A method for detecting microplastics in sediments in an aquatic environment

Abstract

The present invention belongs to the field of environmental pollutant detection, and specifically relates to a method for detecting microplastics in water environment sediments. The present invention successfully overcomes the defect that the sodium chloride solution cannot separate microplastics with high density by adding myristic acid polyethylene glycol active ester to a water / ethanol mixed solution of sodium chloride, utilizing the amphiphilic properties of myristic acid polyethylene glycol active ester and controlling the self-assembly state of myristic acid polyethylene glycol active ester by adjusting the ethanol concentration.

Description

Technical Field

[0001] The present invention belongs to the field of environmental pollutant detection, and in particular relates to a method for detecting microplastics in water environment sediments. Background Art

[0002] Plastic waste is difficult to degrade naturally in the environment. After physical, chemical and biological effects, it will gradually decompose into particles with a size of less than 5mm. Usually, plastic particles with a size of less than 5mm are defined as microplastics. Microplastics have the characteristics of small particle size, strong hydrophobicity and large specific surface area. They are good carriers of many heavy metals and hydrophobic organic pollutants and are easily ingested by organisms. Therefore, they have a great destructive effect on the aquatic ecological environment. As a new type of pollutant, microplastics have attracted close attention from researchers at home and abroad.

[0003] At present, the separation and detection of microplastics in sediments in aquatic environments usually rely on density-based flotation techniques, which use the density difference between sediments and microplastics to separate them and then identify microplastics. When sediment samples are placed in a high-density salt solution, plastic particles tend to float to the surface of the solution, while denser sediment materials remain at the bottom of the solution gradient. Sodium chloride (NaCl; density 1.2g / ml) has been widely used to extract microplastics. However, this method can easily miss higher-density plastics, such as polyvinyl chloride (PVC; density up to 1.58g / ml). Higher-density salts, such as zinc chloride (ZnCl2; density up to 1.7g / ml) and sodium iodide (NaI; density up to 1.8g / ml), have also been used to improve the recovery rate of microplastics. However, these substances are expensive, more dangerous to use, and more toxic to aquatic biota.

[0004] Therefore, there is a need in the art for improved methods of flotation separation and detection of microplastics. Summary of the invention

[0005] In order to solve the above problems, the present invention adds myristic acid polyethylene glycol active ester to a water / ethanol mixed solution of sodium chloride, utilizes the amphiphilic properties of myristic acid polyethylene glycol active ester and controls the self-assembly state of myristic acid polyethylene glycol active ester by adjusting the ethanol concentration, thereby successfully overcoming the defect that sodium chloride solution cannot separate microplastics with higher density.

[0006] Specifically, the present invention provides a method for detecting microplastics in aquatic sediments, which comprises the following steps:

[0007] (1) drying and weighing the water environment sediment in sequence to obtain the dry weight of the water environment sediment;

[0008] (2) mixing the dried water environment sediment with a 30% by mass hydrogen peroxide solution, digesting for 5-6 hours at a stirring speed of 100-150 r / min, and drying the digestion product to obtain digestion dry matter;

[0009] (3) adding the digested dry matter into a saturated sodium chloride solution containing 0.1-0.3 g / mL myristic acid polyethylene glycol active ester and 40 vol% ethanol, and stirring at 100-150 r / min for 1-2 h;

[0010] (4) adding an additional 20 vol% (relative to the total volume of the saturated sodium chloride solution in step (3)) of saturated sodium chloride solution to the solution in step (3) under a stirring speed of 100-150 r / min, and then standing at room temperature for 48 hours for flotation to obtain a flotation solution and a flotation sediment;

[0011] (5) filtering the flotation liquid to obtain a retentate deposited on the filter membrane;

[0012] (6) The intercepted material is washed and dried and then examined under a microscope, and suspected microplastic particles are selected for Fourier microscopic infrared spectroscopy analysis to identify the microplastics.

[0013] Furthermore, in step (1) and step (2), the drying temperature is 50-80° C. and the drying time is 20-26 hours.

[0014] Furthermore, in step (2), the ratio of the water environment sediment to the hydrogen peroxide solution is 10 g:90-120 ml.

[0015] Furthermore, in step (3), the amount of saturated sodium chloride solution added is 270-360 ml.

