diagram of a flower pot with different doses of passivating agent added to moderately contaminated soil according to an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of a flower pot with different doses of passivator added to the heavily contaminated soil proposed in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0051] The terms used in the implementation section of this application are only used to explain the specific embodiments of this application and are not intended to limit this application.

[0052] Heavy metal passivation technology is an improvement measure based on the chemical behavior of heavy metals in soil. By adding heavy metal passivators to contaminated soil, the solubility, migration ability and bioavailability of heavy metals in the soil are reduced, thereby converting heavy metals into chemical forms with low toxicity or low mobility to reduce their harm to the ecosystem. Its main purpose is to reduce the migration ability and bioavailability of soil heavy metal pollutants activated by slight changes in the soil environment or soil biological activities. The addition of passivators cannot remove heavy metal pollution from the soil, but it can affect its morphological distribution. By converting extractable heavy metals into residual states, the harm of soil heavy metal pollution to the environment and human health is reduced.

[0053] Passivators are widely used in agricultural heavy metal pollution control. They have the advantages of low cost and simple and convenient operation. They are divided into two categories: inorganic passivators and organic passivators. Commonly used inorganic passivators mainly include phosphorus-containing materials, calcium silicon materials, clay minerals and metal oxides, which have large specific surface areas, strong adsorption, and can repair most heavy metal pollution. In addition, passivators can increase soil pH. Passivation control technology has the advantages of low cost, wide application, no secondary pollution, and suitability for large-scale and modeled operations. Long-term operation helps to improve soil structure and enhance soil fertility. It is a green, environmentally friendly and sustainable development technology with good application prospects.

[0054] like Figure 1 As shown, this embodiment takes agricultural heavy metal cadmium pollution in Tianjin and North China as an example to provide a method for controlling agricultural heavy metal pollution based on a passivating agent, comprising the following steps:

[0055] Step 1: Select an initial passivating agent;

[0056] In the early stage, data collection was carried out and the commonly used agricultural heavy metal cadmium pollution passivation remediation materials were obtained through the core collection database (Wef Of Science, WOS). They are divided into calcium silicon materials, clay minerals, phosphorus-containing materials, biochar materials, metal oxides, organic materials, industrial waste and new materials. The types of various passivation materials and their advantages and disadvantages are shown in Table 1.

[0057] Table 1

[0058]

[0059] Calcium silicon material: The passivation principle is physical adsorption; calcium can undergo isomorphous substitution with cadmium, which can increase the negative charge on the surface of soil particles, promote the adsorption of heavy metal ions, promote the formation of metal carbonates, reduce the proportion of active heavy metals, and reduce the mobility of heavy metals. Calcium silicon materials are widely available, relatively expensive, and not conducive to large-scale promotion. Test results show that the passivation effect is average.

[0060] Clay minerals: The passivation principle is physical adsorption; they have a large specific surface area and good adsorption performance. They can passivate heavy metal cadmium through adsorption, ion exchange, coordination reaction and coprecipitation, preventing it from migrating into the plant body. Clay minerals as passivators have the advantages of wide availability, low cost and good passivation effect, but the use of clay minerals can easily cause soil compaction and increase the pH value of the soil, which is not conducive to the growth of crops.

[0061] Phosphorus-containing materials: The passivation principle is the formation of insoluble salt precipitation by chemical reaction; according to investigations, it was found that the treatment of soil contaminated by heavy metal cadmium with phosphorus-containing fertilizers has a good remediation effect, and soluble phosphates (such as ammonium phosphate, potassium hydrogen phosphate) can directly participate in the passivation of heavy metals. The amount of Cd dissolved in the soil treated with phosphorus-containing fertilizers is significantly reduced, and the increase in phosphorus content will correspondingly increase the stabilization effect of Cd. As a passivating agent, phosphorus-containing materials have the characteristics of good passivation effect, wide range of materials, low cost, conducive to large-scale promotion, and help to improve soil fertility and soil structure.

[0062] Biochar materials: The passivation principle is physical adsorption and chemical reaction to form insoluble salt precipitation; the adsorption mechanism of biochar on heavy metals mainly includes electrostatic effect, ion exchange, cationic π bond, precipitation reaction, etc., which can effectively passivate heavy metal cadmium in the short term and prevent it from migrating into the plant body. Biochar as a passivation material has the advantages of wide availability, low cost, and waste recycling, but the use of biochar can increase the soil pH value, low cost, general passivation effect, and low durability.

