Soil microplastic pollution risk grade assessment method

Abstract

The invention provides a method for evaluating the pollution risk grade of micro-plastics in soil, and belongs to the technical field of ecological safety evaluation.The method comprises the steps that a soil sample of a target area is collected in a layered mode, the micro-plastics are extracted, and characteristic parameters of the micro-plastics in the soil sample are obtained, the micro-plastic characteristic parameters at least comprise micro-plastic abundance, micro-plastic type distribution, adsorbed pollutant concentration, soil organic matter content, soil porosity and annual average rainfall, and micro-plastic shape, color and material composition, processing the characteristic parameters to generate a plurality of risk assessment values, and performing risk grading on the soil sample according to the risk assessment values, according to the evaluation method for the micro-plastic pollution risk grade in the soil, the micro-plastic soil pollution grade is subdivided, so that agricultural cultivation activities are guided more accurately.

Description

Technical Field

[0001] This invention relates to the field of ecological security assessment technology, and more specifically, to a method for assessing the risk level of microplastic pollution in soil. Background Technology

[0002] While widely used materials have brought convenience to human life, they have also brought serious environmental problems. Plastics and microplastics, in particular, enter the environment through various pathways, including rivers, sewage discharge, marine activities, and atmospheric transport, threatening ecosystems and the survival of organisms. It is estimated that at least 5.25 trillion pieces of plastic debris are already floating on the global ocean surface, and this number continues to grow. Microplastic pollution has become a focal point of global environmental concern. Microplastics typically refer to plastic particles with a diameter of less than 5 millimeters. They not only possess polluting properties themselves but can also act as carriers of other organic pollutants such as phenanthrene, hydrocarbons, and heavy metals, forming complex pollution that can have significant negative impacts on the environment and human health.

[0003] Ecological risk assessment aims to evaluate the potential negative effects of threatening factors through a scientific evaluation system, providing a scientific basis for ecosystem management and protection. However, existing risk assessment methods for microplastics struggle to accurately distinguish the gradient risk differences in moderately polluted soils. Soil microplastic pollution has its unique characteristics: on the one hand, pollutants adsorbed by microplastics (such as polycyclic aromatic hydrocarbons (PAHs)) may migrate to deeper soil layers during the rainy season, resulting in delayed toxicity effects; on the other hand, even in soils with the same microplastic abundance, differences in organic matter content can lead to variations in the bioavailability of microplastics and their complex pollutants. Furthermore, for agricultural land, there is an urgent need to further subdivide "acceptable risk" and "critical risk" levels to more accurately guide agricultural activities. Therefore, existing microplastic risk assessment methods are insufficient to meet the needs of refined risk assessment and management of soil microplastic pollution, particularly in agricultural land.

[0004] Developing a method for assessing the risk level of microplastic pollution that can effectively solve the above problems has become an urgent technical challenge. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for assessing the risk level of microplastic pollution in soil, which further subdivides the level of microplastic soil pollution to more accurately guide agricultural activities.

[0006] The technical solution adopted by this invention to solve its technical problem is: to provide a method for assessing the risk level of microplastic pollution in soil, comprising the following steps: S1. A layered three-dimensional sampling strategy is adopted, and sampling points are set up in the target area according to the grid method to collect soil samples. S2. Soil microplastics were extracted using density flotation-microscopic identification combined technology; S3. Obtain microplastic characteristic parameters; S4. Construct a multi-indicator risk assessment model to generate core valuation; S5. Introduce migration risk factor (M) and couple soil structure parameters with hydraulic properties; S6. Integrating environmental driving factors and hierarchical depth correction to construct a comprehensive risk index ( ); S7, according to The numerical values ​​divide the risk into five levels; S8. Establish a toxicity early warning mechanism.

[0007] In this embodiment, specifically: the soil samples collected in step S2 are at depths of 0–20cm (cultivated layer), 20–50cm (leaching layer) and >50cm (deep layer), and the sampling depth (Depth) of each layer is recorded after the samples are collected.