[0016] As used herein, the myristic acid polyethylene glycol active ester is also called myristic acid PEG N-hydroxysuccinimide (Myristic acid-PEG-NHS), which is an amphiphilic compound that is soluble in most organic solvents and has good solubility in water. Its structural formula is shown below:

[0017]

[0018] Furthermore, the filtration in step (5) includes suction filtration.

[0019] Furthermore, the filter membrane in step (5) is a nitrocellulose filter membrane with a pore size of 5 μm.

[0020] Furthermore, the washing in step (6) includes washing with a 50% ethanol aqueous solution.

[0021] Furthermore, in step (6), the drying temperature is 23-28° C. and the drying time is 12-24 h.

[0022] Furthermore, the Fourier transform infrared spectroscopy analysis in step (6) is performed in transmission mode, and the analysis conditions are as follows: the scanning range is 4000-650 cm -1 , the number of scans is 64 times, the resolution is 8cm -1 .

[0023] Furthermore, the identification of the microplastics in step (6) includes comparing the detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis with the spectrum of standard substances in the spectral library of the Fourier microscopic infrared spectroscopy system, and if the matching degree is greater than 70%, it is judged to be microplastics.

[0024] Beneficial effects of the present invention

[0025] Based on the fact that microplastics are generally lipophilic, the inventors use the amphiphilic properties of myristic acid polyethylene glycol active esters to speculate that it can interact hydrophobically with microplastics through hydrophobic groups, thereby improving the separation effect of denser microplastics in sodium chloride solution. The present invention has found that in an ethanol / sodium chloride mixed solution, the addition of myristic acid polyethylene glycol active esters can indeed improve the separation effect of denser microplastics in sodium chloride solution, while in a separate sodium chloride solution, there is no such effect. It is speculated that this may be due to the formation of spherical micelles by myristic acid polyethylene glycol active esters in a separate sodium chloride solution, resulting in the masking of hydrophobic groups, which makes it impossible to interact hydrophobically with microplastics.

[0026] In addition, the inventors also found that myristic acid polyethylene glycol active ester may have different self-assembly forms in ethanol / sodium chloride mixed solution with the change of ethanol concentration, because the inventors unexpectedly found that the viscosity of the mixed solution at a specific ethanol concentration showed a short rise, indicating that myristic acid polyethylene glycol active ester may form worm-like micelles at this specific ethanol concentration, thereby increasing the solution viscosity. Correspondingly, the inventors found that the separation effect of microplastics with higher density in sodium chloride solution at this specific ethanol concentration was significantly improved. The inventors speculate that such an effect improvement may be due to two reasons. On the one hand, the improvement of solution viscosity slows down the sedimentation rate of microplastic particles. On the other hand, at this specific ethanol concentration, myristic acid polyethylene glycol active ester forms worm-like micelles, but because the ethanol concentration is still high, the morphology of the micelles is not complete, so that the hydrophobic groups of myristic acid polyethylene glycol active ester are not completely masked, so that hydrophobic interactions can still be performed with microplastics, so that the increase in solution viscosity makes these two factors synergistically promote the separation effect of microplastics with higher density. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic flow chart of the method for detecting microplastics in aquatic environment sediments according to the present invention is shown.

[0028] Figure 2 The zero shear viscosity measurement results of ethanol / sodium chloride mixed solutions containing polyethylene glycol active ester of myristic acid at different ethanol concentrations are shown. DETAILED DESCRIPTION

[0029] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0030] Example 1: Zero shear viscosity measurement of ethanol / sodium chloride mixed solution containing myristic acid polyethylene glycol active ester at different ethanol concentrations

[0031] 0.2 g / mL myristic acid polyethylene glycol active ester was dissolved in a saturated sodium chloride solution containing 1-50 vol% ethanol, stirred at 100-150 r / min for 2 h, and the zero shear viscosity of the mixed solution was measured using a Physica MCR 301 rheometer. The results are shown in Figure 2 As shown, it shows that the saturated sodium chloride solution containing myristic acid polyethylene glycol active ester has a short rise in zero shear viscosity in the presence of 25-40vol% ethanol, and the highest value appears near 33vol%. Therefore, the present invention selects a saturated sodium chloride solution containing 0.2g / mL myristic acid polyethylene glycol active ester and about 33vol% ethanol for flotation of microplastics.

