Bio-availability prediction method based on Cd nano-colloid

Abstract

The invention belongs to the technical field of metal bioavailability prediction, and particularly relates to a bioavailability prediction method based on Cd nano colloid. According to the method, the Cd nano-colloid and the ionic Cd are taken as research objects, the difference of the Cd nano-colloid and the ionic Cd on the bioavailability contributed by the rice is disclosed from the aspect of biodynamics, the dynamic bioaccumulation of the Cd nano-colloid and the ionic Cd in a plant body is explored, and a bioaccumulation dynamics prediction method including the Cd nano-colloid is established; a foundation is laid for further research on prevention and control of Cd nano colloid biological accumulation including the rice field by comprehensive regulation and control measures, and a new reference approach is provided for precise prevention and regulation and control of CdS pollution including rice field soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal bioavailability prediction, and more specifically, relates to a bioavailability prediction method based on Cd nano-colloid. Background Art

[0002] Cadmium (Cd) pollution in rice is a major national and people's livelihood issue related to food security. Rice is widely cultivated and is the main carrier of Cd into the human body. For a long time, the biogeochemical behavior and bioavailability of Cd in rice field systems have been scientific issues of key concern in the international academic community. High concentrations of Cd in rice field soils and their accumulation in rice and migration in the food chain are global environmental issues.

[0003] At present, the content level and environmental risk assessment of pollutants in soil are mostly based on the total concentration of pollutants. However, the total concentration is not correlated with the actual biological effects of pollutants in soil. The toxicity of Cd in soil does not depend on the total amount of Cd in the soil, but is related to the existence form of Cd in the soil. Studies have shown that the formation, migration and release process of Cd nanocolloids in paddy soil systems are closely related to the Cd absorption pathway of rice. However, in traditional studies, it is often limited to soil dissolved Cd (i.e., components that can pass through the 450nm filter membrane) and it is assumed that "dissolved is effective", but the existence of nanocolloids and their differences in environmental behavior with dissolved ions are ignored. The mainstream view is that the ionic state is the main form that is easily utilized by organisms. Therefore, the classical model (such as the bio-ligand model) mainly focuses on the biological effects of ionic metals, but rarely involves the contribution of colloidal metals, which leads to deviations in the bioaccumulation assessment of metals. In rice field ecosystems, insufficient knowledge of the bioavailability of Cd nanocolloids not only hinders researchers from accurately predicting the bioavailability of Cd under different environmental conditions, but also poses significant challenges to the precise remediation and safe utilization of Cd-contaminated rice fields.

[0004] Nanocolloids are usually defined as particulate matter with a particle size within the nanoscale (1-1000nm) in at least one dimension. This substance is actually a heterogeneous mixture of nanoparticles mixed with other organic or inorganic components. Based on Tessier's classification method, the forms of Cd in soil can be divided into five categories, including exchangeable, carbonate-bound, organic-bound, iron-manganese oxide-bound, and residual. Among these forms, exchangeable cadmium (i.e., ionic cadmium) has attracted much attention due to its significant bioavailability and fluidity, high toxicity, and easy absorption and utilization by organisms. In paddy soil, nanocolloidal Cd often exists in a composite form, mainly in the form of adsorption or complexation between Cd and soil nanocolloids, such as Cd-kaolin, Cd-iron oxide, and Cd-humic acid complexes, which are the main forms of Cd nanocolloids in soil. In flooded and organic matter (OM)-rich paddy soil, the redox potential (Eh) is low, and Cd 2+ It mainly exists in the form of CdS precipitation.

[0005] Currently, there are few studies on Cd nanocolloids in soil. In paddy fields, the relationship between exposure of rice to Cd nanocolloids and its bioaccumulation is still unclear, making it difficult to accurately assess and predict the environmental risks of cadmium in paddy fields. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the prior art that there is little research on Cd nanocolloids in soil, especially the relationship between the exposure of Cd nanocolloids to rice and its bioaccumulation is still unclear, making it difficult to accurately evaluate and predict the environmental risks of cadmium in rice fields, and to provide a method for predicting the bioavailability based on Cd nanocolloids.

