Method for determining fractionation coefficient of soil composite pollution interface and application thereof

Abstract

The present application belongs to the technical field of soil pollution treatment, and particularly relates to a method for determining a fractionation coefficient of a soil composite pollution interface and application. The present application constructs a composite pollution system with organic pollutants and heavy metals, and systematically simulates the migration and transformation cross-interface process of the composite pollution system in real soil medium. On this basis, by means of isotopic determination of the cross-interface transmission of pollutants at the interface between the air gap layer and the saturated zone layer, and in combination with the Rayleigh fractionation model and the kinetic-thermodynamic fractionation theory, the isotopic fractionation coefficient in the migration process is accurately calculated, so that the quantitative analysis of the metal-organic pollutant composite migration mechanism is realized.

Description

Technical Field

[0001] This invention belongs to the field of soil pollution remediation technology, specifically relating to a method for determining the fractionation coefficient of soil complex pollution interfaces and its application. Background Technology

[0002] Studies have shown that heavy metals such as zinc (Zn), cadmium (Cd), and copper (Cu) often coexist with organic pollutants such as phthalates (PAEs) in the soil environment, forming complex organic-inorganic composite pollution systems. This type of composite pollution not only exacerbates the toxicity and mobility of individual pollutants but also significantly increases the technical difficulty of remediation processes. To deeply analyze the microscopic mechanisms of the synergistic interfacial migration of metals and organic matter in this composite pollution system, stable isotope fractionation technology has been gradually applied to the study of soil pollution processes in recent years. Significant isotope fractionation often occurs in the migration of metals such as Zn, Cd, and Cu at interfaces such as soil-groundwater and organic matter-minerals. The fractionation coefficient, as a key parameter characterizing the preference of light and heavy isotopes during multiphase interfacial migration, can quantitatively reveal the microscopic behavior of organic pollutants and heavy metals in processes such as microbial transformation, physical adsorption, chemical complexation, and co-precipitation, possessing high process identification and quantitative analysis capabilities. The fractionation coefficient is also used in the source tracing model, where it is reflected in the isotopic difference between the source and sink (or mixing) ends in the middle of the model, and can be reflected by correcting or adjusting the isotopic values ​​of the source term during the model construction process.

[0003] However, current research largely focuses on single-pollutant systems or ideal mineral conditions, primarily employing static experiments. Soil column experiments do not simulate the actual interface between the vadose zone and the saturated zone of groundwater. This significantly deviates from real-world pollution conditions, lacking systematic simulation and determination of the various isotopic fractionation characteristics at the interface of actual soil complex pollution. Particularly when phthalate organic pollutants coexist with heavy metals, organic pollutants are affected by microbial transformation during interfacial migration, resulting in differentiated carbon (C) and hydrogen (H) isotope fractionation characteristics. Heavy metals, on the other hand, exhibit significant isotopic fractionation effects through adsorption, complexation, and other cross-interfacial interactions. This makes existing isotopic fractionation models and methods for determining fractionation coefficients insufficient for effectively distinguishing and quantitatively analyzing multiple processes in complex environmental systems.

[0004] Therefore, it is urgent to develop a multi-isotope fractionation calculation and analysis method suitable for actual soil-groundwater composite systems, which comprehensively considers microbial transformation and degradation, heavy metal adsorption / desorption, complexation / competitive synergistic effects and changes in the interfacial microenvironment. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method and application for determining the fractionation coefficient of soil with complex pollution interface. The method provided by this invention can determine the multi-isotope fractionation coefficient in soil with complex pollution of heavy metals and organic pollutants by simulating the cross-interface transport of pollutants at the interface between the vadose zone and the saturated zone.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for determining the fractionation coefficient of a soil complex pollution interface, comprising the following steps:

[0008] A contaminated soil simulation column is provided, which is filled from bottom to top with bottom filter media, a simulated water-saturated zone layer of contaminated soil, a simulated vadose zone layer of contaminated soil, and an upper filter media. Two valves are provided on the side wall of the contaminated soil simulation column: a first valve is located between the simulated water-saturated zone layer and the simulated vadose zone layer of contaminated soil, and a second valve is located below the simulated water-saturated zone layer of contaminated soil. An upper peristaltic pump and a lower peristaltic pump are respectively installed above and below the contaminated soil simulation column.

[0009] Close all valves of the contaminated soil simulation column. Inject the composite contaminated solution containing organic pollutants and heavy metals into the contaminated soil simulation column through the upper peristaltic pump. When the soil in the contaminated soil simulation column is completely wetted and the liquid level reaches the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, open the first valve. After the outflow stabilizes, open the second valve and the lower peristaltic pump. Inject the composite contaminated solution containing organic pollutants and heavy metals at the same flow rate as the upper peristaltic pump, so that the liquid level stabilizes at the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, and collect the outflow.

[0010] The content and isotopic composition of organic pollutants and heavy metals in the effluent were determined. The isotopic fractionation coefficients of C and H were calculated according to the Rayleigh equation formula (1), and the isotopic fractionation coefficients of heavy metals were calculated according to formula (2).

[0011] (1)

[0012] (2),

[0013] In formula (1), ε is the isotopic fractionation factor of C and H. δ C0 and δ t These represent the stable C and H isotope ratios at the initial moment of the fractionation reaction of organic pollutants and at any other moment, respectively. Ct and C 0 These represent the pollutant concentration at any moment during the reaction and the pollutant concentration at the initial moment of the reaction, respectively.

