Method for evaluating cadmium enrichment multi-path contribution rate of soil springtail based on stable isotope

Abstract

A method for evaluating the multi-way contribution rate of cadmium enrichment of soil animals based on stable isotopes comprises the steps that S1, a natural abundance Cd solution and a Cd solution enriched by a certain isotope are adopted to prepare a plurality of solutions composed of different isotopes, and the natural abundance is selected as a source needing a large amount of Cd; s2, adding standards to cadmium food sources, and making food with different 113Cd abundance; s3, culturing a substrate, and adding the Cd solution with natural abundance in the S1 into the substrate; s4, soil springtails are added for cadmium exposure culture; and S5, collecting springtails, measuring the ratio of 113Cd to 114Cd of springtails, and respectively calculating contributions of two Cd sources and a plurality of Cd sources according to a formula. According to the method, the stable isotope Cd is used for marking, overlapping of other elements is avoided, interference of other elements can be avoided, and therefore the accuracy of the experiment is improved, and the contribution rate of more than two sources can be distinguished.

Description

Technical Field

[0001] The present invention relates to the technical field of soil biosafety, and particularly to a method for evaluating the contribution rate of the source pathways of cadmium enrichment in soil animals based on stable isotopes. Background Art

[0002] Soil animals, as key components of the soil ecosystem, play important roles in many aspects. On the one hand, they can crush plant litter, roots, and the feces and corpses of various animals, greatly accelerating the rate of microbial decomposition of these substances; at the same time, the direct predation of soil animals on microorganisms also promotes the process of soil nutrient cycling. On the other hand, the burrowing and moving behaviors of soil animals in the soil strongly promote the construction of the soil pore network, and the substances excreted by them contribute to the formation of soil aggregates, thereby optimizing the physical structure of the soil. In summary, soil animals play an indispensable role in promoting soil material cycling and energy conversion, and maintaining the structure and function stability of the soil ecosystem.

[0003] With the rapid development of industry and agriculture, a large number of heavy metal elements have flooded into the soil, resulting in the imbalance of the soil ecosystem, and the problem of cadmium pollution is particularly prominent. For soil animals that inhabit the soil, they are extremely likely to be exposed to heavy metal environments through various channels. First, soil animals are in close contact with soil pore water, and heavy metals can invade the animal body through the soil solution. Second, when soil animals feed on plant roots, litter, soil organic matter, and microorganisms, they will simultaneously ingest the heavy metal elements enriched in these foods. The enrichment of heavy metals in soil animals will not only interfere with the ecological functions of soil animals themselves, but also have a negative impact on the ecological functions of other organisms through the food chain and the cascade effect among soil organisms.

[0004] To accurately evaluate the ecological risks caused by soil heavy metal pollution, effectively control the enrichment and transmission of heavy metals in the soil biological system, and deeply understand the specific pathways by which pollutants invade the animal body, it is crucial. At present, most related studies focus on the soil solution (pore water) exposure pathway of specific pollutants, but ignore the oral exposure pathway of heavy metals in soil animals; especially in the face of the intake of heavy metals from multiple food sources, there is still a lack of effective quantitative discrimination methods.

[0005] The heavy metal stable isotope technique has the ability to trace the emission sources of heavy metal pollutants in the environment and quantify the contribution ratios of different pollution sources, so it is expected to be applied to the exploration of different exposure pathways of soil animals. However, there are certain limitations in this technique at the present stage: on the one hand, the multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) used in the research has a complicated sample preparation process, strict requirements for experimental conditions, and high instrument purchase and operation and maintenance costs; on the other hand, the existing research methods mostly focus on the distinction and quantification between two pollution sources, while the heavy metal exposure pathways faced by soil animals involve multiple food sources in addition to the soil solution source, so there is an urgent need to develop a technical method that can achieve multi-source distinction and quantification and has low costs. Summary of the Invention

[0006] Technical problems to be solved: In view of the phenomenon that soil animals ingest heavy metals through different exposure pathways, the present invention provides a calculation method for quantifying the contributions of a single food source and a solution source, and multiple food sources and a solution source to heavy metals in soil animals by using the stable isotope technique.

[0007] Technical solution: A method for evaluating the contribution rates of multiple pathways of cadmium enrichment by soil springtails based on stable isotopes includes the following steps:

[0008] S1: Use natural abundance Cd solution and any isotope-enriched Cd solution to prepare at least two Cd isotope solutions, and select the natural abundance Cd solution as the solution source with a larger required amount of Cd.