[0007] The object of the present invention is to provide an application of the bioavailability prediction method in predicting metal bioavailability.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0009] The present invention protects a method for predicting the bioavailability based on Cd nano-colloids, comprising the following steps:

[0010] S1. Conduct plant exposure experiments to expose selected plants to media containing known concentrations and forms of Cd;

[0011] S2. Collect plant samples after exposure and determine the content of different forms of Cd in them;

[0012] S3. Based on the data obtained in step S2, determine the absorption rate constant K of plants for different forms of Cd u ;

[0013] S4. K obtained according to step S3 u , a kinetic model of plant absorption of metal Cd was established to quantitatively predict the bioavailability of Cd in plants when the Cd concentration in the environment was known. The formula of the kinetic model of metal Cd absorption is as follows:

[0014]

[0015] In the formula: [Cd] plants ——Cd concentration accumulated in plants;

[0016] [Cd] total ——Total Cd concentration in the culture system;

[0017] [Cd] diss ——The concentration of ionic Cd in the culture system;

[0018] [Cd] NP ——The concentration of colloidal Cd in the culture system;

[0019] k u，total ——absorption rate constant of total Cd in the culture system;

[0020] K u，diss ——The absorption rate constant of ionic Cd by plants in the culture system;

[0021] K u,NP ——The absorption rate constant of colloidal Cd by plants in the culture system;

[0022] Wherein, in steps S1 to S4, the Cd is in a colloidal state and an ionic state.

[0023] The current mainstream view is that the ionic state is the main form that is easily utilized by organisms. Therefore, the classical models (such as the bio-ligand model) mainly focus on the biological effects of ionic metals, but rarely involve the contribution of colloidal metals, which leads to deviations in the bioaccumulation assessment of metals. The present invention uses Cd nano-colloids and ionic Cd as research objects, reveals the difference in the bioavailability of Cd nano-colloids and ionic Cd to plants from the perspective of biodynamics, explores the dynamic bioaccumulation of Cd nano-colloids and ionic Cd in plants, and establishes a bioaccumulation kinetic prediction method including Cd nano-colloids and ionic Cd, providing a new reference for the precise prevention and regulation of soil colloidal Cd pollution.

[0024] Furthermore, when the plant body refers to the leaves of the plant or the root system of the plant, the absorption kinetic model of the metal Cd is formulated as follows:

[0025] or

[0026]

[0027] [Cd] diss ——The concentration of ionic Cd in the culture system;

[0028] [Cd] NP ——The concentration of colloidal Cd in the culture system;

[0029] K R,diss ——The absorption rate constant of ionic Cd by the roots of plants in the culture system;

[0030] K L,diss ——The absorption rate constant of ionic Cd by the leaves of plants in the culture system;

[0031] K R,NP ——The absorption rate constant of colloidal Cd by the roots of plants in the culture system;

[0032] K L,NP ——The absorption rate constant of colloidal Cd by the leaves of plants in the culture system.

[0033] Furthermore, the absorption rate constant K of Cd is u The method to determine is:

[0034] The accumulation of metal Cd in plants was determined by exposure experiments within the environmental concentration range, and the absorption rate constant K was calculated. u .

[0035] Specifically, the absorption rate constant K of Cd is u It is obtained specifically by the following method: by analyzing the relationship between the cumulative amount of Cd in the plant and the exposure time, the slope obtained after fitting a straight line is the Cd absorption rate; then analyzing the relationship between the plant's absorption rate of Cd and the Cd concentration in the exposure system, fitting a curve, and the obtained slope is the Cd absorption rate constant.

[0036] Furthermore, the accumulation of metal Cd in the plant body is determined using inductively coupled plasma mass spectrometry analysis technology and / or single particle inductively coupled plasma mass spectrometry technology.

[0037] Furthermore, the inductively coupled plasma mass spectrometry analysis technique is to use an inductively coupled plasma mass spectrometer (ICP-MS) for determination, specifically, the determination is carried out in a collision mode, using 50 μg / L In as an internal standard element to correct the instrument baseline drift.

[0038] Furthermore, the single particle inductively coupled plasma mass spectrometry technique is determined using a single particle inductively coupled plasma mass spectrometer (SP-ICP-MS), and the fast TRA mode is selected for single particle analysis, and the (AgNP) 40nm, 0.02mg / mL, Sigma-aldrich) standard solution is diluted to 5ng / L as a reference material. The response factor correction standard requires the preparation of a 1μg / L standard solution of the measured element Cd ion (IonicStd(AN)) and a reference material Ag ion standard solution (IonicStd(RN)); a 2% HNO3 solution is selected as the response factor correction blank (IonicBlk).

[0039] Furthermore, the plant is a grass plant.

[0040] Furthermore, the grass plant includes any one of rice and wheat.

[0041] When the plant is rice, a kinetic model of rice absorption of ionic and colloidal Cd is established to obtain the absorption rate constant K u :K R,diss =0.07874, K R,NP =0.062175, K L,diss =7.623×10 -4 , K L,NP =7.323×10 -4 , which is used to quantify the bioavailability of Cd in rice when the concentration of Cd in the environment is known.

