A method for extracting plant-available cadmium from moderately alkaline paddy soil

Abstract

The invention discloses a method for extracting plant-available cadmium in medium-alkaline paddy soil. After the soil is naturally air-dried, it is ground and sieved to obtain a soil sample. The soil sample is weighed and added with deionized water to make the soil moisture content 35%-110% of the maximum water holding capacity of the soil. After balancing at room temperature for 12-48 hours, a calcium chloride solution is added for constant temperature oscillation extraction. After filtering, an extract is obtained, and the concentration of cadmium in the extract is determined. According to the mass of the measured soil sample and the concentration of cadmium in the measured extract, the content of plant-available cadmium in the measured soil sample is calculated. The method is simple to operate, low in cost, and can better reflect the changing characteristics of the plant effectiveness of cadmium in medium-alkaline paddy soil under field water management mode. There is a better linear correlation between the measured plant-available cadmium content in the medium-alkaline paddy soil and the cadmium content in rice.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural environment detection, and more particularly to a method for extracting plant-available cadmium from moderately alkaline paddy field soil. Background Art

[0002] Cadmium is the heavy metal pollutant with the largest area of ​​excessive paddy soil and the most prominent threat to rice quality and safety. However, the cadmium absorbed and accumulated by rice does not depend on the total cadmium content in the soil, but on the effective cadmium content that can be absorbed and utilized by plant roots. The plant effective cadmium content in paddy soil is affected by the degree of soil cadmium pollution and physical and chemical properties such as pH. Therefore, in the current "Standards for Risk Control of Soil Pollution in Agricultural Land of Soil Environmental Quality (Trial)" (GB15618-2018), the risk screening value and control value are determined according to the pH value (pH value) of the soil. However, in the moderately alkaline paddy soil, there is often a mismatch between "soil cadmium exceeding the standard, but rice cadmium not exceeding the standard" or "soil cadmium not exceeding the standard, but rice cadmium exceeding the standard". The study of plant effective cadmium can provide a reliable basis for the accurate evaluation of the cadmium accumulation risk of rice, the scientific prevention and control of soil cadmium pollution, and even the establishment of soil environmental quality standards.

[0003] At present, the methods for determining the content of plant-available cadmium in soil mainly include single extraction method, continuous extraction method and gradient diffusion membrane (DGT) technology. These methods have their own advantages, but they also have some limitations. For example, the single extraction method has the advantages of relatively simple operation and low cost. The recommended method for determining available cadmium in soil in my country, "Atomic absorption method for determination of available lead and cadmium in soil quality" (GB / T 23739-2009), belongs to this type of method. The correlation between the measured available cadmium content and the absorption of cadmium by crops such as rice is not close. The continuous extraction method takes into account the different binding abilities of cadmium and soil, and uses extractants with different leaching abilities to continuously extract the soil, which can more comprehensively evaluate the mobility, effectiveness and potential toxicity of cadmium in soil. However, this method is more complicated to operate, and has relatively high requirements for analytical instruments and is also more expensive. DGT technology has the advantages of in-situ and bionics, but its determination cost is relatively high.

[0004] Frequent irrigation and drying of paddy fields during rice field management will cause changes in soil redox state, which will cause changes in cadmium forms and plant effectiveness in the soil. There are obvious differences in the patterns of cadmium forms and effectiveness in soils of different properties as soil moisture conditions change. Single extraction methods often recommend the use of air-dried soil for testing, which is difficult to reflect the actual situation in the field, and therefore cannot well characterize the risk of crop absorption and accumulation of cadmium. Summary of the invention

[0005] In view of this, the present invention proposes a method for extracting effective cadmium in plants in moderately alkaline paddy soil based on "soil moisture regulation-constant temperature cultivation-single extraction", and conducts potted plant and regional survey sampling verification. The detection process simulates the actual moisture conditions in the field and can more accurately characterize the risk of rice absorbing and accumulating cadmium.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for extracting plant-available cadmium from moderately alkaline paddy soil comprises the following steps:

[0008] Step 1: Sample collection and processing

[0009] (1.1) Collect soil samples from the plough layer of moderately alkaline paddy fields, air-dry them naturally, crush them, grind them and pass them through a 20-mesh sieve to obtain soil samples;

[0010] (1.2) Weigh the soil sample obtained in step (1.1) and place it in a centrifuge tube. Add deionized water to adjust the moisture content of the soil. Cover the tube and allow it to equilibrate at room temperature for a period of time. Then add calcium chloride extract and perform extraction in a constant temperature horizontal oscillator. After the extraction is completed, filter the tube to obtain the extract for testing.

