JP2023166748A - Microplastic observation method and observation device therefor - Google Patents

Abstract

To provide a method for observing microplastics in water using infrared light, and a small-sized observation device therefor.SOLUTION: An observation method flows water so as to form a flux that flows at a constant speed along an axial line, then linearly irradiates a straight line perpendicular to the axial line with infrared rays from a light source, and guides transmitted light onto a uniaxial array detector in which photodetection elements are arranged in a row, to detect light. The observation device comprises: a flow cell that allows water to flow so as to form a flux flowing at a constant speed along an axial line; and an optical system that linearly irradiates a straight line perpendicular to the axial line with infrared rays from a light source, and guides transmitted light onto a uniaxial array detector in which photodetection elements are arranged in a row, to detect light.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for observing microplastics in water using infrared rays and an apparatus for observing the same.

Plastic waste is broken down into small pieces in the environment, and becomes floating in the oceans and rivers as tiny pieces of plastic called "microplastics", which are less than 5mm in size, and are taken into the bodies of humans and animals. There have been reports of health hazards. In order to observe such microplastics, liquid collected from the ocean (hereinafter simply referred to as "water") is pretreated to separate microplastics, and then the liquid is observed using techniques as necessary. (For example, see Patent Document 1 and Non-Patent Document 1).

JP 2021-183933 Publication

"Characterization of microplastics on filter substrates based on hyperspectral imaging: Laboratory assessments", Chunmao Zhu, Yugo Kanaya, Ryota Nakajima, Masashi Tsuchiya, Hidetaka Nomaki, Tomo Kitahashi, Katsunori Fujikura, Environmental Pollution, Volume 263, Part B, August 2020, 114296

In the above-mentioned documents, water is filtered and microplastics captured on the filter are observed. For example, in Non-Patent Document 1, an infrared lamp is used to illuminate the filter and a spectrometer is used to perform spectroscopic measurements. ing. On the other hand, there was a desire for a small device that could directly observe microplastics in collected water and that could be easily observed even in locations such as offshore ships. Therefore, consideration has been given to using infrared light to optically identify the resin type of microplastics, but the absorption of infrared light in water is extremely large, allowing observation of small, moving particles such as microplastics. It's difficult to do.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for observing microplastics in water using infrared rays and a small-sized observation device for the same. .

The observation method of the present invention is a method for observing microplastics in water using infrared rays, in which the water is caused to flow so as to form a flux flowing at a constant speed along an axis, and then It is characterized by linearly irradiating infrared rays from a light source on a straight line, and guiding the transmitted light onto a uniaxial array detector in which photodetecting elements are arranged in a row to perform photodetection.

The observation device of the present invention is an observation device for microplastics in water using infrared rays, and includes a flow cell through which the water flows so as to form a flux flowing at a constant speed along the axis; An optical system that linearly irradiates infrared rays from a light source on orthogonal straight lines, and conducts light detection by guiding the transmitted light onto a uniaxial array detector in which light detection elements are arranged in a row. It is characterized by

According to this feature, the light intensity per area can be increased with the same light source by reducing the irradiation area, so even infrared rays, which are highly absorbed underwater, can be made into a compact observation device without increasing the size of the light source. It is possible.

FIG. 1 is a block diagram (partially a perspective view) of an observation device as an embodiment of the present invention. These are (a) an external photograph of the inside of the pipe in the demonstration test, and (b) a two-dimensional image obtained by an observation device. These are (a) an external photograph of the inside of the pipe in the demonstration test, and (b) a two-dimensional image obtained by an observation device.

Below, a microplastic observation device and observation method, which is one embodiment of the present invention, will be described using FIG. 1.

As shown in FIG. 1, the observation device 1 is a device for observing microplastics floating in water, and includes a flow cell 10 having a flow channel (pipe) 11 inside for flowing water to be observed, and an infrared ray It includes an irradiation-side optical system 20 for irradiating light, and a light-receiving optical system 30 for observing transmitted light transmitted through the flow cell 10.

The flow cell 10 allows water to flow along axis A to form a flux that flows at a constant speed. For example, such a flux can be formed by making the shape of the cross section perpendicular to the axis A of the flow path 11 constant. In this embodiment, the cross section of the flow path 11 perpendicular to the axis A is rectangular. Further, while the axis A was perpendicular to the direction in which infrared rays pass, the short pieces of the rectangle were arranged to be parallel to the direction in which infrared rays pass.