[0042] Furthermore, the colloidal Cd includes any one of CdS, Cd(OH)2, and CdCO3.

[0043] Preferably, when the plant is rice, the colloidal Cd is CdS. In paddy field soil, the redox potential (Eh) is low, and Cd 2+ It mainly exists in the form of CdS precipitation.

[0044] Furthermore, the CdS is purchased from the market or prepared in-house, and the preparation in-house includes the following steps: fully mixing the cadmium salt solution and the sulfur source dispersion, fully reacting at 250-240° C., and post-treating to obtain CdS.

[0045] Furthermore, the cadmium salt is selected from one or more of CdCl2 and Cd(NO3)2.

[0046] Furthermore, the sulfur source is selected from one or more of thioacetamide and thiourea.

[0047] Furthermore, when the cadmium salt is selected from cadmium acetate, the cadmium salt solution is preferably a cadmium salt oleic acid solution; when the sulfur source is selected from thioacetamide, the sulfur source dispersion is a sulfur source oleic acid dispersion.

[0048] Furthermore, the particle size of the colloidal Cd is 1 to 1000 nm, preferably 1 to 450 nm, and more preferably 1 to 50 nm.

[0049] Furthermore, the ionic Cd is selected from any one of CdCl2 and Cd(NO3)2.

[0050] Furthermore, the mixed sulfur source dispersion is obtained by ultrasonic dissolution at 20-30°C.

[0051] Furthermore, the sufficient mixing is stirring at room temperature for 0.5 to 2 hours, more preferably for 1 hour.

[0052] Furthermore, the sufficient reaction time is 3 to 8 hours, more preferably 5 hours.

[0053] Furthermore, the post-treatment includes centrifugation, washing and drying.

[0054] Furthermore, the centrifugal conditions are: 8000-12000 rpm for 15-300 min.

[0055] Furthermore, the washing is performed with anhydrous ethanol and water for 3 to 6 times respectively.

[0056] Furthermore, the drying is vacuum freeze drying, and the conditions are drying at -70 to -80°C (preferably -80°C) for 1 to 3 days (preferably 2 days).

[0057] Furthermore, the exposure test is a hydroponic exposure experiment.

[0058] Furthermore, in step S2, the processing of the collected exposed plant samples includes pretreatment and formal treatment, wherein the pretreatment is to remove the Cd remaining on the surface of the plant samples.

[0059] Furthermore, the pretreatment includes soaking, washing and drying.

[0060] Furthermore, the soaking is performed by taking a chelating agent solution as a soaking solvent and performing ultrasonic treatment.

[0061] Furthermore, the chelating agent is preferably 15 to 25 mmol / L N a2 -EDTA.

[0062] Furthermore, the washing is washing with ultrapure water.

[0063] Furthermore, the drying is to first absorb the moisture on the surface of the plant sample after washing, then heat it at 100-110°C to kill the green, and then dry it at 50-70°C to constant weight.

[0064] Specifically, the pretreatment is to soak the collected exposed plant samples in 15-25 mmol / L N a2 -EDTA, ultrasonically treat for 10 to 20 minutes, then wash with ultrapure water, dry the surface moisture of the plant sample, heat at 100 to 110°C for 25 to 35 minutes, and dry at 50 to 70°C to constant weight.

[0065] Furthermore, the formal treatment method includes acid digestion or enzymatic hydrolysis.

[0066] Furthermore, the acid digestion method uses 60-70% HNO3 and is sealed and digested at a constant temperature of 85-95°C for 5-7h until the solution is clear and transparent. After diluting it with ultrapure water to an acidity of 1-5% in a certain proportion, it is filtered with a filter membrane (preferably 0.22μm polytetrafluoroethylene), and the Cd content can be determined by mass spectrometry analysis.

[0067] Furthermore, the enzymatic hydrolysis method is as follows: the pretreated plant sample is homogenized, and then added to a mixed enzyme solution containing cellulase and cleavage enzyme, and fully enzymolyzed (enzymolyzed at 30-40°C for 20-30 hours), and then allowed to stand for stratification, and the supernatant is diluted with water and measured using mass spectrometry. The content of colloidal Cd therein can be measured using a single particle inductively coupled plasma mass spectrometer.

[0068] Furthermore, the cellulase is Cellulase R-10.

[0069] Furthermore, the cleavage enzyme is Macerozyme R-10.

[0070] Furthermore, the mass ratio of the cellulase to the maceration enzyme is 1:(8-12).

