Soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables

Abstract

The invention discloses a soil passivation method for reducing the content of heavy metals in high-arsenic-enriched vegetables, which is characterized in that polyferric sulfate with a specific proportion is added into polluted soil, so that the effective-state contents of arsenic, cadmium and lead in the soil are remarkably reduced, and the absorption of purple perilla to the heavy metals is inhibited; by applying 1% of polyferric sulfate, the arsenic content of the aboveground part of purple perilla can be reduced by 67.88%, the lead content can be reduced by 47.34%, and meanwhile, the cadmium content is controlled within the food safety standard. The method has the advantages of being high in passivation efficiency, easy and convenient to operate, environmentally friendly and the like, and is suitable for safe utilization of heavy metal combined pollution farmlands.

Description

Technical Field

[0001] The present invention relates to a soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables, and belongs to the field of remediation of heavy metal contaminated soil. Background Art

[0002] With the intensification of industrial and mining activities, the problem of heavy metal pollution such as arsenic (As), cadmium (Cd), and lead (Pb) in farmland soil has become increasingly serious. Leafy vegetables have well-developed roots and strong absorption ability of heavy metals, which easily lead to excessive levels in the edible parts, threatening human health. Existing passivation technologies mostly use single materials such as ferrous sulfate and biochar, but there are problems such as low passivation efficiency, easy activation of other heavy metals (such as Cd), and high costs. For example, ferrous sulfate may inhibit plant growth at high application rates, while the fixation effect of biochar on As is limited. Therefore, there is an urgent need to develop a soil remediation technology that is efficient, safe, and can passivate multiple metals synergistically.

[0003] The present invention discovers through screening that polyferric sulfate (PFS) can significantly reduce the available contents of As, Cd, and Pb in soil, and by adjusting its chemical form (such as promoting the transformation of weakly acid extractable As to residual form), reduce the absorption of heavy metals by perilla. Compared with traditional passivators, PFS has better stability and economy, and is suitable for the safe production of moderately and mildly contaminated farmland. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables, which can significantly reduce the available contents of As, Cd, and Pb in soil and reduce the absorption of heavy metals by perilla.

[0005] The present invention is achieved by the following scheme: A soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables includes the following steps: uniformly applying polyferric sulfate to the contaminated soil at a ratio of 0.5% - 10% of the soil mass, maturing for 30 - 60 days, and then planting perilla. By the adsorption and fixation of polyferric sulfate on arsenic, cadmium, and lead in the soil, the heavy metal content in the edible part of perilla is reduced.

[0006] The optimal application amount of the polyferric sulfate is 1% - 2% of the soil mass.

[0007] During the maturing process, the soil water content is maintained at 50% - 70% of the field water holding capacity.

[0008] The heavy metal contaminated soil is alkaline or weakly alkaline soil with pH > 7.

[0009] The beneficial effects of the present invention are as follows:

[0010] 1. High passivation efficiency: When the addition amount of 10% PFS is used, the available As, Cd, and Pb in the soil are reduced by 85.43%, 19.54%, and 54.59% respectively.

[0011] 2. Meeting food safety standards: Treatment with 1% PFS reduces the As content in the above-ground part of perilla to 0.30 mg·kg -1 (the limit value in GB 2762-2017 is 0.5 mg·kg -1 ), and the Pb content is reduced to 0.26 mg·kg -1 (the limit value in GB 2762-2017 is 0.3 mg·kg -1 ).

[0012] 3. Soil improvement: After applying PFS, the soil pH decreases moderately (the pH drops by 0.23 - 0.47 units under the addition amount of 0.5% - 10%), avoiding the continuous increase of the pH in alkaline soil. Brief Description of the Drawings Detailed Implementation Modes

[0013] The present invention is further described below, but the protection scope of the present invention is not limited to the content described.