[0009] S2: Grind the food available to springtails into powder, and add the same Cd isotope solutions with different abundances prepared in step S1 for labeling respectively to make foods with the same Cd isotope but different abundances.

[0010] S3: Burn and acid-wash the culture medium to remove organic matter, adjust the pH to 5.5 - 6.5, and add the natural abundance Cd solution prepared in step S1 according to 50% - 70% of the maximum saturated water-holding mass of the culture medium.

[0011] S4: Add the culture medium prepared in S3 to the container. There are at least two feeding points on the surface of the culture medium. The feeding method is divided into dual cadmium sources or multiple cadmium sources. The dual cadmium sources are Cd isotope solution and a single food, and the multiple cadmium sources are Cd isotope solution and at least two foods. Add 100 - 300 springtails and culture them in a growth environment suitable for springtails.

[0012] For the dual cadmium sources, the Cd isotope solutions and foods constructed in step S1 and step S2 contain Cd with different isotope abundances, and formula 1 is constructed to obtain the contribution of Cd from the food to the springtails' bodies.

[0013] Formula 1:

[0014]

[0015] f w-c : Mass fraction of Cd from food to springtails; IR coll : In springtails 113 Cd and 114 Abundance ratio of Cd ( 113 / 114 Cd value); NA 113 , NA 114 : In the Cd isotope solution 113 Cd, 114 Natural abundance of Cd; WA 113 , WA 114 : In food 113 Cd, 114 Relative abundance of Cd;

[0016] For multiple Cd sources, n Cd sources with different abundances are required, where n > 2. At the same time, add n - 2 groups of parallel experimental groups that change the isotope abundance of any one source. Taking n = 3 sources as an example: Cd isotope solution, food 1, and food 2, which have different abundances of Cd isotopes respectively. Construct Equation 2 - 1. At the same time, add n - 2 groups of parallel treatments that change the stable isotope abundance in any one source, and then construct Equation 2 - 2;

[0017] Equation 2 - 1

[0018]

[0019] Equation 2 - 2

[0020]

[0021] IR coll-1 、IR coll-2 Are the abundance ratios of Cd in springtails in food group 2 - 1 and food group 2 - 2 respectively 113 Cd and 114 Cd; f w-c , f s-c Are the mass fractions of Cd from food 1 and Cd isotope solution to springtails respectively; NA 113 , NA 114 : In the Cd isotope solution 113 Cd, 114 Natural abundance of Cd; WA 113 , WA 114 : In food 1 113 Cd, 114 Cd relative abundance; MA1 113 , MA1 114 And MA2 113 , MA2 114They are respectively in Group 1 and Group 2 of parallel processing in Food 2 113 Cd 114 The relative abundance of Cd;

[0022] S5: Collect springtails and measure the content of 113 Cd and 114 The abundance ratio of Cd. Calculate the contributions from dual-Cd sources or multi-Cd sources respectively according to the formula.

[0023] In Steps S1 and S2 113 The abundance ratio of Cd and 114 Cd has differences, and the ratio difference is greater than the detection error of the instrument, 113 The abundance ratio of Cd and 114 Cd is not less than 5%; the Cd abundance in the Cd isotope solution is not limited to natural abundance; the food for the springtails can be wheat straw or saprophytic fungi.

[0024] Preferably, in Step S4, cross-contamination between different Cd sources should be avoided, and the container material used at the feeding point is tin foil.

[0025] The above Step S4 further includes: for a dual-Cd source, obtain the mass fraction f of Cd from food to springtails through Formula 1 w-c , and obtain the mass fraction f of Cd from the Cd isotope solution to springtails according to Formula 3 s-c ; Formula 3: f s-c = 100% - f w-c .

[0026] The above Step S4 further includes: for a multi-Cd source system, obtain the mass fractions f w-c and f s-c of Cd from Food 1 and the Cd isotope solution to springtails through Formulas 2-1 and 2-2, and obtain the mass fraction f f-c of Cd from Food 2 to springtails according to Formula 4 f-c ; Formula 4: f w-c = 100% - f s-c .

[0027] The above Step S5 measures the 113 / 114 Cd value has different error ranges depending on the instrument, and the average mean instrument test error is 1.46%.