[0071] Further, as an optional embodiment, the preparation method of the mixed enzyme solution containing cellulase and cleavage enzyme is as follows: prepare 2mM citrate buffer (0.4203g / L), adjust the pH to 5.5 with NaOH. Dissolve 1g of Macerozyme R-10 enzyme powder and 0.1g of Cellulase R-10 in 20mL of ultrapure water to prepare a 5% Macerozyme R-10 and 0.5% Cellulase R-10 mixed enzymatic solution.

[0072] Furthermore, the homogenization is to cut the pretreated plant sample into segments, add the segments into a citric acid buffer, and prepare the tissue homogenate using a tissue homogenizer. Furthermore, the concentration of the citric acid buffer is 1 to 3 mM.

[0073] The present invention protects the application of the bioavailability prediction method in predicting the bioavailability of metals.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] The present invention takes Cd nano-colloid and ionic Cd as research objects, reveals the difference in the bioavailability of Cd nano-colloid and ionic Cd to rice from the perspective of biodynamics, explores the dynamic bioaccumulation of Cd nano-colloid and ionic Cd in plants, and establishes a bioaccumulation kinetics prediction method including Cd nano-colloid, laying the foundation for further research on comprehensive regulatory measures to prevent the bioaccumulation of Cd nano-colloid including rice fields, and provides a new reference approach for the precise prevention and regulation of CdS pollution including rice field soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 This is the XRD pattern of the CdS nanoparticles obtained in Example 1.

[0077] Figure 2 This is the TEM image of CdS nanoparticles obtained in Example 1.

[0078] Figure 3 This is an enlarged TEM image of the CdS nanoparticles obtained in Example 1.

[0079] Figure 4 This is a curve showing the growth of Cd accumulation in the roots of rice as the exposure time increases in the 9-day exposure experiment under the same concentration.

[0080] Figure 5 This is a curve showing the growth of Cd accumulation in rice leaves as the exposure time increases in the 9-day exposure experiment under the same concentration.

[0081] Figure 6 The graph shows the accumulation of Cd in rice roots (left) and leaves (right) in an ionic system at four concentrations as the exposure time increases.

[0082] Figure 7 The graph shows the accumulation of Cd in rice roots (left) and leaves (right) in the colloidal system at four concentrations as the exposure time increases.

[0083] Figure 8 This is a statistical graph showing the change in rice's absorption rate of ionic Cd as the Cd concentration in the system changes.

[0084] Fig. 9This is a statistical graph showing the change in the colloidal Cd absorption rate of rice as the Cd concentration in the system changes.

[0085] Fig.10 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice roots after exposure to CdSNPs at a concentration of 0.056 mg / L.

[0086] Fig.11 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice roots after exposure to CdSNPs at a concentration of 0.3 mg / L.

[0087] Fig.12 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice roots after exposure to CdSNPs at a concentration of 0.6 mg / L.

[0088] Fig.13 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice roots after exposure to CdSNPs at a concentration of 1.5 mg / L.

[0089] Fig.14 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice leaves after exposure to CdSNPs at a concentration of 0.056 mg / L.

[0090] Fig.15 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice leaves after exposure to CdSNPs at a concentration of 0.3 mg / L.

[0091] Fig.16 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice leaves after exposure to CdSNPs at a concentration of 0.6 mg / L.

[0092] Fig.17 Statistical graph of the measured values ​​(scatter points) and predicted values ​​(shaded area) of Cd concentration in rice leaves after exposure to CdSNPs at a concentration of 1.5 mg / L. DETAILED DESCRIPTION

[0093] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0094] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0095] The ionic Cd in this embodiment is derived from CdCl2.

[0096] Example 1 Preparation of CdS Nanoparticles

[0097] The preparation method of CdS nanoparticles comprises the following steps:

[0098] Take 1.4mmol cadmium acetate (0.3227g) and 11.2mmol thioacetamide (0.8500g) and dissolve them in 90mL oleic acid (thioacetamide is very difficult to dissolve, so it is ultrasonically dissolved at 60℃ in an ultrasonic cleaner). Slowly add the thioacetamide solution to the cadmium acetate solution and mix it evenly (180mL). After stirring at 25℃ for 1h, transfer it to a reactor with a capacity of 300ml polytetrafluoroethylene lining, then put it in an oven for heating, react at 180℃ for 5h, and cool it to room temperature. The reaction produces a yellow suspension, which is evenly divided into 2 50mL centrifuge tubes for centrifugation (30mL*2, 10000rpm, 15min), remove the supernatant, wash it with anhydrous ethanol and deionized water 5 times each, centrifuge (10000rpm, 20min) to separate the CdS nanocolloid solution, and vacuum freeze-dry (-80℃, 2d) to obtain CdS nanoparticles for preservation. The obtained CdS nano-colloid solution was subjected to TEM and XRD measurements. The results are as follows: Figures 1 to 3 As shown in the X-ray polycrystal diffraction (XRD) pattern ( Figure 1 ) Compared with the standard PDF card spectrum, it can be seen that the CdS nanoparticles prepared above have a good crystal morphology, and the material is relatively pure without any other substances mixed. Further characterization observation by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurement showed that the average particle size was 20nm ( Figures 2-3 ).

