Method for determining enrichment and transfer rule of REEs in food web of soil around mining area

Abstract

The invention relates to the technical field of soil metal ecological risk assessment and pollution abatement, in particular to a method for determining the enrichment and transfer rule of REEs in a soil food web around a mining area. Comprising the following steps: S1, collecting a sample; s2, sample detection; s3, data analysis; and S4, analyzing the transfer rule of the REEs in the food web. According to the method, main groups of the soil organisms around the mining area and the nutritional structure of the soil food web can be determined based on biological classification level identification and determination of carbon and nitrogen stable isotopes in the organisms through the research test of the soil organisms around the mining area, and the transmission effect of the rare earth element REEs in different food chains in the soil food web around the mining area is disclosed.

Description

Technical Field

[0001] The present invention relates to the technical field of soil metal ecological risk assessment and pollution control, and in particular to a method for determining the enrichment and transfer rules of REEs in a soil food web around a mining area. Background Art

[0002] Soil animals are an important component of terrestrial ecosystems, playing an important role in soil occurrence, soil aggregation, soil fertility and nutrient cycling, soil respiration, aboveground-underground interactions, climate regulation and other ecosystem functions and stability. Previous studies have shown that soil animal communities are closely related to soil physical structure, nutrient cycling and microbial diversity, and are good indicator species for soil health. Soil animal communities are highly sensitive to exogenous chemicals and are often used as indicator organisms for the effects of exogenous pollutants on soil health.

[0003] Rare earth elements REEs are absorbed and accumulated by producers such as aquatic and terrestrial plants through polluted water and soil, and are transmitted in the food chain / web through predation relationships and decomposition of plant and animal residues. Currently, research on the transmission characteristics of rare earth elements REEs in food webs is mainly focused on aquatic ecosystems such as lakes, estuaries, and oceans, while there are few studies on soil animals and related food webs in terrestrial ecosystems.

[0004] Soil-dwelling animals are often used as indicator organisms for the impact of exogenous pollutants on soil health due to their receptor sensitivity. Therefore, for the healthy development of soil and safe agricultural production, it is urgent to conduct research on the bioaccumulation of rare earth elements (REEs) in soil-dwelling animals and their transmission risks in related food webs. Summary of the invention

[0005] In response to the above-mentioned problems, the present invention provides a method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area.

[0006] The technical solution of the present invention is:

[0007] The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area includes the following steps:

[0008] S1. Sample collection: collecting soil samples and plant samples in the mining area, and extracting large soil animal samples and small and medium-sized soil animal samples from the soil samples;

[0009] S2. Sample testing: Determine the REEs concentration and carbon and nitrogen stable isotope content in each sample collected in step S1;

[0010] S3, data analysis: using the REEs content value in the post-Archaean Australian shale to standardize the REEs concentration values ​​in each sample measured in step S2, to obtain the REEs concentration standard value in each sample, taking the sampling point as the unit, performing fractionation characteristic judgment on the REEs concentration standard value in each sample to obtain the REEs enrichment pattern and typical REEs element abnormal value in each sample, and based on the carbon and nitrogen stable isotope content of each sample measured in step S2, dividing the trophic level TL of each organism in the soil around the mining area;

[0011] S4. Analysis of the transfer rules of REEs in the food web: Establish a linear relationship between the logarithmic value of REEs concentration in plant and animal samples and the trophic level TL of the sample, and evaluate the trophic magnification factor TMFs of REEs in the soil food web, as shown in the following formula:

[0012] log 10 [Rare earth element] = a + b × TL

[0013] TMFs = 10 b

[0014] In the formula, log 10 [REEs] is the logarithmic value of REEs concentration in animal and plant samples, in mg / kg dry weight; a is the intercept of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL; b is the slope of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL;

[0015] Further analysis of the linear correlation between the nutrient magnification factors (TMFs) of REEs in the soil food web and their atomic numbers revealed a positive correlation between the nutrient magnification factors (TMFs) of rare earth element REEs and their fractionation characteristics.

[0016] The biological effect of REEs when they are transferred along the soil food web is judged based on the trophic magnification factor (TMFs) value when REEs are transferred from lower trophic level organisms to higher trophic level organisms. When TMFs is greater than 1, it indicates that REEs have a biological magnification effect when they are transferred along the soil food web. When TMFs is less than 1, it indicates that REEs have a biological dilution effect when they are transferred along the soil food web.

[0017] Furthermore, the step S1 comprises:

[0018] S1-1. Sampling point layout: 4 to 6 sampling points are arranged in sequence from the upstream to the downstream of the river in the study area, 3 to 5 sampling sub-areas are set in each sampling point, and 4 small sample plots are set in each sampling sub-area;

[0019] S1-2, soil sample collection: collect 3 to 4 soil samples in each of the small sample plots, and mix all the soil samples in one of the sampling sub-areas as the soil sample of the sampling sub-area;

[0020] S1-3, plant sample collection: collect 3 to 4 plant samples in each small sample plot, transport all plant samples in one sampling sub-area at low temperature, dry them at high temperature, grind and mix them, and use them as plant samples in the sampling sub-area;

[0021] S1-4. Extraction of large soil animal samples: The large soil animals in each small sample plot are extracted by hand picking, and are stored at low temperatures after bowel cleaning. The large soil animals are identified to the order level;

[0022] S1-5. Extraction of small and medium-sized soil animal samples: The small and medium-sized soil animals in each small sample plot were separated by a dry funnel and stored in animal preservation solution at low temperature. The small and medium-sized soil animals were identified to the order level.