[0011] Step 2: Determination of effective cadmium concentration in the extract

[0012] (2.1) Using inductively coupled plasma mass spectrometry to establish a standard curve for determining different concentrations of available cadmium;

[0013] (2.2) Using an inductively coupled plasma mass spectrometer to measure the concentration of effective cadmium in the extract using a standard curve;

[0014] Step 3: Result Analysis

[0015] According to the mass of the measured soil sample and the concentration of available cadmium in the measured extract, the content of plant available cadmium in the measured soil sample is calculated. The calculation formula is as follows:

[0016]

[0017] Where: W The plant-available cadmium content in the measured soil sample is in mg / kg; c is the concentration of available cadmium in the measured extract, in μg / L; V 1 is the volume of deionized water added, in mL; V 2 is the volume of calcium chloride extract added, in mL; m is the mass of the soil sample measured in g.

[0018] Preferably, in step (1.2), the soil moisture content is adjusted to 35%-110% of the maximum water holding capacity of the soil with deionized water; the equilibrium time is 12h-48h; the concentration of the calcium chloride extract is 0.1mol / L, the volume ratio of the soil sample mass to the calcium chloride extract is 1:5 g / mL, and the total soil-water ratio is 1:5.21-5.66g / mL.

[0019] Furthermore, in step (1.2), deionized water was used to adjust the soil moisture content to 35% of the maximum water holding capacity of the soil; the equilibrium time was 12 h; and the total soil-water ratio was 1:5.21 g / mL.

[0020] Preferably, the extraction conditions in step (1.2) are: 25° C., 180 r / min, and extraction for 2 h.

[0021] Preferably, the process of establishing the standard curve of different concentrations in step (2.1) is specifically as follows:

[0022] (2.1.1) Take 1 mL of 1000 mg / L cadmium standard working solution and place it in a 100 mL volumetric flask. Make up to volume with 1% HNO3 solution to prepare a cadmium standard working solution with a cadmium concentration of 10 mg / L.

[0023] (2.1.2) Take 0 mL, 0.01 mL, 0.05 mL, 0.1 mL, 0.2 mL and 0.4 mL of the cadmium standard working solution with a cadmium concentration of 10 mg / L respectively and place them in a 100 mL volumetric flask, add 10 mL of 0.1 mol / L calcium chloride solution, and dilute to the scale with 1% HNO3 solution to prepare cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L;

[0024] (2.1.3) Inject cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L into the inductively coupled plasma mass spectrometer in sequence. Use the concentration of the cadmium standard working solution as the horizontal axis and the intensity of the effective cadmium as the vertical axis. The inductively coupled plasma mass spectrometer automatically plots standard curves of different cadmium concentrations, and linearly regresses the standard curves to obtain the regression equation for the cadmium concentration relationship.

[0025] Preferably, the specific steps of step (2.2) are:

[0026] The extract was diluted 10-100 times with 1% HNO3 solution and then injected into the inductively coupled plasma mass spectrometer to measure the intensity value of the effective cadmium. The value was substituted into the standard curve regression equation of step (2.1) to calculate the concentration of effective cadmium in the extract.

[0027] Furthermore, in step (1.2), a blank sample is prepared while preparing the extract. The method for preparing the blank sample comprises the following steps:

[0028] Place 25 mL of 0.1 mol / L calcium chloride extract in a centrifuge tube with a lid, extract at 180 r / min for 2 h in a 25°C constant temperature horizontal oscillator, let stand, and take the supernatant to pass through quantitative filter paper to prepare a blank sample.

