Method for presuming soil heavy metal effective state content limit value

Abstract

The invention provides a soil heavy metal effective state content limit value presumption method, and belongs to the technical field of soil environment benchmark research. According to the method, the soil heavy metal effective state content limit value of farmland soil is presumed through root system soil and agricultural product edible part samples which are cooperatively sampled, so that the remediation effect of a stabilization technology can be evaluated through the standard, and the agricultural products can be safely managed and controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil environment benchmark research, and particularly relates to a method for inferring the effective content limit of heavy metals in soil. BACKGROUND

[0002] At present, the situation of farmland heavy metal pollution is relatively serious. From the aspect of the treatment of farmland heavy metal pollution, the stabilization technology is a widely used remediation method in the treatment of farmland heavy metal contaminated soil, which repairs the soil on the premise of reducing the effective state of heavy metals. From the aspect of the harm of farmland heavy metal pollution, farmland heavy metals enter the human body through diet as a way, and long-term consumption of farmland products contaminated by heavy metals may cause serious health problems to the human body.

[0003] However, due to the lack of a standard for the effective content limit of heavy metals in soil in the prior art, the repair effect of the stabilization technology cannot be evaluated and the safety control of the agricultural products cannot be performed through the standard. SUMMARY

[0004] The present application provides a method for inferring the effective content limit of heavy metals in soil, which can infer the effective content limit of heavy metals in soil of farmland through agricultural products and root soil of agricultural products, and further evaluate the repair effect of the stabilization technology and perform safety control of the agricultural products through the standard.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0006] The present application provides a method for inferring the effective content limit of heavy metals in soil, comprising:

[0007] collecting a sample of edible part of agricultural products and a sample of root soil of agricultural products from farmland;

[0008] determining the content A of heavy metals in the edible part of agricultural products H and the effective content P of heavy metals in the root soil of agricultural products H ;

[0009] calculating the heavy metal characteristic data X of agricultural products H ; the heavy metal characteristic data X of agricultural products H satisfies: X H =A H / P H ×100%;

[0010] inferring the effective content limit of heavy metals in soil by using the Burr III type distribution function, the characteristic data X H and the quality standard of agricultural products; wherein the quality standard of agricultural products is the limit value of heavy metals in agricultural products.

[0011] In one implementation of the above estimation method, estimating the limit of available heavy metal content in soil includes:

[0012] X H Substituting the Burr III distribution function, we obtain the cumulative distribution frequency curve of heavy metals in agricultural products; the expression for the Burr III distribution function is:

[0013]

[0014] In the above formula, y is the Burr III type distribution function value, b is the scale parameter of the cumulative distribution frequency curve, c is the first shape parameter of the cumulative distribution frequency curve, and k is the second shape parameter of the cumulative distribution frequency curve.

[0015] Obtain the f% quantile of the cumulative frequency distribution curve, substitute the f% quantile of the cumulative frequency distribution curve into the formula for calculating the limit of available heavy metal content in soil, and obtain the limit of available heavy metal content in soil; the formula for calculating the limit of available heavy metal content in soil is as follows;

[0016]

[0017] In the above formula, S H The limits for the available content of heavy metals in soil, where H represents the category of heavy metal; X Hf The f% quantile of the cumulative distribution frequency curve is determined by the error between the limit of available heavy metal content at the location of agricultural products in farmland soil and the average value of the limit of available heavy metal content at other locations in farmland soil; APQS H For agricultural product quality standards.

[0018] In one implementation of the above estimation method, the method for determining the available content of heavy metals in the root soil of agricultural products is CaCl2 extraction, diethylenetriaminepentaacetic acid extraction, or gradient diffusion membrane extraction.