[0063] Metal oxides: The passivation principle is to form insoluble salt precipitation through chemical reaction; the use of metal oxides can significantly reduce the content of exchangeable and carbonate-bound Cd in the soil, and significantly increase the content of residual Cd, and has a significant effect on the fixation of effective Cd. Metal oxides as passivators have good passivation effects and can achieve repeated recycling of waste, but their cost is relatively high, which is not conducive to large-scale promotion, and widespread use is not conducive to improving soil structure. According to investigations and research, there are currently few actual applications.

[0064] Organic materials: The passivation principle is organic complexation; organic matter reduces the bioavailability of soil heavy metal cadmium by increasing soil PH and increasing soil cation exchange capacity to form insoluble metal-organic complexes, thereby preventing the migration of effective cadmium into plants. As a passivator, organic materials have the advantages of wide availability, low cost, ability to improve soil fertility, and ability to improve soil, but their passivation effect is average and sustainability is not strong.

[0065] Industrial waste: The passivation principle is physical adsorption; some industrial wastes have a porous honeycomb structure, a large specific surface area, alkalinity, and a high ability to adsorb heavy metals. Some industrial wastes can promote the adsorption of heavy metals on the surface by increasing the alkalinity; or the exchange of heavy metal ions with their internal cations, by exchanging cations near the pores to change the size of the pores, increase its adsorption capacity, and prevent the migration of effective cadmium into the plant body. Industrial waste as a passivation material has the advantages of good passivation effect, waste recycling, low cost, and large-scale promotion, but general sustainability, and widespread use is not conducive to improving soil structure.

[0066] New materials: The passivation principle is organic complexation and chemical reaction to form insoluble salt precipitation; the passivation material manufactured by modern technology has the advantages of simple and rapid preparation, high passivation efficiency, scalable promotion, and strong stability. At the same time, it also breaks through the shortcomings of conventional materials such as small loading capacity of heavy metal cadmium and large usage.

[0067] According to the physical and chemical properties of the soil in Tianjin and North China, the selected passivation agent should be widely used; not cause secondary pollution; suitable for large-scale and model operations; relatively small usage; good passivation control effect and relatively low cost; long-term operation helps to improve soil structure; avoid soil compaction. Through data collection and consultation with relevant experts from the Environmental Protection Research and Monitoring Institute of the Ministry of Agriculture and Rural Affairs, the first screening of agricultural heavy metal cadmium pollution passivation remediation materials was carried out, and three passivation agents were determined: calcium magnesium phosphate fertilizer, thiol-modified clay, and cadmium passivation agent No. 1.

[0068] Calcium magnesium phosphate fertilizer: The passivation principle is physical adsorption and organic complexation; the phosphorus in the passivator is a nutrient element necessary for plant growth. Studies have shown that phosphate fertilizer has a certain effect on the activity of heavy metals in the soil and the absorption and accumulation of heavy metals by plants. The use of calcium magnesium phosphate fertilizer has little effect on soil pH. Calcium magnesium phosphate fertilizer mainly inhibits the activity of cadmium in the soil through adsorption, complexation and other mechanisms, prevents cadmium in the soil from migrating into the plant body, and will not cause damage to the soil acid-base environment. It is suitable for long-term application to a certain extent. After consulting the information, the passivator has a good passivation and remediation effect on soils with mild and moderate heavy metal cadmium pollution, and is suitable for acidic and weakly alkaline soils.

[0069] Thiol-modified clay: The passivation principle is organic complexation and chemical reaction to form insoluble salt precipitation; according to the theory of hard and soft acid-base, the passivator introduces thiol functional groups on the surface of inorganic materials through chemical modification, which can improve the selectivity and complexing ability of the material for heavy metal ions. When thiolated clay is used in alkaline rice fields in the north, it can significantly reduce the effective cadmium content in crops at a lower application dose and without increasing the soil pH. This passivation material has the advantages of simple and rapid preparation, high passivation efficiency, and strong stability. It breaks through the shortcomings of conventional materials with small heavy metal cadmium loading and large usage. After consulting the information, the passivator has a good passivation and remediation effect on soils with moderate and partially severe heavy metal cadmium pollution, and is suitable for acidic and weakly alkaline soils.

