Method for analyzing microplastics and method for separating and recovering microplastics for analysis

Abstract

To provide a method capable of accurately analyzing microplastics having a size of 500 μm or less in a sample.SOLUTION: Provided is a method for analyzing microplastics having a size of 500 μm or less in a sample, the method comprising: a microplastic recovery step of separating and recovering microplastics by filtering the sample; and an analysis step of analyzing the microplastics recovered in the microplastic recovery step, wherein an instrument used for the recovery in the microplastic recovery step is washed with an organic solvent having a specific gravity smaller than that of water, and microplastics remaining on a surface of the instrument that is in contact with the sample are captured and recovered.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for analyzing microplastics with a size of 500 μm or less in a sample and a method for separating and recovering microplastics for analysis.

Background Art

[0002] In recent years, the presence of microplastics in the marine environment has become a major concern. The origin of microplastics is plastic waste such as plastic bags, bento boxes at convenience stores, and caps of plastic bottles. Those discarded casually, those that overflow from trash cans and are left untreated, etc. have invaded rivers and sewage, or have been blown by the wind, and finally flowed into the sea and generated.

[0003] Since microplastics have an adverse impact on the environment and the human body, the number of microplastic particles in the ocean has been investigated along the guidelines and carefully verified by comparative experiments between laboratories (see Non-Patent Documents 1 to 3). In addition, in order to quantify the abundance of microplastics in the upper layer of the world's oceans, more than 8,000 trawl surveys have been carried out so far (see Non-Patent Document 4).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, among microplastics, there is currently no established method for measuring fine microplastics with a size of several hundred micrometers or less, and the development thereof has been desired.

[0006] An object of the present invention is to provide a method capable of accurately analyzing microplastics with a size of 500 μm or less in a sample.

Means for Solving the Problems

[0007] In order to solve the above problems, the present inventors first found that there are the following problems in the analysis of microplastics with a size of 500 μm or less among microplastics.

[0008] The number of microplastic particles is considered to be underestimated because microplastics are captured and lost in sampling devices and experimental devices. Specifically, since a part of the microplastics remains and is lost on the inner wall of the filter, container, tube, etc. during the treatment process, it is highly likely that the amount is evaluated as less than the actual amount.

[0009] As a result of various studies on the above problems, the present inventors found that when recovering microplastics, by washing the used instruments with an organic solvent having a specific gravity smaller than that of water and supplementarily recovering the microplastics remaining on the sample contact surface of the instruments, the microplastics in the sample can be more reliably separated and recovered and accurately analyzed, and thus the present invention was completed.

[0010] That is, the present invention is as follows. [1] A method for analyzing microplastics with a size of 500 μm or less in a sample, a microplastic recovery step of filtering the sample to separate and recover microplastics, An analysis step of analyzing the microplastics recovered in the microplastic recovery step; having, a method for analyzing microplastics, characterized in that the instrument used for recovery in the microplastic recovery step is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are additionally recovered.

[0011] [2] The method for analyzing microplastics according to [1] above, characterized in that the microplastics to be analyzed are plastics other than the material of the instrument.

[0012] [3] The method for analyzing microplastics according to [1] or [2] above, characterized in that the microplastics to be analyzed include at least polyethylene, polypropylene, polystyrene, polyester polyol, ethylene vinyl acetate, ethylene propylene rubber, acrylonitrile-butadiene-styrene, and polyethylene terephthalate.

[0013] [4] The method for analyzing microplastics according to any one of [1] to [3] above, characterized in that the organic solvent having a specific gravity smaller than that of water is ethanol.

[0014] [5] The method for analyzing microplastics according to any one of [1] to [4] above, characterized in that the microplastics to be analyzed have a size of 300 μm or less.

[0015] [6] The method for analyzing microplastics according to any one of [1] to [5] above, characterized in that the filtration in the microplastic recovery step is gravity filtration. [7] The method for analyzing microplastics according to [6] above, characterized in that the gravity filtration is siphon filtration.

