Comprehensive evaluation method for soil pollution in decommissioned uranium mine area

Abstract

The invention discloses a comprehensive evaluation method for soil pollution in a decommissioned uranium mine area, relates to the technical field of environmental evaluation, and solves the technical problem that a soil pollution evaluation method is not clear due to lack of soil pollution data in an existing decommissioned uranium mine area. According to the technical scheme, the method is characterized in that the influence of radionuclides, environmental ecology, environment and biological effects in the decommissioned uranium mine area soil on the soil quality is comprehensively considered, key influence factors influencing the uranium mine area soil quality can be screened out, and the problems that existing data is lack, and a research method is not clear are solved; and a basis is provided for subsequent sustainable utilization of soil and environmental health.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental evaluation, and particularly relates to a comprehensive evaluation method for soil pollution in a decommissioned uranium mining area. BACKGROUND

[0002] Soil quality is a comprehensive concept, which cannot be directly measured and evaluated, and can be evaluated or judged only by measuring a series of indexes. Scientific selection of evaluation indexes directly determines whether the result is correct or not. An ideal soil quality index not only has representativeness, sensitivity, universality, operability and repeatability, but also has a threshold and an adaptive range, which can be quantified as data.

[0003] With the rapid development of national defense and nuclear power, the demand for natural uranium is increasing, which requires increasing the scale of uranium mining and smelting, which makes more and more soil contaminated by radionuclides. Unlike other heavy metal contaminated soil, uranium tailing soil pollution is a complex pollution of multiple radionuclides, associated heavy metals and organic matter. Therefore, it is necessary to comprehensively evaluate the soil quality in the uranium mining area to provide reasonable suggestions for the sustainable use of land. Effective soil quality evaluation can improve soil productivity and maintain soil sustainability, and has a positive effect on promoting soil ecological balance and protecting human health.

[0004] At present, the evaluation of soil pollution risk and soil quality mainly focuses on heavy metals such as copper, cadmium and lead, and the evaluation of soil quality of radioactive pollution existing in uranium mining areas has not been carried out. SUMMARY

[0005] The present application provides a comprehensive evaluation method for soil pollution in a decommissioned uranium mining area, which solves the problems of lack of existing data and unclear research methods, and provides a basis for subsequent soil sustainable use and environmental health.

[0006] The above technical purpose of the present application is realized by the following technical scheme:

[0007] A comprehensive evaluation method for soil pollution in a decommissioned uranium mining area, comprising:

[0008] Selecting evaluation indexes, wherein the evaluation indexes include concentration distribution of radioactive pollutants, soil physicochemical properties, soil microbial activity and soil microbial diversity;

[0009] Standardizing each evaluation index, so that the average value of each evaluation index is 0 and the standard deviation is 1, to obtain standardized evaluation indexes;

[0010] Analyzing the standardized evaluation indexes by principal component analysis to obtain a principal component factor score coefficient matrix corresponding to the soil biological indexes;

[0011] The soil fertility comprehensive index value is calculated according to the principal component factor score coefficient matrix;

[0012] The soil fertility comprehensive index value is evaluated according to the improved Nemerow comprehensive pollution index method, and the soil comprehensive environmental quality degree grade is obtained;

[0013] The improved Nemerow comprehensive pollution index method is expressed as:

[0014]

[0015] Among them, The average value of the soil fertility comprehensive index value is represented by S; The maximum value of the soil fertility comprehensive index value is represented by S.

[0016] Preferably, the indicators required to measure the concentration distribution of radioactive pollutants include 238 U, 226 Ra, 90 Sr and 137 Cs.

[0017] Preferably, the indicators required to measure the soil physicochemical properties include pH, organic matter, total nitrogen, total phosphorus, exchangeable calcium, exchangeable magnesium, exchangeable potassium and exchangeable sodium.

[0018] Preferably, the indicators required to measure the soil microbial activity include soil urease, soil phosphatase and soil peroxidase.

[0019] Preferably, the indicators required to measure the soil microbial diversity include the number of bacteria, the number of fungi and the number of actinomycetes.