[0014] In formula (2), R is the heavy metal isotope ratio at a certain time point, R0 is the initial isotope ratio, f is the mass ratio of the remaining reactants, i.e., the heavy metals in the solution, to the initial heavy metal concentration, and ε is the fractionation factor.

[0015] Preferably, the pollutants in the contaminated soil include organic pollutants and heavy metals; the organic pollutants include phthalate organic pollutants.

[0016] Preferably, the phthalate organic pollutants include one or more of diethyl phthalate, dibutyl phthalate, diisononyl phthalate, butyl benzyl phthalate, and di(2-ethylhexyl) phthalate.

[0017] Preferably, the heavy metals in the contaminated soil include one or more of zinc, cadmium, and copper.

[0018] Preferably, the concentration of organic pollutants in the composite pollutant solution containing organic pollutants and heavy metals is 20-50 mg / L, and the concentration of heavy metals is 10-50 mg / L.

[0019] Preferably, the flow rate of the composite pollutant solution containing organic pollutants and heavy metals is 1~2.5 mL / min.

[0020] Preferably, the thickness of the bottom filter material and the upper filter material is 1-3 cm; the thickness of the contaminated soil in the simulated water-saturated zone layer is 12-24 cm; and the thickness of the contaminated soil in the simulated vadose zone layer is 18-32 cm.

[0021] Preferably, the contaminated soil simulation column further includes: a permeable plate disposed above the upper filter material; the thickness of the permeable plate is 2-3 cm.

[0022] Preferably, when determining the C and H isotopic fractionation coefficients of organic pollutants in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 1 to 2 months; when determining the isotopic fractionation coefficients of heavy metals in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 3 to 6 days.

[0023] This invention also provides the application of the method described above in the field of environmental protection; the application includes at least one of the following:

[0024] (1) To reveal the interfacial processes between organic pollutants and heavy metal pollutants;

[0025] (2) Quantitatively simulate and calculate the fractionation coefficient of the combined pollution of organic pollutants and heavy metals;

[0026] (3) Identify the main migration and transformation pathways in the complex pollution process of organic pollutants and heavy metals;

[0027] (4) To achieve synergistic source tracing of heavy metals and organic pollutants, and further optimize the pollution risk assessment system and remediation technology.

[0028] This invention provides a method for determining the fractionation coefficient of a soil complex pollution interface, comprising the following steps:

[0029] A contaminated soil simulation column is provided, which is filled from bottom to top with bottom filter media, a simulated water-saturated zone layer of contaminated soil, a simulated vadose zone layer of contaminated soil, and an upper filter media. Two valves are provided on the side wall of the contaminated soil simulation column: a first valve is located between the simulated water-saturated zone layer and the simulated vadose zone layer of contaminated soil, and a second valve is located below the simulated water-saturated zone layer of contaminated soil. An upper peristaltic pump and a lower peristaltic pump are respectively installed above and below the contaminated soil simulation column.

[0030] Close all valves of the contaminated soil simulation column. Inject the composite contaminated solution containing organic pollutants and heavy metals into the contaminated soil simulation column through the upper peristaltic pump. When the soil in the contaminated soil simulation column is completely wetted and the liquid level reaches the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, open the first valve. After the outflow stabilizes, open the second valve and the lower peristaltic pump. Inject the composite contaminated solution containing organic pollutants and heavy metals at the same flow rate as the upper peristaltic pump, so that the liquid level stabilizes at the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, and collect the outflow.

[0031] The content and isotopic composition of organic pollutants and heavy metals in the effluent were determined. The isotopic fractionation coefficients of C and H were calculated according to the Rayleigh equation formula (1), and the isotopic fractionation coefficients of heavy metals were calculated according to formula (2).

[0032] (1)

[0033] (2),

[0034] In formula (1), ε is the isotopic fractionation factor of C and H. δ C0 and δ tThese represent the stable C and H isotope ratios at the initial moment of the fractionation reaction of organic pollutants and at any other moment, respectively. C t and C 0 These represent the pollutant concentration at any moment during the reaction and the pollutant concentration at the initial moment of the reaction, respectively.

[0035] In formula (2), R is the heavy metal isotope ratio at a certain time point, R0 is the initial isotope ratio, f is the mass ratio of the remaining reactants, i.e., the heavy metals in the solution, to the initial heavy metal concentration, and ε is the fractionation factor.

[0036] This method constructs a complex pollution system using organic pollutants and heavy metals, systematically simulating their migration and transformation across interfaces in real soil media. Based on this, isotopic measurements of the cross-interface transport of pollutants at the vadose zone and saturated zone interface are performed. Combining the Rayleigh fractionation model and kinetic-thermodynamic fractionation theory, the isotopic fractionation coefficients during the migration process are accurately calculated, achieving a quantitative analysis of the complex migration mechanism of metal-organic pollutants. This method is applicable to simulating the migration of complex pollution in complex soil environments. It can fully utilize the identification of cross-interface migration mechanisms of complex pollution, providing scientific basis and technical support for the precise source tracing of contaminated sites, and has strong practical and promotional value. Attached Figure Description

[0037] Figure 1 A schematic diagram of the apparatus provided by this invention for simulating and determining the multi-isotope fractionation coefficient during the process of soil complex pollution interface determination;

[0038] Figure 2 The figure shows the calculated fitting of the C and H isotope fractionation coefficients in the vadose zone and the saturated zone in application case 1.