[0099] Example 2 Rice cultivation and exposure experiment

[0100] The rice variety used in the present invention is Huanghuazhan, which is a high-yield, high-quality and widely adaptable conventional indica rice variety bred by the Rice Research Institute of Guangdong Academy of Agricultural Sciences. Huanghuazhan is a rice variety for both early, mid and late harvests, suitable for a variety of ecological types and adapting to a variety of emerging farming models. In actual production, Huanghuazhan also exhibits excellent lodging resistance, disease resistance and strong regeneration ability. As of 2017, Huanghuazhan has promoted an area of ​​125 million mu in the southern rice-growing areas as a single variety, becoming the country's largest high-quality conventional rice variety in terms of planting area.

[0101] Seed germination: First, soak the rice seeds in 2% NaClO solution for 20 minutes to disinfect the surface, then rinse with deionized water three times, and germinate the sterile seeds in a dark and humid environment for 5 days. Select healthy seedlings with similar growth conditions and transfer them to seedling trays, and then carry out a 16-hour light / 8-hour dark cycle in the greenhouse (temperature controlled at 27±1°C). After the seedlings are allowed to grow and develop for 5 days, the rice is transferred to a new container (a large rectangular storage pot) and cultured with half-concentration rice nutrient solution (the nutrient solution is changed every 3 to 5 days). When the rice grows to the two-leaf and one-heart stage (about 15 days), the rice is transferred to a 2L polypropylene beaker for exposure experiments in different systems.

[0102] Exposure experiment 1: 0.6 mg / L artificially synthesized CdS nanocolloid with a particle size of 20 nm and 0.6 mg / L ionic Cd (derived from CdCl2) were used for 9 days, with 3 parallel samples and a group of blank samples set up in each group. To prevent the nanocolloid from agglomerating and precipitating, a magnetic stirrer was used to stir continuously. There were 11 time periods in 9 days (0h, 6h, 12h, 24h, 36h, 48h (2d), 72h (3d), 96h (4d), 120h (5d), 168h (7d), 216h (9d)).

[0103] Exposure experiment 2: 20nm CdS nanoparticles and CdCl2 were selected as ionic cadmium. The two forms of cadmium were set at four concentrations of 0.056mg / L, 0.3mg / L, 0.6mg / L and 1.5mg / L, respectively. CdS nanocolloid and ionic Cd were exposed to water for 9 days. Three parallel samples and one blank sample were set for each group. To prevent the nanocolloid from agglomerating and precipitating, a magnetic stirrer was used to stir continuously. Rice root and leaf samples were exposed to water for 9 days in 11 time periods (0h, 6h, 12h, 24h, 36h, 48h (2d), 72h (3d), 96h (4d), 120h (5d), 168h (7d), 216h (9d)).

[0104] Example 3 Processing and determination of rice samples

[0105] 1. Experimental methods

[0106] (1) Determination of cadmium content in the hydroponic exposure experiment of ionic Cd

[0107] (1.1) Determination of ionic cadmium content in hydroponic system

[0108] Two samples of nutrient solution were collected from the hydroponic system, each with 0.5 mL. One sample of nutrient solution was centrifuged and filtered through an ultrafiltration tube with a molecular weight cutoff of 3 kDa (5000 g, 20 min) (pre-treated by soaking in 0.1 M CuSO4 to saturate the adsorption sites of the filter membrane) to collect Cd2+ (Ultrafiltration tube method). Another portion of the nutrient solution was added with 1 mL of 65% HNO3 (Fisher Chemical), placed in a dry block heater (IKA) at 90°C for 6 h, and then diluted with ultrapure water to 1-5% acidity (acid digestion method). The Cd in the solution and in the rice body were measured by ICP-MS. 2+ Theoretically, the above ultrafiltration tube method measures the ionic cadmium in the hydroponic system (nutrient solution), and the acid digestion method measures the total cadmium concentration in the hydroponic system (nutrient solution). However, since ionic cadmium was added to the ionic Cd hydroponic exposure experiment, the concentrations of total cadmium and ionic cadmium are consistent, and the results also show that the Cd measured by the two methods is consistent. 2+ The results of the content were consistent. The acid digestion method was then used to directly determine the Cd in the hydroponic system in the ionic Cd hydroponic exposure experiment. 2+ Concentration refers to the concentration of ionic cadmium in the hydroponic system.