[0028] After collecting springtails in the above Step S5, digest the springtails. After digestion of the springtails, use an inductively coupled plasma mass spectrometer to measure that the response value of the Cd isotope is greater than 75000; the number of springtails is greater than 50 - 200, the Cd concentration in the body is 10 - 100 mg / kg; the measured Cd concentration in the solution is greater than 10 mg / kg.

[0029] In the above step S4, the culturing time of springtails is not less than 14 days.

[0030] The above Cd isotope is a stable isotope 106 Cd, 108 Cd, 110 Cd, 111 Cd, 112 Cd, 113 Cd, 114 Cd and 116 Cd.

[0031] The above abundance ratio is not limited to 113 / 114 Cd( 113 The abundance ratio of Cd to 114 Cd), and the labeled isotope and other isotopes can all be used as the ratio.

[0032] Beneficial effects: The present invention provides a quantification method for the phenomenon of soil animals ingesting heavy metals through different exposure pathways, which can accurately calculate the contributions of a single food source and a solution source, as well as multiple food sources and a solution source to heavy metals in soil animals. By using stable isotope technology and ICP-QMS to measure the isotope ratio in springtails, the present invention avoids the problems of complicated sample preparation and high cost in traditional methods, and provides a powerful tool for deeply understanding the specific pathways of pollutants invading soil animals, accurately evaluating the ecological risks caused by soil heavy metal pollution, and effectively controlling the enrichment and transmission of heavy metals in the soil biological system. Description of the Drawings

[0033] Figure 1 : The 113 / 114 Cd value after digestion of springtails polluted by natural abundance cadmium and cadmium reference materials. Among them: the cadmium standard solution used is the GSB-04-1721-2004 solution; the black dotted line on the y-axis in the figure represents the 113 / 114 Cd value of natural abundance, and the green dotted line represents the 113 / 114 Cd value within 5% error range of natural abundance cadmium, and the red dotted line represents the 113 / 114 Cd value within 10% error range of natural abundance cadmium. Specific Embodiments

[0034] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. The materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0035] Example 1 Evaluation of the absorption contribution rate of springtails from two sources (a single food source and a solution source) using stable isotopes

[0036] Collect natural river sand, dry it in an oven at 60 °C, sieve it through a 2-mm sieve, then put it in a muffle furnace and calcine it at 600 °C for 2 h. Then add 1% nitric acid solution to wash it once to remove the organic matter present. Adjust the pH to 5.5 - 6.5 with 0.01 M calcium carbonate suspension. Determine the pH of the sand according to HJ 962 - 2018 and determine the organic matter of the sand according to GB 9834 - 88.

[0037] Prepare a solution of CdCl2 with natural abundance ( 113 Cd = 12.22%) with a concentration of 0.1 mg / kg. Add it to the sand at a mass ratio of 1:1 to prepare sand with a cadmium concentration of 0.1 mg / kg. After standing for 48 h, dry it at 45 °C for later use.

[0038] Prepare a solution of Cd(NO3)2 with high abundance ( 113 Cd = 94.72%) with a concentration of 22 mg / kg. After blanching wheat straw at 105 °C, cut it into pieces, grind it, and sieve it through a 0.2-mm sieve. Mix it with 113 the Cd-labeled solution at a mass ratio of 1:1 to prepare wheat straw with a cadmium concentration of 22 mg / kg. Dry it at 60 °C for later use.

[0039] Take 100 g of sand and put it in a 350-mL (height 5.9 cm, minimum inner diameter 9.4 cm, maximum outer diameter 10.3 cm) plastic container. The sand contains no cadmium or has a cadmium concentration of 0.1 mg / kg. Add 9.6 g of water and keep the moisture at 60% of the maximum water-holding capacity per unit mass of sand saturated. Measure the maximum water-holding capacity per unit mass of sand saturated according to the OECD guidelines to prepare Cd(0 mg / kg) and Cd(0.1 mg / kg) sand culture substrates. Fold tin foil into 1-cm 2 small squares and place them on the surface of the sand for placing food.