[0019] In one implementation of the above estimation method, the CaCl2 extraction method includes:

[0020] Step 1: Place the sieved and air-dried root soil into a centrifuge tube, and add 0.01 mol / L CaCl2 solution into the centrifuge tube at a liquid-to-solid ratio of 10:1 (v:wt);

[0021] Step 2: Shake and centrifuge the centrifuge tubes to obtain the supernatant; filter the supernatant and determine the concentration of heavy metals in the supernatant by ICP-MS, which is the available content (P) of heavy metals in the root soil of agricultural products. H .

[0022] In an implementation form of the above method, the DTPA extraction method comprises the following steps:

[0023] Step 1, configure the DTPA extraction solution;

[0024] Step 2, extract the heavy metals in the root system soil by using the DTPA extraction solution;

[0025] Step 3, centrifuge the DTPA extraction solution after extracting the heavy metals in the root system soil, to obtain the supernatant; filter the supernatant, and then determine the concentration of the heavy metals in the supernatant, which is the effective content P of the heavy metals in the root system soil of the agricultural product. H .

[0026] In an implementation form of the above method, the DTPA extraction method comprises the following steps:

[0027] Step 1, configure the DTPA extraction solution;

[0028] Step 2, extract the heavy metals in the root system soil by using the DTPA extraction solution;

[0029] Step 3, centrifuge the DTPA extraction solution after extracting the heavy metals in the root system soil, to obtain the supernatant; filter the supernatant, and then determine the concentration of the heavy metals in the supernatant, which is the effective content P of the heavy metals in the root system soil of the agricultural product. H .

[0030] In an implementation form of the above method, the DTPA extraction method comprises the following steps:

[0031] Step 1, adjust the water holding capacity of the root system soil after being dried by screening to 50% of the maximum water holding capacity, and then to 80% to 100% of the maximum water holding capacity;

[0032] Step 2, rotate the DGT device into the root system soil obtained in step 1, and then take out the DGT device after being placed at 25℃ for 24 hours;

[0033] Step 3, take out the fixed film in the DGT device and put it into a 2mL centrifuge tube, and then add 1mL of HNO3 solution with a concentration of 1mol / L to perform oscillation, perform ICP-MS analysis on the extraction solution obtained by oscillation, to obtain the effective content P of the heavy metals in the root system soil of the agricultural product. H .

[0034] In an implementation form of the above method, the agricultural product is rice, wheat or rhizome vegetables.

[0035] In an implementation form of the above method, the heavy metal is Cd, Hg, As, Pb or Cr.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) This invention establishes a method for estimating the limit of available cadmium content in soil based on agricultural product quality standards, which can be used for the formulation of the limit of available cadmium content in agricultural land and the acceptance of soil heavy metal pollution remediation projects;

[0038] (2) Compared with species sensitivity analysis, using heavy metal characteristic data X from a single location H The cumulative distribution frequency curve fitting method requires less data processing, is simpler to operate, and is more feasible. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a method for estimating the limit of available heavy metal content in soil, provided in an embodiment of this application. Detailed Implementation

[0040] In the specification and claims of this invention, the terms "first" and "second" are used to distinguish different objects, rather than to describe a specific order of objects.

[0041] In the embodiments of this application, "and / or" indicates a relationship between objects. For example, A and / or B can represent the following three situations: A exists alone, B exists alone, and A and B exist simultaneously.

[0042] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0043] The methods and apparatus provided in this application relate to the field of soil environmental benchmark research technology and can be used for estimation.

[0044] To address the problem in the prior art that the lack of standards for the limits of available heavy metal content in soil makes it impossible to evaluate the remediation effect of stabilization technology and to conduct safety management of agricultural products, this application provides a method for estimating the limits of available heavy metal content in soil. This method can estimate the limits of available heavy metal content in farmland soil based on agricultural products and their root soil, thereby enabling the evaluation of the remediation effect of stabilization technology and the safety management of agricultural products.

[0045] like Figure 1As shown, the method for determining the limit value of the available content of heavy metals in soil provided by the embodiments of the present application comprises S101-S104.