[0020] Preferably, the indicators required to measure the concentration distribution of radioactive pollutants also include heavy metal indicators, namely Ba, Al, Co, Cd, Pb, Ag and Li.

[0021] Preferably, the standardization processing of each evaluation indicator is expressed as:

[0022]

[0023] Among them, i represents the sample number, i = 1, 2, 3, …, n; j represents the index number, j = 1, 2, 3, …, m; S j The standard deviation of the jth index is represented by S The average value of the jth index is represented by S ij The data before standardization is represented by X ij The data after standardization is represented by X

[0024] Preferably, the soil fertility comprehensive index value is represented as:

[0025]

[0026] wherein Ai represents the contribution rate of different concentration blocks of soil; and Yi represents the principal component factor score coefficient.

[0027] Y i = Y ij X ij '

[0028] wherein Y ij represents the value in the principal component factor score coefficient matrix, and X ij ' represents the normalized data.

[0029] Preferably, the soil comprehensive environmental quality degree grade includes:

[0030] When IFI N ≤ 0.7, the soil comprehensive environmental quality degree grade is clean;

[0031] When 0.7 < IFI N ≤ 1, the soil comprehensive environmental quality degree grade is still clean;

[0032] When 1 < IFI N ≤ 2, the soil comprehensive environmental quality degree grade is slightly polluted;

[0033] When 2 < IFI N ≤ 3, the soil comprehensive environmental quality degree grade is moderately polluted;

[0034] When IFI N > 3, the soil comprehensive environmental quality degree grade is moderately polluted.

[0035] Preferably, when IFI N > 2, the external exposure of γ rays of γ nuclides needs to be considered, and the dose coefficient estimation of γ rays of γ nuclides is represented as:

[0036] D = E · (1- φ(E));

[0037] wherein D represents the dose coefficient, φ(E) is the energy absorption fraction, and E represents the energy of the nuclide.

[0038]

[0039] wherein σ, n, a, λ, and m all represent the best fitting parameters for γ photons.

[0040] The application has the beneficial effects that the comprehensive evaluation method for soil pollution in the decommissioned uranium mine area comprehensively considers the influence of radionuclides, environmental ecology, environment and biological effects on the soil quality in the decommissioned uranium mine area, can screen out the key influencing factors affecting the soil quality in the uranium mine area, solves the problems of lack of existing data and unclear research method, and provides a basis for subsequent soil sustainable utilization and environmental health. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The process flow chart of the comprehensive evaluation method for soil pollution in the decommissioned uranium mine area is shown. DETAILED DESCRIPTION

[0042] The technical solutions of the application will be described in detail below with reference to the drawings.

[0043] The comprehensive evaluation method for soil pollution in the decommissioned uranium mine area is shown in Figure 1 The comprehensive evaluation method for soil pollution in the decommissioned uranium mine area is shown in

[0044] 100: selecting evaluation indexes, the evaluation indexes including radionuclide concentration distribution, soil physicochemical properties, soil microbial activity and soil microbial diversity.

[0045] Preferably, there are generally multiple uranium tailing pollutants, and in the radionuclide concentration distribution, the indexes that must be measured include 238 U, 226 Ra, 90 Sr and 137 Cs, and the optional indexes are heavy metals such as Ba, Al, Co, Cd, Pb, Ag and Li.

[0046] Preferably, the indexes that need to be measured in the soil physicochemical properties include pH, organic matter, total nitrogen, total phosphorus, exchangeable calcium, exchangeable magnesium, exchangeable potassium and exchangeable sodium.

[0047] Preferably, the indexes that need to be measured in the soil microbial activity include soil urease, soil phosphatase and soil peroxidase.

[0048] Preferably, the indexes that need to be measured in the soil microbial diversity include the number of bacteria, the number of fungi and the number of actinomycetes.

[0049] 101: standardizing each evaluation index, so that the average value of each evaluation index is 0 and the standard deviation is 1, to obtain a standardized evaluation index.