[0029] Furthermore, the specific steps of step (2.2) are:

[0030] (2.2.1) Dilute the blank sample 10-100 times with 1% HNO3 solution and inject it into the inductively coupled plasma mass spectrometer to measure the intensity value of effective cadmium. Substitute it into the standard curve regression equation to calculate the concentration of effective cadmium in the blank sample;

[0031] (2.2.2) Inject the extract into an inductively coupled plasma mass spectrometer to measure the intensity value of the effective cadmium, substitute it into the regression equation, and calculate the concentration of the effective cadmium in the extract;

[0032] (2.2.3) Determine the concentration of available cadmium in the extract using the formula c = c1 f1 - c0 f0, where c0 is the concentration of available cadmium in the blank sample, in μg / L; c1 is the concentration of available cadmium in the extract calculated in step (2.2), in μg / L; f0 is the dilution factor of the blank sample; and f1 is the dilution factor of the extract.

[0033] Preferably, it also includes:

[0034] Step 4: Verification

[0035] (4.1) Potted plant validation: The soil collected from the test paddy field was used for potted plant experiments. Conventional water management was adopted. Samples were taken at the rice maturity stage and the cadmium content in rice grains was determined. Linear regression analysis was performed between the plant-available cadmium content in the soil samples and the cadmium content in rice grains to verify the accuracy and precision of this method in characterizing the plant-available cadmium in paddy field soil.

[0036] (4.2) Regional validation: Select the corresponding small watershed of the original site of the above-mentioned soil samples, and randomly select sampling points in the neutral-alkaline cadmium-contaminated rice fields on both sides along the direction of the irrigation canal; collect soil samples and rice samples one-to-one in situ during the rice maturity period, determine the content of plant-available cadmium in soil samples and cadmium in rice, and perform linear regression analysis on the two to verify the field applicability of this method.

[0037] Furthermore, the rice varieties tested in potted plant verification were Xiangzaoxian 24 and Zhuliangyou 189. The rice growth conditions in the rice fields selected for regional verification were similar, which could reduce the impact of outdoor environmental factors and facilitate the collection of mature rice and soil samples. The sample pretreatment during regional verification was the same as step (1.2) to determine the content of plant-available cadmium in the soil.

[0038] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for extracting plant-available cadmium from moderately alkaline paddy soil, which has the following beneficial effects:

[0039] At present, all research and existing standards mostly use air-dried soil for detection, and rarely consider the effect of soil moisture content on effective cadmium. The present invention proposes the optimal moisture conditions and cultivation time during soil pretreatment, and the measured results are highly correlated with the cadmium content of rice grains. The present invention has the characteristics of high accuracy, simple operation, low cost, etc., and can better characterize the plant effectiveness of cadmium in paddy soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 This is a linear correlation diagram of the plant-available cadmium in the soil and the cadmium content in the two rice grains under different water content and 12h culture conditions in Examples 1 to 3;

[0042] Figure 2 This is a linear correlation diagram of the plant-available cadmium in the soil and the cadmium content in the two rice grains under different water content and 24h culture conditions in Examples 4 to 6;

[0043] Figure 3 This is a linear correlation diagram of the plant-available cadmium in the soil and the cadmium content in the two rice grains under different water content and 48h culture conditions in Examples 7 to 9;

[0044] Figure 4 It is a linear correlation diagram of the plant-available cadmium in soil and the cadmium content in two types of rice grains measured by different extraction methods in Comparative Examples 1-3;

[0045] Figure 5 This is a linear correlation diagram of the plant-available cadmium in the soil and the cadmium content in the two rice grains determined by the DGT technology in Comparative Example 4;

[0046] Figure 6is a linear correlation diagram of the plant-available cadmium in the soil and the cadmium content in the rice grains in Example 10;

[0047] Figure 7 This is a linear correlation diagram between the plant-available cadmium in the soil and the cadmium content in rice grains in Comparative Example 5. DETAILED DESCRIPTION