[0023] Furthermore, in the step S1-1, the distance between adjacent sampling points is 10 to 100 km, the distance between adjacent sampling sub-areas in each sampling point is 40 to 80 m, the size of the sampling sub-area is 30 m×30 m, the small sample plots in each sampling sub-area are respectively located at the midpoints of the four sides of the sampling sub-area, and the size of the small sample plot is 50 cm×50 cm. In the step S1-2, the soil sampling ring knife used for the soil sample has a diameter of 4 cm and a height of 10 cm. In the step S1-3, the temperature of the plant sample during low-temperature transportation is 4°C, the high-temperature killing temperature is 120°C, the killing time is 15 min, the drying temperature is 70°C, and the sample is dried to constant weight.

[0024] Furthermore, in step S1-4, the large soil animals include Hemiptera, Colubridae, Isopoda, Dermaptera, Corymboptera, Hymenoptera, Scolopendra, Araneae, Stylophora, etc., and in step S1-5, the small and medium-sized soil animals include Acarina, Collembola, etc. In steps S1-4 and S1-5, the low-temperature storage temperature is -80°C.

[0025] Furthermore, the step S2 comprises:

[0026] S2-1. Determination of REEs concentration in each sample: Digest soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples and determine REEs concentration;

[0027] S2-2. Determination of carbon and nitrogen stable isotope contents in each sample: Soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples were placed in an elemental analysis-stable isotope mass spectrometer to detect the content of carbon and nitrogen stable isotopes in each sample. VPDB and atmospheric nitrogen were selected as standards for calculating the relative abundance of carbon and nitrogen stable isotopes in each sample.

[0028] Furthermore, the step S3 comprises:

[0029] S3-1. Judgment of enrichment pattern: The enrichment patterns of REEs concentrations in soil, plants and animals are divided into four types:

[0030] Heavy rare earth enrichment: MREE / LREE>1 and HREE / MREE>1;

[0031] Medium rare earth enrichment: MREE / LREE>1 and HREE / MREE<1;

[0032] Light rare earth enrichment: MREE / LREE<1 and HREE / MREE<1;

[0033] Medium rare earth loss: MREE / LREE<1 and HREE / MREE>1;

[0034] Among them, LREE is the sum of the standard concentration values ​​of light rare earth La, Pr and Nd, MREE is the sum of the standard concentration values ​​of medium rare earth Gd, Tb and Dy, and HREE is the sum of the standard concentration values ​​of heavy rare earth Tm, Yb and Lu.

[0035] Take the standard value of REEs concentration in each soil and plant and animal sample at a sampling point, and determine the REEs enrichment pattern in each soil and plant and animal sample according to the above REEs enrichment pattern type;

[0036] S3-2. Determination of typical REEs abnormal values: The typical REEs abnormal values ​​in soil and animal and plant samples are calculated according to the following formula. The typical REEs include Ce, Eu and Gd, which are:

[0037] Ce abnormal value = Ce N ÷(0.5×La N +0.5×Pr N )

[0038]

[0039] Gd abnormal value = Gd N ÷(0.5×Sm N +0.5×Dy N )

[0040] In the formula, Ce Nis the standard value of Ce concentration in soil and animal and plant samples, La N is the standard value of La concentration in soil and animal and plant samples, Pr N is the standard value of Pr concentration in soil and animal and plant samples, Eu N is the standard value of Eu concentration in soil and animal and plant samples, Sm N is the standard value of Sm concentration in soil and animal and plant samples, Tb N is the standard value of Tb concentration in soil and animal and plant samples, Gd N is the standard value of Gd concentration in soil and animal and plant samples, Dy N It is the standard value of Dy concentration in soil and animal and plant samples;

[0041] Take the standard value of REEs concentration in each soil and animal and plant sample at a sampling point, and calculate the abnormal value of typical REEs in each soil and animal and plant sample according to the above formula. An abnormal value greater than 1 indicates that the element is positively abnormal in the sample, and an abnormal value less than 1 indicates that the element is negatively abnormal in the sample. The Wilcoxon test is used to test the significance of the abnormal value of typical REEs in each soil and animal and plant sample at a sampling point, and the significance level is set at p < 0.05;

[0042] S3-3. Trophic level TL division: Take the δ 15 N, assuming plants as the first trophic level and bioaccumulation of 3.40‰ of δ 15 N, the trophic level of each animal is calculated according to the following formula:

[0043] TL consumer =(δ 15 N consumer -δ 15 N plant )÷3.4+1

[0044] Among them, TL consumer is the trophic level of animals in the soil; 15 N consumer is the δ 15 N, unit is ‰; δ 15 N plant is the δ 15 N, unit is ‰.

