Evaluation method for combined pollution caused by coexistence of multiple heavy metals in regional soil and potential ecological risk of combined pollution

Abstract

The invention discloses a method for evaluating combined pollution of coexistence of multiple heavy metals in regional soil and potential ecological risks of the combined pollution. The method comprises the following steps: sampling, investigating and analyzing the regional soil; determining the toxicity coefficient of each heavy metal after improvement; the improved toxicity coefficient of the heavy metal elements which have no obvious influence on the diversity of soil microbial communities is used as an improved toxicity response factor; the method comprises the following steps: determining an improved toxicity response factor of heavy metal elements having significant influence on diversity of soil microbial communities according to an improved toxicity coefficient of the heavy metal elements and a regional soil microbial sequencing result; determining an improved single potential ecological risk index and an improved comprehensive potential ecological risk index of each heavy metal according to the actually measured concentration of each heavy metal, the environmental background value, the improved toxicity response factor and the contents of various occurrence forms; and evaluating the single heavy metal pollution risk degree and the comprehensive pollution risk degree of the regional soil.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollution assessment, and particularly relates to an assessment method for the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks. Background Art

[0002] Carrying out the risk assessment of heavy metal pollution in regional soil is a prerequisite for understanding the current situation of heavy metal pollution and identifying key polluted areas for control. Considering that heavy metal pollution in regional soil usually involves multiple heavy metal elements, when formulating prevention and control strategies for heavy metal pollution in soil, it is often necessary to first identify the main heavy metal elements and give priority to their control. Therefore, obtaining a true and accurate risk assessment result of heavy metal pollution in regional soil is crucial.

[0003] Using the potential ecological risk index method to evaluate the ecological risk of heavy metal pollution in soil is one of the important methods widely used and generally recognized in the current field of heavy metal risk assessment in soil. The potential ecological risk index method (hereinafter referred to as the Hakanson index method) can objectively reflect the potential ecological risk of heavy metals in the soil of the study area and give a relatively reasonable evaluation result. However, with the increase of relevant research cases, its deficiencies have gradually emerged. First, the Hakanson index method was initially developed based on sediment theory. Due to the different physical and chemical properties of sediments and soils, many parameters and formulas used by Hakanson in the derivation process are not applicable to soils. Second, heavy metals in regional soil often migrate and transform in different occurrence forms, and the migration and biological toxicity of heavy metals in different occurrence forms are different, and their risk contributions to the ecological environment are also different. As a result, it is difficult for the Hakanson index method based on the total amount of heavy metals to obtain a comprehensive and accurate evaluation result. In addition, different environmental conditions (such as soil parent material, land use type, soil pH value, etc.) will also lead to differences in the sensitivity of different regional soils to heavy metal pollution, and the Hakanson index method lacks sufficient consideration of soil ecological heterogeneity, and there are prone to problems such as incomplete risk assessment results and low reliability.

[0004] Heavy metals in soil have the characteristics of wide pollution range, long duration, strong concealment, difficult biodegradation and great ecological harm. As an important environmental pollution prevention and control index for regional soil heavy metals, a comprehensive and scientific risk assessment system needs to be established. Accurately evaluating the ecological risk of regional soil heavy metals is an important basis for realizing risk control and environmental protection.

[0005] A method for assessing the ecological risk of heavy metals in soil in the prior art includes the following steps:

[0006] Determine the concentration of target heavy metals at sampling points in the study area Collect the concentration data of the soil environmental background value of the target heavy metals in the study area Calculate the pollution coefficients of single heavy metals at each point According to the pollution coefficients of single heavy metals Multiply by the corresponding toxicity response factors Calculate the potential ecological risk index of single heavy metals Add up the single potential ecological risk indices of all heavy metals at each point to obtain the potential ecological risk index RI of soil heavy metal pollution at that point. According to the corresponding risk assessment criteria, the potential ecological risk level of soil heavy metal combined pollution at that point is further obtained.

[0007] The disadvantages of the above-mentioned method for evaluating the potential ecological risk of soil heavy metals include:

[0008] (1) Heavy metals in regional soil often migrate and transform in different occurrence forms. The migration and biological toxicity of heavy metals in different occurrence forms are different, and their risk contributions to the ecological environment are also different. As a result, it is difficult for the traditional potential ecological risk index method based on the total amount of heavy metals to obtain a comprehensive and accurate evaluation result.