[0048] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The method for extracting plant-available cadmium from moderately alkaline paddy soil is based on the content of available cadmium in moderately alkaline soil under different soil pretreatment methods, and a linear regression equation is established with the accumulation of cadmium in rice grains. The method includes the following steps:

[0050] S100) Soil sample collection and pretreatment

[0051] S110) Collection, grinding, sieving

[0052] In 2023, the surface soil (0-20cm) of cadmium-contaminated rice fields in Guiyang County, Chenzhou City, Hunan Province, Qiyang City, Yongzhou City, Changning City, Hengyang City and other counties were collected. Three soil samples were collected from each county and city, numbered GY1-3, QY1-3, and CN1-3, and a total of 9 soil samples were collected. The sampling points were all representative local fields, and the five-point sampling method was adopted. The collected paddy field soil was naturally air-dried at room temperature, the sample was crushed, ground and passed through a 20-mesh sieve to obtain a soil sample, which was moderately alkaline (pH ≥ 6.43).

[0053] The method for detecting plant-available cadmium in soil samples numbered GY1-3, QY1-3, and CN1-3 comprises the following steps:

[0054] S120) Preparation of extract

[0055] S121) Weigh 5 g of soil sample into a centrifuge tube with a lid, add a small amount of deionized water, and adjust the soil moisture content to 35%, 65%, and 110% of the maximum water holding capacity of the soil respectively;

[0056] S122) After screwing on the centrifuge tube cap, the tube was incubated at room temperature. The equilibrium time was 12 hours, 24 hours, and 48 hours, respectively.

[0057] S123) After incubation, add 25 mL of 0.1 mol / L calcium chloride extract, extract at 180 r / min for 2 h in a 25°C constant temperature horizontal oscillator, let stand, and take the supernatant to pass through quantitative filter paper to obtain the extract. Repeat each treatment 3 times.

[0058] In the steps S121 and S122, the amount of deionized water added is 35% of the maximum water holding capacity of the soil, and the equilibrium time is 12 hours; in step S123, the volume ratio of the soil sample mass to the calcium chloride extract is 1:5 g / mL, and the total soil-water ratio is 1:5.21 g / mL.

[0059] S124) Preparation of blank sample

[0060] Add 25 mL of 0.1 mol / L calcium chloride extract to a centrifuge tube with a lid, extract at 180 r / min for 2 h in a 25°C constant temperature horizontal oscillator, let stand, and take the supernatant to pass through quantitative filter paper to prepare a blank sample;

[0061] S200) Determination of the concentration of effective cadmium in the extract

[0062] S210) Develop a standard curve

[0063] An inductively coupled plasma mass spectrometer was used to establish a standard curve for determining different concentrations of effective cadmium by inductively coupled plasma mass spectrometry;

[0064] S211) Measure 1 mL of a 1000 mg / L cadmium standard working solution and place it in a 100 mL volumetric flask, and dilute it to volume with a 1% HNO3 solution to prepare a cadmium standard working solution with a cadmium concentration of 10 mg / L;

[0065] S212) 0 mL, 0.01 mL, 0.05 mL, 0.1 mL, 0.2 mL and 0.4 mL of a cadmium standard working solution with a cadmium concentration of 10 mg / L were measured respectively and placed in a 100 mL volumetric flask, 10 mL of a 0.1 mol / L calcium chloride solution was added, and the volume was fixed to the scale line with a 1% HNO3 solution to prepare cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L;

[0066] S213) injecting cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L into the inductively coupled plasma mass spectrometer in sequence, with the concentration value of the cadmium standard working solution as the abscissa and the intensity value of the effective cadmium as the ordinate, the inductively coupled plasma mass spectrometer automatically draws standard curves of different cadmium concentrations, and linearly regresses the standard curves to obtain a regression equation for the relationship between cadmium concentrations;

[0067] S220) Measure the concentration of available cadmium in the extract

[0068] The concentration of effective cadmium in the extract was measured by inductively coupled plasma mass spectrometry using a standard curve;