[0045] Furthermore, the step S3-3 also includes testing the nutrient level: taking the δ 13 The C content is calculated by δ 15 The trophic levels divided by N are summarized;

[0046] If the δ of two adjacent trophic level organisms 13 If the C content is similar, the original trophic level relationship is maintained. If not, the new nutritional relationship is determined by detecting and identifying the intestinal DNA sequences of organisms at two adjacent trophic levels. If the DNA in the intestinal contents of the former comes from the latter, then the former preys on the latter.

[0047] The beneficial effects of the present invention are:

[0048] (1) The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area of ​​the present invention can determine the main groups of soil organisms and the nutritional structure of the soil food web around the mining area through field investigation and experiment of soil organisms around the mining area based on the identification of biological classification level and the determination of carbon and nitrogen stable isotopes in organisms, which is helpful to supplement and improve the soil animal diversity database.

[0049] (2) The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area of ​​the present invention clarifies the pollution characteristics of rare earth elements in the soil around the mining area by measuring the concentration of rare earth elements in the soil and animal and plant samples around the mining area, explores the bioaccumulation characteristics of rare earth elements in animals and plants, and reveals the transfer effect of rare earth elements in different food chains in the soil food web around the mining area, as well as the relationship between rare earth elements and the atomic number of rare earth elements, providing a theoretical basis and basic data for accurately evaluating its soil ecology and human health risks.

[0050] (3) The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area of ​​the present invention clarifies the slight changes in the element combination during the migration of rare earth elements from soil to plants and then to animals through the judgment of fractionation characteristics and outliers, and reveals the intrinsic connection between soil, plants and soil animals. Since there are differences in the biological toxicity of light rare earths and heavy rare earths, understanding the fractionation characteristics and outliers of rare earths in the soil food web is helpful to provide a reference for the food chain transfer mechanism and environmental risk assessment of rare earths.

[0051] (4) The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area of ​​the present invention realizes the effective evaluation and quantitative prediction of the transfer of pollutants in soil animals and related food webs in different soils with many types, great differences and mixed pollution, so as to protect the safety of the soil ecosystem. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is the concentration of light rare earth LREE, medium rare earth MREE, heavy rare earth HREE and total rare earth TREE in the soil at the sampling point of the experimental example of the present invention;

[0053] Figure 2 It is the standardized distribution of REEs in the soil of the sampling point of the experimental example of the present invention, the post-Archaean Australian shale;

[0054] Figure 3 is the abnormal value of Ce in soil and organisms in the experimental examples of the present invention;

[0055] Figure 4 It is the abnormal value of Eu in soil and organisms in the experimental examples of the present invention;

[0056] Figure 5 is the abnormal value of Gd in the soil and organisms of the experimental examples of the present invention;

[0057] Figure 6 is the δ in the soil organisms in the experimental example of the present invention 15 N;

[0058] Figure 7 is the δ in the soil organisms in the experimental example of the present invention 13 C;

[0059] Figure 8 is the trophic level of the soil organisms in the experimental example of the present invention;

[0060] Fig. 9 The concentration of REEs in soil organisms in the experimental example of the present invention and δ 15 N linear relationship;

[0061] Fig.10 It is the linear regression between the nutrient magnification factor in the soil organisms and the atomic number of REEs in the experimental example of the present invention;

[0062] Fig.11 It is a flow chart of the method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area of ​​the present invention. DETAILED DESCRIPTION

[0063] Example 1

[0064] The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area includes the following steps:

[0065] S1. Sample collection: Collect soil samples and plant samples in the mining area, and extract large soil animal samples and small and medium-sized soil animal samples from the soil samples;

[0066] S1-1. Sampling point layout: 5 sampling points are arranged in sequence from the upstream to the downstream of the river in the study area, 4 sampling sub-areas are set up in each sampling point, and 4 small sample plots are set up in each sampling sub-area;

[0067] The distance between adjacent sampling points is 50km, the distance between adjacent sampling sub-areas in each sampling point is 60m, the size of the sampling sub-area is 30m×30m, the small sample plots in each sampling sub-area are located at the midpoints of the four sides of the sampling sub-area, and the size of the small sample plot is 50cm×50cm. In step S1-2, the diameter of the soil ring knife used for the soil sample is 4cm and the height is 10cm. In step S1-3, the temperature of the plant sample during low-temperature transportation is 4°C, the high-temperature fixing temperature is 120°C, the fixing time is 15min, the drying temperature is 70°C, and the sample is dried to constant weight.

[0068] S1-2. Soil sample collection: Collect 4 soil samples in each small sample plot, and mix all soil samples in a sampling sub-area as the soil sample of the sampling sub-area;

[0069] S1-3. Plant sample collection: Collect 4 plant samples in each small sample plot. All plant samples in a sampling sub-area are transported at low temperature, dried at high temperature, ground and mixed, and used as plant samples in the sampling sub-area.