[0039] Figure 3 The figure shows the calculated fitting of the Zn isotope fractionation coefficients in the vadose zone and the saturated zone in application case 1.

[0040] Figure 4 The graph shows the variation of C and H isotope fractionation coefficients in the vadose zone and saturated zone under different scenarios in application cases 1-5.

[0041] Figure 5 The graph shows the variation of heavy metal isotope fractionation coefficients in the vadose zone and saturated zone under different scenarios in application cases 1-5. Detailed Implementation

[0042] This invention provides a method for determining the fractionation coefficient of a soil complex pollution interface, comprising the following steps:

[0043] A contaminated soil simulation column is provided, which is filled from bottom to top with bottom filter media, a simulated water-saturated zone layer of contaminated soil, a simulated vadose zone layer of contaminated soil, and an upper filter media. Two valves are provided on the side wall of the contaminated soil simulation column: a first valve is located between the simulated water-saturated zone layer and the simulated vadose zone layer of contaminated soil, and a second valve is located below the simulated water-saturated zone layer of contaminated soil. An upper peristaltic pump and a lower peristaltic pump are respectively installed above and below the contaminated soil simulation column.

[0044] Close all valves of the contaminated soil simulation column. Inject the composite contaminated solution containing organic pollutants and heavy metals into the contaminated soil simulation column through the upper peristaltic pump. When the soil in the contaminated soil simulation column is completely wetted and the liquid level reaches the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, open the first valve. After the outflow stabilizes, open the second valve and the lower peristaltic pump. Inject the composite contaminated solution containing organic pollutants and heavy metals at the same flow rate as the upper peristaltic pump, so that the liquid level stabilizes at the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, and collect the outflow.

[0045] The content and isotopic composition of organic pollutants and heavy metals in the effluent were determined. The isotopic fractionation coefficients of C and H were calculated according to the Rayleigh equation formula (1), and the isotopic fractionation coefficients of heavy metals were calculated according to formula (2).

[0046] (1)

[0047] (2),

[0048] In formula (1), ε is the isotopic fractionation factor of C and H. δ C0 and δ t These represent the stable C and H isotope ratios at the initial moment of the fractionation reaction of organic pollutants and at any other moment, respectively. C t and C 0 These represent the pollutant concentration at any moment during the reaction and the pollutant concentration at the initial moment of the reaction, respectively.

[0049] In formula (2), R is the heavy metal isotope ratio at a certain time point, R0 is the initial isotope ratio, f is the mass ratio of the remaining reactants, i.e., the heavy metals in the solution, to the initial heavy metal concentration, and ε is the fractionation factor.

[0050] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0051] In one embodiment, the contaminated soil simulation column is filled from bottom to top with bottom filter material, a simulated water-saturated zone layer of contaminated soil, a simulated vadose zone layer of contaminated soil, and an upper filter material; the side wall of the contaminated soil simulation column is provided with two valves, the first valve is located between the simulated water-saturated zone layer of contaminated soil and the simulated vadose zone layer of contaminated soil, and the second valve is located below the simulated water-saturated zone layer of contaminated soil; an upper peristaltic pump and a lower peristaltic pump are respectively provided above and below the contaminated soil simulation column.

[0052] In the contaminated soil simulation column device, valves and peristaltic pumps are used to simulate and maintain the liquid levels of the vadose zone and the water saturation zone. The vadose zone refers to the geological medium in soil or rock located between the surface and the groundwater level, in which the pores or fissures are not completely saturated with water, and air and water coexist and are interconnected. The water saturation zone refers to the geological structure in soil or rock where the pores are completely saturated with water, have a certain degree of water conductivity, and can stably store and supply groundwater.

[0053] As one implementation, the sidewall of the contaminated soil simulation column further includes: a third valve provided in the middle part of the contaminated soil in the simulated water-saturated zone layer; the sidewall of the contaminated soil simulation column further includes: a water sampling port; the water sampling ports are evenly distributed along the height between the contaminated soil in the simulated water-saturated zone layer and the contaminated soil in the simulated vadose zone layer, and the distance between two adjacent water sampling ports is 6~8cm, specifically 6cm in this embodiment.

[0054] As one implementation method, the contaminated soil simulation column further includes: a permeable plate disposed above the upper filter material; the thickness of the permeable plate is 2~3cm, and in a specific embodiment it is 3cm.

[0055] In one embodiment, the contaminated soil simulation column is made of plexiglass, with a diameter of 5-8cm (6cm in a specific embodiment) and a height of 40-60cm (40cm in a specific embodiment).

[0056] In one implementation, the thickness of the bottom filter material and the upper filter material is independently 1~3cm, with 3cm in a specific embodiment; the thickness of the contaminated soil in the simulated water-saturated zone layer is 12~24cm, with 12cm in a specific embodiment; and the thickness of the contaminated soil in the simulated vadose zone layer is 18~32cm, with 18cm in a specific embodiment.