[0070] Cadmium passivation agent No. 1: The passivation principle is physical adsorption and organic complexation; the passivation agent is to add a binder to the calcite ore powder to achieve a suitable bonding strength, and by adding humic acid, on the basis of ensuring the passivation effect of the season, a good subsequent passivation effect is maintained. It contains calcite ore powder, humic acid and a binder, the mass fraction of the humic acid is 1-5%, and the mass fraction of the binder is 3-6%. This passivation agent is applied to the soil, and it improves the passivation effect of the season while maintaining a good subsequent passivation effect. It is a long-term soil cadmium passivation agent. After consulting the information, the passivation agent has a good passivation and remediation effect on soils with mild and partially moderate heavy metal cadmium pollution, and is suitable for acidic soils.

[0071] Step 2: Select target plants for planting;

[0072] According to the characteristics of this embodiment, crops with strong adsorption capacity for heavy metal cadmium, short growth cycle, easy survival, suitable for potted plants, wide food materials, and strong adaptability to climate and environment should be selected for planting. Through preliminary data collection and consultation with relevant experts from the Environmental Protection Research and Monitoring Institute of the Ministry of Agriculture and Rural Affairs, the characteristics of heavy metal cadmium absorption by different vegetable varieties were determined. The characteristics of heavy metal cadmium absorption by specific vegetable varieties are shown in Table 2. The order of the overall ability of vegetables to enrich cadmium is: leafy vegetables>root vegetables>stem vegetables>beans>solan fruits>melons.

[0073] Table 2

[0074]

[0075] In this embodiment, leafy vegetables should be selected as the target planting plants. According to Table 2, among the leafy vegetables, celery has the best adsorption capacity for cadmium, followed by lettuce. However, compared with celery, lettuce has the characteristics of short growth cycle, strong adaptability to the environment, suitability for potted plants, and high survival rate. Therefore, Shanghai green rapeseed is determined to be the target planting plant.

[0076] Step 3: Collect the target soil, and prepare potting soil using the selected calcium magnesium phosphate fertilizer, thiol-modified clay and cadmium passivation agent No. 1, wherein the target soil includes the experimental base soil and the mixing soil, as follows:

[0077] S310, obtaining test base soil and mixing soil;

[0078] High-concentration soil contaminated with heavy metal cadmium was collected from the Wei River beach in Niangniangmiao Houjie Village, Sunxingcun Town, Weihui City, Henan Province, which is a weakly alkaline wheat field cadmium pollution test base in Jiyuan City, Henan Province, under the Ministry of Agriculture and Rural Affairs' environmental protection scientific research monitoring, as the basic soil for the experiment. The average concentration of heavy metal cadmium pollution in the basic soil was 4.5 mg / kg. Unpolluted clean soil was collected from the wheat fields in Zhangniutun Village, Yuhua Street, Baodi District, as the blending soil. The average concentration of heavy metal cadmium pollution in the clean and unpolluted blending soil was 0.2 mg / kg.

[0079] S320, treat the test foundation soil and the soil for mixing;

[0080] The test base soil and blended soil are dried, hammered, ground, sieved and stirred to make uniform and fine granular soil, and then mixed samples are made. In the process of making granular soil, an environmental protection measures plan needs to be formulated to minimize the impact on the environment.

[0081] S330, prepare test soils with different pollution levels;

[0082] According to the Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (GB15618-2018), the screening value of heavy metal cadmium is determined to be 0.6 mg / kg, as shown in Table 3; according to the soil environmental geochemical grade classification in the Land Quality Geochemical Evaluation Specification, the heavy metal cadmium content in the soil is determined to be 0.6-1.8 mg / kg for light pollution; 1.8-3.0 mg / kg for moderate pollution; and greater than 3.0 mg / kg for severe pollution, as shown in Table 4, where p is the concentration of heavy metal cadmium in the soil.

[0083] Table 3

[0084]

[0085] Table 4

[0086]

[0087] The method for preparing test soils with different degrees of pollution is as follows: first, a certain amount of uncontaminated clean soil is mixed into the test base soil; then, the evenly mixed soil is sent for inspection to detect the concentration of the soil after mixing, and the medium concentration (cadmium content is 2.77 mg / kg) and low concentration (cadmium content is 1.63 mg / kg) of contaminated soil are tested, and the mixing ratio is calculated; finally, the high concentration cadmium contaminated soil is mixed according to a certain mixing ratio to make sufficient high concentration, medium concentration and low concentration contaminated soil.