[0008] In this embodiment, the specific steps for extracting microplastics from soil in step S3 include: after pre-treating the sample through a 2mm sieve, adding a saturated sodium chloride solution with a density of 1.2g / cm³, shaking for 30min to promote the floating of microplastics, using a 0.45μm nitrocellulose membrane for vacuum filtration to capture the microplastics, and finally performing morphological identification, counting, and material identification under a Nikon SMZ25 stereo microscope.

[0009] In this embodiment, specifically, the microplastic characteristic parameters obtained in step S3 include, but are not limited to, microplastic abundance ( ), species distribution ( ), concentration of adsorbed pollutants ( ), soil organic matter content (OM), porosity, average annual rainfall (Rain), microplastic shape, color, and polymer composition.

[0010] In this embodiment, specifically: the risk assessment values ​​in S4 include pollution load estimate, composite toxicity estimate, and biodiversity impact.

[0011] In this embodiment, specifically: the risk assessment model in step S4 is as follows, and the calculation formula for the pollution load risk estimate is: N0 represents the regional background abundance, and C0 represents the safety threshold; the formula for calculating the composite toxicity estimate is as follows: , The plastic toxicity index, The weighting factor is the pollutant toxicity weight; the formula for calculating the impact on biodiversity is... α is the organic matter adjustment coefficient.

[0012] In this embodiment, specifically: the calculation formula for the migration risk factor M in step S5 is as follows: Porosity is the porosity, and Permeability is the permeability coefficient.

[0013] In this embodiment, specifically: the formula for calculating the risk assessment value in step S6 is as follows: M is the migration risk factor, Depth is the sampling depth, Rain is the rainfall amount, and β=0.0001 is the rainfall coefficient.

[0014] In this embodiment, specifically: in step S7, the soil samples are classified into five risk levels, with "Level 0", "Level 1", "Level 2", "Level 3", and "Level 4" corresponding to "Safe", "Low Risk", "Medium Risk", "High Risk", and "High Risk", respectively. The range is <0.1, 0.1≤ <0.3, 0.3≤ <<0.7, 0.7≤ <1.5, ≥1.5.

[0015] In this embodiment, specifically: in step S8 when >Λ, where Λ is the preset toxicity warning value. When this value is reached, the risk level is increased by one level.

[0016] The beneficial effects of this invention are as follows: The method for assessing the risk level of microplastic pollution in soil according to this invention includes stratified collection of soil samples from target areas, extraction of microplastics, and acquisition of characteristic parameters of microplastics in the soil samples. These characteristic parameters include at least microplastic abundance, microplastic species distribution, concentration of adsorbed pollutants, soil organic matter content, soil porosity and average annual rainfall, and the shape, color, and material composition of microplastics. The characteristic parameters are processed to generate multiple risk assessment values. Based on these risk assessment values, the soil samples are classified into risk levels. This provides a scientific basis and theoretical support for the governance and control of microplastic pollution in soil, overcoming the shortcomings of current single-method assessments of microplastic pollution levels and providing more precise guidance for agricultural activities. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] In the picture: Figure 1 This is a flowchart illustrating a method for assessing the risk level of microplastic pollution in soil according to the present invention.

[0019] Figure 2This is a technical roadmap for a method for assessing the risk level of microplastic pollution in soil according to the present invention. Detailed Implementation