[0050] Each evaluation index has different dimensions, and there are large differences in the absolute values and amplitudes between the indexes, even several orders of magnitude, so the original data need to be standardized before applying the principal component analysis method to analyze the soil quality.

[0051] Preferably, the evaluation indicators are standardized and represented as:

[0052]

[0053] wherein i represents the sample number, i = 1, 2, 3, …, n; j represents the index number, j = 1, 2, 3, …, m; S j represents the standard deviation of the jth index; i j represents the jth index in the ith sample; represents the average value of the jth index; X ij represents the non-standardized data; X ij represents the standardized data.

[0054] 102: Analyze the standardized evaluation indicators by principal component analysis to obtain a principal component factor score coefficient matrix corresponding to the soil biological indicators.

[0055] Specifically, the obtained biological indicators are processed by principal component analysis software such as SPSS, SIMCA-P, PAST, etc.

[0056] 103: Calculate the soil fertility comprehensive index value according to the principal component factor score coefficient matrix.

[0057] Preferably, the soil fertility comprehensive index value is represented as:

[0058]

[0059] wherein Ai represents the contribution rate of the soil in different concentration blocks; Yi represents the principal component factor score coefficient;

[0060] Y i = Y ij X ij ′; (3)

[0061] wherein Y ij represents the value in the principal component factor score coefficient matrix, X ij ' represents the standardized data.

[0062] 104: Evaluate the soil fertility comprehensive index value according to the improved Nemerow comprehensive pollution index method to obtain the soil comprehensive environmental quality degree grade.

[0063] Preferably, the improved Nemerow comprehensive pollution index method is represented as:

[0064]

[0065] wherein, an average value of the comprehensive index value of soil fertility; a maximum value of the comprehensive index value of soil fertility.

[0066] The traditional Nemerow comprehensive pollution index method focuses on judging the combined effect of multiple pollutants, and ignores environmental ecology, environmental and biological effects, etc. In the present application, the evaluation index is replaced by the comprehensive index value of soil fertility IFI, which can comprehensively reflect the overall apparent characteristics of the harm of the four indexes of radioactive pollutant concentration distribution, soil physical and chemical properties, soil microbial activity, and soil microbial diversity to uranium tailing contaminated soil.

[0067] Specifically, according to the Nemerow pollution index classification standard of uranium tailing low pollution, medium pollution, and high pollution soil, the soil comprehensive environmental quality degree is divided into 5 levels, including:

[0068] When IFI N ≤ 0.7, the soil comprehensive environmental quality degree level is clean (safe);

[0069] When 0.7 < IFI N ≤ 1, the soil comprehensive environmental quality degree level is still clean (warning line);

[0070] When 1 < IFI N ≤ 2, the soil comprehensive environmental quality degree level is slightly polluted;

[0071] When 2 < IFI N ≤ 3, the soil comprehensive environmental quality degree level is moderately polluted;

[0072] When IFI N > 3, the soil comprehensive environmental quality degree level is moderately polluted.

[0073] Preferably, when IFI N > 2, the radioactivity of radioactive pollutants to the surrounding environment (including animals, plants, and microorganisms) should be considered, and the dose coefficient of the main γ nuclides in the uranium mining area can be selected. The main γ nuclides to be considered are 222 Rn, 226 Ra.

[0074] The dose coefficient estimation of γ nuclides is represented as:

[0075] D = E · (1- φ(E));

[0076] Wherein, D represents the dose coefficient, φ(E) is the energy absorption fraction; E represents the energy of the nuclide;

[0077]

[0078] wherein s, n, a, l and m are the best fitting parameters for the gamma photons.

[0079] The following is a specific implementation case:

[0080] A certain southern retired uranium mine soil comprehensive evaluation

[0081] (1) Sampling area overview: the sampling area is located in Guangdong retired uranium mine area, which belongs to the humid subtropical monsoon climate zone, with an average annual temperature of 19.7℃, an average annual rainfall of 1715mm, and vegetation type belonging to subtropical evergreen forest. Four sampling sites were set up, with site numbers D45, D64, D48 and D56.