[0070] S1-4. Extraction of large soil animals: The large soil animals in each small sample plot were extracted by hand picking, cleaned and stored at low temperature, and the large soil animals were identified to the order level;

[0071] S1-5. Extraction of small and medium-sized soil animal samples: The small and medium-sized soil animals in each small sample plot were separated by a dry funnel, stored in animal preservation solution at low temperature, and the small and medium-sized soil animals were identified to the order level;

[0072] Large soil animals include Hemiptera, Scolopendra, Isopoda, Dermaptera, Lumbriata, Hymenoptera, Scolopendra, Araneae, Stylophora, etc. In step S1-5, small and medium-sized soil animals include Acarina, Collembola, etc. In steps S1-4 and S1-5, the cryopreservation temperature is -80°C;

[0073] S2. Sample testing: Determine the REEs concentration and carbon and nitrogen stable isotope content in each sample collected in step S1;

[0074] S2-1. Determination of REEs concentration in each sample: Digest soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples and determine the REEs concentration using a graphite digestion instrument;

[0075] S2-2. Determination of the content of carbon and nitrogen stable isotopes in each sample: soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples were placed in an elemental analysis-stable isotope mass spectrometer to detect the content of carbon and nitrogen stable isotopes in each sample, and VPDB and atmospheric nitrogen were used as standards for calculating the relative abundance of carbon and nitrogen stable isotopes in each sample;

[0076] S3. Data analysis: SPSS22.0 software was used to perform statistics on the experimental data in step S2. The REEs content value in the post-Archean Australian shale was used to standardize the REEs concentration values ​​in each sample measured in step S2 to obtain the standard value of REEs concentration in each sample. The standard value of REEs concentration in each sample was fractionated and judged based on the sampling point to obtain the REEs enrichment pattern and typical REEs element abnormal value in each sample. Based on the carbon and nitrogen stable isotope content of each sample measured in step S2, the trophic level TL of each organism in the soil around the mining area was divided;

[0077] S3-1. Judgment of enrichment pattern: The enrichment patterns of REEs concentrations in soil, plants and animals are divided into four types:

[0078] Heavy rare earth enrichment: MREE / LREE>1 and HREE / MREE>1;

[0079] Medium rare earth enrichment: MREE / LREE>1 and HREE / MREE<1;

[0080] Light rare earth enrichment: MREE / LREE<1 and HREE / MREE<1;

[0081] Medium rare earth loss: MREE / LREE<1 and HREE / MREE>1;

[0082] Among them, LREE is the sum of the standard concentration values ​​of light rare earth La, Pr and Nd, MREE is the sum of the standard concentration values ​​of medium rare earth Gd, Tb and Dy, and HREE is the sum of the standard concentration values ​​of heavy rare earth Tm, Yb and Lu.

[0083] Take the standard value of REEs concentration in each soil and plant and animal sample at a sampling point, and determine the REEs enrichment pattern in each soil and plant and animal sample according to the above REEs enrichment pattern type;

[0084] S3-2. Determination of typical REEs abnormal values: The typical REEs abnormal values ​​in soil and animal and plant samples are calculated according to the following formula. Typical REEs include Ce, Eu and Gd, which are:

[0085] Ce abnormal value = Ce N ÷(0.5×La N +0.5×Pr N )

[0086]

[0087] Gd abnormal value = Gd N ÷(0.5×SmN +0.5×Dy N )

[0088] In the formula, Ce N is the standard value of Ce concentration in soil and animal and plant samples, La N is the standard value of La concentration in soil and animal and plant samples, Pr N is the standard value of Pr concentration in soil and animal and plant samples, Eu N is the standard value of Eu concentration in soil and animal and plant samples, Sm N is the standard value of Sm concentration in soil and animal and plant samples, Tb N is the standard value of Tb concentration in soil and animal and plant samples, Gd N is the standard value of Gd concentration in soil and animal and plant samples, Dy N It is the standard value of Dy concentration in soil and animal and plant samples;

[0089] Take the standard value of REEs concentration in each soil and animal and plant sample at a sampling point, and calculate the abnormal value of typical REEs in each soil and animal and plant sample according to the above formula. An abnormal value greater than 1 indicates that the element is positively abnormal in the sample, and an abnormal value less than 1 indicates that the element is negatively abnormal in the sample. The Wilcoxon test is used to test the significance of the abnormal value of typical REEs in each soil and animal and plant sample at a sampling point, and the significance level is set at p < 0.05;

[0090] S3-3. Trophic level TL division: Take the δ 15 N, assuming plants as the first trophic level and bioaccumulation of 3.40‰ of δ 15 N, the trophic level of each animal is calculated according to the following formula:

[0091] TL consumer =(δ 15 N consumer -δ 15 N plant )÷3.4+1

[0092] Among them, TL consumer is the trophic level of animals in the soil; 15 N consumer is the δ 15 N, unit is ‰; δ 15 N plant is the δ 15 N, unit is ‰;

[0093] It also includes testing the trophic level: taking the δ 13The C content is calculated by δ 15 The trophic levels divided by N are summarized;

[0094] If the δ of two adjacent trophic level organisms 13 If the C content is similar, the original trophic level relationship is maintained. If not, a new trophic relationship is determined by detecting and identifying the intestinal DNA sequences of organisms at two adjacent trophic levels. If the DNA in the intestinal contents of the former comes from the latter, then the former preys on the latter.