[0046] S101, collecting a sample of the edible part of the agricultural product and a sample of the root system soil of the agricultural product from the farmland.

[0047] Optionally, the agricultural product can be rice, wheat, or root vegetables, etc.; the heavy metal can be Cd, Hg, As, Pb, or Cr, etc.; the embodiments of the present application do not limit the types of the agricultural product and the heavy metal.

[0048] In one application scenario, taking rice as an example, the method for collecting the root system soil of rice is as follows: within a range of 10 cm from the rice plant, 2 cm of the surface layer of the soil is dug with a wooden shovel, the rice and the soil are dug out together with the wooden shovel at an angle of 45° with the ground, and then the soil is peeled off from the root system of the rice, and the obtained soil is the root system soil of the rice.

[0049] S102, determining the content A of the heavy metal in the edible part of the agricultural product H and the available content P of the heavy metal in the root system soil of the agricultural product H .

[0050] In the embodiments of the present application, for the edible part of the agricultural product, when the heavy metal is Pb, the content A of the heavy metal is determined by the method specified in GB 5009.12; when the heavy metal is Hg, the content A of the heavy metal is determined by the method specified in GB 5009.17; when the heavy metal is Cd, the content A of the heavy metal is determined by the method specified in GB 5009.15; when the heavy metal is As, the content A of the heavy metal is determined by the method specified in GB 5009.11; and when the heavy metal is Cr, the content A of the heavy metal is determined by the method specified in GB 5009.123. H H H H H It can be understood that the above GB refers to the national standard.

[0051] Continuing to take rice as an example, the edible part of the rice is brown rice. The method for obtaining brown rice is as follows: during the maturation period of the rice, the ear is cut from the rice plant with scissors, and then the ear is air-dried at room temperature, and then the ear is placed in a mortar, and the rice husk is separated from the rice kernel by gently crushing the ear with a pestle, and the obtained rice kernel after removing the rice husk is brown rice.

[0052] Further, the method for determining the available content of the heavy metal in the root system soil of the agricultural product is CaCl2 extraction method, diethylene triamine pentaacetic acid extraction method, or gradient diffusion membrane extraction method.

[0053] ​​​​Specifically, the CaCl2 extraction method includes the following steps:

[0054] Step 1, place the sieved and air-dried root system soil in a centrifuge tube, and add 0.01 mol / L CaCl2 solution to the centrifuge tube according to a liquid-solid ratio of 10:1 (v:wt).

[0055] Step 2, shake and centrifuge the centrifuge tube, and separate the supernatant; filter the supernatant, and then measure the concentration of heavy metals in the supernatant by ICP-MS, which is the effective content P of heavy metals in the root system soil of the agricultural product. H .

[0056] In one application scenario, the detailed operation process of the CaCl2 extraction method is as follows: weigh 3g of air-dried soil sample sieved to 10 mesh in a 50mL centrifuge tube, and add 30mL of 0.01mol / L CaCl2 solution according to a liquid-solid ratio of 10:1 (v:wt). Place the centrifuge tube on a rolling shaker, and shake at 30±2r / min and 25±2℃ for 2h. After shaking, centrifuge and separate the supernatant, filter the supernatant with a 0.45μm filter membrane, and measure the concentration of heavy metals by ICP-MS.

[0057] The DTPA extraction method includes the following steps:

[0058] Step 1, prepare DTPA leaching solution;

[0059] Step 2, extract heavy metals in the root system soil using the DTPA leaching solution;

[0060] Step 3, centrifuge the DTPA leaching solution after extracting heavy metals in the root system soil, to obtain clear liquid; filter the supernatant, and then measure the concentration of heavy metals in the supernatant, which is the effective content P of heavy metals in the root system soil of the agricultural product. H .

[0061] In one application scenario, the detailed operation process of the DTPA extraction method is as follows.

