CN115308320B - A quantitative method for hydrophobic organic pollutants in soil that react with humic acid to form residual binding states - Google Patents

Abstract

The invention discloses a method for quantifying hydrophobic organic pollutants in soil, which is characterized in that the hydrophobic organic pollutants are added into humic acid organic solution, humic acid aggregate is prepared by a dialysis method, the pollutants are wrapped in the aggregate, then a release test is carried out, then the release condition of the organic pollutants wrapped on the humic acid aggregate under different pH values is researched by release dynamics, the residual bonding state on the humic acid aggregate can be further analyzed from microcosmic, and then the formation process of the humic acid aggregate, the wrapping of the humic acid aggregate on the hydrophobic organic pollutants and the release process of the wrapped organic pollutants are inspected by dissipative particle dynamics simulation.

Description

A kind of hydrophobic organic pollution in soil that reacts with humic acid to form a residual combined state. quantitative method

Technical field

The invention belongs to the technical field of environmental chemistry and the fate of organic pollutants, and specifically relates to a quantitative method for hydrophobic organic pollutants in soil that react with humic acid to form a residual combined state.

Background technique

Hydrophobic organic pollutants (HOCs) are a type of organic pollutants that have a large octanol/water partition coefficient, low water solubility, are generally difficult to degrade, easily accumulate in soil and sediments, and are transported over long distances through environmental media. . With the rapid development of the economy and the accelerated pace of people's lives, a large number of HOCs are released into the environment. HOCs have the characteristics of persistence, refractory degradation and high biological toxicity in the environment, which have a huge impact on human health and the ecological environment.

Humic acid in soil and sediments plays an important role in the environment and has a huge impact on the distribution, migration and bioavailability of hydrophobic organic pollutants in the soil environment. Therefore, it is of significant environmental significance to explore the residual binding state formed by the interaction between hydrophobic organic pollutants and humic acid.

In view of the combination of experiments and simulations in the existing technology, there are few studies on quantifying the residual binding state of organic pollutants mediated by humic acid in soil, and it is difficult to explain the mechanism of action from a microscopic perspective. However, simulation methods can to a certain extent Due to the lack of complementary experimental methods, it is urgent to develop a quantitative method for hydrophobic organic pollutants in soil that react with humic acid to form residual bound states.

Contents of the invention

The present invention provides a method for quantifying hydrophobic organic pollutants in soil that react with humic acid to form a residual binding state. By combining experiments and computational simulations, the residual binding state of organic pollutants in soil mediated by humic acid can be quantified. It has significant environmental significance for accurately assessing the environmental behavior and effects of organic pollutants.

In order to achieve the above objects, the technical solutions of the present invention are as follows.

A method for quantifying hydrophobic organic pollutants in soil that react with humic acid to form residual binding states, including the following steps:

(1) The formation of humic acid aggregates encapsulating organic pollutants and the determination of the encapsulation amount:

Dissolve humic acid and hydrophobic organic pollutants in the same organic solvent respectively, then mix the hydrophobic organic pollutant solution and humic acid solution and stir, use a dialysis bag to dialyze in deionized water, change the water regularly, and dialyze Afterwards, it is freeze-dried to obtain humic acid agglomerates, and organic pollutants are wrapped in the agglomerates;

Weigh 1 mg of humic acid aggregates encapsulating organic pollutants and dissolve them in 10 mL of methanol. After 20 min of ultrasonic treatment, all the encapsulated contaminants are dissolved in methanol. Then, they are passed through a 0.45 μm filter membrane and measured by high performance liquid chromatography. The concentration of pollutants is then measured to determine the mass of organic pollutants wrapped on humic acid aggregates. The amount of organic pollutants wrapped on humic acid aggregates can be calculated through the formula E _{wrapped pollutants} :

Combined with the experimental results, it is concluded that It can be concluded that the relationship between m _{humic acid} and m _{wrapped pollutants} is m _{wrapped pollutants} = 0.47m _{humic acid} ;

(2) Release experiment of organic pollutants wrapped on humic acid aggregates:

Put the PBS buffer of humic acid aggregates into a dialysis bag and place it in a beaker containing the same PBS buffer. Keep the temperature at room temperature constant, stir, and draw out the cup at intervals (1 to 24 hours). In order to keep the total volume of the solution unchanged, an equal amount of fresh buffer was immediately added, and high-performance liquid chromatography was used to determine the cumulative release amount of organic pollutants Er on the humic acid aggregates:

In the formula: Er is the cumulative release of organic pollutants, %; Ve is the buffer replacement volume, mL; V ₀ is the total volume of the buffer, mL; C _i is the sample concentration during the i-th replacement sampling, mg/L ; m _{wrapped contaminants} is the mass of organic pollutants wrapped on humic acid aggregates, mg; n is the number of buffer replacements;

The amount of hydrophobic organic pollutants wrapped in humic acid aggregates in the soil will be released as the soil pH conditions change. The relationship between the release amount and the pH value is Y = -0.0501X + 0.7215, R ² = 0.9964, Y is the cumulative release amount of organic pollutants, %; That is, the mass m _residue of the bound state of pollutant residues. The mass of the bound state of pollutant residues can be calculated by the following formula:

m _residue =0.47m _{humic acid} ×(1+0.0501X-0.7215)

=0.47m _{humic acid} ×(0.2785+0.0501X)

In the formula, m _{humic acid} is the mass of humic acid in the soil, and X is the pH value of the soil.

Further, the mass ratio of humic acid to hydrophobic organic pollutants in step (1) is 1:1, and the hydrophobic organic pollutants are dibutyl phthalate.

Further, the organic solvent in step (1) is preferably dimethyl sulfoxide or dimethylformamide.

Further, the stirring time in step (1) is preferably 4 to 6 hours, more preferably 4 hours.

Further, the molecular weight cutoff of the dialysis bag described in step (1) is preferably 8000 Da.

Further, the dialysis time in step (1) is preferably 24 hours. During the dialysis process, the water is changed every 1 hour in the first 4 hours, the water is changed every 4 hours from 4 to 12 hours, and the water is changed every 6 hours after 12 hours.

Further, the molecular weight cutoff of the dialysis bag in step (2) is preferably 8000 Da.

Further, the concentration of humic acid aggregates in the PBS buffer of the humic acid aggregates described in step (2) is 0.5-1.5 mg/mL, preferably 1 mg/mL.

Further, the temperature in step (2) is preferably 20-30°C, more preferably 25°C; the stirring rate is preferably 70-150r/min, more preferably 100r/min.

Further, the volume of the buffer solution in each extraction cup in step (2) is preferably 3 to 6 mL, and more preferably 4 mL.

Further, the method for obtaining the relationship curve Y=-0.0501X+0.7215 between the release amount and the pH value in step (2), the specific steps are as follows:

(1) Accurately weigh 5 mg of humic acid aggregates and dissolve them in 5 mL of prepared PBS buffer with pH = 4.0 to 9.0. Divide the solution into three equal parts under each pH value and transfer them to three parts with a molecular weight cutoff of 8000 Da. In the dialysis bag, place the dialysis bag in a beaker, add 115mL of PBS buffer corresponding to the dialysis bag into the beaker as the release medium, place the beaker on the magnetic stirrer, and set the stirring rate to 100r/min. Conduct a release experiment at a temperature of 25°C. During the release period, take out 3 to 6 mL of solution from the beaker every 1 to 24 hours, and add the same volume of corresponding fresh buffer. All samples are filtered through a 0.45 μm filter. , use high performance liquid chromatography to measure the concentration of organic pollutants released from humic acid aggregates, and calculate the cumulative release amount of organic pollutants Er:

In the formula: Er is the cumulative release of organic pollutants, %; Ve is the buffer replacement volume, mL; V ₀ is the total volume of the buffer, mL; C _i is the sample concentration during the i-th replacement sampling, mg/L ;m _{wrapped contaminants} are the mass of organic contaminants on humic acid aggregates, mg; n is the number of buffer replacements;

(2) Fit the cumulative release amount of organic pollutants corresponding to different pH conditions, draw a functional relationship diagram of the cumulative release amount of organic pollutants corresponding to different pH conditions, and obtain the relationship between the cumulative release amount of organic pollutants and pH value. It is Y=-0.0501X+0.7215, Y is the cumulative release of organic pollutants, %; X is the pH value.

The present invention also uses dissipative particle dynamics simulation to investigate the formation process of humic acid aggregates, the encapsulation of hydrophobic organic pollutants by humic acid aggregates, and the release process of the encapsulated organic pollutants to quantify soil from a microscopic perspective. The residual binding state of organic pollutants mediated by humic acid, and then combined with experiments, can quantify the residual binding state of organic pollutants mediated by humic acid in soil.

