A method for extracting organic pollutants of different forms in sediments

Abstract

The present invention provides a method for extracting organic pollutants in different forms in sediments, which mainly includes: first centrifuging the mud-water mixture to separate the supernatant, extracting the supernatant with a suitable organic solvent, and then concentrating it with nitrogen to obtain a water-soluble state; after absorbing the water, adding a certain amount of suitable organic solvent, and separating it after multiple ultrasonic crushing and extraction to obtain a bound state; finally, extracting the bottom sediment left after centrifugation of the bound state with hot alkali or adding an organic solvent for microwave digestion, and separating to obtain a residue state. This method solves the problem of how to quantify adsorbed organic pollutants (such as residue states) that are difficult to desorb. It can not only more accurately evaluate the biological effectiveness of adsorbed organic pollutants in water environments, but is also particularly suitable for research on the migration and transformation of organic pollutants in water environments, the biological effectiveness prediction of microbial degradation, and ecological risk assessment under laboratory conditions.

Description

Technical Field

[0001] The invention relates to a method for extracting organic pollutants in different forms in sediments, and in particular to a method for evaluating the bioavailability of adsorbed organic pollutants in sediments. Background Art

[0002] In recent years, with the rapid development of my country's industry, agriculture and pharmaceutical industries, more and more organic pollutants (such as pesticides, polycyclic aromatic hydrocarbons, antibiotics, etc.) have entered the water environment. Affected by environmental factors, media and biological factors, these organic pollutants and their metabolites will be adsorbed, migrated and transformed. Even if they are attenuated by photodegradation, hydrolysis, chemical oxidation degradation, microbial degradation, plant absorption and degradation, some of them will still persist in sediments, thus posing a great threat to water bodies, animals and humans. Therefore, it is very necessary to accurately assess the ecological risks of organic pollutants. The prediction of bioavailability is usually a key step in assessing the ecological risks of pollutants in the environment. In fact, in the natural environment, organic pollutants exist in different forms due to a series of changes in their physical and chemical properties, namely, water-soluble states that can be used by organisms by diffusion from water, bound states that are weakly adsorbed on the surface of sediments (electrostatic effects, etc.), residue states that are tightly adsorbed by sediments through covalent bonds, etc., but can still be desorbed, and non-extractable states that cannot be extracted and bioavailable due to adsorption through covalent bonds, micropore locking, etc. Different forms have different bioavailabilities, which can have a significant impact on the actual prediction of the bioavailability of organic pollutants.

[0003] At present, there are few reports and patents on the extraction and analysis methods of organic pollutants in different forms in sediments at home and abroad. Most of them use assisted desorption methods (such as kaolin, β-cyclodextrin, Tenax resin, etc.) to study, but these methods have certain limitations. For example, these methods cannot accurately quantify adsorbed organic pollutants with low biological effectiveness (such as residual state), and the desorption method may have large errors in the recovery rate of adsorbed organic pollutants.

[0004] Therefore, how to provide a method for extracting organic pollutants in different forms in sediments to evaluate the bioavailability of adsorbed organic pollutants in sediments is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] In view of this, the present invention provides a method for extracting and analyzing organic pollutants of different forms from sediments. The organic pollutants include organic pollutants such as nonylphenol, sulfamethoxazole, carbamazepine, etc., especially hydrophobic organic pollutants such as nonylphenol.

[0006] It should be noted that the present invention proposes a three-step continuous extraction method. First, a simulation system of a water environment is established under laboratory conditions. Secondly, suitable extractants, such as n-hexane, methanol, a mixed solvent of methanol and toluene, a mixed solvent of acetonitrile and water, etc., are used to extract organic pollutants from water and sediments in sequence according to the steps to represent three different forms (water-soluble state, bound state, and residual state). Finally, relevant data processing and analysis methods can be combined to predict the changes in the bioavailability of adsorbed organic pollutants.

[0007] The present invention can provide methods and means for predicting the bioavailability and ecological risk assessment of organic pollutants in natural water bodies, thereby providing theoretical support for organic pollution control and remediation.