[0095] S4. Analysis of the transfer rules of REEs in the food web: Establish a linear relationship between the logarithmic value of REEs concentration in plant and animal samples and the trophic level TL of the sample, and evaluate the trophic magnification factor TMFs of REEs in the soil food web, as shown in the following formula:

[0096] log 10 [Rare earth element] = a + b × TL

[0097] TMFs = 10 b

[0098] In the formula, log 10 [REEs] is the logarithmic value of REEs concentration in animal and plant samples, in mg / kg dry weight; a is the intercept of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL; b is the slope of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL;

[0099] SPSS22.0 software was further used to analyze the linear correlation between the nutrient magnification factors (TMFs) of REEs in the soil food web and their atomic numbers, and a positive correlation was found between the nutrient magnification factors (TMFs) of rare earth element REEs and their fractionation characteristics.

[0100] The biological effect of REEs when they are transferred along the soil food web is judged based on the trophic magnification factor (TMFs) value when REEs are transferred from lower trophic level organisms to higher trophic level organisms. When TMFs is greater than 1, it indicates that REEs have a biological magnification effect when they are transferred along the soil food web. When TMFs is less than 1, it indicates that REEs have a biological dilution effect when they are transferred along the soil food web.

[0101] Example 2

[0102] The difference between this embodiment and embodiment 1 is that:

[0103] S1-1. Sampling point layout: 4 sampling points are arranged in sequence from the upstream to the downstream of the river in the study area. 3 sampling sub-areas are set in each sampling point, and 4 small sample plots are set in each sampling sub-area. The distance between adjacent sampling points is 100km, and the distance between adjacent sampling sub-areas in each sampling point is 80m. The size of the sampling sub-area is 30m×30m. The small sample plots in each sampling sub-area are located at the midpoints of the four sides of the sampling sub-area, and the size of the small sample plot is 50cm×50cm.

[0104] S2. Soil sample collection: Collect 4 soil samples in each small sample plot;

[0105] S3. Plant sample collection: Collect 3 plant samples in each small sample plot.

[0106] Example 3

[0107] S1. Sampling point layout: Six sampling points are arranged in the study area from upstream to downstream of the river. Five sampling sub-areas are set in each sampling point, and four small sample plots are set in each sampling sub-area. The distance between adjacent sampling points is 10km, and the distance between adjacent sampling sub-areas in each sampling point is 40m. The size of the sampling sub-area is 30m×30m. The small sample plots in each sampling sub-area are located at the midpoints of the four sides of the sampling sub-area, and the size of the small sample plot is 50cm×50cm.

[0108] S2. Soil sample collection: Collect 3 soil samples in each small sample plot;

[0109] S3. Plant sample collection: Collect 3 plant samples in each small sample plot.

[0110] Experimental example

[0111] Next, we use a field investigation experiment to verify the method of the present invention. The address is a county in southern my country. The county is rich in rare earth minerals and has a long history of mining. It is one of the important production areas of ion-adsorption rare earth minerals in China. We completed the adoption and data analysis according to the method in Example 1. Through the data analysis in step S3, the concentration of LREE (La, Ce, Pr, Nd and Pm) in the soil of the sampling points was 255-682 mg / kg, the concentration of MREE (Sm, Eu, Gd, Tb, Dy and Ho) was 28-111 mg / kg, the concentration of HREE (Er, Tm, Yb, Lu, Sc and Y) was 35-145 mg / kg, and the concentration of TREE was 309-937 mg / kg. The concentration of REEs in the soil of the sampling points located upstream of the river, such as Site 2, Site 3 and Site 4, was higher than that of the downstream sampling points. The fixed REEs in the soil weathering layer migrated and diffused to the surrounding water bodies, soil and other environmental media under the action of surface runoff, precipitation and soil biochemical activities. The main driving force for the spread of soil REEs pollution in the study area is water flow.

[0112] like Figure 2 As shown, through step S8-1, the fractionation characteristics judge that the REEs fractionation effect in the soil is similar overall, and both show positive Gd anomalies. Among them, the REEs fractionation effect in the soil of Site2 and Site4 is MREE enrichment, while the REEs fractionation effect in the soil of Site1, Site3 and Site5 is LREE enrichment. The main source of soil REEs pollution in the study area is rare earth mines. Based on S8-2, the calculation formula for the abnormal value of Ce, Eu and Gd of typical rare earth elements REEs abnormal value judgment, the abnormal values ​​are as follows Figure 3-5 As shown, the Ce anomaly values ​​in the soil samples were 0.362-0.952, the Eu anomaly values ​​were 0.752-1.05, and the Gd anomaly values ​​were 1.35-2.01, all significantly lower or higher than 1. This further shows that the soil REEs at all sampling points were Ce negative anomalies and Gd positive anomalies.

[0113] The nitrogen and carbon stable isotope values ​​of representative organisms in the soil were obtained through S8-3 and trophic level TL division. Figures 6 to 8 As shown. The representative soil organisms in the study area can be divided into three trophic levels. Among them, Hemiptera, plants, Scolopendra, Coleoptera larvae, Isopoda and Dermaptera are in the first trophic level; Monopterida, Blattodea, Lepidoptera larvae, Hymenoptera, Collembola, Coleoptera and Acarina are in the second trophic level; Scolopendra, Araneae and Stylophora are in the third trophic level. Studies have reported that Arachnids feed on Diptera and Hymenoptera in soil food webs such as forests, indicating that the trophic relationship between soil organisms established in this chapter is credible.