[0062] Weigh 1.967g of DTPA (diethylene triamine pentaacetic acid), 14.92g of TEA (triethanolamine), and 1.470g of calcium chloride dihydrate (CaCl2·2H2O) in a 100ml beaker, add deionized water to fully stir until completely dissolved, and continue to dilute with water to about 800mL. Prepare a 6mol / L hydrochloric acid aqueous solution, adjust the pH of the DTPA solution to 7.3±0.2 with a pH meter, then transfer to a 1000mL volumetric flask, dilute to volume, shake well, and store in the dark.

[0063] Accurately weigh 10.0 g of the air-dried soil sample passed through a 10-mesh sieve into a 100-mL flask, and add 20.0 mL of the DTPA extraction solution into the flask with a syringe. Tighten the rubber stopper on the flask. Place the flask in a reciprocating shaker, and adjust the temperature to 20℃±2℃, and the oscillation frequency to 180±20 r / min for 2 h. Transfer the extraction solution into a 50-mL centrifuge tube, and centrifuge at 4000 r / min for 10 min. Filter the supernatant through a 0.45-μm filter membrane, and store in a transparent plastic bottle for determination and analysis within 48 h.

[0064] The gradient diffusion membrane extraction method comprises the following steps:

[0065] Step 1: Adjust the water-holding capacity of the root soil after sieving and air-drying to 50% of the maximum water-holding capacity, and then to 80%-100% of the maximum water-holding capacity.

[0066] Step 2: Rotate the DGT device into the root soil obtained in Step 1, and then take out the DGT device after placing at 25℃ for 24 h.

[0067] Step 3: Take out the fixed membrane in the DGT device and place it into a 2-mL centrifuge tube, and then add 1 mL of HNO3 solution with a concentration of 1 mol / L for oscillation. Perform ICP-MS analysis on the extraction solution obtained by oscillation to obtain the available content P of the heavy metal in the root soil of the agricultural product. H .

[0068] In Step 3, the available content P H extracted by the DGT device satisfies: P H =MΔg / (DAt). Wherein, M represents the mass (μg) of H in the DGT fixed membrane; Δg represents the thickness (cm) of the diffusion membrane; D represents the diffusion coefficient (cm 2 / s) of the heavy metal in the diffusion layer; A represents the area (cm 2 ) of the DGT exposure window; and t represents the placement time (s).

[0069] It should be understood that the DGT device (Diffusive Gradients in Thin-films) is a device for in-situ passive sampling and analysis of the effective state concentration (bioavailable state) of heavy metals (or other dissolved ions). Its core principle is to control the migration of heavy metal ions through a diffusion gradient, simulate the biological absorption process, and thus more accurately reflect the environmental behavior and ecological risk of heavy metals. The internal structure of the DGT device includes an outer filter membrane (0.45 μm), a diffusion layer (usually polyacrylamide hydrogel, corresponding to the diffusion film described above), a binding layer (corresponding to the fixed film described above), and a plastic base. Among them, the binding layer includes Chelex resin and Ferrihydrite colloid, Chelex resin is used to bind divalent metal ions (such as Cd 2+ , Pb 2+ , Zn 2+ , etc.), and Ferrihydrite colloid is used to bind anions such as arsenic (As), phosphorus (P), etc. Since the DGT device is a commonly used technical means in the technical field, the embodiments of the present application do not further elaborate on the DGT device.

[0070] In one application scenario, the detailed operation process of the gradient diffusion film extraction method described above is as follows.

[0071] After the soil sample is air-dried and impurities are removed, it is passed through a 10-mesh sieve, 50g is weighed in a PVC box, water is added to 50% of the maximum water holding capacity, and a glass rod is used to stir it evenly., place at 25°C for 48h, then add water to 80%-100% of the maximum water holding capacity, stir evenly to make the surface appear a shiny water film, and place at 25°C for 24h. Slowly spin the DGT device into the soil, and after 24h at 25°C, remove the DGT device. Rinse with deionized water, disassemble the DGT device, remove the fixed film and place it in a 2mL centrifuge tube, add 1mL of 1mol / L HNO3, and shake on a shaker for 24h.