[0032] Example 2: Separation and detection of microplastics in aquatic sediments

[0033] Water environment sediment collection

[0034] First, set up water quality sampling points. The selection of sampling points is in accordance with the "Technical Specifications for Surface Water and Sewage Monitoring" (HJ91-2002). The sampling location and number are determined according to the river width. The river width is 100-1000m, so three vertical lines are set on the left, middle and right. The water depth is 5-10 meters, so samples are taken 0.5 meters below the water surface and 0.5 meters above the bottom of the water.

[0035] Sediment sampling is carried out simultaneously with water quality sampling, and is combined with the existing surface water monitoring sampling vertical line according to the monitoring purpose and the hydraulic characteristics of the water body (such as river topography, water flow pattern, etc.) and functional requirements. Sampling points are selected in places where the water flow is gentle and the scouring effect is weak. Sampling points are arranged near the shore and in the middle of both banks, and the nearshore sampling points are 2 to 10 meters away from the wet bank.

[0036] Sediment collection is done with a grab bucket. Before sampling, rinse the grab bucket with water sample, and avoid stirring the bottom sediment during sampling. Samples can be collected 2 to 3 times at the same sampling point to mix well. After the sample is collected, water is drained and debris such as stones and branches are removed. About 1000g of sediment is collected and packaged in an aluminum foil bag and labeled.

[0037] Detection of microplastics in aquatic sediments

[0038] (1) After the sediment is collected and brought back to the laboratory, it is placed in a 60°C oven and dried for 24 h. The dry weight of the sediment is weighed. Each parallel sample requires 30-100 g (dry weight) of sediment, and 5 parallel samples are collected at each sampling point.

[0039] Each sediment sample was spiked with 20 of the following polymer microplastics: polyvinyl chloride (PVC) (density approximately 1.3-1.45 g / ml), acrylonitrile-butadiene-styrene copolymer (ABS) (density approximately 1.01-1.08 g / ml), polyamide (PA) fiber (density approximately 1.01-1.15 g / ml), and polyester (PES) fiber (density approximately 1.3-1.4 g / ml). Each spiked microplastic was carefully hand-selected under a microscope and thoroughly mixed into the sample to ensure that the spiked microplastic was distributed throughout the sediment;

[0040] (2) 30 g of dried spiked water environment sediment was mixed with 300 ml of 30% hydrogen peroxide solution, and digested for 5 h at a stirring speed of 100-150 r / min. The digested product was placed in an oven at 60°C and dried for 24 h to obtain digested dry matter;

[0041] (3) adding the digested dry matter into 300 ml of a saturated sodium chloride solution containing 0.2 g / mL myristic acid polyethylene glycol active ester and 40 vol% ethanol, and stirring at 100-150 r / min for 2 h;

[0042] (4) adding 60 ml of saturated sodium chloride solution to the solution in step (3) at a stirring speed of 100-150 r / min, and then standing at room temperature for 48 hours to perform flotation to obtain a flotation liquid and a flotation sediment;

[0043] (5) filtering the flotation liquid through a nitrocellulose filter membrane with a pore size of 5 μm to obtain a retentate deposited on the filter membrane;

[0044] (6) The intercepted material was rinsed in a 50% ethanol aqueous solution for 3-5 times, dried at room temperature for 24 hours, and then examined under a microscope. The suspected microplastic particles were selected for Fourier microscopic infrared spectroscopy analysis. The analysis conditions were as follows: the scanning range was 4000-650 cm -1, the number of scans is 64 times, the resolution is 8cm -1 The detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis is compared with the spectrum of standard substances in the spectrum library of the Fourier microscopic infrared spectroscopy system. If the matching degree is greater than 70%, it is judged as microplastic.

[0045] The recovery rate was calculated by quantifying each spiked microplastic in the retentate to determine the effectiveness of the method of the present invention for detecting microplastics in sediments in an aquatic environment.

[0046] Comparative Example 1 (using only saturated sodium chloride solution)

[0047] Water environment sediment collection

[0048] Same as Example 2.

[0049] Detection of microplastics in aquatic sediments

[0050] (1) After the sediment is collected and brought back to the laboratory, it is placed in a 60°C oven and dried for 24 h. The dry weight of the sediment is weighed. Each parallel sample requires 30-100 g (dry weight) of sediment, and 3 parallel samples are collected at each sampling point.