[0009] (2) Regional soil heavy metal pollution usually has the characteristic of coexistence of multiple metals, and there are complex interactions among heavy metals. The traditional potential ecological risk index method has relatively independent evaluation results for the ecological risks of each heavy metal, does not consider the influence of the interaction of heavy metals, and does not clarify the risk assessment receptor and the toxicity effect of soil organisms. Therefore, it cannot accurately evaluate the ecological risk of regional soil heavy metal combined pollution.

[0010] (3) When characterizing the risk of regional soil heavy metal pollution, due to the small grading discrimination and strong subjectivity of the evaluation results of the traditional single and comprehensive potential ecological risk index methods, there are certain differences between the evaluation results and the actual heavy metal content change trend, and problems such as overestimation / underestimation of the risk of regional soil heavy metal pollution are likely to occur. Summary of the Invention

[0011] In view of the above technical problems and the deficiencies in the art, the present invention provides a method for evaluating the combined pollution and potential ecological risks of multiple heavy metals coexisting in regional soil, which can realize the comprehensive evaluation of the ecological risks of regional soil heavy metal pollution and improve the reliability of the evaluation results.

[0012] The method for evaluating the combined pollution and potential ecological risks of multiple heavy metals coexisting in regional soil of the present invention has the following characteristics:

[0013] 1) By incorporating the contents of different occurrence forms of each heavy metal, the present invention reasonably distinguishes the different toxicological characteristics of heavy metals in different occurrence forms, and can solve the problems that the traditional potential ecological risk index method is too one-sided and the evaluation results are inaccurate.

[0014] 2) By measuring the actual situation of combined pollution under the coexistence of multiple heavy metals, the present invention takes soil microorganisms as the receptor for ecological risk assessment, focuses on microbial diversity indicators, and uses ecological theories and related models to quantify the ecological risks caused by heavy metals to soil microorganisms. The evaluation process is more scientific and reasonable, further improving the applicability of this method.

[0015] 3) By optimizing the evaluation standard classification system of the traditional potential ecological risk index method, further considering the differences in toxicity coefficients of each heavy metal element, and reasonably deriving the risk threshold values for each level, the evaluation results are more in line with the actual situation of regional soil heavy metal pollution surveys.

[0016] The specific technical solutions are as follows:

[0017] An evaluation method for combined pollution and its potential ecological risks of multiple heavy metals coexisting in regional soil, including:

[0018] Sampling, investigating, and analyzing regional soil to obtain the measured concentrations of multiple heavy metals in regional soil, the environmental background values of regional soil heavy metals, the contents of various occurrence forms of each heavy metal, and the regional soil microbial sequencing results;

[0019] Determine the improved toxicity coefficient of each heavy metal according to the abundance of heavy metals in soil and related media;

[0020] For heavy metal elements that have no significant impact on soil microbial community diversity, use the improved toxicity coefficient of this heavy metal as its improved toxicity response factor;

[0021] For heavy metal elements that have a significant impact on soil microbial community diversity, determine its improved toxicity response factor according to the improved toxicity coefficient of this heavy metal and the regional soil microbial sequencing results;

[0022] Determine the improved single - item potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal according to the measured concentration, environmental background value, improved toxicity response factor of each heavy metal, and the content of various occurrence forms;

[0023] Evaluate the single - heavy - metal pollution risk degree and the comprehensive pollution risk degree of regional soil according to the improved single - item potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal.

[0024] In the described evaluation method for combined pollution and its potential ecological risks of multiple heavy metals coexisting in regional soil, the related media may include one or more of igneous rocks, terrestrial plants, terrestrial animals, and the upper crust.

[0025] The evaluation method for the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks. The specific calculation method of the improved toxicity coefficient may include:

[0026] First, determine the target heavy metal elements in the study area, obtain the abundance values of the target heavy metal elements in the soil and related media, calculate the ratio of the highest heavy metal element abundance in each medium to the abundances of each heavy metal element, and obtain the relative abundance values of each heavy metal element in each medium.

[0027] Second, for any target heavy metal element, eliminate the maximum value in the relative abundance values of this element in all media, and then sum up the relative abundance values of this element in the remaining media to obtain the summed relative abundance value of this heavy metal element.