[0014] For clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not described in detail because they would clutter the present invention with unnecessary details. It should be considered that in the development of any actual embodiment, a large number of implementation details must be made to achieve the specific goals of the developer, such as changing from one embodiment to another according to the relevant system or business restrictions. Additionally, it should be considered that such development work may be complex and time-consuming, but it is only routine work for those skilled in the art.

[0015] Example 1: Screening and Optimization of Passivators

[0016] Test soil: Collected from farmland in Gejiu Mining Area, Yunnan, with total As of 439.35 mg·kg -1 , Cd of 15.2 mg·kg -1 , Pb of 670.36 mg·kg -1 .

[0017] Passivation treatment: Set the addition amounts of PFS as 0%, 0.5%, 1%, 2%, 5%, and 10%. Each treatment has 3 replicates, and after ripening for 60 days, the content of available heavy metals is measured.

[0018] Measurement method: The contents of available Pb and Cd in the soil are measured according to "Soil Quality: Determination of Available Lead and Cadmium - Atomic Absorption Spectrometry" (GB / T 23739 - 2009), and available As is measured by the AB-DTPA method

[0019] Determination results: The determination results are shown in Table 1. PFS can significantly reduce the content of available As, Cd, and Pb in the soil. Moreover, with the increase in the application amount of the passivator, the passivation effect on available As, Cd, and Pb also increases significantly. Especially under the treatment of 10% PFS, the available As, Cd, and Pb are reduced by 85.43%, 19.54%, and 54.59% respectively.

[0020] Table 1 Effects of applying PFS on available As, Cd, and Pb in the soil

[0021]

[0022] Example 2: Verification of perilla seed planting Soil treatment: The tested soil is farmland soil from Gejiu Mining Area in Yunnan (total As 439.35 mg·kg -1 , Cd 15.2 mg·kg -1 , Pb 670.36 mg·kg -1 ). Add 1% - 10% PFS, mix it with the soil and let it mature for 30 days.

[0023] Planting conditions: Greenhouse potting, each pot contains 2 kg of soil. Sow perilla in the soil after 30 days of maturation, and manage it conventionally. Harvest and measure after perilla grows for 60 days.

[0024] Determination method: After harvesting perilla, first wash it clean with tap water and deionized water. Then soak the plant in 20 mmol·L -1 EDTA·Na 2 solution for 20 minutes to remove heavy metals on the plant surface. Finally, wash it clean with tap water and deionized water again. After drying the moisture on the plant surface, store it in a refrigerator at 4°C for testing. Determine the arsenic content in perilla according to the "National Food Safety Standard Determination of Total Arsenic and Inorganic Arsenic in Foods" (GB 5009.11—2024), determine the lead content in perilla according to the "National Food Safety Standard Determination of Lead in Foods" (GB 5009.12 - 2017), and determine the cadmium content in perilla according to the "National Food Safety Standard Determination of Cadmium in Foods" (GB 5009.15 - 2014).

[0025] Determination results: The determination results are shown in Table 2. At the application amount of 1%, the As content in the above-ground part of perilla decreases from 0.55 mg·kg -1 to 0.30 mg·kg -1 , the Cd content remains 0.06 mg·kg -1 , and the Pb content decreases from 0.45 mg·kg -1 to 0.24 mg·kg -1Complies with the limit of As: 0.5 mg·kg specified in the "National Food Safety Standard: Limits of Contaminants in Foods" (GB 2762—2017). -1 Cd: 0.2 mg·kg -1 Pb: 0.3 mg·kg -1 It can achieve the safe production of highly enriched perilla vegetables.

[0026] Table 2 Effects of Applying PFS on the Contents of As, Cd, and Pb in Perilla frutescens L. Seeds

[0027]

[0028] Example 3: Verification of Perilla frutescens L. Seedling Planting

[0029] Soil treatment: The tested soil is the farmland soil in Gejiu Mining Area, Yunnan (total As 439.35 mg·kg -1 Cd 15.2 mg·kg -1 Pb 670.36 mg·kg -1 ). Add 1% - 10% PFS, mix with the soil and cure for 30 days.