[0051] Each sediment sample was spiked with 20 of the following polymer microplastics: polyvinyl chloride (PVC) (density approximately 1.3-1.45 g / ml), acrylonitrile-butadiene-styrene copolymer (ABS) (density approximately 1.01-1.08 g / ml), polyamide (PA) fiber (density approximately 1.01-1.15 g / ml), and polyester (PES) fiber (density approximately 1.3-1.4 g / ml). Each spiked microplastic was carefully hand-selected under a microscope and thoroughly mixed into the sample to ensure that the spiked microplastic was distributed throughout the sediment;

[0052] (2) 30 g of dried spiked water environment sediment was mixed with 300 ml of 30% hydrogen peroxide solution, and digested for 5 h at a stirring speed of 100-150 r / min. The digested product was placed in an oven at 60°C and dried for 24 h to obtain digested dry matter;

[0053] (3) adding the digested dry matter into 300 ml of saturated sodium chloride solution, stirring for 2 h at 100-150 r / min, and then standing at room temperature for 48 h for flotation to obtain a flotation liquid and a flotation sediment;

[0054] (4) filtering the flotation liquid through a nitrocellulose filter membrane with a pore size of 5 μm to obtain a retentate deposited on the filter membrane;

[0055] (5) The intercepted material was rinsed in a 50% ethanol aqueous solution for 3-5 times, dried at room temperature for 24 hours, and then examined under a microscope. The suspected microplastic particles were selected for Fourier microscopic infrared spectroscopy analysis. The analysis conditions were as follows: the scanning range was 4000-650 cm -1 , the number of scans is 64 times, the resolution is 8cm -1 The detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis is compared with the spectrum of standard substances in the spectrum library of the Fourier microscopic infrared spectroscopy system. If the matching degree is greater than 70%, it is judged as microplastic.

[0056] The recovery was calculated by quantifying each spiked microplastic in the retentate.

[0057] Comparative Example 2 (without using water / ethanol mixed solvent)

[0058] Water environment sediment collection

[0059] Same as Example 2.

[0060] Detection of microplastics in aquatic sediments

[0061] (1) After the sediment is collected and brought back to the laboratory, it is placed in a 60°C oven and dried for 24 h. The dry weight of the sediment is weighed. Each parallel sample requires 30-100 g (dry weight) of sediment, and 3 parallel samples are collected at each sampling point.

[0062] Each sediment sample was spiked with 20 of the following polymer microplastics: polyvinyl chloride (PVC) (density approximately 1.3-1.45 g / ml), acrylonitrile-butadiene-styrene copolymer (ABS) (density approximately 1.01-1.08 g / ml), polyamide (PA) fiber (density approximately 1.01-1.15 g / ml), and polyester (PES) fiber (density approximately 1.3-1.4 g / ml). Each spiked microplastic was carefully hand-selected under a microscope and thoroughly mixed into the sample to ensure that the spiked microplastic was distributed throughout the sediment;

[0063] (2) 30 g of dried spiked water environment sediment was mixed with 300 ml of 30% hydrogen peroxide solution, and digested for 5 h at a stirring speed of 100-150 r / min. The digested product was placed in an oven at 60°C and dried for 24 h to obtain digested dry matter;

[0064] (3) adding the digested dry matter into 300 ml of a saturated sodium chloride solution containing 0.2 g / mL myristic acid polyethylene glycol active ester, stirring for 2 h at 100-150 r / min, and then standing at room temperature for 48 h for flotation to obtain a flotation liquid and a flotation sediment;

[0065] (4) filtering the flotation liquid through a nitrocellulose filter membrane with a pore size of 5 μm to obtain a retentate deposited on the filter membrane;

[0066] (5) The intercepted material was rinsed in a 50% ethanol aqueous solution for 3-5 times, dried at room temperature for 24 hours, and then examined under a microscope. The suspected microplastic particles were selected for Fourier microscopic infrared spectroscopy analysis. The analysis conditions were as follows: the scanning range was 4000-650 cm -1 , the number of scans is 64 times, the resolution is 8cm -1 The detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis is compared with the spectrum of standard substances in the spectrum library of the Fourier microscopic infrared spectroscopy system. If the matching degree is greater than 70%, it is judged as microplastic.