[0028] Subsequently, divide the summed relative abundance values of each heavy metal element by the minimum value in the summed relative abundance values of the target heavy metal elements, and normalize to obtain the corrected summed relative abundance values of each heavy metal element; take the square root of the corrected summed relative abundance values of each heavy metal element to obtain the improved toxicity coefficient of each heavy metal.

[0029] The evaluation method for the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks. The heavy metal elements that have no significant impact on the soil microbial community diversity may include As.

[0030] The evaluation method for the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks. The heavy metal elements that have a significant impact on the soil microbial community diversity may include one or more of Cr, Cd, Pb, Zn, and Hg.

[0031] The evaluation method for the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks. For the heavy metal elements that have a significant impact on the soil microbial community diversity, according to the improved toxicity coefficient of this heavy metal and the regional soil microbial sequencing results, determine its improved toxicity response factor. The specific calculation method may include:

[0032] Through the regional soil microbial sequencing results, determine the abundances of soil microorganisms at the species level at each sampling point.

[0033] For the soil microbial community at any sampling point j, count all species with an individual number not exceeding N. Use the individual numbers 1, 2,..., N as the abscissa, where N is a positive integer, and the number of species corresponding to the individual numbers as the ordinate, draw a dot plot and fit it with the Fisher logarithmic series distribution model to obtain the fitting parameters a j value and b j value: In the formula, φ jrepresents the number of species with the same individual number x, where x = 1, 2, …, N;

[0034] Traverse all sampling points to obtain the corresponding fitting parameter a j value, where j = 1, 2, …, M, and M represents the total number of sampling points;

[0035] For any sampling point j, calculate the improved toxicity response factor of the i-th heavy metal according to the following formula where i represents the type of heavy metal, and TF i represents the improved toxicity coefficient of the i-th heavy metal, and A represents the normalization threshold.

[0036] Optionally, in some embodiments, the normalization threshold λ is the 95% quantile of {a j}.

[0037] In some embodiments, for the evaluation method of the combined pollution and potential ecological risks of multiple heavy metals in regional soils, the method for determining the improved single potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal according to the measured concentration, environmental background value, improved toxicity response factor of each heavy metal, and the content of various occurrence forms is as follows:

[0038]

[0039] In the formula: is the content of the weak acid extractable fraction of the i-th heavy metal in the soil, with the unit of mg / kg; is the content of the oxidizable fraction of the i-th heavy metal in the soil, with the unit of mg / kg; is the content of the reducible fraction of the i-th heavy metal in the soil, with the unit of mg / kg; is the content of the residual fraction of the i-th heavy metal in the soil, with the unit of mg / kg; MF i is the migration component of the i-th heavy metal in the soil; PMF i is the potential migration component of the i-th heavy metal in the soil; RF i is the residual component of the i-th heavy metal in the soil; is the corrected total concentration of the i-th heavy metal in the soil, with the unit of mg / kg; is the environmental background value concentration of the i-th heavy metal in the soil, with the unit of mg / kg; is the pollution coefficient of the corrected i-th heavy metal; is the improved toxicity response factor of the i-th heavy metal; The improved single potential ecological risk index for the i-th heavy metal; MRI is the improved comprehensive potential ecological risk index for heavy metal compound pollution in regional soil; n is the number of target heavy metal types in regional soil.

[0040] The evaluation method for the compound pollution of multiple heavy metals coexisting in regional soil and its potential ecological risk. According to the improved single potential ecological risk index for each heavy metal and the improved comprehensive potential ecological risk index, the risk degree of single heavy metal pollution and the comprehensive pollution risk degree of regional soil can be evaluated, and the grades can be divided as follows to form the improved ecological risk evaluation grading:

[0041] The first-level boundary value of the single potential ecological risk index for each heavy metal is the value of the single heavy metal potential ecological risk index assuming that the heavy metal is not polluted, that is, the heavy metal pollution coefficient is equal to 1 and the toxicity response factor is equal to the toxicity coefficient of the heavy metal. The boundary values of other risk levels are obtained by doubling in turn;

[0042] The first-level boundary value of the comprehensive potential ecological risk index for all heavy metals is obtained by summing or further taking a higher value of the first-level boundary values of the single potential ecological risk indices for each heavy metal. The boundary values of other risk levels are obtained by doubling in turn.