[0057] The upper filter media is used to remove impurities from the composite pollutant solution and prevent them from entering the experimental system and interfering with the simulation results; the bottom filter media is used to trap clay mineral particles that flow with the solution and prevent them from being lost from the outlet, thus avoiding blockage or affecting the balance of experimental materials.

[0058] In one embodiment, both the bottom filter media and the top filter media are quartz sand; the particle size of the quartz sand is 4-8 mesh, and in a specific embodiment it is 6 mesh; the particle size of the contaminated soil is 8-10 mesh, and in a specific embodiment it is 8 mesh.

[0059] In one embodiment, the quartz sand is pretreated quartz sand; the pretreatment includes washing and drying in sequence; the reagent used for washing is nitric acid solution; the concentration of the nitric acid solution is 0.1 mol / L; the drying is oven drying; the present invention does not have a special limitation on the drying method, and any drying method well known in the art can be used.

[0060] In one embodiment, the pollutants in the contaminated soil include organic pollutants and heavy metals; the organic pollutants include phthalate esters; the phthalate esters include one or more of diethyl phthalate (DEP), dibutyl phthalate (DBP), diisononyl phthalate (DINP), butyl benzyl phthalate (BBP), and di(2-ethylhexyl) phthalate (DEHP), with a specific embodiment being diethyl phthalate (DEP) and dibutyl phthalate (DBP). The pollutants are diisononyl phthalate (DINP), butyl benzyl phthalate (BBP), or di(2-ethylhexyl) phthalate (DEHP); the heavy metals include one or more of zinc (Zn), cadmium (Cd), and copper (Cu), with Zn, Cd, or Cu being used in specific embodiments; the content of organic pollutants in the contaminated soil is 5000~7000 mg / kg, with 5000 mg / kg being used in specific embodiments, and the content of heavy metals is 0.1~1 mg / g, with 0.2~0.5 mg / g being used in specific embodiments.

[0061] In one implementation method, the types of organic pollutants and heavy metals in the composite pollution solution containing organic pollutants and heavy metals are the same as those in the polluted soil, and will not be repeated here; the concentration of organic pollutants in the composite pollution solution containing organic pollutants and heavy metals is 20~50 mg / L, specifically 25~40 mg / L in this embodiment, and the concentration of heavy metals is 10~50 mg / L, specifically 15~40 mg / L in this embodiment.

[0062] In one implementation method, the flow rate of the composite pollutant solution containing organic pollutants and heavy metals is 1~2.5 mL / min, specifically 1.5~2.5 mL / min in this embodiment. To simulate different seepage conditions, such as special situations like rainfall or sudden sewage discharge, as well as normal seepage processes, this invention achieves simulation of multi-scenario composite pollution interface processes and acquisition of fractionation parameters by setting different flow rates (controlled at 1~2.5 mL / min) and different pollutant combinations.

[0063] In one embodiment, the content of organic pollutants in the effluent is determined by liquid chromatography, the content of heavy metals is determined by ICP-MS, C and H isotopes are measured by GC-IRMS, and heavy metal isotopes are measured by MC-ICP-MS. This invention does not specifically limit the specific methods for liquid chromatography, ICP-MS, GC-IRMS, and MC-ICP-MS determinations; methods well-known in the art can be used.

[0064] As one implementation method, when determining the C and H isotopic fractionation coefficients of organic pollutants in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 1 to 2 months, specifically 2 months in this embodiment; when determining the isotopic fractionation coefficients of heavy metals in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 3 to 6 days, specifically 3 to 4 days in this embodiment.

[0065] Fractionation of organic matter (C and H) mainly relies on the degradation by microorganisms along the process, so the incubation time before sampling is relatively long, ranging from 1 to 2 months. Fractionation of heavy metals is mainly an adsorption process, and the sampling time depends on the properties of different soils and the characteristics of heavy metals, approximately 3 to 6 days.

[0066] This invention constructs a complex pollution system of phthalic acid esters (PAEs) and heavy metals (such as zinc, cadmium, and copper), and uses an acrylic glass column to simulate the migration process in the actual soil environment. The experiment uses a column with a diameter of 6 cm and a height of 40 cm, filled with contaminated soil to a height of approximately 30 cm. Multiple sampling points at different depths are set up. The flow rate of the peristaltic pump is controlled within the range of 1–2.5 mL / min, and the water level is adjusted to simulate the conditions of the vadose zone and the saturated zone. Water and soil samples are collected periodically at different times and depths to determine the pollutant concentrations and the carbon, hydrogen, and heavy metal isotope composition. The fractionation coefficients are calculated using the Rayleigh fractionation model. Experimental results show that the carbon isotope fractionation coefficient (εC) in the vadose zone ranges from -3.45‰ to -5‰, and the hydrogen isotope fractionation coefficient (εH) ranges from -19.82‰ to -26.08‰; in the saturated zone, εC ranges from -2.39‰ to -3.2‰, and εH ranges from -11.56‰ to -15.36‰. The heavy metal fractionation coefficients were quantitatively characterized using a kinetic model. This method can simultaneously analyze the interfacial processes and isotope fractionation characteristics of phthalate ester organic pollutants and heavy metals, solving the challenges of isotope behavior analysis and accurate fractionation coefficient determination in practical complex pollution systems. Its applications include pollutant interfacial process research, fractionation coefficient calculation, pollution pathway identification, synergistic source tracing, and isotope fingerprint construction, providing technical support for risk assessment and remediation optimization of soil complex pollution.