[0069] S221) Dilute the blank sample 10 times with 1% HNO3 solution and inject it into the inductively coupled plasma mass spectrometer to measure the intensity value of effective cadmium, substitute it into the regression equation, and calculate the concentration of effective cadmium in the blank sample;

[0070] S222) diluting the extract 10 times with a 1% HNO3 solution and injecting the solution into an inductively coupled plasma mass spectrometer to measure the intensity of the effective cadmium and substitute it into the regression equation to calculate the concentration of the effective cadmium in the extract;

[0071] S223) Determine the concentration of effective cadmium in the extract by the formula c=c1 f1-c0 f0, wherein c0 is the concentration of effective cadmium in the blank sample, in μg / L; c1 is the concentration of effective cadmium in the extract calculated in step S222, in μg / L; f0 is the dilution factor of the blank sample; f1 is the dilution factor of the extract;

[0072] S300) Result Analysis

[0073] S310) Determine the content of plant-available cadmium in soil samples

[0074] According to the mass of the measured soil sample and the concentration of the measured extract, the content of plant-available cadmium in the measured soil sample is calculated using the following formula:

[0075]

[0076] Where: W The plant-available cadmium content in the measured soil sample is in mg / kg; c is the concentration of available cadmium in the measured extract, in μg / L; V 1 is the volume of deionized water added, in mL; V 2 is the volume of calcium chloride extract added, in mL; m is the mass of the measured soil sample, in g;

[0077] S400) Verification

[0078] S410) Potted Plant Verification

[0079] S411) The test soils were soil samples numbered GY1-3, QY1-3, and CN1-3. Plastic pots with a diameter of 25 cm and a height of 25 cm were used, each pot was filled with 5 kg of soil, and 2 rice plants were planted in each pot. Each treatment was repeated three times;

[0080] There are two rice varieties for testing, namely Xiangzaoxian 24 and Zhuliangyou 189;

[0081] Before transplanting rice seedlings, nitrogen, phosphorus and potassium fertilizers need to be mixed with the soil, and tap water is added to the potting soil to maintain a 2-3 cm water layer. After 7 days of balancing, transplant the rice seedlings. Maintain the same water depth throughout the growth period. Sunbathe the fields for 10 days in the late tillering stage and 15 days in the late filling stage.

[0082] S412) Samples were collected during the rice maturity period, and the cadmium content of rice grains was determined according to the national standard method;

[0083] S413) Linear regression analysis was performed between the plant-available cadmium content in soil samples and the cadmium content in rice to verify the accuracy and precision of this method in characterizing the plant availability of cadmium in moderately alkaline paddy soils;

[0084] S420) Regional Verification

[0085] S421) During the rice maturity period, the corresponding small watersheds of the original sites where the soil samples numbered GY1-3, QY1-3, and CN1-3 were collected (Guiyang County, Chenzhou City, Hunan Province, Qiyang City, Yongzhou City, and Changning City, Hengyang City) were selected, and soil-rice one-to-one samples were collected in the moderately alkaline cadmium-contaminated rice fields on both sides along the irrigation canal. The rice growth conditions of the selected rice fields were similar. A total of 50 groups of soil samples and rice samples were collected. The sampling points were all representative local fields, and the five-point sampling method was adopted;

[0086] S422) Verify the moderately alkaline paddy field soil samples (pH ≥ 6.12) and determine the content of plant-available cadmium in the soil samples, the same as steps S100, S200 and S300; the cadmium content in rice grains is determined according to the national standard method; perform a linear regression analysis between the content of plant-available cadmium in the soil samples and the content of cadmium in rice to verify the field applicability of this method.

[0087] Embodiment 1~3

[0088] Under the incubation time of 12 hours, the moisture content of Example 1 is 35% of the maximum water holding capacity of the soil; the moisture content of Example 2 is 65% of the maximum water holding capacity of the soil; and the moisture content of Example 3 is 110% of the maximum water holding capacity of the soil.