[0043] The evaluation method for the compound pollution of multiple heavy metals coexisting in regional soil and its potential ecological risk can use Kriging interpolation to draw the spatial distribution map of soil heavy metal content and the distribution map of heavy metal potential ecological risk index, and determine the heavy metal ecological risk level of regional soil according to the improved ecological risk evaluation grading standard.

[0044] The present invention links the occurrence forms of heavy metals with ecological effects and environmental effects, comprehensively considers the migration and transformation differences of different occurrence forms of heavy metals in soil and the corresponding biological toxicity effects, and reflects the scientificity, feasibility of the regional soil heavy metal ecological risk evaluation process and the accuracy of the evaluation results.

[0045] As can be seen from the above technical solutions, an evaluation method for the compound pollution of multiple heavy metals coexisting in regional soil and its potential ecological risk provided by the present invention improves the toxicity coefficient of heavy metals on the basis of the traditional potential ecological risk index method, and combines the occurrence forms, microbial diversity levels of each heavy metal and the corresponding ecological risk contributions, realizes the consideration of different ecological risks caused by different occurrence forms of heavy metals in regional soil, comprehensively considers the heavy metal pollution level, occurrence form, microbial response and its potential ecological risk, makes the evaluation results more real and reliable, and makes up for the lack of sufficiency of the Hakanson index method based on total heavy metals for potential ecological risk evaluation.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The present invention fully considers the characteristics of coexistence of multiple heavy metals in regional heavy metal contaminated soil, incorporates the contents of different occurrence forms of each heavy metal, can reflect to a certain extent the different toxicological characteristics of heavy metals in different occurrence forms, and can solve the problems that the grading of the evaluation results using the single-factor index method in the traditional potential ecological risk index method is inaccurate, and it is easy to cause overestimation / underestimation of heavy metal pollution risks.

[0048] 2. The improved potential ecological risk index adopted by the present invention successfully incorporates the additional contribution of the bioexchangeable fraction to the potential ecological risk of heavy metals, and at the same time reasonably distinguishes the different bioavailabilities of the non-residual fractions (i.e., oxidizable fraction and reducible fraction) and the residual fraction of heavy metals, making the evaluation process more scientific and reasonable, and the evaluation results more in line with the actual situation of regional soil heavy metal pollution investigation.

[0049] 3. The present invention takes soil microorganisms as the ecological risk assessment receptor, focuses on the degree of change in microbial diversity affected by heavy metal pollution, and uses ecological theory and related models to quantify the ecological risk caused by heavy metals to microorganisms, which can reflect to a certain extent the spatial heterogeneity of soil ecological risk.

[0050] 4. The present invention establishes a full-process system from obtaining risk assessment information of multiple heavy metals in regional soil heavy metal pollution to calculating the potential ecological risk index and then to risk level assessment. The calculation method is simple and efficient, can simultaneously quantify the comprehensive ecological risks of single heavy metals and multiple heavy metals, and the assessment system is more comprehensive and has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a flow chart of the method for evaluating the potential ecological risk of heavy metals in regional soil in the embodiment of the present invention;

[0052] Figure 2 is a schematic diagram of the general situation of the research area and the distribution of sampling points in the embodiment of the present invention;

[0053] Figure 3 is the result of fitting the Fisher logarithmic series distribution model for some soil microorganism samples in the research area in the embodiment of the present invention;

[0054] Figure 4 is a spatial distribution map of the contents of 6 heavy metals (namely Cr, Cd, Pb, Zn, Hg and As) in the soil of the research area in the embodiment of the present invention;

[0055] Figure 5 is a Hakanson potential ecological risk distribution map of 6 heavy metals in the soil of the research area in the embodiment of the present invention;

[0056] Figure 6This is the improved potential ecological risk distribution map of 6 heavy metals in the soil of the research area in the embodiment of the present invention;

[0057] Figure 7 This is the Hakanson comprehensive potential ecological risk distribution map of 6 heavy metals in the soil of the research area in the embodiment of the present invention;

[0058] Figure 8 This is the improved comprehensive potential ecological risk distribution map of 6 heavy metals in the soil of the research area in the embodiment of the present invention. Detailed implementation manners