[0040] Synchronized larvae at 9 - 12 days old were selected and introduced into Cd (0 mg / kg) and Cd (0.1 mg / kg) sand culture media respectively, with 3 replicates. Each replicate had 300 springtails and they were cultured in a climate chamber (20 ± 1°C, humidity 75%, dark: light = 12:12, light intensity 800 lux) for 21 days. During this period, the food was fed twice a week. For the Cd (0 mg / kg) and Cd (0.1 mg / kg) sand culture media treatments, wheat straws with corresponding cadmium concentrations were fed: wheat straw with 0 mg / kg cadmium concentration and wheat straw with 22 mg / kg cadmium concentration. After 21 days, the live animals were extracted from the springtails using a temperature gradient insect dryer. The extracted animals were given a 24 - 48 - hour intestinal purge, floating on the water surface for 24 h to 48 h until no obvious inclusions were observed in their white and transparent intestines by the naked eye. The insects were transferred to 2 - mL centrifuge tubes, added with ultrapure water, sonicated for 15 minutes, and then rinsed three times with ultrapure water to remove the heavy metal ions attached to the surface. The washed animals were frozen at - 80°C for 30 min and then taken out after being freeze - dried in a freeze - drying machine for 48 h. The materials required for digestion were soaked in a 10% - 20% nitric acid solution one day in advance. The polytetrafluoroethylene jars and beakers were rinsed twice with tap water and deionized water and once with ultrapure water after acid soaking, and then air - dried for later use. 1 - 2 mg of the sample was weighed on a one - millionth balance and placed in a polytetrafluoroethylene tube. 0.45 mL of chromatographic - grade nitric acid and 0.15 mL of analytical - grade hydrogen peroxide were added to each tube. At the same time, three blanks and three standard sample controls were set. The tubes were placed on a hot plate, heated at 105°C for 4 h to drive off the acid, and then heated at 180°C to drive off the acid until there was only one drop of thick liquid left in the tube. Then it was transferred to a 10 - mL centrifuge tube, and 1% chromatographic - grade nitric acid was added to make the volume up to 3 mL. After passing through a 0.45 - micron filter membrane, it was stored in a 4°C refrigerator for later use. Inductively coupled plasma mass spectrometry (ICP - MS, PerkinElmer NexION 2000) was used to measure the 113 / 114 molar ratio of Cd in the digestion solution. By the isotope dilution traceability method, the amount of the isotope - labeled element in the digestion solution was calculated. The contribution of cadmium straw source in springtails was:

[0041]

[0042] f w-c : the mass fraction of cadmium from wheat straw to springtails; IRcoll: the 113 / 114 Cd value in springtails; NA 113 ,NA 114 : in the soil solution 113 Cd, 114 Cd natural abundance; WA 113 ,WA 114 : in wheat straw 113 Cd, 114 the relative abundance of Cd.

[0043] The specific results are as follows:

[0044] (1) Isotope ratios of sand culture solution and straw food

[0045] Table 1 Isotope abundances and isotope ratios of Cd in sand culture solution and wheat straw after labeling 113 Cd and 114 Isotope abundances and isotope ratios of Cd

[0046] Cadmium source <![CDATA 113 Cd abundance (%)]]> <![CDATA 114 Cd abundance (%)]]> <![CDATA 113 / 114 Cd]]> Wheat straw 94.66 2.66 35.59 Solution 12.22 24.73 0.49

[0047] Calculations can be performed using the known abundances (Table 1) and the cadmium isotope ratios of each sample (mean and standard deviation of isotope ratios in springtails: 5.33 ± 0.44).

[0048] (2) Contributions of straw and solution - sourced cadmium to springtails

[0049] Following the above - mentioned method, by measuring the cadmium isotope ratios in springtails, the contributions of food - sourced cadmium and solution - sourced cadmium to the cadmium uptake in springtails were calculated, as shown in Table 2

[0050] Table 2 Contributions of cadmium from single food - source wheat straw and sand solution to cadmium in springtails

[0051] Concentration of sand culture medium (mg / kg) Contribution of cadmium in straw (%) Contribution of cadmium in solution (%) 0.1 64.7 35.3

[0052] Data are the means of 3 biological replicates.

[0053] The above results indicate that in low - pollution areas, the food exposure risk of springtails is very high, and more cadmium is obtained from food than from the solution.

[0054] Example 2 Evaluation of the contribution rates of three cadmium sources (dual food sources and solution source) enriched by springtails using stable isotopes

[0055] Prepare a solution of high - abundance Cd(NO3)2( 113 Cd = 80.16%, 113 Cd = 63.99%) with a concentration of 60 mg / kg. The saprophytic fungus (Phanerochaete chrysosporium) was inoculated into a glucose - potato liquid medium for cultivation and enrichment, then filtered and freeze - dried to obtain the dry matter of the saprophytic fungus. It was respectively mixed with 113 Cd = 80.16%, 113 Cd = 63.99% solutions in a mass ratio of 1:1, and then freeze - dried to obtain high - and low - standard saprophytic fungus food for springtails.