[0089] The linear regression relationship between the test results and the cadmium content in rice grains is as follows: Figure 1As shown in a, b, and c, it can be seen that Example 1 ( Figure 1 a) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Xiangzaoxian 24 (R1 2 =0.9143) is better than Example 2 ( Figure 1 b)(R1 2 =0.8872) and Example 3 (R1 2 =0.9056); Example 3 ( Figure 1 c) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Zhuliangyou 189 (R2 2 =0.9386) is better than Example 1 (R2 2 =0.9383) and Example 2 (R2 2 =0.9269).

[0090] Embodiment 4-6

[0091] Under the 24-hour cultivation time, the moisture content of Example 4 is 35% of the maximum water holding capacity of the soil; the moisture content of Example 5 is 65% of the maximum water holding capacity of the soil; and the moisture content of Example 6 is 110% of the maximum water holding capacity of the soil.

[0092] The linear regression relationship between the test results and the cadmium content in rice grains is as follows: Figure 2 As shown in a, b, and c, it can be seen that Example 5 ( Figure 2 b) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Xiangzaoxian 24 (R1 2 =0.8992) is better than Example 4 ( Figure 2 a)(R1 2 =0.8888) and Example 6 (R1 2 =0.8972); Example 6 ( Figure 2 c) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Zhuliangyou 189 (R2 2 =0.9395) is better than Example 4 (R2 2 =0.9245) and Example 5 (R2 2 =0.9130).

[0093] Embodiment 7~9

[0094] Under the 48-hour incubation time, the moisture content of Example 7 was 35% of the maximum soil water holding capacity; the moisture content of Example 8 was 65% of the maximum soil water holding capacity; and the moisture content of Example 9 was 110% of the maximum soil water holding capacity. The linear regression relationship between the test results and the cadmium content in rice grains is as follows: Figure 3 As shown in a, b, and c, it can be seen that Example 8 ( Figure 3b) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Xiangzaoxian 24 (R1 2 =0.9099) is better than Example 7 ( Figure 3 a)(R1 2 =0.8962) and Example 9 ( Figure 3 c)(R1 2 =0.8771); Linear correlation between the effective cadmium content determined in Example 8 and the cadmium content in rice grains of Zhuliangyou No. 189 (R2 2 =0.9349) is better than Example 7 (R2 2 =0.9293) and Example 9 (R2 2 =0.9243).

[0095] from Figure 1 , Figure 2 and Figure 3 In summary, compared with Examples 2 to 9, the extraction results of Example 1 are better, and the correlation between the available cadmium content in soil and the cadmium content in the two rice grains (R1 2 =0.9143, R2 2 =0.9383) is the best. This shows that this method can better characterize the phytoavailability of cadmium in moderately alkaline paddy soil.

[0096] Comparative Example 1

[0097] Chemical extraction method, the extractant is CaCl2.

[0098] Comparative Example 2

[0099] Chemical extraction method, the extractant is HCl.

[0100] Comparative Example 3

[0101] Chemical extraction method, the extraction agent is DTPA.

[0102] The linear regression results between the plant-available cadmium content in the soil and the rice grain content determined in Comparative Examples 1-3 are as follows: Figure 4 As shown in a, b, and c, the CaCl2 extraction method ( Figure 4 a) Linear correlation between the measured available cadmium content and the cadmium content in rice grains of Xiangzaoxian 24 (R1 2 =0.5475) and the linear correlation between the cadmium content in the grain of Zhuliangyou 189 rice (R2 2 =0.7565) are superior to the other two chemical extraction states ( Figure 4 b: HCl: R1 2 =0.4265, R2 2 =0.4289; Figure 4 c:DTPA:R1 2=0.4546, R2 2 =0.4156).

[0103] Then, the results of Examples 1 to 9 of the present invention (R 2 > 0.87) are superior to the CaCl2 extraction method, so the present invention can better characterize the plant effectiveness of cadmium in moderately alkaline paddy soil than the conventional chemical extraction method.

[0104] Comparative Example 4

[0105] DGT technical measurement.