[0067] This invention also provides the application of the method described above in the field of environmental protection; the application includes at least one of the following:

[0068] (1) To reveal the interfacial processes between organic pollutants and heavy metal pollutants;

[0069] (2) Quantitatively simulate and calculate the fractionation coefficient of the combined pollution of organic pollutants and heavy metals;

[0070] (3) Identify the main migration and transformation pathways in the complex pollution process of organic pollutants and heavy metals;

[0071] (4) To achieve synergistic source tracing of heavy metals and organic pollutants, and further optimize the pollution risk assessment system and remediation technology.

[0072] The method for determining the multi-isotope fractionation coefficient in the process of soil composite pollution interface provided by this invention is a set of multi-isotope fractionation calculation and analysis methods applicable to actual soil-groundwater composite systems. It comprehensively considers microbial transformation and degradation, heavy metal adsorption / desorption, complexation / competitive synergistic effects and changes in the interfacial microenvironment, and combines Rayleigh model for quantitative modeling. This enables the identification of fractionation behavior mechanisms and migration path reconstruction of organic matter and heavy metals in composite pollution interfaces, aiming to provide effective technical support for pollutant cross-interface behavior identification, master process mechanism analysis and pollution source tracing.

[0073] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0074] Example 1

[0075] A method for determining the fractionation coefficient of a soil complex pollution interface includes the following steps:

[0076] Provide contaminated soil simulation columns, such as Figure 1As shown, the contaminated soil simulation column is filled from bottom to top with bottom filter media (6-mesh quartz sand, 3cm thick), a simulated water-saturated zone layer of contaminated soil (12cm thick), a simulated vadose zone layer of contaminated soil (18cm thick), upper filter media (3cm), and a permeable plate (6-mesh quartz sand, 3cm thick). Two valves are installed on the side wall of the contaminated soil simulation column: the first valve is located between the simulated water-saturated zone layer and the simulated vadose zone layer, and the second valve is located below the simulated water-saturated zone layer. An upper peristaltic pump and a lower peristaltic pump are installed above and below the contaminated soil simulation column, respectively. A third valve is located in the middle of the simulated water-saturated zone layer. The contaminated soil simulation column is made of plexiglass, with a diameter of 6cm, a height of 40cm, and an effective volume of 847.8cm³. 3 Five sampling ports are set along the height of the device (spaced 6cm apart).

[0077] Close all valves of the contaminated soil simulation column. Inject the composite contaminated solution containing organic pollutants and heavy metals into the contaminated soil simulation column through the upper peristaltic pump. When the soil in the contaminated soil simulation column is completely wetted and the liquid level reaches the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, open the first valve. After the outflow stabilizes, open the second valve and the lower peristaltic pump. Inject the composite contaminated solution containing organic pollutants and heavy metals at the same flow rate as the upper peristaltic pump, so that the liquid level stabilizes at the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, and collect the outflow.

[0078] The content and isotopic composition of organic pollutants and heavy metals in the effluent were determined. The isotopic fractionation coefficients of C and H were calculated according to the Rayleigh equation formula (1), and the isotopic fractionation coefficients of heavy metals were calculated according to formula (2).

[0079] (1)

[0080] (2),

[0081] In formula (1), ε is the isotopic fractionation factor of C and H. δ C0 and δ t These represent the stable C and H isotope ratios at the initial moment of the fractionation reaction of organic pollutants and at any other moment, respectively. C t and C 0 These represent the pollutant concentration at any moment during the reaction and the pollutant concentration at the initial moment of the reaction, respectively.

[0082] In formula (2), R is the heavy metal isotope ratio at a certain time point, R0 is the initial isotope ratio, f is the mass ratio of the remaining reactants, i.e., the heavy metals in the solution, to the initial heavy metal concentration, and ε is the fractionation factor.

[0083] When determining the C and H isotopic fractionation coefficients of organic pollutants in the effluent, a composite pollution solution containing organic pollutants and heavy metals was continuously injected into the contaminated soil simulation column for 2 months; when determining the isotopic fractionation coefficients of heavy metals in the effluent, a composite pollution solution containing organic pollutants and heavy metals was continuously injected into the contaminated soil simulation column for 3 days.

[0084] Application Case 1

[0085] Following the method in Example 1, 6-mesh quartz sand was first washed with 0.1 mol / L high-purity HNO3, dried, and then approximately 1 g of quartz sand was weighed and filled into the bottom 1-2 cm of the contaminated soil column. Contaminated soil from a lead-zinc mine in Guangdong Province was selected as the experimental soil; the main pollutants in this area were diethyl phthalate (DEP) and heavy metals Zn and Pb. The experimental soil was filled to a depth of 30 cm from the top of the soil column, and then covered with another 1-2 cm of quartz sand.

[0086] First, close the lower outlet and turn on the constant flow pump to inject DEP at a concentration of 22 mg / L and Zn at a rate of 2.5 mL / min. 2+ For a 25 mg / L solution, when the water level reaches -18 cm, open the valve at -18 cm. Once the liquid level stabilizes, start the lower pump, maintaining the same flow rate as the inlet pump. Start a timer and collect the effluent from different locations and at different times. The DEP content of the effluent was determined using liquid chromatography, the Zn content was determined using ICP-MS, C and H isotopes were measured using GC-IRMS, and Zn isotopes were determined using MC-ICP-MS.