[0020] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will now be described in detail with reference to the accompanying drawings. This drawing is a simplified schematic diagram, illustrating only the basic aspects of the invention, and therefore only shows the components relevant to the invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] like Figure 1 As shown, this invention provides a method for assessing the risk level of microplastic pollution in soil, comprising the following steps: S1. A layered three-dimensional sampling strategy is adopted, and sampling points are set up in the target area according to the grid method to collect soil samples. Sampling points are set up in the target area using a grid method. Based on the area and terrain features of the target area, sampling points are set up using a 100m×100m (small area) or 500m×500m (large area) grid method. Sampling points are densified around pollution sources (such as landfill boundaries) and in areas with dense human activity (such as farmland irrigation areas). Three parallel sampling points are set up in each grid to reduce random errors. Soil samples were collected in layers: using a fully automated soil sampler (accuracy ±0.5cm), soil samples were collected from the topsoil layer (0-20cm), leaching layer (20-50cm), and deep layer (>50cm). The sample volume for each layer was no less than 1kg. After sampling, the samples were immediately placed in plastic-free sampling bags, and the sampling point, depth, time, and environmental parameters (such as air temperature and humidity at the time of sampling) were marked. The samples were transported to the laboratory at 4℃ to avoid cross-contamination of microplastics and sample deterioration.

[0022] S2. Soil microplastics were extracted using density flotation-microscopic identification combined technology; a) The soil samples were first screened through a 2mm sieve to effectively remove any large particulate impurities that might be present in the samples, ensuring the purity of the samples. 100g of the sieved sample was weighed for microplastic extraction. b) Density flotation treatment: Add 200 mL of saturated sodium chloride solution (1.2 g / cm³) to the sample, place it in a constant temperature shaker (25℃, 220 r / min) and shake for 30 min, let it stand for 1 h, and take advantage of the density difference between microplastics (density mostly 0.9~1.4 g / cm³) and soil particles (density >2.6 g / cm³) to make the microplastics float to the surface of the solution; c) Vacuum filtration operation: A vacuum filtration system is used to filter the floating liquid through a 0.45μm nitrocellulose membrane to collect microplastics. During the filtration process, the container is rinsed three times with ultrapure water to ensure that no microplastics remain. d) Microscopic imaging analysis: The nitrocellulose membrane was placed under a Nikon SMZ25 stereo microscope and observed at different magnifications. The quantity, shape (fibrous, granular, film, fragment), and color (transparent, white, colored) of the microplastics were recorded. The particle size of the microplastics was measured using the microscope's built-in image analysis system to preliminarily identify the material type, providing a basis for subsequent toxicity index assignment.

[0023] S3. Obtain microplastic characteristic parameters; Microplastic characteristic parameters include, but are not limited to, microplastic abundance. (Particles / kg), Distribution of Microplastic Types Adsorbed pollutant concentration (mg / kg), soil organic matter content OM (%), soil porosity and average annual rainfall Rain, shape, color and material composition of microplastics; A multi-dimensional characteristic parameter system was constructed to comprehensively characterize the features of soil microplastic pollution. The methods for measuring each parameter are as follows: Microplastic abundance ( ): The number of microplastic particles in a unit mass (kg) of soil was counted by microscopic counting, and the average value of three parallel samples was calculated; Distribution of Microplastic Species ( Fourier transform infrared spectroscopy (FTIR) was used to accurately identify the material of microplastic particles identified by microscopy, determine the polymer types such as PE, PP, and PVC, and calculate the mass percentage of each type of microplastic. Adsorbed pollutant concentration ( The content of heavy metals adsorbed by microplastics was determined by inductively coupled plasma mass spectrometry (ICP-MS), and the content of organic pollutants (such as PAHs) was determined by high performance liquid chromatography-mass spectrometry (HPLC-MS / MS). Soil organic matter content (OM): determined by potassium dichromate oxidation-external heating method; Soil porosity: determined using the ring sampler method; Soil permeability: measured using a constant head permeameter; Average annual rainfall (Rain): obtained by averaging the rainfall data of the past five years from meteorological stations around the target area.