[0030] Planting conditions: First, raise perilla frutescens L. seedlings in a pollution - free seedling substrate. After the perilla frutescens L. seedlings grow 4 true leaves, select perilla frutescens L. seedlings with the same growth vigor for greenhouse potting. Each pot is filled with 2 kg of soil, transplant the seedlings into the cured soil after 30 days, and conduct conventional management. Harvest and measure after the perilla frutescens L. grows for 60 days.

[0031] Determination method: After harvesting perilla frutescens L., first wash it clean with tap water and deionized water, then soak the plant in 20 mmol·L -1 EDTA·Na 2 solution for 20 min to remove heavy metals on the plant surface, and finally wash it clean with tap water and deionized water again. After drying the moisture on the plant surface, store it in a refrigerator at 4°C for testing. Determine the arsenic content in perilla frutescens L. according to the "National Food Safety Standard Determination of Total Arsenic and Inorganic Arsenic in Foods" (GB 5009.11—2024), determine the lead content in perilla frutescens L. according to the "National Food Safety Standard Determination of Lead in Foods" (GB 5009.12 - 2017), and determine the cadmium content in perilla frutescens L. according to the "National Food Safety Standard Determination of Cadmium in Foods" (GB 5009.15 - 2014).

[0032] Determination results: The determination results are shown in Table 3. At the application rate of 1%, the As content in the above - ground part of perilla frutescens L. decreased from 0.51 mg·kg -1 to 0.27 mg·kg -1 , and the Cd content was 0.12 mg·kg -1, there was no significant difference compared with the case without addition. The Pb content decreased from 0.44 mg·kg -1 to 0.28 mg·kg -1 . It meets the requirements of "National Food Safety Standard: Limits of Contaminants in Foods" (GB 2762—2017) for As: 0.5 mg·kg -1 , Cd: 0.2 mg·kg -1 , Pb: 0.3 mg·kg -1 . The safe production of highly enriched perilla vegetables can be achieved.

[0033] Table 3 Effects of applying PFS on the contents of As, Cd, and Pb in perilla plants

[0034]

[0035] From the above embodiments, the following characteristics of the method can be obtained:

[0036] Synergistic passivation: PFS can simultaneously fix As, Cd, and Pb, overcoming the difference in passivation effects of traditional materials on anionic (As) and cationic (Cd, Pb) heavy metals.

[0037] Low cost: PFS is an industrial by-product, and its unit price is lower than that of modified biochar and organic chelating agents.

[0038] Environmentally friendly: The hydrolysis product of PFS is iron oxide, without the risk of secondary pollution.

[0039] Although the technical solutions of the present invention have been described in detail and listed, it should be understood that for those skilled in the art, making modifications to the above embodiments or adopting equivalent alternative solutions are obvious to those skilled in the art. These modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A soil passivation method for reducing heavy metal content in high arsenic-enriched vegetables, characterized in that: The method comprises the following steps: applying polyferric sulfate evenly to the polluted soil at a ratio of 0.5% to 10% of the soil mass, planting perilla after ripening for 30 to 60 days, and reducing the heavy metal content of the edible part of perilla through the adsorption and fixation of arsenic, cadmium and lead in the soil by polyferric sulfate.

2. The soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables according to claim 1, characterized in that: The optimal application amount of the polyferric sulfate is 1% to 2% of the soil mass.

3. The soil passivation method for reducing heavy metal content in high arsenic-enriched vegetables according to claim 1, characterized in that: During the maturation process, the soil moisture content is maintained at 50% to 70% of the field water holding capacity.

4. The soil passivation method for reducing heavy metal content in high-arsenic-enriched vegetables according to claim 1, characterized in that: The heavy metal contaminated soil is alkaline or weakly alkaline soil with a pH value > 7.

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