[0087] Based on isotope ratios obtained from sampling and measurement at different times and locations, model fitting yields the C and H isotope fractionation coefficients, as well as the Zn fractionation coefficient, in the DEP. Specifically, the εC value for the vadose zone is -4.24±0.222‰ to -5±0.319‰, and the εH value is -21.52±0.699‰ to -25.26±2.32‰. For the saturated zone, the εC value is -2.41±0.117‰ to -3.2±0.143‰, and the εH value is -11.56±0.332‰ to -15.34±1.1‰. The Zn fractionation coefficient εZn, after fitting analysis, is 0.105±0.0396‰.

[0088] Application Case 2

[0089] Following the method in Example 1, 6-mesh quartz sand washed with 0.1 mol / L HNO3 was dried and used for later use. It was then used to fill 1-2 cm at the top and bottom of the soil column, with soil taken from a petrochemical-type contaminated site in Yanshan filling the middle. The main pollutants in this site were dibutyl phthalate (DBP) and heavy metals Zn and Cd.

[0090] Dibutyl phthalate (DBP) at a concentration of 30 mg / L and Cd were injected via a peristaltic pump at a flow rate of 2.5 mL / min. 2+ Concentration 30mg / L, Zn 2+ A 30 mg / L concentration of compound pollutant solution was used to periodically collect water and soil samples.

[0091] DBP content was determined by liquid chromatography, Cd and Zn content by ICP-MS, C and H isotopes by GC-IRMS, and Zn and Cd isotopes by MC-ICP-MS. The isotopic fractionation coefficients were calculated using the Rayleigh equation and related formulas.

[0092] Based on the isotope ratios obtained from sampling and measurement at different times and locations, model fitting can be used to obtain the fractionation coefficients of C and H isotopes in organic matter, as well as the fractionation coefficient of Zn. The εC value of the vadose zone is -3.86±0.215‰ to -4.25±0.124‰ and the εH value is -20.48±0.587‰ to -24.14±2.448‰. The εC value of the saturated zone is -2.58±0.269‰ to -2.95±0.152‰ and the εH value is -12.14±0.294‰ to -14.59±2.6‰. The fractionation coefficient of heavy metal Cd, εCd, is 0.68±0.885‰ after fitting analysis, and the fractionation coefficient of Zn, εZn, is 0.112±0.641‰ after fitting analysis.

[0093] Application Case 3

[0094] Following the method in Example 1, 6-mesh quartz sand was first washed with 0.1 mol / L high-purity HNO3, dried, and then about 1 g of quartz sand was weighed and filled into the bottom 1-2 cm of the soil column. The soil was filled with soil contaminated by a mine in Inner Mongolia. The main pollutants in this area were diisononyl phthalate (DINP) and heavy metal Cu. The soil was filled to 30 cm above the top of the soil column and then covered with another 1-2 cm of quartz sand.

[0095] Close the lower outlet and turn on the constant flow pump to inject DINP at a concentration of 40 mg / L and Cu at a rate of 2.5 mL / min. 2+For a 40 mg / L solution, when the water level reaches -18 cm, open the valve at -18 cm. Once the liquid level stabilizes, turn on the lower pump, maintaining the same flow rate as the inlet pump. Start a timer and collect the outflow from different locations at different times.

[0096] The DEP content of the effluent was determined by liquid chromatography, the Zn content was determined by ICP-MS, the carbon and hydrogen isotopes were measured by GC-IRMS, and the Zn isotopes were determined by MC-ICP-MS.

[0097] Based on isotope ratios obtained from samples taken at different times and locations, model fitting yields the fractionation coefficients of C and H isotopes in organic matter, as well as the fractionation coefficient of Cu. Specifically, the εC value for the vadose zone is -3.72±0.183‰ to -4.41±0.198‰, and the εH value is -21.65±1.032‰ to -25.08±2.117‰. For the saturated zone, the εC value is -2.43±0.317‰ to -3.02±0.188‰, and the εH value is -11.87±0.412‰ to -15.36±2.083‰. The Cu fractionation coefficient εCu, obtained through fitting analysis, is 0.356±0.054‰.

[0098] Application Case 4

[0099] Following the method in Example 1, 6-mesh quartz sand was first washed with 0.1 mol / L high-purity HNO3, dried, and then approximately 1 g of quartz sand was weighed and filled into the bottom 1-2 cm of a soil column. This was then used to fill contaminated soil from a plastic industrial area in Hebei Province, where the main pollutants were DEHP, DEP, and the heavy metal Zn. The soil was filled to a depth of 30 cm from the top of the soil column, and then covered with another 1-2 cm of quartz sand.

[0100] Turn on the constant flow pump and inject phthalic acid (2-ethylhexyl) diester (DEHP), diethyl phthalate (DEP) at a concentration of 45 mg / L, and Zn at a rate of 2.5 mL / min. 2+ A 45 mg / L solution was used, and the timer was started to collect the effluent from different locations and at different times.