[0088] S340, preparing potting soil;

[0089] According to the three kinds of soils polluted by heavy metal cadmium with high concentration, medium concentration and low concentration, three kinds of passivators, namely calcium magnesium phosphate fertilizer, thiol modified clay and cadmium passivator No. 1, which have been selected, are added. According to the characteristics of the three kinds of passivators, high dose, medium dose and low dose of passivators are added to the soils of three different concentrations and stirred evenly and placed in the planting pots. The dosage ratio of the three passivators is shown in Table 5. The specific concentrations are determined after consulting relevant papers and consulting relevant experts from the Environmental Protection Research and Monitoring Institute of the Ministry of Agriculture and Rural Affairs. The specific process of making potted soil is: weighing the passivator, weighing the potted soil, mixing the passivator, basin cushioning, potting and soil aging. Among them, the model of the planting pot is about 22 cm in upper diameter, 13.5 cm in bottom diameter and 17 cm in height. The soil is filled to about four-fifths of the volume of the planting pot, and about 5 kg of soil is filled in each pot. Deionized water is added to balance for 1 week for aging.

[0090] Table 5

[0091]

[0092] Two replicates were set for each planting test pot for the calculation of the accuracy and discreteness of the test. Two control planting pots without any passivation agent were set for each concentration of heavy metal cadmium contaminated soil. One of them was planted with Shanghai rape for the passivation effect comparison test, and the other was not planted with any plants for the comparison of the changes of heavy metal cadmium and effective cadmium in the natural state. The specific distribution of the potted test is as follows: Figure 2-4 As shown, Figure 2 The potted plant experiment distribution is for slightly contaminated soil (cadmium content 0.6-1.8mg / kg). Figure 3 The potted plant test distribution is for moderately contaminated soil (cadmium content 1.8-3.0 mg / kg). Figure 4 The pot test distribution of heavily polluted soil (cadmium content greater than 3.0 mg / kg) was carried out. One test pot soil of each pollution degree, each type of passivator, and each dose of passivator was prepared, totaling 27 samples; two replicates were set for each sample, totaling 81 samples, and 18 blank control test pots of three pollution degrees were prepared; a total of 99 potted soils were prepared.

[0093] Step 4: Plant plants according to the planting target of potted soil and collect them to obtain soil sample group and plant sample group. Specifically:

[0094] Plant 10-15 high-quality Shanghai rapeseed seeds in the prepared potting soil, carry out daily watering, weeding, pesticide control, thinning, fertilization and other daily maintenance to ensure the survival rate of the seeds, and then collect soil sample groups and plant sample groups;

[0095] Aphids and cabbage worms are the most common pests, and are also one of the most destructive pests with strong reproductive capacity. Therefore, during the growth of Shanghai rapeseed, attention should be paid to the prevention and control of aphids and cabbage worms. Metarhizium anisopliae is the latest generation of environmentally friendly, broad-spectrum, and highly effective fungal live insecticides. Due to its wide host range, strong pathogenicity, harmlessness to humans, livestock, and crops, easy large-scale production, and ability to produce sustained control effects, it does not pollute the environment, soil, and agricultural products, and has no toxic side effects on humans, livestock, and aquatic organisms. It is a green and environmentally friendly insecticide. Therefore, Metarhizium anisopliae is used for pest control.

[0096] In addition, Shanghai green rapeseed has a large demand for nutrients in the soil during its growth process, so maintaining soil fertility is a necessary condition for the growth of Shanghai green rapeseed. If there is a lack of nutrients, the leaves of Shanghai green rapeseed will turn yellow and fall off. Therefore, foliar fertilizer is sprayed to supplement the nutrients needed for the growth of Shanghai green rapeseed.