[0059] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0060] In order to realize the comprehensive evaluation of the ecological risk of heavy metals in regional soil, improve the scientificity and reliability of the risk assessment results, and take into account the efficiency of the calculation method, in the context of the coexistence of multiple heavy metals in regional soil pollution, see Figure 1 , the embodiment of the present invention provides an evaluation method for the combined pollution and potential ecological risks of multiple heavy metals coexisting in regional soil, including:

[0061] Carry out sampling surveys and analysis of regional soil to obtain risk assessment information on multiple target heavy metals in the soil of the research area. This risk assessment information includes: the measured concentrations of multiple heavy metals in the regional soil, the environmental background values of soil heavy metals in the local area, the contents of different occurrence forms of various heavy metals, the results of regional soil microbial sequencing, and the improved toxicity coefficients of various heavy metal elements; among them, the improved toxicity coefficient of each heavy metal is determined according to the abundance of heavy metals in soil and related media;

[0062] For heavy metal elements that have no significant impact on the diversity of soil microbial communities, use the improved toxicity coefficient of this heavy metal as its improved toxicity response factor; for heavy metal elements that have a significant impact on the diversity of soil microbial communities, determine the improved toxicity response factor of this heavy metal according to the improved toxicity coefficient of each heavy metal and the results of regional soil microbial sequencing;

[0063] According to the measured concentration, environmental background value, improved toxicity response factor of each heavy metal, and the content of various occurrence forms, determine the improved single potential ecological risk index and the improved comprehensive potential ecological risk index of this heavy metal;

[0064] According to the single potential ecological risk index improved for each heavy metal and the improved comprehensive potential ecological risk index, the single heavy metal pollution risk degree and the comprehensive pollution risk degree of the regional soil are evaluated, and the improved ecological risk assessment grading is formed. In ArcGIS, ordinary Kriging interpolation is used to draw the spatial distribution map of soil heavy metal content and the distribution map of heavy metal potential ecological risk index, and the regional soil heavy metal ecological risk level is determined according to the improved ecological risk assessment grading standard.

[0065] The basis for Hakanson to derive the heavy metal toxicity coefficient is the principle of the evolution of the adaptability of the earth's organisms, that is, the higher the content of heavy metals in the lithosphere, hydrosphere, pedosphere and biosphere, the lower their toxicity. Therefore, in the embodiments of the present invention, the abundance values of heavy metal elements in the global upper crust, soil, igneous rock, terrestrial plants, terrestrial animals, etc. (such as Table 1) are obtained from authoritative literature, and referring to Hakanson's calculation method, the toxicity coefficient for the potential ecological risk assessment of soil heavy metal pollution after improvement is derived.

[0066] The present invention can obtain risk assessment information of various heavy metals through on-site investigation and sampling of regional soil, and the types of target heavy metals can be preset in advance. Based on the data in Table 1, in the embodiments of the present invention, taking six elements of chromium (Cr), cadmium (Cd), lead (Pb), zinc (Zn), mercury (Hg), and arsenic (As) as examples, the calculation method and results of the toxicity coefficient of heavy metals after improvement are as follows:

[0067] First, determine the target heavy metal elements in the research area. The abundance values of the target heavy metal elements in the soil and related media can be obtained through means such as consulting literature materials, and the ratio of the highest abundance of heavy metal elements in each medium to the abundance of each heavy metal element is calculated to obtain the relative abundance value of each heavy metal element in each medium;

[0068] Secondly, for any target heavy metal element, remove the maximum value in the relative abundance values of all media, and then sum up the relative abundance values in the remaining media to obtain the sum of the relative abundance values of the heavy metal element;

[0069] Subsequently, divide the sum of the relative abundance values of each heavy metal element by the minimum value in the sum of the relative abundance values of the target heavy metal element, and normalize to obtain the sum of the relative abundance values of each heavy metal element after correction; take the square root of the sum of the relative abundance values of each heavy metal element after correction and round to obtain the toxicity coefficient of each heavy metal after improvement (see Table 1).