[0101] Based on the changes in isotope ratios under different depths and time periods, the fractionation coefficients of C and H isotopes in organic matter and the fractionation characteristics of the heavy metal Zn were obtained through model fitting. Specifically, the εC value of DEHP in the vadose zone ranged from -3.45±0.236‰ to -4.12±0.174‰, and the εH value ranged from -19.82±0.671‰ to -22.96±1.841‰; while in the saturated zone, the εC value ranged from -2.63±0.281‰ to -3.07±0.159‰, and the εH value ranged from -13.54±1.384‰ to -15.12±0.942‰. The εC value of DEP in the vadose zone is -2.94±0.128‰ to -3.26±0.254‰, and the εH value is -22.12±0.618‰ to -22.85±1.752‰; the εC value in the water-saturated zone is -2.21±0.598‰ to -2.49±0.123‰, and the εH value is -14.77±1.74‰ to -16.86±0.985‰. The fractionation coefficient εZn for heavy metal Zn, obtained through fitting analysis, is 0.228±0.0784‰.

[0102] Application Case 5

[0103] Following the method in Example 1, 6-mesh quartz sand was first washed with 0.1 mol / L high-purity HNO3, dried, and then about 1 g of quartz sand was weighed and filled into the bottom 1-2 cm of the soil column. This was used to fill the contaminated soil from an auto parts processing plant in the Yangtze River Delta region, where the pollution mainly consisted of butyl benzyl phthalate (BBP) and heavy metal Zn, up to 30 cm from the top of the soil column. Then, another 1-2 cm of quartz sand was placed on top.

[0104] Turn on the constant flow pump and inject BBP at a concentration of 20 mg / L and Zn at a rate of 2.5 mL / min. 2+ A solution with a concentration of 15 mg / L was used, and the eluent was collected from different locations and at different times.

[0105] Based on multi-point time series sampling and isotope ratio fitting, the fractionation coefficients of organic carbon and hydrogen in the vadose zone and water-saturated zone of typical profiles were obtained. The results show that the εC value in the vadose zone is -4.11±0.157‰ to -3.72±0.201‰, and the εH value is -20.63±1.027‰ to -24.50±1.624‰; while in the water-saturated zone, the εC value is concentrated in the range of -2.53±0.278‰ to -2.91±0.185‰, and the εH value is -11.87±0.412‰ to -13.68±1.305‰. The fractionation coefficient of heavy metal Zn, εZn, was obtained as 0.163±0.045‰ through fitting analysis.

[0106] Comparative Example 1

[0107] The difference from Example 1 is that only a single heavy metal pollutant (such as Zn) was used to construct the experimental system, and isotopic fractionation was measured in a conventional batch adsorption experiment without introducing phthalate esters. The experimental results showed that although the fractionation coefficient of Zn could be obtained, it failed to reflect the synergistic effect between organic pollutants and heavy metals when they are prevalent in the soil environment. Especially in actual pollution scenarios, organic pollutants are affected by microbial transformation during migration, and their C and H isotopes often exhibit significant fractionation, while heavy metals undergo differentiated fractionation under interfacial interactions such as adsorption and complexation. This comparative example can only obtain fractionation results for a single pollutant and lacks a systematic characterization of multi-process, multi-element isotopic fractionation in complex pollution systems. Compared with this invention, this method has significant shortcomings in both mechanism analysis and synergistic source tracing.

[0108] Comparative Example 2

[0109] The difference from Example 1 lies in the use of a saturated soil column for the experiment, but the interface between the vadose zone and the saturated zone was not simulated; the pollutant migration process was studied only under a single saturated environment. Experimental results show that the obtained C, H, and Zn isotope fractionation signals are singular and cannot reflect the differences in fractionation caused by the interfacial environment. For example, under these conditions, no significant difference in the fractionation coefficients between the vadose zone and the saturated zone was observed, while the results of this invention show that the εC and εH values ​​between the vadose zone and the saturated zone can differ by approximately 5-10‰, which is of significant distinguishing importance for migration mechanisms. Therefore, this comparative example lacks consideration of interfacial effects, and the results deviate significantly from real soil environments, making it difficult to reveal the key control mechanisms of pollutant cross-interfacial migration. Compared with this invention, this method lacks environmental representativeness and practical application value.

[0110] Performance testing

[0111] Figure 2 The figure shows the calculated and fitted C and H isotope fractionation coefficients in the vadose zone and the saturated zone in Application Case 1. The figure reveals the fitting results for the C and H isotope fractionation coefficients of organic pollutants in the vadose zone and the saturated zone in the application example. The figure shows that the εC and εH values ​​in the vadose zone are generally more negative and have a larger amplitude, while the fractionation values ​​in the saturated zone are smaller. This difference reflects that organic pollutants in the vadose zone are more significantly degraded by microorganisms, leading to strong fractionation of C and H isotopes; while in the saturated zone, the degree of transformation of organic pollutants is weakened, thus the fractionation effect is relatively weaker.

[0112] Figure 3 This is a fitting graph showing the calculated Zn isotope fractionation coefficients in the vadose zone and saturated zone in Application Case 1. From the graph, we can obtain the Zn isotope composition δ0 in the dynamic adsorption experiment of the soil column. 66The ln(f) of Zn and the remaining Zn fraction f shows a good linear relationship, which is consistent with the Rayleigh fractionation model, indicating that the complex soil environment has a moderate comprehensive influence on Zn isotope fractionation.