[0016] [8] A method for separating and recovering microplastics from a sample for analyzing microplastics with a size of 500 μm or less contained in the sample, wherein the instrument used for separating and recovering microplastics from the sample is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are recovered, characterized in that it is a method for separating and recovering analytical microplastics. [9] The method for separating and recovering analytical microplastics according to [8] above, characterized in that the organic solvent having a specific gravity smaller than that of water is ethanol.

[0017]

[10] A method for analyzing microplastics with a size of 500 μm or less present in water, comprising a sample collection step of collecting a sample containing microplastics from water, a microplastic recovery step of filtering the sample collected in the sample collection step to separate and recover microplastics, an analysis step of analyzing the microplastics recovered in the microplastic recovery step, characterized in that, the instrument used for recovery in the microplastic recovery step is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are recovered, which is a method for analyzing microplastics.

[11] A method for separating and recovering microplastics from a sample for analyzing microplastics with a size of 500 μm or less contained in a sample collected from water, wherein the instrument used for separating and recovering microplastics from the sample is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are recovered, characterized in that it is a method for separating and recovering analytical microplastics. [Advantages of the Invention]

[0018] According to the method for analyzing microplastics and the method for separating and recovering microplastics for analysis of the present invention, microplastics with a size of 500 μm or less can be more reliably separated and recovered from a sample and analyzed with high accuracy.

Brief Description of the Drawings

[0019]

Figure 1

Embodiments for Carrying Out the Invention

[0020] The method for analyzing microplastics according to the present invention is a method for analyzing microplastics with a size of 500 μm or less in a sample, and includes a microplastic recovery step of filtering the sample to separate and recover microplastics, and an analysis step of analyzing the microplastics recovered in the microplastic recovery step. The instrument used for recovery in the microplastic recovery step is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are additionally recovered.

[0021] In addition, the method for analyzing microplastics of the present invention may include steps other than the above-described microplastic recovery step and analysis step, such as a preparation step and a sample collection step performed before the microplastic recovery step.

[0022] In the preparation step, for example, from the viewpoint of preventing contamination (hereinafter simply referred to as contamination), when there is a possibility that microplastics or other substances may be mixed into the sample from the outside, means for preventing such mixing are taken. That is, the number of microplastic particles may be overestimated due to plastic particle contamination in the analysis environment, and means for preventing such particle contamination are taken.

[0023] In addition, the sample collection step is, for example, a step of collecting a sample from water such as seawater, river water, or lake water when analyzing microplastics.

[0024] In addition, the method for separating and recovering microplastics for analysis of the present invention is a method for separating and recovering microplastics from a sample in order to analyze microplastics of 500 μm or less contained in the sample, and is characterized in that the tool used to separate and recover the microplastics from the sample is washed with an organic solvent having a lower specific gravity than water, and the microplastics remaining on the sample contact surface of the tool are captured and recovered.

[0025] The microplastic analysis method and the method for separating and recovering microplastics for analysis of the present invention are novel techniques that use an organic solvent with a specific gravity lower than that of water to wash the equipment used to separate and recover microplastics to be analyzed from a sample containing microplastics. The use of such an organic solvent allows for more reliable recovery of microplastics. In other words, washing with an organic solvent with a specific gravity lower than that of water makes it easier for fine microplastics with low specific gravity to disperse in the organic solvent, allowing the microplastics to be effectively washed away from the walls of the equipment.

[0026] The sample to be treated in the microplastic analysis method and the method for separating and recovering microplastics for analysis of the present invention is not particularly limited as long as it contains microplastics, and examples include water collected from the sea, rivers, lakes, drinking water, etc., as well as blood and soil. By analyzing water collected from the sea, rivers, lakes, etc., the state of environmental pollution can be understood.

[0027] The size (particle diameter) of the microplastics contained in the sample is 500 μm or less, but a smaller size of 300 μm or less is preferable because the effects of the present invention are more pronounced. On the other hand, the lower limit of the size is not particularly limited, but is, for example, about 10 μm.