[0070] Table 1 Abundance (unit: ppm) and toxicity coefficient of heavy metal elements in soil and related media

[0071]

[0072] In this embodiment, the specific calculation method of the toxicity response factor after heavy metal improvement includes: determining the abundance of soil microorganisms at the sampling points at the species level through the results of regional soil microorganism sequencing. For the sampling point locations, refer to Figure 2 . For the soil microbial community at any sampling point j, count all species with an individual number not exceeding N. In this embodiment, N is 10. Using the individual numbers 1, 2,..., 10 as the abscissa and the number of species corresponding to the individual numbers as the ordinate, plot a dot graph and fit it with the Fisher logarithmic series distribution model to obtain the fitting parameters a j value and b j value: In the formula, φ j represents the number of species with the same individual number x, where x = 1, 2,..., N. The present invention uses Hubbell's neutral theory of communities to fit the species abundance distribution of the soil microbial community with the Fisher logarithmic series distribution model at the regional scale ( Figure 3 shows an exemplary curve fitting result of a sampling point). In the present invention, the fitting parameter a j value is a biodiversity parameter, representing the basic biodiversity quantity, and the b j value is the ratio of the average birth rate to the average death rate, which is related to the birth, death, immigration, and emigration of individuals. Traverse all sampling points to obtain the fitting parameter a j values corresponding to each sampling point, where j = 1, 2,..., M, and M represents the total number of sampling points. For any sampling point j, calculate the toxicity response factor after improvement of the i-th heavy metal according to the following formula where i represents the type of heavy metal, TF i represents the toxicity coefficient after improvement of the i-th heavy metal, and A represents the normalization threshold. The normalization threshold λ is the 95% quantile of {a j}. The ecological significance of the fitting parameter a j value is the characterization of the basic biodiversity of the community. Considering the significant impact of heavy metals on the diversity of the microbial community and that the traditional microbial diversity index cannot meet the calculation requirements, the present invention uses the a j value to replace the BPI value (bioproduction index) in the Hakanson index method as the characterization of the sensitivity of regional soil microorganisms to heavy metals, that is, the ecological heterogeneity of soil microorganisms. Considering that the environmental background value of regional soil heavy metals is commonly replaced by the 95% quantile of the order statistic, in this embodiment, the 95% quantile of the a j value (specifically 634 in Table 2 in this embodiment) is used as the threshold to calculate the toxicity response factor after improvement of the target heavy metal (see Table 2).

[0073] Table 2 Heavy metal toxicity response factors and Hakanson potential ecological risk classification criteria before and after improvement

[0074]

[0075] In this embodiment, the single potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal are calculated according to the following specific formulas:

[0076]

[0077] In the formula: is the content of the weakly acid extractable fraction of the i-th heavy metal in the soil, in mg / kg; is the content of the oxidizable fraction of the i-th heavy metal in the soil, in mg / kg; is the content of the reducible fraction of the i-th heavy metal in the soil, in mg / kg; is the content of the residual fraction of the i-th heavy metal in the soil, in mg / kg; MF i is the migration component of the i-th heavy metal in the soil; PMF i is the potential migration component of the i-th heavy metal in the soil; RF i is the residual component of the i-th heavy metal in the soil; is the corrected total concentration of the i-th heavy metal in the soil, in mg / kg; is the environmental background value concentration of the i-th heavy metal in the soil, in mg / kg; is the pollution coefficient of the corrected i-th heavy metal; is the toxicity response factor of the improved i-th heavy metal; is the single potential ecological risk index of the improved i-th heavy metal; MRI is the improved comprehensive potential ecological risk index of the regional soil heavy metal combined pollution; n is the number of target heavy metal types in the regional soil.

[0078] Furthermore, in this embodiment, according to the single potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal, the single heavy metal pollution risk degree and the comprehensive pollution risk degree of the regional soil are evaluated. The grades are divided according to the following method to form the improved ecological risk assessment classification:

[0079] The first-level boundary value of the single potential ecological risk index of each heavy metal is the single heavy metal potential ecological risk index value assuming that the heavy metal is not polluted, that is, the heavy metal pollution coefficient is equal to 1 and the toxicity response factor is equal to the toxicity coefficient of the heavy metal. The boundary values of other risk levels are obtained by doubling in turn;

[0080] The first-level boundary value of the comprehensive potential ecological risk index for all heavy metals is obtained by summing up the first-level boundary values of the single potential ecological risk index for each heavy metal and rounding up, and the boundary values for other risk levels are obtained by doubling them successively.

[0081] The improved ecological risk assessment classification criteria in this embodiment are shown in Table 3.