[0109] (1.2) Determination of total cadmium content in rice samples

[0110] Rice root and leaf samples were collected. After collection, the rice samples were immersed in 20 mmol / L Na2-EDTA solution for 15 min of ultrasound to remove the Cd residual on the root or leaf surface. Then they were washed with ultrapure water, the surface moisture was absorbed with absorbent paper, and they were placed in a 105°C oven for 30 min. Then they were placed in an oven at 60°C to dry to constant weight. They were weighed with a microbalance (Mettler ToledoXPR2U, 0.1 μg), and the weight of the leaf part and the root was recorded.

[0111] The weighed rice samples were transferred to Corning tubes, 0.8 mL of 65% HNO3 (Fisher Chemical) was added, and the samples were placed in a dry block heater (IKA) at 90°C for 6 h until the solution became clear and transparent. The samples were diluted with ultrapure water to 1-5% acidity in a certain proportion, and then filtered with a 0.22 μm polytetrafluoroethylene filter membrane. The total Cd concentration in all samples was determined using an inductively coupled plasma mass spectrometer (ICP-MS, PerkinElmer, NexIon350D, USA). In collision mode, 50 μg / L In was used as the internal standard element to correct the instrument baseline drift.

[0112] (2) Determination of cadmium content in the hydroponic system in the colloidal Cd hydroponic exposure experiment

[0113] (2.1) Determination of ionic cadmium and colloidal cadmium content in hydroponic system

[0114] Two samples of nutrient solution were collected from the hydroponic system, each with 0.5 mL. One sample of nutrient solution was centrifuged and filtered through an ultrafiltration tube with a molecular weight cutoff of 3 kDa (5000 g, 20 min) (pre-treated by soaking in 0.1 M CuSO4 to saturate the adsorption sites of the filter membrane) to collect Cd 2+ , the concentration of ionic cadmium was measured; another portion of the nutrient solution was added with 1 mL of 65% HNO3 (Fisher Chemical), placed in a dry block heater (IKA) at 90°C for 6 h, and diluted with ultrapure water to 1-5% acidity in a certain proportion, and the Cd content of the solution was measured using ICP-MS. 2+ The concentration corresponds to the total cadmium concentration in the rice sample. The total cadmium concentration determined by acid digestion method minus the ionic cadmium determined by ultrafiltration tube is the colloidal cadmium concentration in the hydroponic system.

[0115] (2.2) Determination of colloidal cadmium content in rice samples

[0116] The rice root and leaf samples were collected. After the rice samples were collected, they were soaked in 20mmol / L Na2-EDTA solution for 15min ultrasonic treatment to remove the Cd remaining on the root or leaf surface, and then washed with ultrapure water, and the surface moisture was dried with absorbent paper, and placed in a 105℃ oven for 30min, and then placed in an oven at 60℃ to dry to constant weight, and weighed with a microbalance (Mettler ToledoXPR2U, 0.1μg), and the weight of the leaf part and the root was recorded. Two rice root and leaf samples were prepared according to the above method.

[0117] Prepare 2 mM citrate buffer (0.4203 g / L) and adjust the pH to 5.5 with NaOH. Dissolve 1 g of Macerozyme R-10 enzyme powder and 0.1 g of Cellulase R-10 in 20 mL of ultrapure water to prepare a 5% Macerozyme R-10 and 0.5% Cellulase R-10 mixed enzymatic solution.

[0118] One of the weighed rice samples was cut into small pieces of about 0.5 mm, immediately placed in 8 mL of 2 mM citric acid buffer, and prepared with a tissue homogenizer. Then, 2 mL of the above-obtained mixed enzymatic solution was added and shaken in a 37°C incubator for 24 h. After being taken out and allowed to settle for 1 h, the supernatant was diluted 100 times with ultrapure water for SP-ICP-MS (ICP-MS, Agilent, 7900, Singapore) determination. The Agilent ICP-MS was used for single particle analysis in fast TRA mode, and the AgNP (40 nm, 0.02 mg / mL, Sigma-aldrich) standard solution was diluted to 5 ng / L as a reference material. The response factor calibration standard required the preparation of a 1 μg / L standard solution of the element Cd ion (IonicStd (AN)) and a reference material Ag ion standard solution (IonicStd (RN)); a 2% HNO3 solution was selected as the response factor calibration blank (IonicBlk). That is, the enzymatic hydrolysis method is used to obtain the colloidal Cd in different parts of the rice roots and leaves, and the single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) technology is combined to quantitatively analyze the colloidal Cd concentration in different tissues and organs of rice.