[0028] This microplastic is, for example, fine plastic floating in water or on the water surface. Specific examples of its material include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyester polyol (PEP), ethylene vinyl acetate (EVA), ethylene propylene rubber (EPDM), acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), nylon (polyamide: PA), and the like.

[0029] The microplastic to be analyzed is preferably made of a material other than the material of the instrument used for collecting the microplastic or the like. For example, since polyvinyl chloride is often used in instruments, it is preferably excluded from the analysis target in order to perform more accurate analysis. In addition, when an instrument made of polyvinyl chloride is not used, it is preferable to use polyvinyl chloride as the analysis target. In other words, the instrument used for collecting the microplastic or the like is preferably made of a material other than the microplastic to be analyzed.

[0030] Examples of the organic solvent having a specific gravity smaller than that of water include alcohols such as methanol, ethanol, isopropanol, butanol, pentanol, and hexanol, and acetone, hexane, and the like. Among these, ethanol, which is easy to handle and inexpensive, is preferable. Note that two or more organic solvents having a specific gravity smaller than that of water may be mixed and used. In addition, the organic solvent having a specific gravity smaller than that of water may contain water, but the water content is preferably 30% by mass or less, more preferably 10% by mass or less, and particularly preferably substantially not contained.

[0031] Hereinafter, each step of the present invention will be described with reference to the drawings. As shown in FIG. 1, the method for analyzing microplastics of the present invention has, for example, a preparation step (S1), a sample collection step (S2), a microplastic collection step (S3), an organic matter decomposition step (S4), and an analysis step (S5). In this embodiment, the case of using water collected from the sea as a sample containing microplastics will be described, but the same applies when the sample is water collected from a river, a lake, or the like.

[0032] Hereinafter, each step will be specifically described.

[0033] [Preparation Step] The preparation step is a step prepared to prevent microplastics and other substances from the external environment from mixing into the sample at various stages such as when collecting the sample and when recovering and analyzing microplastics, from the perspective of contamination prevention. For example, in order to avoid dust in the air, a clean booth is installed inside the ship or the analysis room, or a clean room is installed. In addition, since the bottle containing the reagent may be made of plastic to be analyzed, in order to avoid the mixing of plastics and the like from the reagent used for analysis, it is preferable to use a reagent that has been filtered in advance and then transferred to a glass bottle. It should be noted that it is preferable to use ultrapure water (Milli-Q water) for the water used in the analysis.

[0034] [Sample Collection Step] The sample collection step is a step of collecting water from the sea. For example, when sampling on board, a Niskin bottle (Niskin sampler) or the like is used to collect a sample from the surface layer of seawater.

[0035] [Microplastic Recovery Step] The microplastic recovery step is a step of filtering the sample to separate and recover microplastics. Specifically, first, the collected sample is transferred from the Niskin bottle (Niskin sampler) to a container. At this time, in order to prevent the sample from coming into contact with air, it is transferred from the Niskin bottle to a polycarbonate container through a silicon tube (a rubber tube made of silicone). Here, it is preferable that the instruments used for transferring the sample from the Niskin bottle and the instruments used in this step are made of materials other than the microplastics to be analyzed contained in the sample.

[0036] Next, filter the sample transferred to the container. The filtration is preferably gravity filtration that can be performed while maintaining a slow filtration rate in order to suppress damage to brittle microplastics. That is, microplastics deteriorated in the natural environment are easily broken, and if a part of the microplastics is finely crushed by physical or chemical stimuli during sample treatment, the number of microplastic particles may be overestimated, and it is necessary to prevent this. As the gravity filtration, it is particularly preferable to be siphon filtration using the principle of a siphon. For example, the sample is sucked up only at the beginning with a vacuum pump through a silicon tube from the upper part of the container, and then filtration is performed at a slow speed using the principle of a siphon. In addition, it is preferable to use a stainless-steel filter for filtration. The mesh (aperture) of this filter is appropriately selected according to the size of the microplastics to be recovered. Thereby, the microplastics can be recovered on the filter.