[0067] The recovery was calculated by quantifying each spiked microplastic in the retentate.

[0068] Comparative Example 3 (without addition of saturated sodium chloride solution)

[0069] Water environment sediment collection

[0070] Same as Example 2.

[0071] Detection of microplastics in aquatic sediments

[0072] (1) After the sediment is collected and brought back to the laboratory, it is placed in a 60°C oven and dried for 24 h. The dry weight of the sediment is weighed. Each parallel sample requires 30-100 g (dry weight) of sediment, and 3 parallel samples are collected at each sampling point.

[0073] Each sediment sample was spiked with 20 of the following polymer microplastics: polyvinyl chloride (PVC) (density approximately 1.3-1.45 g / ml), acrylonitrile-butadiene-styrene copolymer (ABS) (density approximately 1.01-1.08 g / ml), polyamide (PA) fiber (density approximately 1.01-1.15 g / ml), and polyester (PES) fiber (density approximately 1.3-1.4 g / ml). Each spiked microplastic was carefully hand-selected under a microscope and thoroughly mixed into the sample to ensure that the spiked microplastic was distributed throughout the sediment;

[0074] (2) 30 g of dried spiked water environment sediment was mixed with 300 ml of 30% hydrogen peroxide solution, and digested for 5 h at a stirring speed of 100-150 r / min. The digested product was placed in an oven at 60°C and dried for 24 h to obtain digested dry matter;

[0075] (3) adding the digested dry matter into 300 ml of a saturated sodium chloride solution containing 0.2 g / mL myristic acid polyethylene glycol active ester and 40 vol% ethanol, stirring at 100-150 r / min for 2 h, and then standing at room temperature for 48 h for flotation to obtain a flotation liquid and a flotation sediment;

[0076] (4) filtering the flotation liquid through a nitrocellulose filter membrane with a pore size of 5 μm to obtain a retentate deposited on the filter membrane;

[0077] (5) The intercepted material was rinsed in a 50% ethanol aqueous solution for 3-5 times, dried at room temperature for 24 hours, and then examined under a microscope. The suspected microplastic particles were selected for Fourier microscopic infrared spectroscopy analysis. The analysis conditions were as follows: the scanning range was 4000-650 cm -1 , the number of scans is 64 times, the resolution is 8cm -1 The detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis is compared with the spectrum of standard substances in the spectrum library of the Fourier microscopic infrared spectroscopy system. If the matching degree is greater than 70%, it is judged as microplastic.

[0078] The recovery was calculated by quantifying each spiked microplastic in the retentate.

[0079] Comparative Example 4 (different amounts of saturated sodium chloride solution added)

[0080] Water environment sediment collection

[0081] Same as Example 2.

[0082] Detection of microplastics in aquatic sediments

[0083] The other steps are the same as those in Example 2, except that in step (4), 10 ml of saturated sodium chloride solution is added dropwise to the solution in step (3) at a stirring speed of 100-150 r / min, and then the solution is allowed to stand at room temperature for 48 hours for flotation to obtain a flotation liquid and a flotation sediment.

[0084] Comparative Example 5 (different amounts of saturated sodium chloride solution added)

[0085] Water environment sediment collection

[0086] Same as Example 2.

[0087] Detection of microplastics in aquatic sediments

[0088] The other steps are the same as those in Example 2, except that in step (4), 30 ml of saturated sodium chloride solution is added dropwise to the solution in step (3) at a stirring speed of 100-150 r / min, and then the solution is allowed to stand at room temperature for 48 hours for flotation to obtain a flotation solution and a flotation sediment.

[0089] Comparative Example 6 (different amounts of saturated sodium chloride solution added)

[0090] Water environment sediment collection

[0091] Same as Example 2.

[0092] Detection of microplastics in aquatic sediments

[0093] The other steps are the same as those in Example 2, except that in step (4), 90 ml of saturated sodium chloride solution is added dropwise to the solution of step (3) at a stirring speed of 100-150 r / min, and then the solution is allowed to stand at room temperature for 48 hours for flotation to obtain a flotation liquid and a flotation sediment.

[0094] The recovery results of spiked microplastics measured in Example 2 and Comparative Examples 1-5 are shown in Table 1 below.