[0082] Table 3 Classification Criteria for Improved Potential Ecological Risk

[0083]

[0084] In this embodiment, an investigation and research is carried out on the heavy metal pollution situation of the soil in a certain regional area as shown in Figure 2 . A total of 231 pieces of heavy metal concentration data of soil samples are obtained. The characteristics of the heavy metal content in the soil of the research area are shown in Table 4, and the background values of heavy metals in the soil refer to the local soil environmental background value standard (DB 4402 / T08-2021).

[0085] Table 4 Statistical Characteristics of Heavy Metal Content in the Soil of the Research Area (unit: mg / kg)

[0086]

[0087] As a comparison, the single potential ecological risk index and the comprehensive potential ecological risk index of the heavy metals in the regional soil before improvement can be calculated according to the following formula:

[0088]

[0089] In the formula: is the measured concentration of the i-th heavy metal in the regional soil (mg / kg); is the environmental background value concentration of the i-th heavy metal in the soil (mg / kg); is the pollution coefficient of the i-th heavy metal in the regional soil; is the Hakanson toxicity response factor of the i-th heavy metal in the regional soil; is the single potential ecological risk index of the i-th heavy metal in the regional soil; RI is the traditional potential ecological risk index of the combined pollution of heavy metals in the regional soil; n is the number of heavy metal types.

[0090] The heavy metal content and the potential ecological risk index before and after improvement of some soil samples are shown in Table 5 (unit: mg / kg).

[0091] Table 5 Heavy Metal Content and Potential Ecological Risk Index of Some Soil Samples in the Research Area

[0092]

[0093] The spatial distribution map of the contents of 6 heavy metals in the soil of the study area was drawn by ordinary Kriging interpolation of ArcGIS, and on this basis, the distribution map of the potential ecological risk index of heavy metals in the regional soil was obtained. According to the improved ecological risk assessment and classification criteria, the potential ecological risk levels of single heavy metals and the comprehensive potential ecological risk levels were determined respectively, so as to provide a theoretical basis for the risk prevention and control of heavy metals in the regional soil. In the embodiments of the present invention, the spatial distribution map of the contents of 6 heavy metals in the soil of the study area and the improved potential ecological risk distribution map are shown in Figure 4 and Figure 6 .

[0094] Figure 5 It shows the distribution of the Hakanson potential ecological risks of 6 heavy metals in the soil of the study area.

[0095] Figure 7 It shows the distribution of the comprehensive potential ecological risks of 6 heavy metals in the soil of the study area.

[0096] Figure 8 It shows the distribution of the improved comprehensive potential ecological risks of 6 heavy metals in the soil of the study area.

[0097] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks, characterized in that: include: Regional soil sampling survey and analysis to obtain the measured concentrations of various heavy metals in regional soils, the regional soil heavy metal environmental background values, the contents of various heavy metals in different occurrence forms, and the sequencing results of regional soil microorganisms; According to the abundance of heavy metals in soil and related media, determine the improved toxicity coefficient of each heavy metal; For heavy metal elements that have no significant effect on the diversity of soil microbial communities, the improved toxicity coefficient of the heavy metal is used as its improved toxicity response factor; For heavy metal elements that have a significant impact on the diversity of soil microbial communities, their improved toxicity response factors are determined based on the improved toxicity coefficients of the heavy metals and the sequencing results of regional soil microorganisms; According to the measured concentration of each heavy metal, the environmental background value, the improved toxicity response factor and the content of various occurrence forms, the improved single potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal are determined; Based on the improved single potential ecological risk index of each heavy metal and the improved comprehensive potential ecological risk index, the single heavy metal pollution risk level and comprehensive pollution risk level of the regional soil are evaluated.

2. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 1, characterized in that: The relevant media include one or more of igneous rocks, terrestrial plants, terrestrial animals, and the upper crust.

3. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 1, characterized in that: The specific calculation method of the improved toxicity coefficient includes: First, determine the target heavy metal elements in the study area, obtain the abundance values ​​of the target heavy metal elements in the soil and related media, calculate the ratio of the highest abundance of heavy metal elements in each medium to the abundance of each heavy metal element, and obtain the relative abundance value of each heavy metal element in each medium; Secondly, for any target heavy metal element, the maximum value of its relative abundance values ​​in all media is eliminated, and then its relative abundance values ​​in the remaining media are added up to obtain the summed relative abundance value of the heavy metal element; Subsequently, the summed relative abundance values ​​of each heavy metal element were normalized by dividing the minimum value of the summed relative abundance values ​​of the target heavy metal elements by the summed relative abundance values, and the corrected summed relative abundance values ​​of each heavy metal element were normalized. The square root of the corrected summed relative abundance values ​​of each heavy metal element was taken to obtain the improved toxicity coefficient of each heavy metal.

4. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 1, characterized in that: The heavy metal elements that have no significant effect on the diversity of soil microbial communities include As; The heavy metal elements that have a significant impact on the diversity of soil microbial communities include one or more of Cr, Cd, Pb, Zn, and Hg.

5. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 1, characterized in that: The heavy metal elements that have a significant impact on the diversity of soil microbial communities are used to determine their improved toxicity response factors based on the improved toxicity coefficients of the heavy metals and the sequencing results of regional soil microorganisms. The specific calculation method includes: The abundance of soil microorganisms at the species level at each sampling point was determined through regional soil microbial sequencing results; For the soil microbial community at any sampling point j, all species with a number of individuals not exceeding N are counted, with the number of individuals 1, 2, ..., N as the horizontal axis, where N is a positive integer; the number of species corresponding to the number of individuals is used as the vertical axis, and a dot plot is drawn and fitted with the Fisher logarithmic series distribution model to obtain the fitting parameter a of the sampling point j. j Value and b j value: Where φ j represents the number of microbial species with the same number of individuals x, x = 1, 2, ..., N; Traverse all sampling points and get the corresponding fitting parameters a j Value, j = 1, 2, ..., M, M represents the total number of sampling points; For any sampling point j, the improved toxicity response factor MT of the i-th heavy metal is calculated as follows: r i : Among them, i represents the type of heavy metal, TF i represents the improved toxicity coefficient of the i-th heavy metal, and A represents the normalized threshold.

6. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 5, characterized in that: Normalization Threshold λ is {a j } 95% quantile.

7. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 1, characterized in that: According to the measured concentration of each heavy metal, the environmental background value, the improved toxicity response factor and the content of various occurrence forms, the improved single potential ecological risk index and the improved comprehensive potential ecological risk index of each heavy metal are determined. The specific calculation formula is as follows: Where: is the weak acid extractable content of the i-th heavy metal in the soil, in mg / kg; is the content of the oxidizable state of the i-th heavy metal in the soil, in mg / kg; is the content of the reducible form of the i-th heavy metal in the soil, in mg / kg; is the content of the ith heavy metal residue in the soil, in mg / kg; MF i is the migration component of the i-th heavy metal in soil; PMF i is the potential migration component of the i-th heavy metal in soil; RF i is the residual component of the i-th heavy metal in the soil; is the total concentration of the i-th heavy metal in the soil after correction, in mg / kg; is the environmental background concentration of the ith heavy metal in the soil, in mg / kg; is the pollution coefficient of the ith heavy metal after correction; is the improved toxicity response factor of the i-th heavy metal; is the improved potential ecological risk index of the i-th heavy metal; MRI is the improved comprehensive potential ecological risk index of regional soil heavy metal complex pollution; n is the number of target heavy metal types in regional soil.

8. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risk according to claim 1 or 7, characterized in that: According to the improved single potential ecological risk index and improved comprehensive potential ecological risk index of each heavy metal, the single heavy metal pollution risk degree and comprehensive pollution risk degree of regional soil are evaluated, and the levels are divided according to the following method to form an improved ecological risk assessment classification: The first-level limit value of the single potential ecological risk index of each heavy metal is the single heavy metal potential ecological risk index value assuming that there is no pollution of the heavy metal, that is, the pollution coefficient of the heavy metal is equal to 1 and the toxicity response factor is equal to the toxicity coefficient of the heavy metal. The limit values ​​of other risk levels are doubled in turn; The first-level limit value of the comprehensive potential ecological risk index of all heavy metals is obtained by adding up the first-level limit value of the single potential ecological risk index of each heavy metal or further taking the value upward, and the limit values ​​of other risk levels are doubled in turn.

9. The method for evaluating the combined pollution of multiple heavy metals coexisting in regional soil and its potential ecological risks according to claim 8, characterized in that: Kriging interpolation was used to draw the spatial distribution map of soil heavy metal content and the distribution map of heavy metal potential ecological risk index, and the regional soil heavy metal ecological risk level was determined according to the improved ecological risk assessment classification standard.

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