[0072] In order to verify whether the selection of the determination method of the effective state content of heavy metals in the above-mentioned estimation method provided by the embodiments of the present application can ensure the reliability of the soil heavy metal effective state content limit value obtained by estimation.

[0073] The embodiments of the present application collect whole rice plants and root system soil from farmland in a certain area of Hubei Province at the mature stage of rice, take multiple rice plants and multiple root system soil to make mixed samples at each sampling point, and obtain 109 soil samples and corresponding rice samples. The available content of cadmium (Cd) in the soil is determined by CaCl2 (0.01 mol / L) extraction method, DTPA extraction method, gradient diffusion membrane technology and soil solution method. For the CaCl2 (0.01 mol / L) extraction method, the available content limit value based on the quality standard of agricultural products is 0.02 mg / kg.

[0074] Similarly, for the DTPA extraction method, the gradient diffusion membrane technology and the soil solution method, the available content limit value of cadmium of different available state extraction methods is calculated by the method of the present application. For each extraction method, the qualified rate of brown rice in the point where the available content of soil Cd is not higher than the derived limit value is calculated. The limit value and the qualified rate of brown rice obtained by each extraction method are shown in Table 1 below.

[0075] Table 1 Cd available content limit value and brown rice qualified rate table of different extraction methods

[0076] Extraction method Cd available content limit Rice eligible rate CaCl2(0.01 mol / L) extraction method 0.02 mg / kg 83.3％ DTPA extraction method 0.23 mg / kg 90.4％ Gradient diffusion membrane technique 0.36 μg / L 80.0％ Soil solution method 0.19 μg / L 50.5％

[0077] As shown in Table 1 above, the brown rice qualified rates of the CaCl2 (0.01 mol / L) extraction method, the DTPA extraction method and the gradient diffusion membrane technology are all higher than 80%, and the limit values obtained are relatively reliable, but the brown rice qualified rate of the soil solution method is only 50.5%, which shows that the soil solution method is not suitable for the derivation method provided by the embodiments of the present application.

[0078] S103, calculating the heavy metal characteristic data X of the agricultural products H .

[0079] The heavy metal characteristic data X of the agricultural products H satisfies: X H = A H / P H × 100%.

[0080] S104, deriving the available content limit value of soil heavy metal by using the Burr III type distribution function, the characteristic data X H and the quality standard of agricultural products.

[0081] It can be understood that the agricultural product quality standard (Agricultural Product Quality Standards) is a technical specification system formulated to protect food safety, promote trade fairness, and protect consumer rights. In the embodiments of the present application, the agricultural product quality standard refers to the limit value of heavy metals in agricultural products. The limit value of heavy metals in agricultural products can be obtained by international standard or regional standard, and the embodiments of the present application are not limited.

[0082] Optionally, the S104 includes S1041-S0142.

[0083] S1041, the heavy metal characteristic data X of the agricultural product is obtained. H The cumulative distribution frequency curve of the heavy metal in the agricultural product is obtained by substituting the Burr III distribution function.

[0084] The expression of the Burr III distribution function is as follows:

[0085]

[0086] In the above formula, y is the value of the Burr III distribution function, b is the scale parameter of the cumulative distribution frequency curve, c is the first shape parameter of the cumulative distribution frequency curve, and k is the second shape parameter of the cumulative distribution frequency curve.

[0087] It can be understood that the cumulative distribution frequency curve is determined by calculating the parameter values of b, c and k in the expression of the Burr III distribution function using the Burrlioz 2.0 software. Since the Burrlioz 2.0 software and the Burr III distribution function are both common technical means in the technical field, the determination process of the cumulative distribution frequency curve is not further described in the embodiments of the present application.