[0056] Select larvae at 9 - 12 days of synchronization and introduce them into sand culture media with Cd(0mg / kg) and Cd(0.1mg / kg) respectively. Repeat 3 times, with 300 springtails in each repetition. Place them in a climate chamber (20±1℃, humidity 75%, dark:bright = 12:12, light intensity 800lux) for 21 days. The food sources are straw and saprophytic fungal food sources. The straw source is the above 113 Cd = 94.72% labeled food source. For each concentration, set up straw + high - labeled saprophytic fungal food source and straw + low - labeled saprophytic fungal food source, with 6 culture bottles.

[0057] The process of collecting and digesting springtails is the same as above.

[0058]

[0059] f w-c ,f s-c : The mass fraction of cadmium from wheat straw, soil solution to springtails; IR coll-1 ,IR coll-2 : Cd values in high - and low - labeled springtails 113 / 114 ; NA 113 ,NA 114 : Cd in soil solution 113 Cd, 114 Cd natural abundance; WA 113 ,WA 114 : Cd in wheat straw 113 Cd, 114 Relative abundance of Cd; MA1 113 、MA 2 113 ,MA1 114 、MA 2 114 : Cd in high - and low - labeled saprophytic fungi 113 Cd, 114 Relative abundance of Cd.

[0060] The specific results are as follows:

[0061] (1) Isotope ratios of sand culture solution and straw food

[0062] Table 3 Isotope abundances and isotope ratios of Cd and 113 Cd in sand solution, labeled wheat straw, and saprophytic fungi 114 Cd

[0063] Cadmium source <![CDATA 113 Cd abundance (%)]]> <![CDATA 114 Cd abundance (%)]]> <![CDATA 113 / 114 Cd]]> Wheat straw 94.66 2.66 35.59 Solution 12.22 24.73 0.49 Saprophytic fungi parallel group 1 80.15 8.15 9.83 Saprophytic fungi parallel group 2 63.99 14.14 4.53

[0064] Based on the known abundances (Table 3) and the cadmium isotope ratios of each sample, calculations can be carried out (mean and standard deviation of isotope ratios in springtails: parallel group 1 is 7.43±0.79, parallel group 2 is 4.04±0.91).

[0065] According to the above method, by measuring the cadmium isotope ratio in springtails, the contributions of cadmium from dual food sources and cadmium from solution sources to the cadmium uptake in springtails were calculated, as shown in Table 4.

[0066] Table 4 Contributions of cadmium from wheat straw of dual food sources, cadmium from saprophytic fungi, and cadmium from sand solution to cadmium in springtails

[0067] Concentration of sand culture medium (mg / kg) Contribution of cadmium in straw (%) Contribution of cadmium in solution (%) Contribution of saprophytic fungi (%) 0.1 7.22 14.1 78.68

[0068] The above results indicate that springtails have obvious feeding preference behaviors for food. Although the contamination of saprophytic fungi is higher, springtails tend to feed on saprophytic fungi. Secondly, under low contamination, the main source of cadmium in springtails is obtained through food.