[0082] (2) Evaluation index:

[0083] A, the index for measuring the concentration distribution of radioactive pollutants is 238 U, 226 Ra, 90 Sr, 137 Cs;

[0084] B, the index for measuring the soil physical and chemical properties is pH, organic matter, total nitrogen, total phosphorus, exchangeable calcium, exchangeable magnesium, exchangeable potassium and exchangeable sodium;

[0085] C, the index for measuring soil microbial activity is soil urease, soil phosphatase and soil peroxidase.

[0086] D, the index for measuring microbial diversity is the number of bacteria, fungi and actinomycetes.

[0087] (3) Standardization of evaluation system index: the original values of different soil indexes in different sample sites were determined, and the standardized values were calculated by formula (1). The original values and standardized values of soil indexes in different concentration blocks are shown in Table 1.

[0088] Table 1 Original values and standardized values of soil indexes in different concentration blocks

[0089]

[0090]

[0091] Wherein E is the measured value, F is the value after standardization, and the positive and negative values do not represent the actual meaning, but only represent the relative size.

[0092] (4) Principal component analysis of evaluation index: the principal component analysis software used is SPSS17.0, and the coefficient matrix, eigenvalue and contribution rate are obtained, as shown in Table 2.

[0093] From Table 2, the first principal component Y1 mainly reflects the comprehensive variables of radium, cesium, strontium, uranium, soil phosphatase, peroxidase, organic matter, pH, exchangeable calcium, exchangeable magnesium, number of fungi, and number of actinomycetes, which accounts for 58.32% of the total, indicating that these indexes play a very important role in soil quality evaluation and can sensitively indicate the change of soil quality.

[0094] The second principal component Y2 reflects total phosphorus and exchangeable potassium, which accounts for 26.98% of the total, indicating that these indexes also have a certain effect on soil quality evaluation, but not as obvious as Y1.

[0095] The third principal component Y3 reflects the number of soil bacteria, which accounts for 14.69% of the total, and has a smaller effect.

[0096] Table 2 Principal component factor coefficient matrix, eigenvalue and contribution rate of soil quality evaluation indexes

[0097]

[0098]

[0099] Among them, the evaluation indexes are 18 in total.

[0100] The 8 biological indexes obtained by analysis are processed to obtain the score coefficient matrix of the principal components Y1, Y2, and Y3 of soil biological indexes, as shown in Table 3.

[0101] Table 3 Principal component score coefficient matrix

[0102]

[0103] Among them, the evaluation indexes are 18 in total.

[0104] According to the regression method, the score functions of the three principal components can be obtained from Table 3, as shown in formulas (5), (6), and (7):

[0105] F1 = -0.078x1 + 0.089x2 + 0.084x3 - 0.085x4 + … + 0.077x 17 -0.089x 18 ; (5)

[0106] F2 = 0.09x1 + 0.068x2 + 0.095x3 - 0.011x4 + … + 0.118x 17 -0.069x 18 ; (6)

[0107] F3 = 0.146x1 - 0.054x2 - 0.025x3 + 0.173x4 + … - 0.047x17 -0.028x 18 (7)

[0108] (5) Construction and application of a comprehensive evaluation system for uranium-contaminated soil

[0109] Formula (2) was used to calculate and rank the soil quality of uranium-contaminated soil samples as the final evaluation of soil quality. The calculation results are shown in Table 4.

[0110] As shown in Table 4, after comprehensively ranking the indicators, the results are D45 > D48 > D64 > D56, indicating that uranium concentration has a significant impact on soil quality. The lowest uranium concentration was found in plot D45, at 14.68 mg·kg⁻¹. -1 Its soil comprehensive evaluation index score was the highest, and the D56 uranium contamination concentration in the sample plot was the highest, at 154 mg·kg⁻¹. -1 Its soil comprehensive evaluation index score was the lowest. This indicates that in decommissioned uranium mining areas, the content of radioactive nuclides in the soil can affect soil quality. When making subsequent comprehensive utilization of the soil, effective measures should be taken to remove radioactive nuclides from the soil.