[0097] The soil sample group and plant sample group are collected as follows:

[0098] (1) Collection of soil samples

[0099] Collection method: Soil samples were collected by using the quartering method for each pot of soil. Specifically, the collected soil was air-dried at room temperature of 20-30°C to a moisture content of less than 2%, ground in a mortar and passed through a 200-mesh sieve to obtain soil samples;

[0100] Collection time and frequency: before planting Shanghai green rapeseed and after Shanghai green rapeseed matures and is dug up, a total of two times;

[0101] Number of soil samples: 3 mixed samples were collected after processing into soil contaminated with high concentration of heavy metal cadmium (concentration greater than 3.0 mg / kg); 2 mixed samples of clean and uncontaminated soil after processing were collected; 6 mixed test samples were collected, and three mixed soil samples of each degree of pollution were collected before planting Shanghai rapeseed, totaling 9 samples; mixed samples of soil from test pots of each degree of pollution, each type of passivator, and each dose of passivator were collected after Shanghai rapeseed matured; two replicate samples were set up at the same time, plus soil samples from blank control test pots of three degrees of pollution (18 samples); a total of 99 soil samples were collected, collected twice, and a total of 119 soil samples were collected.

[0102] (2) Collection of plant sample groups

[0103] Collection method: Use a wooden shovel to dig out the entire rapeseed root, try to avoid breaking the roots, dig out the entire Shanghai green rapeseed, clean off dirt such as dirt and dust, and then bake it in an oven at a low temperature for a short time, the purpose is to dry out the moisture on the surface of the entire Shanghai green rapeseed to avoid affecting the test results. The baked Shanghai green rapeseed is divided at the root, and the root sample and the aboveground stem and leaf sample are sent for inspection;

[0104] Collection time and frequency: Collect once after Shanghai rapeseed matures;

[0105] Number of plant samples: Each pot of Shanghai green rapeseed was treated as one sample, totaling 90 samples. Three Shanghai green rapeseeds in each pot were cut at the root, and the roots and above-ground stems and leaves were tested separately, for a total of 180 plant samples.

[0106] Step 5: testing the soil sample group and the plant sample group respectively to obtain the effective cadmium content of the soil sample group and the cadmium content of the roots and stems and leaves of the plant sample group, and then obtaining the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency, wherein the plant cadmium passivation efficiency includes the cadmium passivation efficiency in the plant roots and the cadmium passivation efficiency in the plant stems and leaves;

[0107] S510, performing an effective cadmium detection method on a soil sample group including a soil sample and a soil blank sample, comprising the following steps:

[0108] S511. Weigh 10 g of soil sample and soil blank sample respectively, place them in a 100 mL first centrifuge tube and a second centrifuge tube, add 50 mL of diethylenetriaminepentaacetic acid (DTPA) solution, oscillate on a constant temperature oscillator at a frequency of 180 times / min for 2 hours, and filter with dry filter paper to obtain the extract of the soil sample and the soil blank sample. DTPA can effectively simulate the effective cadmium that can be dissolved by plant roots, and under certain time and temperature conditions, it can ensure that the dissolution of effective cadmium reaches a balanced state;

[0109] S512, using an inductively coupled plasma mass spectrometer to establish a standard curve for determining different concentrations of biologically available cadmium by inductively coupled plasma mass spectrometry, and then measuring the concentration of biologically available cadmium in the extract of the soil sample and the soil blank sample respectively;

[0110] S513, respectively calculating the effective cadmium content in the soil sample and the soil blank sample according to the measured sample mass and the effective cadmium concentration in the extract by the formula W=cV / 1000m;

[0111] S514. Compare the effective cadmium content in the soil sample with that in the soil blank sample, and calculate the passivation efficiency of the effective cadmium in the soil.

[0112] S520, performing a cadmium detection method on a plant sample group including a plant sample and a plant blank sample, comprising the following steps:

[0113] S521. Grind the plant samples and plant blank samples separately, digest the ground samples with a digestion solution of V(HNO3):V(HCLO4)=87:13, digest them in a digestion furnace according to a certain temperature increase program, and use a flame or graphite furnace atomic absorption spectrometer to determine the cadmium content in the roots and aboveground stems and leaves of the plant samples, as well as the cadmium content in the roots and aboveground stems and leaves of the plant root blank samples;

[0114] S522. Compare the cadmium content in the roots and aboveground stems and leaves in the plant samples with the cadmium content in the roots and aboveground stems and leaves in the plant blank samples, respectively, to obtain the cadmium passivation efficiency in the roots and the cadmium passivation efficiency in the stems and leaves.