[0008] Specifically, in order to achieve the above object, the present invention provides the following technical solutions:

[0009] A method for extracting and analyzing organic pollutants in different forms from sediments, the extraction steps are as follows:

[0010] (1) Extraction of water-soluble state: Put the mud-water mixture into a centrifuge tube, centrifuge it, take the supernatant and add an organic solvent (generally n-hexane, acetone) for liquid-liquid extraction, vortex mix it, suck out the upper organic solvent, concentrate it with nitrogen, and then make up the volume with a suitable solvent to obtain a water-soluble state for later use;

[0011] (2) Extracting the bound state: adding anhydrous sodium sulfate to the bottom sediment remaining after centrifugation to absorb water, then adding an organic solvent and extracting in an ultrasonic crusher for 5 to 20 minutes, repeating 3 to 4 times, and after extraction and separation, concentrating by nitrogen blowing, and fixing the volume with a suitable solvent to obtain a bound state for use;

[0012] It should be noted that since the extraction time will affect the extraction rate, three blank groups were set up in the preliminary optimization experiment and extracted for 5, 10, 15, 20, 30, 40 and 60 min respectively to obtain the best extraction time. The results showed that the recovery rate of different organic pollutants was the best within 5 to 20 min, and the highest could reach 101.16 ± 0.022%;

[0013] In addition, the number of extractions will also affect the extraction rate. The preliminary optimization experiment set up three blank groups and extracted 6 times. The concentration of organic pollutants in the supernatant was measured each time to obtain the optimal number of extractions for bound organic pollutants in the sediment. The results showed that for different organic pollutants, the recovery rate obtained from the 3rd to 4th extraction was higher.

[0014] (3) Extraction of the residue state: adding an organic solvent to the bottom sediment remaining after centrifugation of the extraction of the bound state in step (2) and mixing, followed by microwave digestion at 120° C. to 150° C. for 20 to 30 min, centrifuging and collecting the supernatant, concentrating by nitrogen blowing, and then fixing the volume with a suitable solvent to obtain a residue state.

[0015] It should be noted that the previous experiments on the optimization of the extraction process showed that for different sediments, the recovery rate can reach up to 90% to 99% after microwave digestion treatment at 120°C to 150°C for 20 to 30 minutes.

[0016] Optionally, step (3) uses a more violent extraction method to introduce extraction analysis of the residue state, and step (3) can be replaced by: adding 1 mol / L sodium hydroxide to the bottom sediment remaining after centrifugation after extracting the bound state in step (2), heating in a water bath at 60°C to 80°C for 8 to 12 hours, freeze-drying after cooling, then adding an organic solvent (generally n-hexane, acetone) and mixing, then aspirating the upper clear liquid, concentrating it with nitrogen blowing, and then fixing the volume with a suitable solvent to obtain a residue state.

[0017] Optionally, an organic solvent is added to the aqueous extraction to perform liquid-liquid extraction and finally a nitrogen blowing concentration treatment is performed to ensure the recovery rate, and in step (1), the volume ratio of the organic solvent added to the mud-water mixture is 1:1, the organic solvent is n-hexane or a n-hexane-acetone mixed solvent, and the constant volume solvent is methanol.

[0018] Optionally, the bound state is directly extracted without desorption and then extraction, and the organic solvent can be determined according to the characteristics of the pollutants. Specifically, in step (2), the volume ratio of the organic solvent to the mud-water mixture is 1:1, and the mass / volume ratio of the anhydrous sodium sulfate to the mud-water mixture is 1:5; and the organic solvent is a methanol-toluene mixed solvent with a volume ratio of 6:1, a methanol-1% acetic acid mixed solvent with a volume ratio of 1:1, or methanol, and the constant volume solvent is methanol.

[0019] Optionally, in step (3), the volume ratio of the organic solvent added to the mud-water mixture is 1:1, and the organic solvent is acetonitrile or an acetonitrile-water mixed solvent with a volume ratio of 1:4.

[0020] Due to the heterogeneity of sediments, different sediment components have different adsorption energies, so there are differences in the adsorption strength of pollutants. Therefore, different extraction conditions are needed to extract organic pollutants of different forms. The previous work showed that the recovery rate of organic pollutants in sediments by this method is generally around 98.12% ± 4.15% ~ 103.51 ± 0.051%. The correlation analysis with the results obtained by Tenax assisted desorption technology showed that the water-soluble and fast desorption parts of the two F rapIt has a certain relevance. Previous studies have pointed out that the fast desorption portion is usually used to represent the bioavailable portion, which proves that this method has a certain feasibility in predicting the bioavailability of organic pollutants.