[0119] (2.3) Determination of total cadmium content in rice samples

[0120] Determine the total cadmium content in rice samples according to the method (1.2).

[0121] 2. Experimental results

[0122] Rice was exposed to 0.6 mg / L colloidal Cd and ionic Cd for 9 days. Figures 4-5 As shown in Figure 2, the Cd accumulation in rice increased linearly with exposure time. Figure 4 ) and leaves ( Figure 5 ) was significantly higher than that of ionic Cd, indicating that rice can absorb colloidal Cd and that colloidal Cd has a significant contribution to the bioavailability of rice.

[0123] In order to further explore the correlation between colloidal Cd exposure concentration and bioaccumulation, it is necessary to quantify the absorption rate constant of Cd nanocolloids and establish a kinetic model of bioaccumulation of Cd nanocolloids in rice. By setting four concentrations of 0.056 mg / L, 0.3 mg / L, 0.6 mg / L and 1.5 mg / L, only ionic Cd or colloidal Cd was applied to rice for a 9-day hydroponic exposure experiment. It can be observed that the accumulated Cd in rice increases linearly with the exposure time. The slope of the fitted straight line is the absorption rate of Cd ( Figures 6-7). With the increase of exposure concentration, the accumulated Cd concentration in rice also increased significantly, and the cumulative absorption of Cd by the root system was still significantly higher than that by the leaves. The absorption rate of Cd by rice was fitted with the Cd concentration in the exposure system ( Figures 8-9 ) can be used to obtain the absorption rate constant K u .

[0124] The bioabsorption rate constant was quantified based on the relationship between bioaccumulation of CdS and exposure time:

[0125] I A =K u ×C w (1)

[0126] Where: I A ——Cd absorption rate, obtained by linear fitting the relationship between Cd accumulation in rice and time;

[0127] C w ——Cd concentration in the hydroponic system;

[0128] K u ——Rate constant of Cd absorption by rice.

[0129] According to the absorption rate constant of rice Cd under different conditions, the bioaccumulation of Cd in rice was finally predicted:

[0130]

[0131] K u，total ×[Cd] total =K u,NP ×[Cd] NP +K u,diss ×[Cd] diss (2)

[0132] The present invention mainly uses the root system and leaves of rice as representatives to study the absorption of cadmium (Cd) by plants. Therefore, the bioaccumulation relationship formulas of Cd in the roots and leaves of rice are calculated according to the following formulas (3) and (4), respectively:

[0133] K u,total ×[Cd] total =K R，NP ×[Cd] NP +K R，diss ×[Cd] diss (3)

[0134] K u，total ×[Cd] total =K L，NP ×[Cd] NP +K L,diss ×[Cd]diss (4)

[0135] In the formula: [Cd] plants ——Cd concentration accumulated in plants;

[0136] [Cd] total ——Total Cd concentration in the hydroponic system;

[0137] [Cd] diss ——Ionized Cd concentration in the hydroponic system;

[0138] [Cd] NP ——Colloidal Cd concentration in the hydroponic system;

[0139] k u，total ——Absorption rate constant of total Cd in hydroponic system;

[0140] k u，diss ——Absorption rate constant of ionic Cd in hydroponic system;

[0141] k u,NP ——Absorption rate constant of colloidal Cd in hydroponic system;

[0142] K R,diss ——The absorption rate constant of ionic Cd by rice roots in hydroponic system;

[0143] K L,diss ——The absorption rate constant of ionic Cd by rice leaves in the hydroponic system;

[0144] K R,NP ——The absorption rate constant of colloidal Cd by rice roots in the hydroponic system;

[0145] K L,NP ——Absorption rate constant of colloidal Cd by rice leaves in hydroponic system.

[0146] According to the parameter k obtained from the above experiment u，diss , k u,N P, [Cd] diss , [Cd] NP , where K R,diss =0.07874, K R,NP =0.062175, K L,diss =7.623×10 -4 , K L,NP =7.323×10 -4 A kinetic model for the absorption of ionic and colloidal Cd by rice was established to quantitatively predict the bioavailability content in rice when the Cd concentration in the environment is known.

[0147] Example 4 Verification of the absorption kinetics model

[0148] The Cd content data absorbed by rice at different times were imported into R language (v4.1.3) for equation verification and fitting, and the results were obtained. Figures 10 to 17 , where the points are measured values ​​and the curves are predicted values. The predicted values ​​are specifically K obtained according to the above embodiment 3. u Substituting the Cd concentrations of different forms in the above-mentioned culture system into formula (3) or formula (4), the red shaded area is the confidence interval and prediction band with a confidence level of 95%. It can be observed from the figure that most of the measured values ​​fall within the range of 1.5 to 2 times the predicted values. There are differences in Ku between different organ parts, indicating that there are differences in the accumulation of Cd in different rice organs.