The bioavailability of the residual bound state is low, and the formation of the residual bound state is considered to be a process that reduces the toxicity of pollutants. Therefore, the amount of residual bound state formed by hydrophobic organic pollutants mediated by soil humic acid aggregates is calculated as It provides certain theoretical guidance for judging the environmental behavior and effects of organic pollutants in soil.

The present invention mainly explores the process of encapsulation of hydrophobic organic matter by humic acid agglomerates, and the release of organic pollutants wrapped on humic acid agglomerates under different pH conditions. The dissipative particle dynamics simulation can be used to intuitively reflect humic acid agglomerates. The morphological change process of humic acid aggregates and the release process of organic pollutants from the aggregates will be more helpful to quantify the residual binding state of organic pollutants in soil mediated by humic acid from a microscopic perspective.

The present invention quantifies the residual binding state formed by the interaction between hydrophobic organic pollutants and humic acid through experiments. This method first adds hydrophobic organic pollutants to humic acid organic solution, and then prepares it through dialysis. Humic acid agglomerates, pollutants are wrapped in the agglomerates; the release kinetics of organic pollutants wrapped on humic acid agglomerates under different pH conditions are studied, and then humic acid agglomerates can be analyzed quantitatively from a macro perspective The residual bound state (the part that cannot be released during the release process); the present invention also uses dissipative particle dynamics simulation to investigate the formation process of humic acid aggregates and the encapsulation of hydrophobic organic pollutants by humic acid aggregates, The release process of the wrapped organic pollutants reflects the residual binding state of organic pollutants mediated by humic acid from a microscopic perspective. With the help of simulation, the present invention can intuitively reflect the process of morphological changes of humic acid aggregates and the effect of humic acid aggregates on The encapsulation of hydrophobic organic pollutants and the release process of the encapsulated organic pollutants, combined with experiments, can quantify the residual binding state of organic pollutants mediated by humic acid in the soil, which is important for accurately assessing the environmental behavior of organic pollutants. and effects have significant environmental significance.

Description of drawings

Figure 1 shows the cumulative release of DBP from humic acid aggregates under different pH conditions;

Figure 2 is a fitting diagram of the functional relationship corresponding to the cumulative release of organic pollutants under different pH conditions;

Figure 3 shows the structural model of humic acid, DBP and water molecules and their coarse-grained model;

Figure 4 is a schematic diagram of the formation process of humic acid aggregates;

Figure 5 is a schematic diagram of DBP encapsulation by humic acid aggregates;

Figure 6 is a radial distribution function analysis diagram of the equilibrium phase diagram of humic acid aggregates wrapped with DBP;

Figure 7 is a dynamic schematic diagram of the release of DBP from humic acid aggregates and an analysis diagram of its radius of gyration.

Detailed ways

In order to better understand the present invention, the technical solution of the present invention will be further described in detail below with reference to specific embodiments.

The humic acid selected in the present invention is extracted from soil, and dibutyl phthalate (DBP) is purchased from Aladdin.

Example 1

Preparation of humic acid aggregates encapsulating DBP and determination of encapsulation amount:

20 mg of humic acid and 20 mg of DBP were accurately weighed and dissolved in 40 mL of dimethyl sulfoxide, and the DBP solution was added to the humic acid solution, stirred for 4 hours, and then placed in a dialysis bag with a molecular weight cutoff of 8000 Da for 24 hours. During the dialysis process, the water was changed every 1 hour for the first 4 hours, every 4 hours from 4 to 12 hours, and every 6 hours after 12 hours. After the dialysis, the water was freeze-dried to obtain humic acid aggregates encapsulating DBP, and the organic pollutant DBP was encapsulated in the aggregates;

Weigh 1 mg of humic acid aggregates wrapped with DBP and dissolve it in 10 mL of methanol. After 20 minutes of ultrasonic treatment, all the wrapped DBP is dissolved in methanol. Then, pass through a 0.45 μm filter membrane and use high-performance liquid chromatography to measure the DBP concentration. Measure the mass of DBP wrapped on the humic acid aggregates, and then calculate the amount of DBP wrapped on the humic acid aggregates through formula (1):

Combining the experimental results, it is concluded that It can be concluded that the relationship between m _{-wrapped DBP} and m _{humic acid} is m _{-wrapped DBP =} 0.47m _{humic acid} .