[0037] After performing the above filtration, the instruments used for recovery in this step are washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instruments are recovered additionally. Specifically, after washing various instruments, the organic solvent containing the microplastics used for washing is filtered by gravity filtration using the filter used for this recovery, and the microplastics remaining on the instruments are recovered additionally. Thereby, the microplastics adhering and remaining on the instruments can be recovered more reliably.

[0038] As described above, by using an organic solvent with a specific gravity smaller than that of water as the cleaning liquid, microplastics with a smaller specific gravity are more likely to mix rather than float in the cleaning liquid, making them easier to be removed from the sample contact surface of the instrument, and thus it is considered that microplastics can be recovered more effectively. As will be described later, when cleaning with water, the recovery rate of microplastics was about 35%, while when cleaning with ethanol, it was about 90%, indicating a dramatic improvement in the recovery rate. As the cleaning liquid, an organic solvent having a specific gravity smaller than that of water and smaller than that of all the microplastics to be analyzed is particularly preferable.

[0039] As the above-described instrument, there are instruments with which the sample directly comes into contact from sample collection to filtration, specifically, the above-described silicon tube, container, filter, filter holder, etc. It is preferable to clean all of these instruments with an organic solvent, but for example, only some instruments with a large amount of microplastics attached may be cleaned. The above-described filter is preferably heated and cleaned with an organic solvent (especially ethanol) to remove lipids mixed in the microplastics.

[0040] [Organic matter decomposition step] The organic matter decomposition step is a step of decomposing and removing organic matter other than microplastics attached to the filter. Although it is preferable to perform the treatment of this step, it may be omitted.

[0041] For example, the filter with microplastics attached recovered in the above microplastic recovery process is subjected to two-stage digestion at a low temperature. This can reduce the physical and chemical damage of the microplastics. For the two-stage digestion, conventionally known methods can be used. For example, "Alfonso, M. B., Takashima, K., Yamaguchi, S., Tanaka, M., Isobe, A., 2021. Microplastics on plankton samples: multiple digestion techniques assessment based on weight, size, and FTIR spectroscopy analyses, Mar. Pollut. Bull., 173, 113027." can be cited.

[0042] After the decomposition treatment, the filter is rinsed sequentially with ultrapure water and an organic solvent having a specific gravity smaller than that of water to recover the organic solvent containing microplastics in a container. Since there is a possibility that the microplastics remain attached to the filter, the filter is further, for example, placed in an ultrasonic cleaner to separate the microplastics from the filter, and the organic solvent containing this microplastics is recovered in a container.

[0043] [Analysis step] The analysis step is a step of analyzing the microplastics treated in the above organic matter decomposition step (when the organic matter decomposition step is omitted, the microplastic recovery step). For identifying the type of polymer of the microplastics, it is preferable to use, for example, a micro-FTIR (infrared spectrophotometer). First, the organic solvent containing the microplastics obtained in the above organic matter decomposition step and recovered in a container is poured onto an analysis filter, and the microplastics are accumulated on the analysis filter. To improve the analysis accuracy, it is preferable to concentrate the microplastics within a small area in the center of the filter. In addition, the instruments used in this step, such as the container, are also preferably washed with an organic solvent having a specific gravity smaller than that of water, poured onto the analysis filter, and the microplastics are recovered more reliably.

[0044] Also, since it is necessary to eliminate wrinkles and deflections of the filter and the associated analysis errors, for example, it is preferable to cover the filter with a metal ring-shaped jig and fix its periphery with a ring-shaped rubber (O-ring) to dry the filter.

[0045] Set the above filter on the sample support stage of the micro-FTIR, and examine the type, number of particles, size, etc. of the microplastic polymer. The type of microplastic to be analyzed is not particularly limited, but by limiting it to those that are not used as the material of the instrument by the method of the present invention and that are likely to be present relatively abundantly in the ocean, etc., the processing time can be shortened, which is preferable. Specifically, one or more of polyethylene, polypropylene, polystyrene, polyester polyol, ethylene vinyl acetate, ethylene propylene rubber, acrylonitrile-butadiene-styrene, and polyethylene terephthalate can be mentioned.