[0114] The concentrations of LREE / MREE / HREE / TREE in the first trophic level organisms Hemiptera are 3.46-4.83 / 0.516-0.546 / 0.416-0.718 / 4.43-6.09 mg / kg; the concentrations of LREE / MREE / HREE / TREE in the first trophic level organisms Serinidae are 9.14-20.4 / 1.14-1.63 / 1.35-2.02 / 12.0-24.1 mg / kg; the concentrations of LREE / MREE / HREE / TREE in the larvae of Coleoptera are 64.6-84.3 / 7.09-10.1 / 7.87-11.3 / 81.3-105mg / kg; the concentrations of LREE / MREE / HREE / TREE in Isopoda are 71.7-100 / 6.79-8.70 / 10.3-11.7 / 90.8-119mg / kg; the concentrations of LREE / MREE / HREE / TREE in Dermaptera are 4.65-10.2 / 2.08-2.39 / 7.13-10.1 / 16.8-19.7mg / kg. The concentrations of LREE / MREE / HREE / TREE in the second trophic level organisms, the order Lumbricata, are 68.7-117 / 7.64-18.7 / 10.2-17.8 / 90.3-153 mg / kg; the concentrations of LREE / MREE / HREE / TREE in the order Blattodea are 41.2-44.8 / 5.93-9.94 / 6.48-10.3 / 56.3-63.6 mg / kg; the concentrations of LREE / MREE / HREE / TREE in the larvae of Lepidoptera are 53.5-67.2 / 7.70-8.12 / 7.54-10.2 / 71.8-82.4 mg / kg; the concentrations of LREE / MREE / HREE / TREE in the Hymenoptera are 13. 6-17.2 / 1.15-1.78 / 1.45-1.94 / 16.3-21.0mg / kg; the concentrations of LREE / MREE / HREE / TREE in Collembola are 73.7-143 / 21.0-25.7 / 20.5-35.8 / 131-199mg / kg; the concentrations of LREE / MREE / HREE / TREE in Coleoptera are 6.42-8.45 / 0.532-0.753 / 0.731-0.947 / 7.71-9.93mg / kg; the concentrations of LREE / MREE / HREE / TREE in Acarina are 267-307 / 28.3-51.1 / 38.6-47.1 / 336-380mg / kg.The concentrations of LREE / MREE / HREE / TREE in the third trophic level organisms, Centipedeta, are 26.1-44.8 / 2.70-5.26 / 4.13-6.00 / 34.6-56.1 mg / kg; the concentrations of LREE / MREE / HREE / TREE in Araneae, are 7.00-9.77 / 0.810-1.46 / 0.884-1.24 / 8.96-11.5 mg / kg; the concentrations of LREE / MREE / HREE / TREE in Stylophora, are 22.5-29.7 / 1.82-2.93 / 2.32-4.07 / 28.0-35.1 mg / kg.

[0115] This experiment compared the concentration of REEs in representative soil organisms with the field survey results of other metals such as Ag, As, Cu, Cr, Cd, Pb, and Mn. According to previous studies, the concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in spiders are higher than those in beetles, and the concentrations of Fe, Zn, Cu, Pb, and Cd in mites are higher, which is consistent with the results of this experiment. In addition, the concentration of REEs in Coleoptera larvae is significantly higher than that in Coleoptera adults, indicating that the age of the organism affects the bioaccumulation of metals. However, studies have reported that the concentration of REEs in brook trout is weakly positively linearly correlated with its age, indicating that environmental media may affect the relationship between the concentration of REEs in organisms and the age of organisms. The concentration of REEs in Hymenoptera is higher than that in Coleoptera. This result is inconsistent with the results of previous studies. Studies have found that the concentrations of Cd, Cr, Mg, and Mn in Hymenoptera are comparable to those in Coleoptera, indicating that metal bioaccumulation varies depending on the type of metal. The above results show that metal bioaccumulation varies depending on the species of organisms, the age of organisms, the type of elements, etc., and is affected by environmental media, etc.

[0116] like Fig. 9 and 10As shown in the figure, the relationship between the logarithm of REEs concentration and trophic level varies with the trophic level. The trophic magnification factor (TMF) was obtained based on the linear relationship between REEs and trophic level. The results show that REEs have a positive linear relationship between the first and second trophic level organisms, namely biomagnification (TMF = 1.17); while they have a negative linear relationship between the second and third trophic level organisms, namely biodilution (TMF = 0.857). This can be observed from the increasing trend of REEs concentration in organisms from the first trophic level to the second trophic level and the decreasing trend of REEs concentration in organisms from the third trophic level in the food web. Studies have reported that the concentration of REEs in organisms has a decreasing trend with increasing trophic level in aquatic and terrestrial food webs, namely biodilution. However, some studies have found that the transfer factor of REEs in plants-snails in the terrestrial food chain is greater than 1, namely biomagnification. Due to differences in physicochemical properties, the physiological processes of REEs in organisms, such as absorption, metabolism, and excretion, are different, which may affect their bioaccumulation and transmission in the food chain / web. This shows that the transmission law of REEs in the food chain / web varies depending on the environmental medium and trophic level, and further exploration is needed.