[0111] Table 4. Ranking of Principal Component Scores and Soil Biological Indicators

[0112]

[0113] (5) Comprehensive Environmental Quality Index Assessment

[0114] The IFI of the uranium ore area was calculated using equation (4). N =0.8, the evaluation result is still clean (warning line). The above are exemplary embodiments of this application, and the scope of protection of this application is defined by the claims and their equivalents.

Claims

1. A comprehensive evaluation method for soil pollution in a decommissioned uranium mine area, characterized in that, The method comprises the following steps: selecting evaluation indexes, including radioactive pollutant concentration distribution, soil physicochemical properties, soil microbial activity, and soil microbial diversity; standardizing each evaluation index, so that the average value of each evaluation index is 0 and the standard deviation is 1, to obtain standardized evaluation indexes; analyzing the standardized evaluation indexes by principal component analysis to obtain a principal component factor score coefficient matrix corresponding to the soil biological indexes; calculating the soil fertility comprehensive index value according to the principal component factor score coefficient matrix; evaluating the soil fertility comprehensive index value according to the improved Nemerow comprehensive pollution index method to obtain the soil comprehensive environmental quality degree grade; The improved Nemerow comprehensive pollution index method is expressed as: wherein, represents an average value of the comprehensive index value of soil fertility; represents a maximum value of the comprehensive index value of soil fertility.

2. The method of claim 1, wherein, The radioactive contaminant concentration profile needs to be measured for indicators including 238 U, 226 Ra, 90 Sr and 137 Cs.

3. The method of claim 1, wherein, The indexes of the soil physicochemical properties that need to be measured include pH, organic matter, total nitrogen, total phosphorus, exchangeable calcium, exchangeable magnesium, exchangeable potassium, and exchangeable sodium.

4. The method of claim 1, wherein, The indexes of the soil microbial activity that need to be measured include soil urease, soil phosphatase, and soil peroxidase.

5. The method of claim 1, wherein, The indexes of the soil microbial diversity that need to be measured include the number of bacteria, the number of fungi, and the number of actinomycetes.

6. The method of claim 2, wherein, The indexes of the radioactive pollutant concentration distribution that need to be measured also include heavy metal indexes, namely Ba, Al, Co, Cd, Pb, Ag, and Li.

7. The method of claim 1, wherein, The standardization of each evaluation index is expressed as: where i represents the sample number, i = 1, 2, 3, …, n; j represents the index number, j = 1, 2, 3, …, m; S j represents the standard deviation of the jth index; ij represents the jth index in the ith sample; represents the average value of the jth index; X ij represents the data without standardization; X ij represents the data after standardization.

8. The method of claim 1, wherein, The soil fertility comprehensive index value is expressed as: wherein Ai represents the contribution rate of the soil in different concentration blocks, and Yi represents the principal component factor score coefficient. Y i = Y ij X' ij where Y ij represents a value in the principal component factor score coefficient matrix, X ij represents the standardized data.

9. The method of claim 1, wherein, The soil comprehensive environmental quality degree grade includes: When IFI N ≤ 0.7, the soil comprehensive environmental quality degree is clean; When 0.7 < IFI N When 0.7 < IFI N When 0.7 < IFI N When 0.7 < IFI N When 0.7 < IFI < When 1 < IFI N When 1 < IFI N When 1 < IFI N When 1 < IFI N When 1 < IFI N When 1 < When 2 < IFI N When 2 < IFI When IFI N >3, the degree of soil comprehensive environmental quality is moderate pollution.

10. The method of claim 9, wherein, When IFI N >2, the gamma external exposure of the gamma emitters has to be considered and the dose coefficient estimate for the gamma emitters is expressed as: D = E · (1-φ(E)); wherein D represents the dose coefficient, φ(E) is the energy absorption fraction, and E represents the energy of the nuclide; wherein σ, n, a, λ, and m all represent the best fitting parameters for γ photons.

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