[0046] When using micro-FTIR for analysis, it is preferably not to perform density separation for separating plastics and small stones, etc., which is usually performed during analysis exceeding 500 μm. This is because excessive deposition and coloring on the filter of NaI used in density separation may lead to a decrease in the spectral signal. When using other analysis methods, density separation may be performed.

[0047] Also, after performing the organic matter decomposition step and further after performing density separation, division for subsampling may be performed. In a sample with a high concentration of microplastics, the sample can be divided in order to facilitate the analysis in the subsequent analysis step.

Example

[0048] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In order to minimize the contamination of the sample (microplastics), the breakage of microplastics, and the loss of microplastics, the microplastic analysis in the sample was performed by the following operations.

[0049] 1.1 Preparation process (prevention of contamination) In order to obtain accurate results of the abundance of microplastics, it is very important to avoid contamination by other microplastics and dust and fibers other than plastics in the analysis room or the like. These small substances generate noise in the spectral signals for identifying plastic particle polymers and also significantly increase the processing time for particle counting by FTIR.

[0050] Therefore, when collecting samples from seawater, on board the ship, in order to prevent the mixing of suspicious microplastics, a clean booth was installed to avoid dust in the air containing microplastics. Similarly, on land, processes such as filtration and two-stage digestion were performed in a clean bench. An electrostatic eliminator was installed in the clean bench to prevent the adhesion of dust from the outside to the experimental apparatus. In addition, three HEPA filters were installed to continuously remove floating dust. Furthermore, on both the ship and land, experimental apparatuses made of non-plastic materials such as silicone resin, fluororesin, glass, and metal were used.

[0051] For all experiments including the cleaning of all used instruments and the preparation of reagents, ultrapure water (Milli-Q water) produced by an ultrapure water production system was used. In addition, polyethersulfone, which hardly exists in nature, was selected as the final filter material of the ultrapure water production system, and the water intake cover made of polystyrene was removed because it is the polymer of the microplastics to be analyzed.

[0052] The reagents used for digestion (10% KOH, 30% H2O2, 0.05 M Fe(II)) and 99.5% ethanol might also be sources of contamination due to the plastic caps of reagent bottles and the plastic released during the manufacturing process. Therefore, all reagents were filtered through a 1-μm polytetrafluoroethylene (hereinafter referred to as PTFE) membrane filter and transferred to a washed reagent glass bottle covered with a PTFE lid. Specifically, filtration was repeated by FTIR microscopic analysis until no microplastics were contained in the reagent, and finally, the reagent without microplastics was stored in a glass bottle with a PTFE lid. Hereinafter, unless otherwise specified, "ethanol" refers to a 99.5% ethanol solution filtered by the above method.

[0053] 1.2 Sample collection process (sampling of microplastics on board) Eight L-shaped Niskin bottles made of polyvinyl chloride (PVC) were used to collect surface seawater from the ship under conditions that minimized contamination. The seawater was directly transferred from the Niskin bottle to a polycarbonate container through a silicone tube without being exposed to air. The container containing the seawater sample was immediately covered with a rubber stopper to avoid contamination.

[0054] 1.3 Microplastic recovery process (filtration of microplastics from seawater samples) Filtration of microplastics from seawater samples was performed in a clean bench (analysis room) using a filtration device with a stainless-steel filter (pore size 10 μm, diameter 47 mm). The seawater was transferred from the polycarbonate container to the filtration device through a silicone tube (inner diameter 7.94 mm). Specifically, only a vacuum pump was used at the beginning, and then, in order to maintain a filtration rate slow enough not to break the microplastics, the siphon principle was used to transfer and filter the seawater to the filtration device.

[0055] When the filtration of seawater was completed, the parts of the silicone tube and the polycarbonate container that had come into contact with the seawater were washed with ethanol to remove the microplastics adhering to the surface. Subsequently, the ethanol used for washing was filtered through the above-mentioned filter.