[0117] Studies have reported that the bioaccumulation of REEs varies depending on the type of element, so this experiment analyzed the linear relationship between the TMF of REEs and their atomic number. Fig.10 As shown in the figure, when REEs are transferred from the first trophic level to the second trophic level, TMF increases significantly with the increase of REEs atomic number (r=0.584, p<0.05); however, when REEs are transferred from the second trophic level to the third trophic level, there is no significant linear relationship between TMF and REEs atomic number. The REEs fractionation effect in organisms is manifested as the REEs with heavier atomic mass are easily enriched with the increase of trophic level. This indicates that when REEs are transferred from the first trophic level to the second trophic level, MREEs are more easily enriched by organisms in the second trophic level than LREEs, and thus the TMF value of MREEs is larger. However, the REEs fractionation effect in organisms at the second and third trophic levels is basically MREE enrichment, indicating that different types of REEs elements do not change significantly during the transfer process, and thus there is no significant linear relationship between the TMF of REEs and their atomic number.

[0118] The above results show that the linear relationship between TMF and REEs atomic number changes with trophic level. In the soil food web, REEs with heavier atomic mass tend to be transferred to organisms at higher trophic levels. This shows that the REEs fractionation effect is manifested as the trophic level increases, and REEs with heavier atomic mass are easily enriched by organisms. This result is consistent with the results of aquatic food web research. The study found that the enrichment degree of HREE showed an increasing trend with the increase of trophic level. This shows that the REEs fractionation effect is manifested as the trophic level increases, and REEs with heavier atomic mass are easily enriched by high trophic level aquatic organisms. Studies have reported that the physiological processes of REEs in organisms, such as intake, metabolism, storage and excretion, may affect their accumulation and fractionation effects in organisms.

Claims

1. A method for determining the accumulation and transfer rules of REEs in the soil food web around the mining area, characterized in that: The following steps are involved: S1. Sample collection: collecting soil samples and plant samples in the mining area, and extracting large soil animal samples and small and medium-sized soil animal samples from the soil samples; S2. Sample testing: Determine the REEs concentration and carbon and nitrogen stable isotope content in each sample collected in step S1; S3, data analysis: using the REEs content value in the post-Archaean Australian shale to standardize the REEs concentration values ​​in each sample measured in step S2, to obtain the REEs concentration standard value in each sample, taking the sampling point as the unit, performing fractionation characteristic judgment on the REEs concentration standard value in each sample to obtain the REEs enrichment pattern and typical REEs element abnormal value in each sample, and based on the carbon and nitrogen stable isotope content of each sample measured in step S2, dividing the trophic level TL of each organism in the soil around the mining area; S4. Analysis of the transfer rules of REEs in the food web: Establish a linear relationship between the logarithmic value of REEs concentration in plant and animal samples and the trophic level TL of the sample, and evaluate the trophic magnification factor TMFs of REEs in the soil food web, as shown in the following formula: log 10 [Rare earth element] = a + b × TL TMFs=10 b In the formula, log 10 [REEs] is the logarithm of REEs concentration in animal and plant samples, expressed in mg / kg dry weight; a is the intercept of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL; b is the slope of the linear relationship between the logarithmic value of REEs concentration in animal and plant samples and the trophic level TL; Further analysis of the linear correlation between the nutrient magnification factors (TMFs) of REEs in the soil food web and their atomic numbers revealed a positive correlation between the nutrient magnification factors (TMFs) of rare earth element REEs and their fractionation characteristics. The biological effect of REEs when they are transferred along the soil food web is judged based on the trophic magnification factor (TMFs) value when REEs are transferred from lower trophic level organisms to higher trophic level organisms. When TMFs is greater than 1, it indicates that REEs have a biological magnification effect when they are transferred along the soil food web. When TMFs is less than 1, it indicates that REEs have a biological dilution effect when they are transferred along the soil food web.

2. The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area according to claim 1, characterized in that: The step S1 comprises: S1-1. Sampling point layout: 4 to 6 sampling points are arranged in sequence from the upstream to the downstream of the river in the study area, 3 to 5 sampling sub-areas are set in each sampling point, and 4 small sample plots are set in each sampling sub-area; S1-2, soil sample collection: collect 3 to 4 soil samples in each of the small sample plots, and mix all the soil samples in one of the sampling sub-areas as the soil sample of the sampling sub-area; S1-3, plant sample collection: collect 3 to 4 plant samples in each small sample plot, transport all plant samples in one sampling sub-area at low temperature, dry them at high temperature, grind and mix them, and use them as plant samples in the sampling sub-area; S1-4. Extraction of large soil animal samples: The large soil animals in each small sample plot are extracted by hand picking, and are stored at low temperatures after bowel cleaning. The large soil animals are identified to the order level; S1-5. Extraction of small and medium-sized soil animal samples: The small and medium-sized soil animals in each small sample plot were separated by a dry funnel and stored in animal preservation solution at low temperature. The small and medium-sized soil animals were identified to the order level.