[0095] Table 1: Recovery determination results of spiked microplastics in Example 2 and Comparative Examples 1-5

[0096]

[0097] As can be seen from the results in Table 1, the saturated sodium chloride solution alone has a poor effect on the emergence of denser PVC and PES (Comparative Example 1). When myristic acid polyethylene glycol active ester is added to the saturated sodium chloride solution, a water / ethanol mixed solvent is required to effectively improve the separation effect of microplastics (Comparative Examples 2 and 3). When a water / ethanol mixed solvent is used, as the volume percentage of ethanol decreases from 40% to about 20%, the microplastic recovery rate initially shows an upward trend, and when the volume percentage of ethanol further decreases, the microplastic recovery rate begins to decrease again. This may be because the self-assembly state of myristic acid polyethylene glycol active ester in a water / ethanol mixed solvent is related to the ethanol concentration. When the volume percentage of ethanol is above 40%, myristic acid polyethylene glycol active ester is basically in an unassembled state. When the volume percentage of ethanol begins to decrease, myristic acid polyethylene glycol active ester begins to self-assemble. During this period, at a specific ethanol concentration, myristic acid polyethylene glycol active ester can form worm-like micelles, resulting in a brief increase in solution viscosity, and then as the ethanol concentration decreases, spherical micelles are formed, which makes the microplastic recovery rate show a trend of first increasing and then decreasing.

[0098] It should be noted that the preferred embodiments of the present invention are given in the specification and drawings of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments are not used as additional limitations on the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. In addition, the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the present invention; further, for ordinary technicians in this field, they can be improved or transformed according to the above description, and all these improvements and transformations should belong to the protection scope of the claims attached to the present invention.

Claims

1. A method for detecting microplastics in aquatic sediments, characterized in that: The following steps are involved: (1) drying and weighing the water environment sediment in sequence to obtain the dry weight of the water environment sediment; (2) mixing the dried water environment sediment with a 30% by mass hydrogen peroxide solution, digesting for 5-6 hours at a stirring speed of 100-150 r / min, and drying the digestion product to obtain digestion dry matter; (3) adding the digested dry matter into a saturated sodium chloride solution containing 0.1-0.3 g / mL myristic acid polyethylene glycol active ester and 40 vol% ethanol, and stirring at 100-150 r / min for 1-2 h; (4) adding an additional 20 vol% saturated sodium chloride solution to the solution of step (3) at a stirring speed of 100-150 r / min, and then standing at room temperature for 48 hours for flotation to obtain a flotation liquid and a flotation sediment; (5) filtering the flotation liquid to obtain a retentate deposited on the filter membrane; (6) The intercepted material is washed and dried and then examined under a microscope, and suspected microplastic particles are selected for Fourier microscopic infrared spectroscopy analysis to identify the microplastics.

2. The method according to claim 1, characterized in that In step (1) and step (2), the drying temperature is 50-80°C and the drying time is 20-26h.

3. The method according to claim 1, characterized in that In step (2), the ratio of the water environment sediment to the hydrogen peroxide solution is 10g:90-120ml.

4. The method according to claim 1, characterized in that In step (3), the amount of saturated sodium chloride solution added is 270-360 ml.

5. The method according to claim 1, characterized in that The filtration in step (5) includes suction filtration.

6. The method according to claim 1, characterized in that The filter membrane in step (5) is a nitrocellulose filter membrane with a pore size of 5 μm.

7. The method according to claim 1, characterized in that The washing in step (6) includes washing with a 50% ethanol aqueous solution.

8. The method according to claim 1, characterized in that The drying temperature in step (6) is 23-28° C. and the drying time is 12-24 hours.

9. The method according to claim 1, characterized in that: The Fourier transform infrared spectroscopy analysis in step (6) was performed in transmission mode, and the analysis conditions were as follows: the scanning range was 4000-650 cm -1 , the number of scans is 64 times, the resolution is 8cm -1 .

10. The method according to claim 1, characterized in that The identification of microplastics in step (6) includes comparing the detection spectrum obtained by Fourier microscopic infrared spectroscopy analysis with the spectrum of standard substances in the spectrum library of the Fourier microscopic infrared spectroscopy system, and determining that the microplastics are microplastics if the matching degree is greater than 70%.

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