Example 2

Release experiments of DBP wrapped on humic acid aggregates under different pH conditions:

Accurately weigh 5 mg of humic acid aggregates and dissolve them in 5 mL of prepared PBS buffer with pH values of 4.0, 7.0, and 9.0. The solution is equally divided into three parts under each pH condition and transferred to three parts with a molecular weight cutoff of 8000 Da. In the dialysis bag, place the dialysis bag in a beaker, add 115mL of PBS buffer corresponding to the dialysis bag into the beaker as the release medium, place the beaker on the magnetic stirrer, and set the stirring rate to 100r/min. The release experiment of organic pollutants was carried out at a temperature of 25°C. During the release period, the time intervals for taking points were 1h, 2h, 4h, 6h, 8h, 12h, 24h, 36h, 60h, 84h, 108h, 132h, 156h. Take out 4 mL of solution from the beaker each time. In order to keep the total volume of the solution unchanged, 4 mL of the corresponding buffer solution is immediately added. All the samples are passed through a 0.45 μm filter membrane, and high performance liquid chromatography is used to determine the content of humic acid within 156 hours. The concentration of DBP released on the aggregates is then used to calculate the cumulative release amount Er of DBP through formula (2):

In the formula: Er: cumulative release amount of DBP, %; Ve: buffer replacement volume, mL; V ₀ : total volume of buffer, mL; C _i : sample concentration during the i-th replacement sampling, mg/L; m _DBP : mass of DBP on humic acid aggregates, mg; n: number of buffer replacements;

The cumulative release of DBP in release media with pH values of 4.0, 7.0 and 9.0 is shown in Figure 1. When pH=4.0, the cumulative release of DBP is the highest, reaching about 60%; when pH=7.0, the cumulative release of DBP The amount is about 40%; when pH=9.0, the cumulative release amount of DBP is about 25%. The corresponding cumulative release amount of organic pollutants within 156 hours under different pH value conditions is shown in the left figure, see Figure 2, and the fitting is obtained The relationship between cumulative release and pH value is:

Y＝-0.0501X+0.7215 (3)

Among them, Y is the cumulative release of organic pollutants, %; X is the pH value, R ² =0.9964;

Then we can get the _calculation formula for the residual bound mass m of the corresponding organic pollutant DBP on humic acid aggregates under different pH conditions:

m _residue = 0.47m _{humic acid} × (1-Y)

=0.47m _{humic acid} ×(1+0.0501X-0.7215)

=0.47m _{humic acid} ×(0.2785+0.0501X) (4)

In the formula, m _{humic acid} is the mass of humic acid in the soil, and X is the pH value of the soil.

As soil pH conditions change, the DBP wrapped in soil humic acid aggregates will be released to a certain extent, but some pollutants will not be released, forming a residual bound state of pollutants. As the pH value rises, High, the cumulative release of DBP is gradually decreasing, indicating that under protonation conditions, humic acid aggregates are unstable and DBP is easily released from the aggregates, while under deprotonation conditions, humic acid aggregates It is relatively stable and forms a "core-shell" spherical structure, which can better wrap DBP in the core area, making it difficult for DBP to be released.

Dissipative particle dynamics is used to simulate the formation process of humic acid agglomerates, the encapsulation of hydrophobic organic pollutants by humic acid agglomerates, and the release process of the encapsulated organic pollutants. The specific steps are as follows:

(1) Use Materials Studio software to construct models of humic acid, DBP (black beads) and water molecules in the simulation system, and perform coarse-graining. The corresponding beads are shown in Figure 3. All-atom dynamics is used to calculate the Flory of each bead. -Huggins parameters, and then calculate the interaction force parameters between beads according to the dissipative particle dynamics theory, and construct a simulation system with a size of A system of this size can effectively avoid the impact of periodic boundary effects;

(2) Use the Build Mesostructure part of Materials Studio software to build The simulation system is filled with a quantitative ratio of humic acid:water of 5:95. Use the Mesocite module to select the Geometry Optization task to optimize the structure of the constructed simulation system, and then use the DPD task to simulate the formation process of humic acid aggregates. See Figure 4. At the beginning, the humic acid and water in the system were randomly dispersed in the solution. As the number of simulation steps increased, different fragments of humic acid began to agglomerate under the hydrophilic/hydrophobic interaction; As the number of steps continues to increase, the small agglomerates formed by humic acid gradually tend to form a spherical shape due to surface tension. The small agglomerates move closer and collide with each other, and then merge into large agglomerates;