[0113] Figure 4 The graphs show the variations in C and H isotope fractionation coefficients in the vadose zone and saturated zone under different scenarios in application cases 1-5. The graphs illustrate the changes in C and H isotope fractionation coefficients for different organic pollutants (such as DEP, DBP, and DEHP) in the vadose zone and saturated zone. It can be seen that there are significant differences in the fractionation magnitude and trend among different types of organic pollutants, with fractionation generally being stronger in the vadose zone than in the saturated zone.

[0114] Figure 5 The graphs show the variations in heavy metal isotope fractionation coefficients in the vadose zone and saturated zone under different scenarios in application cases 1-5. These graphs illustrate the changes in heavy metal isotope fractionation coefficients under different complex pollution systems, including elements such as Zn, Cd, and Cu. The results show that different heavy metals exhibit different fractionation behaviors in the vadose zone and saturated zone. Zn and Cd generally show negative fractionation, while Cu shows positive fractionation under certain conditions.

[0115] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for determining the fractionation coefficient of a soil complex pollution interface, characterized in that, Includes the following steps: A contaminated soil simulation column is provided, which is filled from bottom to top with bottom filter media, a simulated water-saturated zone layer of contaminated soil, a simulated vadose zone layer of contaminated soil, and an upper filter media. Two valves are provided on the side wall of the contaminated soil simulation column: a first valve is located between the simulated water-saturated zone layer and the simulated vadose zone layer of contaminated soil, and a second valve is located below the simulated water-saturated zone layer of contaminated soil. An upper peristaltic pump and a lower peristaltic pump are respectively installed above and below the contaminated soil simulation column. Close all valves of the contaminated soil simulation column. Inject the composite contaminated solution containing organic pollutants and heavy metals into the contaminated soil simulation column through the upper peristaltic pump. When the soil in the contaminated soil simulation column is completely wetted and the liquid level reaches the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, open the first valve. After the outflow stabilizes, open the second valve and the lower peristaltic pump. Inject the composite contaminated solution containing organic pollutants and heavy metals at the same flow rate as the upper peristaltic pump, so that the liquid level stabilizes at the interface between the contaminated soil in the simulated water-saturated zone and the contaminated soil in the simulated vadose zone, and collect the outflow. The content and isotopic composition of organic pollutants and heavy metals in the effluent were determined. The isotopic fractionation coefficients of C and H were calculated according to the Rayleigh equation formula (1), and the isotopic fractionation coefficients of heavy metals were calculated according to formula (2). （1） （2）， In formula (1), ε is the isotopic fractionation factor of C and H. δ C0 and δ t These represent the stable isotope ratios of C and H at the initial moment of the fractionation reaction of organic pollutants and at any other moment, respectively. C t and C 0 These represent the pollutant concentration at any moment during the reaction and the pollutant concentration at the initial moment of the reaction, respectively. In formula (2), R is the heavy metal isotope ratio at a certain time point, R0 is the initial isotope ratio, f is the mass ratio of the remaining reactants, i.e., the heavy metals in the solution, to the initial heavy metal concentration, and ε is the fractionation factor.

2. The method according to claim 1, characterized in that, The pollutants in the contaminated soil include organic pollutants and heavy metals; the organic pollutants include phthalate organic pollutants.

3. The method according to claim 2, characterized in that, The phthalate ester organic pollutants include one or more of diethyl phthalate, dibutyl phthalate, diisononyl phthalate, butyl benzyl phthalate, and di(2-ethylhexyl) phthalate.

4. The method according to claim 2, characterized in that, The heavy metals in the contaminated soil include one or more of zinc, cadmium, and copper.

5. The method according to claim 1, characterized in that, The concentration of organic pollutants in the compound pollutant solution containing organic pollutants and heavy metals is 20-50 mg / L, and the concentration of heavy metals is 10-50 mg / L.

6. The method according to claim 1 or 5, characterized in that, The flow rate of the complex pollutant solution containing organic pollutants and heavy metals is 1~2.5 mL / min.

7. The method according to claim 1, characterized in that, The thickness of the bottom filter media and the top filter media is 1-3 cm; the thickness of the contaminated soil in the simulated water-saturated zone layer is 12-24 cm; and the thickness of the contaminated soil in the simulated vadose zone layer is 18-32 cm.

8. The method according to claim 1, characterized in that, The contaminated soil simulation column also includes a permeable plate placed above the upper filter material; the thickness of the permeable plate is 2-3 cm.

9. The method according to claim 1, characterized in that, When determining the C and H isotopic fractionation coefficients of organic pollutants in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 1 to 2 months; when determining the isotopic fractionation coefficients of heavy metals in the effluent, a composite pollution solution containing organic pollutants and heavy metals is continuously injected into the contaminated soil simulation column for 3 to 6 days.

10. The application of the method according to any one of claims 1 to 9 in the field of environmental protection, characterized in that, The application includes at least one of the following: (1) To reveal the interfacial processes between organic pollutants and heavy metal pollutants; (2) Quantitatively simulate and calculate the fractionation coefficient of the combined pollution of organic pollutants and heavy metals; (3) Identify the main migration and transformation pathways in the complex pollution process of organic pollutants and heavy metals; (4) To achieve synergistic source tracing of heavy metals and organic pollutants, and further optimize the pollution risk assessment system and remediation technology.

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