[0024] S4. Construct a multi-indicator risk assessment model to generate core valuation; The risk assessment model is as follows: Pollution load estimation: The formula for calculating pollution load estimation is as follows: , For regional background abundance, For safety threshold; pollution load estimation ( Correlating microplastic abundance with pollutant concentration, and combining regional background values ​​with safety thresholds, avoids the limitations of a single abundance indicator. A value greater than 1 indicates that the soil microplastic and pollutant load exceeds the safe level; Combined toxicity assessment: Combined toxicity assessment , The plastic toxicity index, As the pollutant toxicity weight, the composite toxicity estimate ( By coupling the toxicity index of microplastic materials with the toxicity weight of pollutants, the toxicity intensity of the "microplastic-pollutant" composite system is quantified. The higher the value, the stronger the combined toxicity; Impacts on biodiversity: The formula for calculating the impacts on biodiversity is as follows: α is the organic matter moderating coefficient; the estimated impact of biodiversity ( Introducing a soil organic matter adjustment coefficient to account for the reducing effect of organic matter on the bioavailability of microplastics. The value reflects the degree to which microplastic pollution disturbs the diversity of soil ecosystems.

[0025] S5. Introduce migration risk factor (M) and couple soil structure parameters with hydraulic properties; The formula for calculating the migration risk factor M is: Porosity and permeability are used in this study. The migration risk factor (M) couples soil porosity and permeability to quantify the migration potential of microplastics in soil. Lower soil porosity results in more significant obstruction of microplastic migration, and a smaller M value. Conversely, a larger permeability indicates stronger water leaching and greater microplastic migration capacity, leading to a larger M value. The introduction of this factor fills the gap in existing assessment methods that neglect the spatial migration risk of microplastics, providing a basis for assessing deep soil pollution.

[0026] S6. Integrating environmental driving factors and hierarchical depth correction to construct a comprehensive risk index ( ); Generate a risk assessment value; the formula for calculating the risk assessment value is as follows: M is the migration risk factor, Depth is the sampling depth, Rain is the rainfall amount, and β=0.0001 is the rainfall coefficient; By integrating core valuation, migration risk factors, environmental driving factors (rainfall), and depth correction terms, a comprehensive risk index is constructed. The average annual rainfall (Rain), as an environmental factor, is corrected using a β coefficient to reflect the promoting effect of rainwater leaching on microplastic migration during the rainy season; the sampling depth (Depth), as the denominator depth correction, reflects the deeper layers. S7. Classify the risk level of soil samples according to the risk assessment value; Level Classification Determination Value Table 1:

[0027] S8. Establish a toxicity early warning mechanism; when When the value is >Λ (Λ is the preset toxicity warning value), the risk level is increased by one level.

[0028] In this embodiment, specifically: when Risk escalation was triggered at 5:20.

[0029] Parameter standardization To eliminate the interference of different parameter dimensions on risk assessment, the "extreme value standardization-weight assignment" method is used to preprocess the parameters to ensure the scientific nature of the parameter contribution.

[0030] Positive parameters (abundance, pollutant concentration; higher values ​​indicate higher risk):

[0031] Negative parameters (organic matter content, microbial diversity; higher values ​​indicate lower risk): ; in, This represents the original value of the j-th parameter for the i-th sample. , These are the maximum and minimum values ​​of the j-th parameter, respectively. The value is the standardized value (range 0-1).

[0032] Example 1: Determining the risk level of a farmland soil sample using the soil microplastic pollution risk assessment method of the present invention. Using typical farmland as the target area, stratified sampling was conducted using a grid method. After extracting microplastics, characteristic parameters were obtained and multiple risk assessment values ​​were generated. The soil risk level was determined as shown in Table 2 below. Example 2: Determining the risk level of a soil sample from an urban park using the soil microplastic pollution risk assessment method of the present invention. Using urban parks as the target area, stratified sampling was conducted using a grid method. After extracting microplastics, characteristic parameters were obtained and multiple risk assessment values ​​were generated. The soil risk level was determined as shown in Table 2 below. Example 3: Determining the risk level of a wetland soil sample using the soil microplastic pollution risk assessment method of the present invention. Using wetlands as the target area, stratified sampling was conducted using a grid method. After extracting microplastics, characteristic parameters were obtained and multiple risk assessment values ​​were generated. The soil risk level was determined as shown in Table 2 below. Example 4: Determining the risk level of soil samples surrounding a landfill using the microplastic pollution risk assessment method in this invention. Using the area surrounding the landfill as the target area, stratified sampling was conducted using a grid method. After extracting microplastics, characteristic parameters were obtained and multiple risk assessment values ​​were generated. The soil risk level was determined as shown in Table 2 below.