[0021] It can be seen from the above technical solution that, compared with the prior art, the method for extracting organic pollutants in different forms from sediments provided by the present invention has the following excellent effects:

[0022] 1) The present invention clarifies the fate of organic pollutants in the water environment, divides the adsorbed organic pollutants into water-soluble state, bound state and residual state according to the adsorption strength of the sediment, then introduces the quantitative analysis of the residual state, and gradually extracts the organic pollutants in various adsorbed forms using extraction methods under different conditions for analysis and determination. The advantage of the present invention is that the adsorbed organic pollutants are directly extracted without desorption, thereby ensuring the recovery rate of each adsorbed form;

[0023] 2) The present invention divides the adsorbed organic pollutants into more detailed categories according to the strength of adsorption by sediments and the level of bioavailability, especially introduces quantitative analysis of the residue state, and gradually adopts different extraction methods, which greatly improves the accuracy of bioavailability prediction;

[0024] 3) The present invention is particularly suitable for conducting research on the migration and transformation of organic pollutants in water environments, the bioavailability prediction of microbial degradation, and ecological risk assessment under laboratory conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0026] Figure 1 Flow chart of the three-step extraction method for organic pollutants in different adsorption states.

[0027] Figure 2 Correlation analysis between the ratio of nonylphenol in different adsorption states and the desorption kinetic parameters of Tenax; a water-soluble state and F rap ; b Binding state and F slow ; c Residue state and F nd .

[0028] Figure 3 These are the optimal extraction conditions for sulfamethoxazole in different adsorption states.

[0029] Figure 4Comparison of the recovery rate of the total amount of adsorbed CBZ on day 0 and day 7. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention and the drawings of the specification to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The embodiment of the invention discloses a method for extracting organic pollutants in different forms from sediments.

[0032] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content are also considered to fall within the protection scope of the present invention.

[0033] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] Extraction of adsorbed nonylphenol (NP) in sediments:

[0036] The mud-water mixture was placed in a centrifuge tube and centrifuged. The supernatant was added with n-hexane and mixed well, and the upper supernatant was sucked out. Then, it was concentrated by nitrogen blowing and fixed to volume with methanol, which is the water-soluble NP; the water was sucked dry, and a certain amount of methanol: toluene = 6:1 (v / v) mixed solvent was added, and then it was crushed in an ultrasonic crusher, and the supernatant was collected by centrifugation. The process was repeated 3 times, and then it was concentrated by nitrogen blowing and fixed to volume with a suitable solvent, which is the bound NP; 1 mol / L sodium hydroxide was added to the sediment, heated in a water bath at 80°C for 8h, cooled and freeze-dried, and then extracted with n-hexane 3 times, the supernatant was collected, and the volume was fixed by nitrogen blowing, which is the residual NP.

[0037] In order to verify the recovery rate of this method, a control group was set up after three high-pressure steam sterilization, and the concentrations of water-soluble, bound and residual NPs were measured. The results showed that the total recovery rate of NPs in the experimental group and the control group was 98.12% ± 4.15% and 99.05% ± 6.54%.

[0038] Tenax desorption kinetics divides the adsorbed organic pollutants in the sediment into fast desorption parts (F rap ), slow desorption part (F slow ), non-desorbable part (F nd), we conducted Tenax desorption kinetics experiments in the early stage, and analyzed the correlation between the concentration of NPs of various forms and the Tenax desorption kinetic parameters of nonylphenol. We found that the water-soluble and fast desorption parts of the two rap There is a certain correlation ( Figure 2 ), which proves that this method is feasible.

[0039] Example 2

[0040] Extraction of adsorbed sulfamethoxazole (SMX) in water-sediment system:

[0041] Weigh a certain amount of mud-water mixture and put it into a centrifuge tube. Collect the supernatant by centrifugation, which is the water-soluble SMX; add a certain amount of anhydrous sodium sulfate to the lower sediment to absorb the water, add a certain amount of methanol-1% acetic acid (1:1) mixed solvent, and crush it in an ultrasonic crusher. Repeat the process 4 times, centrifuge, concentrate with nitrogen, and then make up the volume with a suitable solvent, which is the bound SMX; add a certain amount of mixed solvent acetonitrile-water (1:4) to the lower sediment, mix well, digest at 150℃ for 30 minutes, collect the supernatant by centrifugation, and make up the volume with nitrogen, which is the residual SMX.