[0088] S1042, the f% quantile value of the cumulative distribution frequency curve is obtained, and the f% quantile value of the cumulative distribution frequency curve is substituted into the soil heavy metal available content limit value calculation formula to obtain the soil heavy metal available content limit value.

[0089] The soil heavy metal available content limit value calculation formula is as follows:

[0090]

[0091] In the above formula, S H is the soil heavy metal available content limit value, H represents the category of heavy metals; X Hf is the f% quantile value of the cumulative distribution frequency curve, and the value of f is determined by the error between the soil heavy metal available content limit value of the point of the agricultural product in the farmland soil and the average value of the soil heavy metal available content limit values of other points in the farmland soil; APQSH This is a quality standard for agricultural products. Preferably, the value of f can be 20, but the value of f can also be other values ​​within a reasonable range. This application embodiment does not further limit the value of f.

[0092] Furthermore, taking rice as an agricultural product and cadmium (Cd) as a heavy metal as an example, we will give a method for obtaining the value of f.

[0093] (1) The farmland soil was divided into multiple sampling points (also known as sampling sites), and the sampling points of the same rice variety were grouped together according to the rice variety. The cadmium content of brown rice and the available content of heavy metals in the root soil of different rice varieties were obtained. The cadmium characteristic data X of different rice varieties were calculated by the formula provided in S103. H The geometric mean;

[0094] (2) X the cadmium characteristic data of each rice variety H The geometric mean was input into Burrlioz 2.0 software for fitting, and the 95th percentile of the cumulative distribution frequency curve was obtained. The value was then multiplied by the agricultural product quality standard and divided by 100 to obtain the cadmium available content limit S1.

[0095] (3) Cadmium characteristic data X not grouped according to rice variety H The geometric mean was used to calculate the cadmium characteristic data X at each point. H Then X the cadmium characteristic data of each point H The data was fitted using Burrlioz 2.0 software to obtain the f% quantile of the cumulative distribution frequency curve. This value was then multiplied by the agricultural product quality standard and divided by 100 to obtain the cadmium available content limit S. f .

[0096] (4) Calculate S1 and S f The error is such that when the error is no greater than 10%, f = 20.

[0097] Finally, to verify the reliability of the above-mentioned presumed method provided in the embodiments of this application, this embodiment selected a passivated farmland in Hubei Province as the research object, collected soil and rice samples before and after treatment with different passivating agents, and used the DTPA extraction method as the evaluation method for the available Cd content. The main pollutant in the farmland soil was cadmium (Cd), with an average concentration of 0.79 mg / kg, which is 2.6 times the risk screening value for agricultural land. Before passivation remediation, the available Cd content in the soil and the Cd content in brown rice were measured. The Cd content in brown rice at each point was divided by the available Cd content, and then multiplied by 100 to obtain X. Cd X CdThe input is put into the Burrlioz 2.0 software, and a cumulative distribution frequency curve is fitted. The 20% quantile value of the cumulative distribution frequency curve is 125. According to the agricultural product quality standard, the effective state safety content limit value of Cd is obtained as 0.25 mg / kg, and 0.25 mg / kg is taken as the target value of the passivation remediation. After the passivation remediation, the effective state content of Cd in 91 point positions is lower than the remediation target value. Among the 91 point positions, the Cd content in 81 rice husks is lower than the agricultural product limit standard, and the qualified rate is 89%, indicating that the passivation remediation target value calculated is relatively reliable, so that most of the rice can meet the agricultural product Cd limit standard, and therefore the above-mentioned deduced method provided in the embodiment of the application is relatively reliable.

[0098] Each of the embodiments in the specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other. Each of the embodiments mainly describes the difference from other embodiments.