Claims

1. A method for evaluating the contribution rates of multiple pathways of cadmium enrichment by soil springtails based on stable isotopes, characterized in that, It includes the following steps: S1: Prepare at least two Cd isotope solutions using natural abundance Cd solution and any isotope-enriched Cd solution, and select the natural abundance Cd solution as the solution source with a larger required amount of Cd; S2: Grind the food that can be eaten by springtails into powder, and add the same Cd isotope solutions with different abundances prepared in step S1 for labeling to make foods with the same Cd isotope but different abundances; S3: Burn and acid-wash the culture medium to remove organic matter, adjust the pH to 5.5 - 6.5, and add the natural abundance Cd solution prepared in step S1 according to 50% - 70% of the maximum saturated water-holding mass of the culture medium; S4: Add the culture medium prepared in S3 to the container. There are at least two feeding points on the surface of the culture medium. The feeding methods are divided into dual Cd sources or multiple Cd sources. The dual Cd source is the Cd isotope solution and a single food, and the multiple Cd sources are the Cd isotope solution and at least two foods. Add 100 - 300 springtails and culture them in a suitable growth environment for springtails; For the dual Cd source, the Cd isotope solutions and foods constructed in step S1 and step S2 contain Cd with different isotope abundances, construct formula 1 to obtain the contribution of Cd from the food to the springtails' bodies; Formula 1: f w-c : Mass fraction of Cd from food to springtails; IR coll : In springtails 113 Abundance ratio of Cd to 114 Cd in springtails ([[]] 113 / 114 Cd value); NA 113 , NA 114 : In Cd isotope solution 113 Cd, 114 Natural abundance of Cd; WA 113 , WA 114 : In food 113 Cd, 114 Relative abundance of Cd; For multiple Cd sources, n Cd sources with different abundances are required, n > 2. At the same time, add n - 2 groups of parallel experimental groups that change the isotope abundance of any one source. Taking n = 3 sources as an example: Cd isotope solution, food 1, and food 2, which respectively have different abundances of Cd isotopes, construct formula 2 - 1. At the same time, add n - 2 groups of parallel treatments that change the stable isotope abundance in any one source, and then construct formula 2 - 2; Formula 2 - 1 Formula 2 - 2 IR coll-1 and IR coll-2 are respectively the abundance ratios of Cd in the springtails in Food Group 2-1 and Food Group 2-2 113 to 114 Cd; f w-c and f s-c are respectively the mass fractions of Cd from Food 1 and the Cd isotope solution in the springtails; NA 113 and NA 114 : 113 Cd 114 in the Cd isotope solution 113 is the natural abundance of 114 Cd; WA 113 and WA 114 : 113 Cd 114 in Food 1 113 is the relative abundance of 114 and MA2 113， MA2 114 are respectively the relative abundances of 113 Cd 114 in the parallel treatment groups 1 and 2 of Food 2 S5: Collect springtails and measure the abundance ratio of 113 Cd to 114 Cd in the springtails, and calculate the contributions from dual Cd sources or multiple Cd sources respectively according to the formula. 113 Cd and 114 Cd, and calculate the contributions from dual Cd sources or multiple Cd sources respectively according to the formula.

2. The method according to claim 1, wherein In steps S1 and S2 113 The Cd and 114 The abundance ratio of Cd has a difference, and the ratio difference is greater than the detection error of the instrument. 113 The Cd and 114 The abundance ratio difference of Cd is not less than 5%; the cadmium abundance of the Cd isotope solution is not limited to natural abundance; the edible food of the springtail is wheat straw or saprophytic fungi.

3. The method according to claim 1, wherein In step S4, cross-contamination should be avoided for different Cd sources, and the container material used for the feeding points is tin foil.

4. The method according to claim 1, wherein The step S4 further includes: for the dual cadmium sources, obtaining the mass fraction f of Cd from food to the springtails through Formula 1 w-c , and obtaining the mass fraction f of Cd from the Cd isotope solution to the springtails according to Formula 3 s-c ; Formula 3: f s-c = 100% - f w-c .

5. The method according to claim 1, characterized in that The step S4 further includes: for a multi-cadmium source system, obtaining the mass fraction f of Cd in food 1 and Cd isotope solution in the springtails through Formulas 2-1 and 2-2 w-c and f s-c , and obtaining the mass fraction f of Cd in food 2 in the springtails according to Formula 4 f-c ; Formula 4: f f-c = 100% - f w-c - f s-c .

6. The method according to claim 1, characterized in that, The step S5 measures the 113 / 114 The error range of the Cd value varies according to different instruments, and the average error of instrument testing is 1.46%.

7. The method according to claim 6, characterized in that, In step S5, after collecting the springtails, digest the springtails. After digestion of the springtails, the response value of the Cd isotope measured by inductively coupled plasma mass spectrometry is greater than 75000; the number of springtails is greater than 50 - 200, and the Cd concentration in the body is 10 - 100 mg / kg; the measured Cd concentration in the solution is greater than 10 mg / kg.

8. The method according to claim 6, wherein In step S4, the culture time of the springtails is not less than 14 days.

9. The method according to claim 1, characterized in that The Cd isotopes are stable isotopes 106 Cd, 108 Cd, 110 Cd, 111 Cd, 112 Cd, 113 Cd, 114 Cd and 116 Cd.

10. The method according to claim 1, characterized in that, The abundance ratio is not limited to 113 / 114 Cd( 113 the abundance ratio of Cd to 114 Cd), and the labeled isotope and other isotopes can both be used as the ratio.

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