[0106] The linear regression results are as follows Figure 5 As shown in the figure, there is a linear correlation between the effective cadmium content determined by DGT technology and the cadmium content in the grains of the two rice varieties (R1 2 =0.7514, R2 2 =0.7163) is lower than that of Examples 1 to 9 (R 2 > 0.87), so the present invention can better characterize the plant effectiveness of cadmium in moderately alkaline paddy soil.

[0107] Example 10

[0108] This method was validated in a regional manner. The corresponding small watershed of the original site of the soil sample was selected. Sample points were randomly selected in the medium-alkaline cadmium-contaminated rice fields on both sides along the irrigation canal. Soil samples and rice samples were collected in situ during the rice maturity period. The content of plant-available cadmium in the soil samples and the cadmium in the rice were determined, and a linear regression analysis was performed on the two to verify the field applicability of this method. The moisture content of Example 10 was 35% of the maximum water holding capacity of the soil, and the incubation time was 12h. According to the linear regression results (such as Figure 6 As shown in Figure 10, it can be seen that the linear correlation R between the effective cadmium content measured in Example 10 and the cadmium content in rice grains 2 =0.4572, slope k=1.3536, which is consistent with the slope trend of the equation in Example 1 (k1=1.4427, k2=1.1469).

[0109] Comparative Example 5

[0110] The test soil and rice samples were the same as those in Example 10, and the content of available cadmium was directly determined by the conventional method of air-dried soil samples. The linear regression relationship between the test results of Comparative Example 5 and the cadmium content of rice grains is shown in Figure 7 The linear correlation between the effective cadmium content and the cadmium content in rice grains measured in Comparative Example 5 is R 2 =0.2223, lower than Example 10 (R 2=0.4572); slope k=1.4670, which is consistent with the trend of Example 10 (k=1.3536). This shows that this method can better characterize the plant effectiveness of cadmium in moderately alkaline paddy soil than conventional methods.

[0111] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. Various modifications to these embodiments will be obvious to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown in this article, but will comply with the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for extracting plant-available cadmium from moderately alkaline paddy soil, characterized in that: The following steps are involved: Step 1: Sample collection and processing (1.1) Collect soil samples from the plough layer of moderately alkaline paddy fields, air-dry them naturally, crush them, grind them and pass them through a 20-mesh sieve to obtain soil samples; (1.2) Weigh the soil sample from step (1.1) and place it in a centrifuge tube. Add deionized water to adjust the soil moisture content to 35%-110% of the maximum water holding capacity of the soil. Cover the tube and balance at room temperature for 12h-48h. Then add calcium chloride extract and extract in a constant temperature horizontal oscillator. After the extraction is completed, filter to obtain the extract for testing; Step 2: Determination of effective cadmium concentration in the extract (2.1) Using inductively coupled plasma mass spectrometry to establish a standard curve for determining different concentrations of available cadmium; (2.2) Using an inductively coupled plasma mass spectrometer to measure the concentration of effective cadmium in the extract using a standard curve; Step 3: Result Analysis According to the mass of the measured soil sample and the concentration of available cadmium in the measured extract, the content of plant available cadmium in the measured soil sample is calculated. The calculation formula is as follows: Where: W The plant-available cadmium content in the measured soil sample is in mg / kg; c is the concentration of available cadmium in the measured extract, in μg / L; V 1 is the volume of deionized water added, in mL; V 2 is the volume of calcium chloride extract added, in mL; m is the mass of the soil sample measured in g.

2. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 1, characterized in that: The concentration of the calcium chloride extract in step (1.2) is 0.1 mol / L, the volume ratio of the soil sample mass to the calcium chloride extract is 1:5 g / mL, and the total soil-water ratio is 1:5.21-5.66 g / mL.

3. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 2, characterized in that: In step (1.2), deionized water was used to adjust the soil moisture content to 35% of the maximum water holding capacity of the soil; the equilibrium time was 12 h, and the total soil-water ratio was 1:5.21 g / mL.

4. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 1, characterized in that: The extraction conditions in step (1.2) were: 25°C, 180 r / min, and extraction for 2 h.

5. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 1, characterized in that: The specific process of establishing the standard curve of different concentrations in step (2.1) is as follows: (2.1.1) Take 1 mL of 1000 mg / L cadmium standard working solution and place it in a 100 mL volumetric flask. Make up to volume with 1% HNO3 solution to prepare a cadmium standard working solution with a cadmium concentration of 10 mg / L. (2.1.2) Take 0 mL, 0.01 mL, 0.05 mL, 0.1 mL, 0.2 mL and 0.4 mL of the cadmium standard working solution with a cadmium concentration of 10 mg / L and place it in a 100 mL volumetric flask, add 10 mL of 0.1 mol / L calcium chloride solution, and dilute to the scale with 1% HNO3 solution to prepare cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L; (2.1.3) Inject cadmium standard working solutions with cadmium concentrations of 0 μg / L, 1 μg / L, 5 μg / L, 10 μg / L, 20 μg / L and 40 μg / L into the inductively coupled plasma mass spectrometer in sequence. Use the concentration of the cadmium standard working solution as the horizontal axis and the intensity of the effective cadmium as the vertical axis. The inductively coupled plasma mass spectrometer automatically plots standard curves of different cadmium concentrations, and linearly regresses the standard curves to obtain the regression equation for the cadmium concentration relationship.

6. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 1, characterized in that: The specific steps of step (2.2) are: The extract was diluted 10-100 times with 1% HNO3 solution and then injected into the inductively coupled plasma mass spectrometer to measure the intensity value of the effective cadmium. The value was substituted into the standard curve regression equation of step (2.1) to calculate the concentration of effective cadmium in the extract.

7. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 6, characterized in that: In step (1.2), a blank sample is prepared while preparing the extract. The method for preparing the blank sample comprises the following steps: Place 25 mL of 0.1 mol / L calcium chloride extract in a centrifuge tube with a lid, extract at 180 r / min for 2 h in a 25°C constant temperature horizontal oscillator, let stand, and take the supernatant to pass through quantitative filter paper to prepare a blank sample.

8. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 7, characterized in that: The specific steps of step (2.2) are: (2.2.1) Dilute the blank sample 10-100 times with 1% HNO3 solution and inject it into the inductively coupled plasma mass spectrometer to measure the intensity value of effective cadmium. Substitute it into the standard curve regression equation to calculate the concentration of effective cadmium in the blank sample; (2.2.2) Inject the extract into an inductively coupled plasma mass spectrometer to measure the intensity value of the effective cadmium, substitute it into the regression equation, and calculate the concentration of the effective cadmium in the extract; (2.2.3) Determine the concentration of available cadmium in the extract using the formula c = c1 f1 - c0 f0, where c0 is the concentration of available cadmium in the blank sample, in μg / L; c1 is the concentration of available cadmium in the extract calculated in step (2.2), in μg / L; f0 is the dilution factor of the blank sample; and f1 is the dilution factor of the extract.

9. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 1, characterized in that: Also includes: Step 4: Verification (4.1) Potted plant validation: The soil collected from the test paddy field was used for potted plant experiments. Conventional water management was adopted. Samples were taken at the rice maturity stage and the cadmium content in rice grains was determined. Linear regression analysis was performed between the plant-available cadmium content in the soil samples and the cadmium content in rice grains to verify the accuracy and precision of this method in characterizing the plant-available cadmium in paddy field soil. (4.2) Regional validation: Select the corresponding small watershed of the original site of the above-mentioned soil samples, and randomly select sampling points in the neutral-alkaline cadmium-contaminated rice fields on both sides along the direction of the irrigation canal; collect soil samples and rice samples one-to-one in situ during the rice maturity period, determine the content of plant-available cadmium in soil samples and cadmium in rice, and perform linear regression analysis on the two to verify the field applicability of this method.

10. The method for extracting plant-available cadmium from moderately alkaline paddy soil according to claim 9, characterized in that: The rice varieties tested in potted plant verification were Xiangzaoxian 24 and Zhuliangyou 189. The rice growth conditions in the sample rice fields selected for regional verification were similar.

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