(3) Use the Build Mesostructure part of Materials Studio software to build The simulation system is filled with a quantitative ratio of humic acid: DBP: water of 4:1:95. Use the Mesocite module to select the Geometry Optization task to optimize the structure of the constructed simulation system, and then use the DPD task to simulate protonation and deionization. The process of humic acid aggregates against hydrophobic organic pollutants under protonated conditions is shown in Figure 5. Initially, humic acid and DBP are randomly dispersed in the solution. As the number of steps continues to increase, humic acid The formed small agglomerates move closer and collide with each other, and then merge into large agglomerates; the hydrophobic organic pollutant DBP also gradually begins to agglomerate under the action of hydrophobicity, and gradually diffuses into the core layer area of the humic acid agglomerates (see Figure 6) (A), then continue to increase the number of steps, and the shape and size of the humic acid aggregates have remained unchanged, indicating that the simulation system has reached equilibrium and the humic acid aggregates surrounding DBP have been formed. Compared with the protonation, the humic acid aggregates have been removed. Under protonation conditions, the initial state and the intermediate state of the system are basically similar. The pollutant agglomerates are also in the core layer area of the humic acid agglomerates, as shown in Figure 6(B). The difference is that the agglomerates formed by humic acid are relatively small. Since the pH-responsive fragments change from protonation to deprotonation, the hydrophilicity of the aggregate fragments is caused, which leads to changes in the structure of humic acid aggregates;

(4) Using the Mesocite module, the simulation step size is 100,000 steps to simulate the release process of DBP wrapped in humic acid aggregates under deprotonation conditions, as shown in Figure 7. Initially, DBP is wrapped in the core of humic acid aggregates. In the layer region, as the number of simulation steps increases, the humic acid aggregate fragments undergo a transition from protonation to deprotonation. The pH value response fragments extend from hydrophobicity to hydrophilicity toward the hydrophilic area, and the spherical structure of the agglomerates occurs. From swelling to rupture from the inside to the outside, the agglomerates are in the loosest state, exposing and diffusing DBP from the hydrophobic area, releasing a certain amount of DBP; as the number of steps continues to increase, the degree of swelling decreases until it disappears; agglomeration The core layer fragment (P) and the middle layer fragment (D) of the body shrink toward the core respectively, and the pH value response fragment (A) also shrinks slightly, and the DBP is re-wrapped in the core area of the agglomerate, forming a "core-middle layer- Shell" has a three-layer, relatively compact spherical structure. At this time, DBP is difficult to release from the agglomerates (corresponding to low experimental pH values), indicating that under high pH conditions, the contamination wrapped by humic acid agglomerates The amount of pollutants is relatively large. As the pH value decreases, the amount of pollutants wrapped by humic acid aggregates gradually decreases. This describes in a semi-quantitative manner a dynamic process of pollutants forming residual bound states mediated by humic acid. process.

Example 3

To verify the method provided in Example 1, randomly take 200 mg of farmland soil from a certain place and pour it into a beaker. First, measure the pH of the soil = 7.4. Then, according to the conventional method, add 100 mL of deionized water and adjust the pH value of the solution to 10. Stir for 1 hour and then let stand for 12 hours. Collect the supernatant. Then centrifuge the supernatant to collect the lower precipitate (humic acid and possible organic pollutants). Dissolve the precipitate in 50 mL of methanol and ultrasonic for 20 minutes. Treat so that the contaminants are completely dissolved in methanol. Take 4mL of the solution and pass it through a 0.45um filter membrane. Use a high-performance liquid chromatography ultraviolet detector at a wavelength of 220nm to measure the concentration of atrazine in it. After detection, you can get The mass of the residual bound state of atrazine in humic acid is 0.89 mg. When the pH is 10, calculated by the formula (4) of Example 1, the mass of the residual bound state of atrazine in humic acid is about 0.84 mg. , compared with the experimental results, there is a certain deviation because the pH value was adjusted in the experiment and there were other substances interfering in the experiment, but there is not much difference between the two, indicating that formula (4) is reasonable.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, and simplifications that do not deviate from the spirit and principles of the present invention are all Equivalent substitutions are all included in the protection scope of the present invention.