[0042] Since the extraction solvent, extraction time and number of extractions will affect the extraction rate, the three conditions were optimized and three mixed solvents of ① methanol: 1% acetic acid = 1:1, ② methanol: (EDTA-Mcllvaine buffer) = 1:1, and ③ acetonitrile: phosphate buffer = 1:1 were selected as extraction solvents and extracted for 5, 10, 15, 20, 30, 40 and 60 minutes. The number of extractions was 6 times, and the concentration of SMX in the supernatant was measured each time to obtain the optimal extraction conditions for different forms of SMX in the sediment.

[0043] The results show that Figure 3 ), when methanol-1% acetic acid (1:1) was used as the solvent, each ultrasonic extraction was 20 min, and a total of 4 extractions were performed, the recovery rate of SMX in different adsorption forms could reach 103.51±0.051%.

[0044] Example 3

[0045] Extraction of adsorbed carbamazepine (CBZ) in water-sediment system:

[0046] Weigh a certain amount of mud-water mixture and put it into a centrifuge tube. Collect the supernatant by centrifugation, which is the water-soluble CBZ; add a certain amount of anhydrous sodium sulfate to the lower sediment to absorb the water, add a certain amount of methanol, and crush it in an ultrasonic crusher. Repeat the process 4 times. Centrifuge and then concentrate it with nitrogen, then make up the volume with a suitable solvent, which is the bound CBZ; add a certain amount of acetonitrile to the lower sediment, mix well, digest it at 150℃ for 30 minutes, collect the supernatant by centrifugation, and make up the volume with nitrogen, which is the residual CBZ.

[0047] In order to verify the extraction conditions, the recovery rate of the total amount of adsorbed CBZ experimental group on day 0 and day 7 was compared and it was found that ( Figure 4 ), even with the extension of time, the total recovery rate of adsorbed CBZ can still be maintained above 90%.

[0048] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for extracting organic pollutants of different forms in sediments, characterized in that: The organic pollutants in different forms in the sediment are extracted step by step. The extraction method specifically comprises the following steps: (1) Extraction of water-soluble state: Put the mud-water mixture into a centrifuge tube, centrifuge it, take the supernatant and add the organic solvent for liquid-liquid extraction, vortex mix it, suck out the upper organic solvent, concentrate it with nitrogen, and then make up the volume with the solvent to obtain the water-soluble state for later use; The volume ratio of the organic solvent to the mud-water mixture is 1:1, and the organic solvent is n-hexane or a n-hexane-acetone mixed solvent, and the constant volume solvent is methanol; (2) Extracting the bound state: first, add anhydrous sodium sulfate to the bottom sediment remaining after centrifugation to absorb water, then add an organic solvent, and extract in an ultrasonic crusher for 5 to 20 minutes, repeat 3 to 4 times, and after extraction and separation, condense with nitrogen, and make up to volume with solvent to obtain the bound state for use; The volume ratio of the organic solvent to the muddy water mixture is 1:1, and the mass / volume ratio of the anhydrous sodium sulfate to the muddy water mixture is 1:5; and the organic solvent is a methanol-toluene mixed solvent with a volume ratio of 6:1, a methanol-1% acetic acid mixed solvent with a volume ratio of 1:1, or methanol, and the constant volume solvent is methanol; (3) Extracting the residue state: adding an organic solvent to the bottom sediment remaining after centrifugation of the bound state extracted in step (2) and mixing, then subjecting to microwave digestion at 120° C. to 150° C. for 20 to 30 min, centrifuging and collecting the supernatant, concentrating by nitrogen blowing, and then fixing the volume with a solvent to obtain a residue state; The volume ratio of the organic solvent to the mud-water mixture is 1:1, and the organic solvent is acetonitrile or an acetonitrile-water mixed solvent with a volume ratio of 1:4; The water-soluble state refers to organic pollutants that diffuse from water and can be utilized by organisms; the bound state refers to organic pollutants that are weakly adsorbed on the sediment surface; and the residual state refers to organic pollutants that are tightly adsorbed by sediments through covalent bonds but can still be desorbed.

2. The method for extracting organic pollutants of different forms in sediments according to claim 1, characterized in that: The step (3) can be replaced by: Add 1 mol / L sodium hydroxide to the bottom sediment remaining after centrifugation after extracting the bound state in step (2), heat in a water bath at 60°C to 80°C for 8 to 12 hours, freeze-dry after cooling, then add n-hexane and mix well, then suck out the supernatant, concentrate with nitrogen blow-through and make up to volume with methanol to obtain a residue state.

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