[0056] In addition, to remove lipids, a stainless-steel filter was immersed in ethanol for 1 minute and heated to 60 °C using a hot plate stirrer. Subsequently, the stainless-steel filter was washed with water by suction filtration. All filters were stored in a container made of perfluoroalkoxy alkane (hereinafter referred to as PFA).

[0057] 1.4 Organic matter decomposition process (two-stage digestion) In this protocol, two-stage digestion at low temperature was adopted to reduce the physical and chemical damage of microplastics. All the stainless-steel filters in the PFA containers were placed in a tall beaker containing 30 mL of 10% KOH solution and immersed at 40 °C for 72 hours, and then oxidized and digested at 40 °C or lower with 60 mL of 30% H2O2 + 20 mL of Fe(II) 0.05M. Subsequently, the stainless-steel filters were rinsed with ultrapure water and ethanol and collected in a tall beaker. Specifically, the washed stainless-steel filters were placed in a PFA container containing 30 mL of ethanol solution. Next, the capped PFA container was placed in an ultrasonic cleaner for 1 minute to separate all the microplastics that might still be attached to the filters. Then, the ethanol solution containing the microplastics was transferred to a tall beaker and stored for the next treatment.

[0058] 1.5 Analysis process (identification of microplastics by micro-FTIR) The types of plastic polymers were analyzed using micro-FTIR (Nicolet iN10 MX, manufactured by Thermo Fisher Scientific). Generally, micro-FTIR scans a small area (an area of 8 mm × 8 mm in the "focal plane array (FPA)" mode). Here, a PTFE filter was covered with a metal ring-shaped jig, and its periphery was fixed with a ring-shaped rubber, and then dried in a petri dish on a clean bench. Finally, the PTFE filter was set on a micro-FTIR sample support stage to identify the polymer types of the microplastics.

[0059] Note that here, in order to shorten the processing time, the types of polymers to be identified using micro-FTIR were pre-determined to be those that may exist in the ocean. The plastic polymers targeted in this study were those with a density lower than that of seawater (~1.025 g / cm 3 ), such as polyethylene, polypropylene, polyester polyol, ethylene vinyl acetate, and ethylene propylene rubber. Also, polystyrene with a density of 0.96 - 1.05 g / cm 3 was targeted because there is a possibility that fragments of foamed polystyrene (lighter than seawater) may be detected. Furthermore, polyethylene terephthalate has a density higher than that of seawater, so it has a low possibility of long-distance movement in the ocean. However, since polyester SMP fibers may reach the upper layer of the ocean by atmospheric deposition, it was targeted.

[0060] The polymer types, particle numbers, and sizes of the microplastics on the PTFE filter were examined using a micro-FTIR scan image (FPA mode, transmission mode, 715 - 4000 / cm range, 8 / cm resolution, obtained by 16-fold cumulative scans) in an 8 mm × 8 mm filter area, and the spectra of the polymers were compared with the spectra in the library. The selection criteria were that the hit quality index of the infrared absorption spectrum of the plastic particles was 60% or more (correlation coefficient 0.6; statistically significant value), and all the spectral peaks expected for each polymer type were detected.

[0061] On the one hand, microplastics with a very high hit quality index (e.g., 90% or more), such as those contained in a library of polymers that are not degraded or are degraded to the same extent as those in a library of polymers damaged by ultraviolet rays or heat, are likely to be of anthropogenic origin because they are unlikely to exist in nature. However, it is difficult to determine a unique maximum hit quality index suitable for marine microplastics. Therefore, overestimation by contaminated microplastics during observation was reduced by subtracting the number of particles detected in the contamination test. The size was defined by the Feret diameter of each particle displayed on the monitor and measured using the image processing software attached to the micro-FTIR. The size of the microplastics measured by micro-FTIR was confirmed by measuring the particles with a stereomicroscope (Olympus, Japan, SZX7), and it was confirmed that the reliable LOD was 10 μm or more.