[0115] In addition, when analyzing each batch of samples, each test item must be analyzed in parallel with two samples. In each batch of analyzed samples, 5% of the samples should be randomly selected for parallel double sample analysis to obtain the parallel double sample measurement values ​​and calculate the relative deviation; when the number of batch samples is less than 20, at least one sample should be randomly selected for parallel double sample analysis. Among them, the parallel double sample analysis should generally be coded by the quality management personnel of the laboratory into the analysis sample and handed over to the test personnel for analysis and testing.

[0116] If the relative deviation (RD) of the parallel double sample measurement value (A, B) is within the allowable range, the precision control of the parallel double sample is qualified, and the qualified rate of the parallel double sample analysis test is judged. Otherwise, it is unqualified and returns to the step until RD is within the allowable range. The RD calculation formula is as follows:

[0117]

[0118] The pass rate of parallel double sample analysis test is calculated based on the single test item in each batch of samples of the same type. The calculation formula is as follows:

[0119]

[0120] The qualified rate of parallel double sample analysis test should reach 95%. When the qualified rate is less than 95%, the cause of the unqualified result should be found out and appropriate corrective and preventive measures should be taken. In addition to re-analyzing and testing the unqualified results, the proportion of parallel double sample analysis should be increased by 5% to 15% until the total qualified rate reaches 95% for the next step.

[0121] After the test, a certain amount of solidifier needs to be added to the soil contaminated with heavy metal cadmium to stabilize the heavy metals and prevent them from migrating to the outside, and then transport them to a landfill for disposal; or use them as construction backfill soil. The screening value for cadmium content in soil for construction land is 20 mg / kg. The maximum concentration of the soil used this time is far less than the screening value for construction land and will not affect human health.

[0122] Step 6: Analyze the effective cadmium content of the soil sample group, the cadmium content of the roots, stems and leaves of the plant sample group, the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency to obtain the analysis results;

[0123] S610, analysis of soil test results;

[0124] The average contents of cadmium and effective cadmium in the soils contaminated with different concentrations of cadmium produced in the early stage, the blank soils without Shanghai green rapeseed planted, and the blank soils with Shanghai green rapeseed planted were tested and analyzed, as shown in Table 6. According to the test results, it can be analyzed that part of the cadmium in the heavy metal cadmium in the natural state is converted into effective cadmium, and Shanghai green rapeseed mainly absorbs effective cadmium during its growth.

[0125] Table 6

[0126]

[0127] The content of effective cadmium in high-concentration, medium-concentration and low-concentration heavy metal cadmium contaminated soils with different types and dosages of passivators added was detected and analyzed, and the effective cadmium passivation efficiency was calculated by comparing with the soil blank, as shown in Table 7-9.

[0128] Table 7

[0129]

[0130] Table 8

[0131]

[0132] Table 9

[0133]

[0134] In summary, according to the analysis of the test results of the effective cadmium content in the soil, it can be seen that: in the natural state, part of the cadmium in the heavy metal cadmium is converted into effective cadmium, and Shanghai rape mainly absorbs effective cadmium during its growth. The passivation control efficiency of the three passivators for effective cadmium in soils with different degrees of cadmium pollution is ranked as follows: mercapto-modified clay> cadmium passivator No. 1> calcium magnesium phosphate; within a certain dosage range, the higher the dosage of the same passivator, the better the passivation effect.

[0135] S620, analysis of plant test results;

[0136] The test results of cadmium content in roots and stems of Shanghai rapeseed grown in high, medium and low concentration contaminated soils were shown in Tables 10-12 when three passivators, namely, mercapto-modified clay, cadmium passivator No. 1 and calcium magnesium phosphate, were mixed at low, medium and high doses respectively. The passivation efficiency compared with the blank Shanghai rapeseed is shown in Tables 13-15.

[0137] Table 10

[0138]

[0139] Table 11

[0140]

[0141] Table 12

[0142]

[0143] Table 13

[0144]

[0145] Table 14

[0146]

[0147] Table 15

[0148]

[0149] In summary, according to the results of cadmium detection in the roots, stems and leaves of Shanghai green rapeseed, it is concluded that: for soils contaminated with high concentrations of heavy metal cadmium, only medium and high doses of thiol-modified clay can make the cadmium content in the stems and leaves of Shanghai green rapeseed reach the cadmium limit standard requirements in the "National Food Safety Standard for Limits of Contaminants in Food" (GB2762-2017); for soils contaminated with medium and low concentrations of heavy metal cadmium, various types and doses of passivators can make the cadmium content in the stems and leaves of Shanghai green rapeseed reach the cadmium limit standard requirements in the "National Food Safety Standard for Limits of Contaminants in Food" (GB2762-2017). For soils contaminated with high, medium and low concentrations of heavy metal cadmium, high doses of thiol-modified clay have the best passivation control effect; high doses of thiol-modified clay have the best control effect on the migration of heavy metal cadmium from soil to the roots of Shanghai green rapeseed and then to the stems and leaves.