[0033] Although farmland (Example 1) had plastic film input (microplastic abundance 80 particles / kg), the high organic matter content (2.5%) reduced microplastic bioavailability through the moderating coefficient α, thus affecting the estimated impact on biodiversity. =0.2) is the lowest, and the comprehensive risk index is 0.42, which is classified as "medium risk", reflecting the buffering effect of the soil's own properties on pollution risk in agricultural scenarios. The control direction of Example 1 is to optimize the use of plastic agricultural film and increase the application of organic fertilizer, which meets the needs of agricultural production safety.

[0034] Urban parks (Example 2) are affected by human activities (such as plastic waste disposal), resulting in higher microplastic abundance (120 particles / kg) than farmland. Adsorption of polycyclic aromatic hydrocarbons (PAHs, 100 mg / kg) leads to a higher estimated combined toxicity. The value of organic pollutants (PAHs) increased to 0.65, with a comprehensive risk index of 0.85, indicating a "higher risk". Therefore, the frequency of organic pollutant monitoring needs to be increased to address the PAHs pollution observed in Example 2.

[0035] Comparative Example 1 ( =0.55) and Example 2 ( =0.65): The difference in microplastic abundance between the two is 40 particles / kg. However, because the toxicity weight of PAHs in Example 2 (0.8) is higher than that of Pb in Example 1 (0.9, the values ​​are similar but PAHs are organic pollutants and have stronger bioaccumulation), the risk level of Example 2 is higher than that of Example 1. This shows that the impact of pollutant type and toxicity weight on risk assessment is no less than that of microplastic abundance.

[0036] The wetland (Example 3) was affected by high rainfall (1000 mm), which promoted the migration of microplastics (migration risk factor M=0.2). Combined with the adsorption effect of pesticide (glyphosate 10 mg / kg), the comprehensive risk index reached 1.62, which was also classified as "high risk". This indicates that the hydrological conditions of the wetland will aggravate the ecological impact of microplastic pollution. Example 3 needs to control pesticide input and restore hydrological pathways.

[0037] Comprehensive Risk Index of Landfill Surrounding Area (Example 4) =2.15) is the highest, reaching the "high risk" level, with its microplastic abundance (200 particles / kg), adsorbed pollutant concentration (benzo[a]pyrene 80 mg / kg) and estimated composite toxicity ( =1.0) were the highest in all four regions, confirming that landfills are a strong source of soil microplastic pollution and are prone to the accumulation of highly toxic organic pollutants. Example 4 requires the delineation of isolation zones and the use of engineering technologies such as soil washing, demonstrating the precise guiding value of the tiered system for control strategies in different scenarios.

[0038] The beneficial effects of this invention's method for assessing the risk level of microplastic pollution in soil are as follows: 1. Breaking through the limitations of traditional single-indicator assessments (such as relying solely on abundance), this approach comprehensively incorporates multiple parameters, including microplastic abundance, material toxicity (PE / PVC / PS, etc.), speciation distribution, adsorbed pollutant concentration (heavy metals, PAHs), soil physicochemical properties (organic matter, porosity), and environmental factors (rainfall, sampling depth). It comprehensively characterizes pollution features from the perspectives of pollution load, complex toxicity, ecological impact, and migration risk, thus avoiding misjudgment of risks.

[0039] 2. By linking pollution load estimates with background values ​​and safety thresholds, coupling composite toxicity estimates with plastic toxicity indices and pollutant toxicity weights, and combining the impact of biodiversity values ​​with organic matter regulation and migration risk factors to quantitatively calculate rainfall and depth, a comprehensive risk assessment model is constructed to achieve quantitative expression of risk. The five-level risk classification further refines the degree of pollution, providing a precise basis for differentiated management.