[0062] Using the method described above, measurements were made for two locations in the coastal waters of Japan for each polymer type of microplastics. The results showing the number of particles and the concentration (number of particles per liter of seawater) are shown in Table 1, and the results showing the number of particles and the concentration (number of particles per liter of seawater) for each size range are shown in Table 2, respectively. The concentration is described in parentheses next to the number of particles.

[0063] [Table 1]

[0064] [Table 2]

[0065] As described above, it was found that microplastics with a size of 500 μm or less can be separated, recovered, and analyzed.

[0066] Hereinafter, tests for confirming the effects of the method of the present invention and the results thereof are shown. 1. Confirmation of the effect of the method of washing with an organic solvent having a specific gravity smaller than that of water In this test, the test was conducted three times using spherical red beads made of polystyrene with a diameter of 100 μm (Thermo Fisher, RD100T).

[0067] First, 100 red beads were mixed with 5 liters of ultrapure water, and filtration (the operation in 1.3 above), two-step digestion (the operation in 1.4 above), and final filtration with a PTFE filter for spectroscopic analysis (the previous operation in 1.5 above) were performed. Then, the number of beads on the filter was counted using a stereomicroscope, and the recovery rate (R100) was calculated. Furthermore, the above ethanol was replaced with ultrapure water to rinse the instrument, and a comparison was made with this particle recovery rate.

[0068] As a result, when washed with ethanol, the recovery rate was about 88%, but when washed with ultrapure water instead of ethanol, the recovery rate decreased sharply to 33.6%. This is presumably because microplastics with a specific gravity greater than that of ethanol become more likely to move from the sample contact surface of the instrument when they come into contact with ethanol and can be recovered. In addition, the same tendency can be obtained for organic solvents with a specific gravity smaller than that of water other than ethanol.

[0069] 2. Confirmation of the effect of siphon filtration in the present invention As a result of confirming the destruction rate of polystyrene beads by siphon filtration, the destruction rate was less than 2%. Considering that in the case of conventional filtration using a mechanical pump, the average was about 9%, it can be seen that the destruction of microplastics is sufficiently suppressed by applying siphon filtration.

Industrial applicability

[0070] Since the present invention can accurately analyze microplastics with a size of 500 μm or less in a sample, it is industrially useful.

Claims

1. A method for analyzing microplastics with a size of 500 μm or less in a sample, comprising: a microplastic recovery step of filtering the sample to separate and recover microplastics; an analysis step of analyzing the microplastics recovered in the microplastic recovery step; and characterized in that the instrument used for recovery in the microplastic recovery step is washed with an organic solvent having a specific gravity smaller than that of water, and the microplastics remaining on the sample contact surface of the instrument are additionally recovered.

2. The method for analyzing microplastics according to claim 1, wherein the microplastics to be analyzed are plastics other than the material of the instrument.

3. The method for analyzing microplastics according to claim 1 or 2, wherein the microplastics to be analyzed include at least polyethylene, polypropylene, polystyrene, polyester polyol, ethylene vinyl acetate, ethylene propylene rubber, acrylonitrile-butadiene-styrene, and polyethylene terephthalate.

4. The method for analyzing microplastics according to claim 1 or 2, wherein the organic solvent having a specific gravity smaller than that of water is ethanol.

5. The method for analyzing microplastics according to claim 1 or 2, wherein the microplastics to be analyzed have a size of 300 μm or less.

6. The method for analyzing microplastics according to claim 1 or 2, wherein the filtration in the microplastic recovery step is gravity filtration.

7. The method for analyzing microplastics according to claim 6, wherein the gravity filtration is siphon filtration.

8. A method for separating and recovering microplastics from a sample for analyzing microplastics with a size of 500 μm or less contained in the sample, comprising: washing the instrument used for separating and recovering microplastics from the sample with an organic solvent having a specific gravity smaller than that of water, and additionally recovering the microplastics remaining on the sample contact surface of the instrument.

9. The method for separating and recovering microplastics for analysis according to claim 8, wherein the organic solvent having a specific gravity smaller than that of water is ethanol.

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