[0150] Step 7: Select the target passivator based on the analysis results and spray it on the heavy metal contaminated soil in the target area to achieve agricultural heavy metal pollution control based on the passivator. Specifically:

[0151] According to the analysis results of step six, thiol-modified clay is selected as a passivator and sprayed on heavy metal contaminated soil in Tianjin and North China, thereby achieving agricultural heavy metal pollution control based on passivators.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for controlling agricultural heavy metal pollution based on a passivator, characterized in that: The specific steps include: S1. Selecting an initial passivation agent and a target plant, wherein the initial passivation agent includes calcium magnesium phosphate fertilizer, thiol-modified clay and cadmium passivation agent No. 1; S2. Collecting target soil and using the initial passivator to prepare potted soil, wherein the target soil includes experimental basic soil and mixed soil, the experimental basic soil is a soil with high concentration of heavy metal cadmium contamination, and the heavy metal cadmium content is greater than 3.0 mg / kg, which is the soil with high concentration of heavy metal cadmium contamination; Collecting target soil and using the initial passivator to prepare potting soil, including: The test base soil and the blended soil are collected and blended to obtain a mixed soil, wherein the average concentration of heavy metal cadmium pollution in the test base soil is 4.5 mg / kg, and the average concentration of heavy metal cadmium pollution in the blended soil is 0.2 mg / kg; Testing the mixed soil after mixing until obtaining low-concentration mixed soil and medium-concentration mixed soil, and calculating the mixing ratio, wherein the low-concentration mixed soil has a heavy metal cadmium content of 0.6-1.8 mg / kg, and the medium-concentration mixed soil has a heavy metal cadmium content of 1.8-3.0 mg / kg; Mixing the test base soil according to the mixing ratio to obtain test soil; According to the characteristics of the initial passivating agent, obtaining a plurality of initial passivating agents of different dosages; Adding several initial passivators of different dosages to the test soil respectively, stirring evenly and placing in a planting pot, and adding deionized water to balance for one week for aging, thereby obtaining the potting soil; S3, planting the target plant according to the potting soil and collecting the plant to obtain a soil sample group and a plant sample group; Obtain soil sample sets and plant sample sets, including: The potted soil before the target plant is planted and the potted soil after the target plant is mature are collected by the quartering method, and air-dried, ground and sun-dried to obtain the soil sample group, wherein the soil sample group includes soil samples and soil blank samples; Performing routine maintenance on the target plant to obtain mature target plants, washing, baking and dividing them, and then obtaining the plant sample group, wherein the plant sample group includes plant samples and plant blank samples; S4, respectively testing the soil sample group and the plant sample group, obtaining the effective cadmium content of the soil sample group and the cadmium content of the roots and stems and leaves of the plant sample group, and then obtaining the soil effective cadmium passivation efficiency and the plant cadmium passivation efficiency, wherein the plant cadmium passivation efficiency includes the cadmium passivation efficiency in the roots and the cadmium passivation efficiency in the stems and leaves; The soil sample group and the plant sample group are tested respectively to obtain the effective cadmium content of the soil sample group and the cadmium content of the roots, stems and leaves of the plant sample group, and then the effective cadmium passivation efficiency of the soil and the cadmium passivation efficiency of the plant are obtained, which further includes: The target number of soil samples and plant samples are respectively extracted for parallel double sample analysis, the parallel double sample measurement values ​​are obtained, and the relative deviation is calculated, wherein the relative deviation is: In the formula, A and B are the values ​​of parallel double samples, and RD is the relative deviation; Determine the relative deviation. If the relative deviation is within the target range, the precision control of the parallel double samples is qualified, and then calculate the qualified rate of the parallel double sample analysis test and make a judgment; If the parallel double sample analysis test pass rate is greater than the target threshold, proceed to S5, otherwise take corrective and preventive measures, and increase the parallel double sample analysis ratio to re-analyze and test the unqualified results until the parallel double sample analysis test pass rate is reached; If the relative deviation is not within the target range, the precision control of the parallel double samples is unqualified, and the process returns to S1 until the relative deviation is within the target range; S5. Analyze the effective cadmium content of the soil sample group, the cadmium content of the roots and stems and leaves of the plant sample group, the soil effective cadmium passivation efficiency, and the plant cadmium passivation efficiency to obtain analysis results; S6. Select a target passivator according to the analysis results, and spray it on the heavy metal contaminated soil in the target area, thereby achieving agricultural heavy metal pollution control based on the passivator.