[0099] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for estimating a limit value of an available content of a heavy metal in soil, characterized by, The method comprises the following steps: collecting a sample of an edible part of a farm product and a root soil sample of the farm product from a farmland; determining the content of heavy metals A in the edible part of the agricultural product H and the available content P of heavy metals in the soil of the root system of the agricultural product H ; calculating heavy metal characteristic data X of the agricultural product H ; heavy metal characteristic data X of the agricultural product H satisfying: X H = A H / P H x 100%; Adopting Burr III type distribution function, the characteristic data X H And the agricultural product quality standard, the effective state content limit value of heavy metal in soil is inferred; wherein, the agricultural product quality standard is the heavy metal limit value of the agricultural product.

2. The method of claim 1, wherein, the limit value of the effective content of the soil heavy metal comprises: characteristic data X of heavy metals of the agricultural products H The cumulative distribution frequency curve of heavy metals in the agricultural products is obtained by substituting the Burr III distribution function, wherein an expression of the Burr III distribution function is: In the formula, y is a value of a Burr III distribution function, b is a scale parameter of a cumulative distribution frequency curve, c is a first shape parameter of the cumulative distribution frequency curve, and k is a second shape parameter of the cumulative distribution frequency curve; obtaining an f% quantile value of the cumulative distribution frequency curve, and substituting the f% quantile value of the cumulative distribution frequency curve into a limit value calculation formula of the effective content of the soil heavy metal to obtain the limit value of the effective content of the soil heavy metal; the limit value calculation formula of the effective content of the soil heavy metal is as follows: In the above formula, S H is the effective content limit of heavy metals in the soil, H represents the category of heavy metals; X Hf is the f% quantile value of the cumulative distribution frequency curve, the value of f is determined by the error between the average value of the effective content limit of heavy metals at the point where the agricultural product is located in the farmland soil and the effective content limit of heavy metals at other points in the farmland soil; APQS H is the quality standard of the agricultural product.

3. The method of claim 1, wherein, the method for determining the effective content of the heavy metal in the root soil of the farm product is CaCl2 extraction, diethylene triamine pentaacetic acid extraction or gradient diffusion membrane extraction.

4. The method of claim 3, wherein, The CaCl2 extraction comprises the following steps: Step 1, placing the sieved and air-dried root soil in a centrifuge tube, and adding 0.01 mol / L CaCl2 solution to the centrifuge tube according to a liquid-solid ratio of 10:1 (v:wt); Step 2, shake and centrifuge the centrifugal tube, and separate the supernatant; filter the supernatant, and determine the concentration of heavy metals in the supernatant by ICP-MS, which is the effective content P of heavy metals in the root system soil of the agricultural product H .

5. The method of claim 3, wherein, The diethylene triamine pentaacetic acid extraction comprises the following steps: Step 1, preparing diethylene triamine pentaacetic acid extraction solution; Step 2, extracting the heavy metal in the root soil by using the diethylene triamine pentaacetic acid extraction solution; Step 3, centrifuging the diethylene triamine pentaacetic acid extract solution after extracting heavy metals in the root system soil to obtain a clear liquid; filtering the supernatant, and determining the concentration of heavy metals in the supernatant, which is the available content P of heavy metals in the root system soil of the agricultural product H .

6. The method of claim 3, wherein, The gradient diffusion membrane extraction comprises the following steps: Step 1, adjusting the water holding capacity of the sieved and air-dried root soil to 50% of the maximum water holding capacity, and then adjusting the water holding capacity to 80%-100% of the maximum water holding capacity; Step 2, rotating the DGT device into the root soil obtained in step 1, and then taking out the DGT device after placing the DGT device at 25°C for 24 hours; Step 3, the fixed film in the DGT device is taken out and put into a 2 mL centrifuge tube, 1 mL of HNO3 solution with a concentration of 1 mol / L is added for shaking, and the extract obtained by shaking is analyzed by ICP-MS to obtain the available state content P of heavy metals in the root system soil of the agricultural product H .

7. The method of claim 1, wherein, the farm product is rice, wheat or root vegetable.

8. The method of claim 1, wherein, the heavy metal is Cd, Hg, As, Pb or Cr.

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