3. The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area according to claim 2, characterized in that: In the step S1-1, the distance between adjacent sampling points is 10 to 100 km, the distance between adjacent sampling sub-areas in each sampling point is 40 to 80 m, the size of the sampling sub-area is 30 m×30 m, the small sample plots in each sampling sub-area are respectively located at the midpoints of the four sides of the sampling sub-area, and the size of the small sample plot is 50 cm×50 cm. In the step S1-2, the soil sampling ring knife used for the soil sample has a diameter of 4 cm and a height of 10 cm. In the step S1-3, the temperature of the plant sample during low-temperature transportation is 4°C, the high-temperature killing temperature is 120°C, the killing time is 15 min, the drying temperature is 70°C, and it is dried to constant weight.

4. The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area according to claim 2, characterized in that: In step S1-4, the large soil animals include Hemiptera, Scolopendra, Isopoda, Dermaptera, Lumbriata, Hymenoptera, Scolopendra, Araneae, Stylophora, etc. In step S1-5, the small and medium-sized soil animals include Acarina, Collembola, etc. In steps S1-4 and S1-5, the low-temperature storage temperature is -80°C.

5. The method for determining the enrichment and transfer rules of REEs in the soil food web around a mining area according to claim 1, characterized in that: The step S2 comprises: S2-1. Determination of REEs concentration in each sample: Digest soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples and determine REEs concentration; S2-2. Determination of carbon and nitrogen stable isotope contents in each sample: Soil samples, plant samples, large soil animal samples, and small and medium-sized soil animal samples were placed in an elemental analysis-stable isotope mass spectrometer to detect the content of carbon and nitrogen stable isotopes in each sample. VPDB and atmospheric nitrogen were selected as standards for calculating the relative abundance of carbon and nitrogen stable isotopes in each sample.

6. The method for determining the enrichment and transfer rules of REEs in the soil food web around a mining area according to claim 1, characterized in that: The step S3 comprises: S3-1. Judgment of enrichment pattern: The enrichment patterns of REEs concentrations in soil, plants and animals are divided into four types: Heavy rare earth enrichment: MREE / LREE>1 and HREE / MREE>1; Medium rare earth enrichment: MREE / LREE>1 and HREE / MREE<1; Light rare earth enrichment: MREE / LREE<1 and HREE / MREE<1; Medium rare earth loss: MREE / LREE<1 and HREE / MREE>1; Among them, LREE is the sum of the standard concentration values ​​of light rare earth La, Pr and Nd, MREE is the sum of the standard concentration values ​​of medium rare earth Gd, Tb and Dy, and HREE is the sum of the standard concentration values ​​of heavy rare earth Tm, Yb and Lu. Take the standard value of REEs concentration in each soil and plant and animal sample at a sampling point, and determine the REEs enrichment pattern in each soil and plant and animal sample according to the above REEs enrichment pattern type; S3-2. Determination of typical REEs abnormal values: The typical REEs abnormal values ​​in soil and animal and plant samples are calculated according to the following formula. The typical REEs include Ce, Eu and Gd, which are: Ce abnormal value = Ce N ÷(0.5×La N +0.5×Pr N ) Gd abnormal value = Gd N ÷(0.5×Sm N +0.5×Dy N ) In the formula, Ce N is the standard value of Ce concentration in soil and animal and plant samples, La N is the standard value of La concentration in soil and animal and plant samples, Pr N is the standard value of Pr concentration in soil and animal and plant samples, Eu N is the standard value of Eu concentration in soil and animal and plant samples, Sm N is the standard value of Sm concentration in soil and animal and plant samples, Tb N is the standard value of Tb concentration in soil and animal and plant samples, Gd N is the standard value of Gd concentration in soil and animal and plant samples, Dy N It is the standard value of Dy concentration in soil and animal and plant samples; Take the standard value of REEs concentration in each soil and animal and plant sample at a sampling point, and calculate the abnormal value of typical REEs in each soil and animal and plant sample according to the above formula. An abnormal value greater than 1 indicates that the element is positively abnormal in the sample, and an abnormal value less than 1 indicates that the element is negatively abnormal in the sample. The Wilcoxon test is used to test the significance of the abnormal value of typical REEs in each soil and animal and plant sample at a sampling point, and the significance level is set at p < 0.05; S3-3. Trophic level TL division: Take the δ 15 N, assuming plants as the first trophic level and bioaccumulation of 3.40‰ of δ 15 N, the trophic level of each animal is calculated according to the following formula: TL consumer =(δ 15 N consumer -d 15 N plant )÷3.4+1 Among them, TL consumer is the trophic level of animals in the soil; 15 N consumer is the δ 15 N, unit is ‰; δ 15 N plant is the δ 15 N, unit is ‰.

7. The method for determining the enrichment and transfer rules of REEs in the soil food web around the mining area according to claim 6, characterized in that: The step S3-3 also includes testing the nutrient level: taking the δ of the soil and plants and animals at a sampling point 13 The C content is calculated by δ 15 The trophic levels divided by N are summarized; If the δ of two adjacent trophic level organisms 13 If the C content is similar, the original trophic level relationship is maintained. If not, the new nutritional relationship is determined by detecting and identifying the intestinal DNA sequences of organisms at two adjacent trophic levels. If the DNA in the intestinal contents of the former comes from the latter, then the former preys on the latter.

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