2. The agricultural heavy metal pollution control method based on a passivator according to claim 1, characterized in that: The initial passivating agent is selected, including: Through the core collection database, agricultural heavy metal pollution passivation and remediation materials are collected, wherein the agricultural heavy metal pollution passivation and remediation materials include calcium silicon materials, clay minerals, phosphorus-containing materials, biochar materials, metal oxides, organic materials, and agricultural waste; The physical and chemical properties of the soil in the target area are obtained, and the agricultural heavy metal pollution passivation and remediation materials are preliminarily screened through expert opinions to select the initial passivating agent.

3. The agricultural heavy metal pollution control method based on a passivator according to claim 1, characterized in that: The test base soil and the blended soil are collected and before blending, the process also includes: airing, hammering, grinding, sieving and stirring the base soil and the blended soil to make them into uniform and fine granular soil.

4. The agricultural heavy metal pollution control method based on a passivator according to claim 3, characterized in that: Several different dosages of passivators include: 0.5% calcium magnesium phosphate, 1.5% calcium magnesium phosphate, 3% calcium magnesium phosphate, 0.05% thiol-modified clay, 0.1% thiol-modified clay, 0.2% thiol-modified clay, 0.05% cadmium passivator No. 1, 0.1% cadmium passivator No. 1 and 0.2% cadmium passivator No.

1.

5. The agricultural heavy metal pollution control method based on passivator according to claim 1, characterized in that: Testing the soil sample group to obtain the effective cadmium content of the soil sample group, and then obtaining the effective cadmium passivation efficiency of the soil, including: Weighing the target mass of the soil sample and the soil blank sample respectively, adding diethylenetriaminepentaacetic acid solution into centrifuge tubes respectively for shaking, and then filtering through dry filter paper to obtain the extract of the soil sample and the extract of the soil blank sample; Using an inductively coupled plasma mass spectrometer to measure the extract of the soil sample and the extract of the soil blank sample respectively, to obtain the effective cadmium concentration of the soil sample and the effective cadmium concentration of the soil blank sample; Based on the target mass, calculating the effective cadmium content of the soil sample and the effective cadmium content of the soil blank sample according to the effective cadmium concentration of the soil sample and the effective cadmium concentration of the soil blank sample, respectively; The effective cadmium content of the soil sample is compared with the effective cadmium content of the soil blank sample to obtain the passivation efficiency of the effective cadmium in the soil.

6. The agricultural heavy metal pollution control method based on passivator according to claim 5 is characterized in that: Testing the plant sample group to obtain the cadmium content in the roots, stems and leaves of the plant sample group, and then obtaining the plant cadmium passivation efficiency, including: Grinding the plant sample and the plant blank sample respectively to obtain a ground plant sample and a ground plant blank sample; The ground plant sample and the ground plant blank sample are digested and boiled by digestion solution, and the cadmium content is measured by an absorption meter to determine the cadmium content of the roots and stems and leaves in the plant sample and the cadmium content of the roots and stems and leaves in the plant blank sample; The cadmium contents in the roots and stems and leaves of the plant sample are compared with the cadmium contents in the roots and stems and leaves of the plant blank sample, respectively, to obtain the cadmium passivation efficiency in the roots and the cadmium passivation efficiency in the stems and leaves.

7. The agricultural heavy metal pollution control method based on a passivator according to claim 1, characterized in that: The analysis results show that the passivation and control effect of the mercapto-modified clay is greater than that of the cadmium passivation agent No. 1, which is greater than that of the calcium magnesium phosphate fertilizer, and within a certain dosage range, the higher the dosage of the same passivation agent, the better the passivation and control effect on the effective cadmium in the soil.

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