[0040] 3. Introduce a toxicity verification mechanism triggered by prioritizing the control of pollutant exceedances, through... The risk level is adjusted by comparing it with the calibration value Λ to avoid highly toxic pollutants being masked by the "average risk" and to improve the sensitivity of the assessment to potential highly toxic pollutants.

[0041] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0043] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the scope of the present invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for assessing the risk level of microplastic pollution in soil, characterized in that: Includes the following steps: S1. A layered three-dimensional sampling strategy is adopted, and sampling points are set up in the target area according to the grid method to collect soil samples. S2. Soil microplastics were extracted using density flotation-microscopic identification combined technology; S3. Obtain microplastic characteristic parameters; S4. Construct a multi-indicator risk assessment model to generate core valuation; S5. Introduce migration risk factor (M) and couple soil structure parameters with hydraulic properties; S6. Integrating environmental driving factors and hierarchical depth correction to construct a comprehensive risk index ( ); S7, according to The numerical values ​​divide the risk into five levels; S8. Establish a toxicity early warning mechanism.

2. The method for assessing the risk level of microplastic pollution in soil according to claim 1, characterized in that: In step S2, soil samples were collected at depths of 0–20 cm (cultivated layer), 20–50 cm (leaching layer), and >50 cm (deep layer). After the samples were collected, the sampling depth (Depth) of each layer was recorded.

3. The method for assessing the risk level of microplastic pollution in soil according to claim 2, characterized in that: The specific steps for extracting microplastics from soil in step S3 include: after pre-treating the sample through a 2mm sieve, adding a saturated sodium chloride solution with a density of 1.2g / cm³, shaking for 30min to promote the floating of microplastics, using a 0.45μm nitrocellulose membrane for vacuum filtration to capture the microplastics, and finally performing morphological identification, counting, and material identification under a Nikon SMZ25 stereo microscope.

4. The method for assessing the risk level of microplastic pollution in soil according to claim 1, characterized in that: The microplastic characteristic parameters obtained in step S3 include, but are not limited to: microplastic abundance ( ), species distribution ( ), concentration of adsorbed pollutants ( ), soil organic matter content (OM), porosity, average annual rainfall (Rain), microplastic shape, color, and polymer composition.

5. The method for assessing the risk level of microplastic pollution in soil according to claim 4, characterized in that: The risk assessment values ​​in S4 include pollution load estimates, composite toxicity estimates, and biodiversity impacts.

6. The method for assessing the risk level of microplastic pollution in soil according to claim 5, characterized in that: The risk assessment model in step S4 specifically involves the calculation formula for the pollution load risk estimate. , For regional background abundance, The safety threshold is used; the formula for calculating the composite toxicity estimate is as follows: , The plastic toxicity index, The weighting factor is the pollutant toxicity weight; the formula for calculating the impact on biodiversity is... α is the organic matter adjustment coefficient.

7. The method for assessing the risk level of microplastic pollution in soil according to claim 6, characterized in that: The formula for calculating the migration risk factor M in step S5 is as follows: Porosity is the porosity, and Permeability is the permeability coefficient.

8. The method for assessing the risk level of microplastic pollution in soil according to claim 7, characterized in that: The formula for calculating the risk assessment value in step S6 is as follows: M is the migration risk factor, Depth is the sampling depth, Rain is the rainfall amount, and β=0.0001 is the rainfall coefficient.

9. The method for assessing the risk level of microplastic pollution in soil according to claim 8, characterized in that: In step S7, the soil samples are classified into five risk levels: "Level 0", "Level 1", "Level 2", "Level 3", and "Level 4" correspond to "Safe", "Low Risk", "Medium Risk", "High Risk", and "High Risk", respectively. The range is: <0.1, 0.1≤ <0.3, 0.3≤ <0.7, 0.7≤ <1.5, ≥1.

5.

10. The method for assessing the risk level of microplastic pollution in soil according to claim 9, characterized in that: In step S8, when When the value is >Λ (Λ is the preset toxicity warning value), the risk level is increased by one level.

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