[0149] From the perspective of absorption kinetics, the present invention compares the cumulative concentration of Cd in the colloidal system and the cumulative concentration of ionic Cd in the rice body after 9 days of exposure in the exposure system of colloidal Cd and ionic Cd at the same concentration of 0.6 mg / L. The results show that rice absorbs colloidal Cd, and colloidal Cd has a significant contribution to the bioavailability of rice. At the same time, by applying only ionic Cd and colloidal Cd to rice for 9 days of hydroponic exposure experiments, the biodynamic absorption parameters of rice for Cd were obtained, and a biodynamic model was established to predict the bioavailability of colloidal Cd. The prediction results show that whether for the root system or the leaves, 94% to 100% of the measured data fall into the 95% credible interval predicted by the model, and the model fitting is relatively successful.

[0150] In summary, the present invention proposes a more accurate bioaccumulation prediction method based on the difference in bioavailability between nanocolloidal Cd and ionic Cd, which is of great significance for providing theoretical guidance for improving the environmental quality of Cd-contaminated paddy soil, optimizing rice production safety strategies, and ensuring the safety of agricultural products.

[0151] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for predicting the bioavailability of Cd nanocolloids, characterized in that: The steps include: S1. Conduct plant exposure experiments to expose selected plants to media containing known concentrations and forms of Cd; S2. Collect plant samples after exposure and determine the content of different forms of Cd in them; S3. Based on the data obtained in step S2, determine the absorption rate constant K of plants for different forms of Cd u ; S4. K obtained according to step S3 u , a kinetic model of plant absorption of metal Cd was established to quantify the bioavailability of Cd in plants when the concentrations of different forms of Cd in the environment were known. The formula of the kinetic model of metal Cd absorption is as follows: In the formula: [Cd] plants ——Cd concentration accumulated in plants; [Cd] total ——Total Cd concentration in the culture system; [Cd] diss ——The concentration of ionic Cd in the culture system; [Cd] NP ——The concentration of colloidal Cd in the culture system; k u，total ——absorption rate constant of total Cd in the culture system; K u，diss ——The absorption rate constant of ionic Cd by plants in the culture system; K u,NP ——The absorption rate constant of colloidal Cd by plants in the culture system; Wherein, in steps S1 to S4, the Cd is in a colloidal state and an ionic state.

2. The method for predicting biological effectiveness according to claim 1, characterized in that: When the plant body refers to the leaves or the root system of the plant, the absorption kinetic model of the metal Cd is as follows: or [Cd] diss ——The concentration of ionic Cd in the culture system; [Cd] NP ——The concentration of colloidal Cd in the culture system; K R,diss ——The absorption rate constant of ionic Cd by the roots of plants in the culture system; K L,diss ——The absorption rate constant of ionic Cd by the leaves of plants in the culture system; K R,NP ——The absorption rate constant of colloidal Cd by the roots of plants in the culture system; K L,NP ——The absorption rate constant of colloidal Cd by the leaves of plants in the culture system.

3. The method for predicting biological effectiveness according to claim 1 or 2, characterized in that: The Cd absorption rate constant K u The method to determine is: The accumulation of metal Cd in plants was determined by exposure experiments within the environmental concentration range, and the absorption rate constant K was calculated. u .

4. The method for predicting biological effectiveness according to claim 3, characterized in that: The Cd absorption rate constant K u It is obtained specifically by the following method: by analyzing the relationship between the cumulative amount of Cd in the plant and the exposure time, the slope obtained after fitting a straight line is the Cd absorption rate; then analyzing the relationship between the plant's absorption rate of Cd and the Cd concentration in the exposure system, fitting a curve, and the obtained slope is the Cd absorption rate constant.

5. The method for predicting biological effectiveness according to claim 1, characterized in that: The plant is a grass plant.

6. The method for predicting biological effectiveness according to claim 5, characterized in that: The grass plant includes any one of rice and wheat.

7. The method for predicting biological effectiveness according to claim 1, characterized in that: The colloidal Cd includes any one or more of CdS, Cd(OH)2, and CdCO3.

8. The method for predicting biological effectiveness according to claim 1, characterized in that: The ionic Cd is selected from any one or more of CdCl2, Cd(NO3)2.

9. The method for predicting biological effectiveness according to claim 1, characterized in that: The exposure test is a hydroponic exposure experiment.

10. Use of the bioavailability prediction method according to any one of claims 1 to 9 in predicting the bioavailability of metals.

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