Claims (6)

1. A method for quantifying hydrophobic organic contaminants in soil that interact with humic acid to form a residual bound state, comprising the steps of:

(1) Respectively dissolving humic acid and hydrophobic organic pollutants in the same organic solvent, mixing the hydrophobic organic pollutant solution and the humic acid solution, stirring, dialyzing in deionized water by using a dialysis bag, periodically changing water, and freeze-drying after the dialysis is finished to obtain humic acid aggregates coated with the organic pollutants; 1mg of humic acid aggregate coated with organic pollutants is weighed and dissolved in 10mL of methanol, ultrasonic treatment is carried out, the coated organic pollutants are completely dissolved in the methanol, the mixture passes through a filter membrane with the thickness of 0.45 mu m, the pollutant concentration is measured by high performance liquid chromatography, the mass of the organic pollutants coated on the humic acid aggregate is measured, and the quantity E of the organic pollutants coated on the humic acid aggregate is calculated _{Wrapping contaminants} ：

Combining the experimental results to obtain E _{Wrapping contaminants} ＝0.32，m _{Package contamination =} 0.47m _{Humic acid} ；

(2) Placing PBS buffer solution of humic acid aggregate into dialysis bag, placing in the same PBS buffer solution, stirring at constant temperature, extracting buffer solution every 1-24 h, supplementing fresh buffer solution with equal amount, and measuring accumulated release amount Er of organic pollutant on humic acid aggregate by high performance liquid chromatography:

wherein: er is the cumulative release of organic contaminants,%; ve is the buffer displacement volume, mL; v (V) ₀ Is the total volume of the buffer solution, mL; c (C) _i Sample concentration, mg/L, at the time of sampling for the ith displacement; m is m _{Wrapping contaminants} The mass of the organic pollutants coated on the humic acid aggregate is mg; n is the number of times the buffer is replaced;

the amount of the humic acid aggregate coated with the hydrophobic organic pollutant in the soil can be released along with the change of the pH value of the soil, and the relation between the release amount and the pH value is shown as follows:

Y＝-0.0501X+0.7215 (3)

wherein Y is the accumulated release amount of the organic pollutants,%; x is the pH value of the soil;

calculating the mass m of the residual combination state of pollutants in humic acid aggregates in soil with different pH values _{Residue (C)} ：

m _{Residue (C)} ＝0.47m _{Humic acid} ×(0.2785+0.0501X) (4)

Wherein m is _{Humic acid} The mass of humic acid in the soil is shown, and X is the pH value of the soil.

2. The method for quantifying hydrophobic organic contaminants in soil that react with humic acid to form residual bound according to claim 1, wherein the mass ratio of humic acid to hydrophobic organic contaminants in step (1) is 1:1; the hydrophobic organic pollutant is dibutyl phthalate and the organic solvent is dimethyl sulfoxide or dimethylformamide.

3. The method for quantifying hydrophobic organic pollutants in a residual combined state formed by the action of humic acid in soil according to claim 1, wherein the stirring time in the step (1) is 4-6 h; the dialysis time is 24h, water is changed every 1h in the first 4h in the dialysis process, water is changed every 4h, and water is changed every 6h after 12 h.

4. The method for quantifying hydrophobic organic contaminants in soil that interact with humic acid to form residual bound according to claim 1 wherein the molecular weight cut-off of the dialysis bags of step (1) and step (2) is 8000Da.

5. The method for quantifying hydrophobic organic contaminants in soil that react with humic acid to form residual bound according to claim 1, wherein the concentration of humic acid aggregate in PBS buffer of the humic acid aggregate in the step (2) is 0.5-1.5 mg/mL.

6. The method for quantifying hydrophobic organic pollutants in a residual combined state formed by the action of humic acid in soil according to claim 1, wherein the relation curve Y= -0.0501X+0.7215 of the release amount and the pH value in the step (2) is obtained by the following steps:

(1) Weighing 5mg of humic acid aggregate, dissolving in 5mL of prepared PBS buffer solution with pH value of 4.0-9.0, dividing each pH value solution into three equal parts, respectively transferring into three dialysis bags with molecular weight cut-off of 8000Da, placing the dialysis bags into a beaker, adding 115mL of PBS buffer solution which is the same as that in the dialysis bags into the beaker as a release medium, carrying out a release experiment at a stirring speed of 100r/min and a temperature of 25 ℃, taking out 3-6 mL of solution from the beaker at intervals of 1-24 h during release, supplementing the fresh buffer solution with the same volume corresponding to the solution, filtering the obtained samples with a filter membrane with the volume of 0.45 mu m, measuring the concentration of organic pollutants released from the humic acid aggregate by using high performance liquid chromatography, and calculating the accumulated release Er of the pollutants, wherein the calculation formula is shown as formula (2);

(2) Fitting the corresponding organic pollutant accumulated release amounts under different pH conditions to obtain the relationship between the organic pollutant accumulated release amounts and the pH value as Y= -0.0501X+0.7215, wherein Y is the organic pollutant accumulated release amount,%; x is the pH value of the soil.