Note that since infrared rays are easily absorbed by water, it depends on the intensity of the light source, but from the perspective of suppressing the attenuation of infrared rays, the length of such short pieces is shortened so that the water in the flow path 11 can pass through the infrared rays. It is preferable to reduce the thickness. Furthermore, by making the cross-sectional shape perpendicular to the axis A of the channel 11 rectangular, the distance through which infrared rays pass through the channel 11 can be made constant in the width direction of the channel 11, and transmitted light can be obtained under uniform conditions. It is preferable. Furthermore, it is preferable that the water is allowed to flow so as to fill the inside of the channel 11, since the transmitted light can also be obtained under uniform conditions in the width direction of the channel 11.

There is no restriction on the direction of the axis A of the channel 11 with respect to gravity, but in consideration of the difference in specific gravity between water and floating microplastics, it is preferable to orient the axis A horizontally. If the axis A is horizontal, even if the microplastic has a relative velocity with water due to a difference in specific gravity, no velocity difference will occur in the direction in which the flux of the flow path 11 flows. Therefore, the shape of the microplastics observed with the observation device 1 can be prevented from being affected.

Therefore, here, the flow cell 10 was arranged so that the axis A was oriented horizontally. Further, among the rectangular cross sections of the flow path 11 described above, the short pieces were oriented in the vertical direction, and infrared rays were irradiated from the upper side of the flow cell 10 and transmitted downward. This arrangement will be described below.

On the other hand, the irradiation side optical system 20 includes a light source 21 that emits infrared light while changing the wavelength, a beam expander 22 that expands the emitted infrared light beam, a mirror 23 that reflects the light beam, and a light beam from the mirror 23. and a cylindrical lens 24 that condenses the light into a line. The light source 21 is one that can emit infrared rays while changing the wavelength. For example, a quantum cascade laser that can quickly change the emission wavelength can be used. As described above, the beam expander 22, the mirror 23, and the cylindrical lens 24 can linearly irradiate infrared rays by passing through them, and can guide this to the upper surface of the channel 11 of the flow cell 10. It is arranged so that it can be done. In other words, the irradiation side optical system 20 functions as a so-called laser line generator. In particular, the infrared rays irradiated onto the flow path 11 are made to be focused on a straight line that is perpendicular to and horizontal to the axis A. As a result, the infrared rays are irradiated so as to pass through the channel 11 from top to bottom along a plane perpendicular to the axis A. Here, in particular, the mirror 23 and the cylindrical lens 24 can be replaced by optical elements known for that purpose.

Further, among the infrared rays emitted by the light source 21, in the wavelength range of 1 to 10 μm, the shorter the wavelength, the more difficult it is to be absorbed by water. Therefore, from the viewpoint of suppressing the attenuation of infrared rays, it is preferable to use near-infrared rays with a wavelength of about 1 to 2 μm. On the other hand, from the viewpoint of identifying the resin type of microplastics, it is also important to use infrared rays in a wavelength range suitable for this purpose. Although most of the wavelengths absorbed by microplastics are within the infrared wavelength range, the amount of information obtained differs depending on the wavelength. Here, the observation device 1 includes an optical system that focuses infrared rays on the premise that infrared rays are attenuated by absorption. Therefore, the wavelength range of infrared rays used in the observation device 1 is preferably selected with priority given to the viewpoint suitable for identifying the resin type, rather than the viewpoint of suppressing the attenuation of infrared rays.

The light-receiving optical system 30 includes a uniaxial array detector 32 that receives transmitted light transmitted through the channel 11 by infrared rays irradiated onto the flow cell 10, and a light-receiving lens 31 that guides the transmitted light onto the uniaxial array detector 32. including. The arrangement of the light-receiving side lens 31 is adjusted according to the focal position so that an image of the inside of the flow path 11 caused by the transmitted light can be formed on the uniaxial array detector 32. The uniaxial array detector 32 is a photodetector in which a plurality of photodetecting elements 33 are arranged in a line, and can receive transmitted light from the flow path 11 and perform photodetection. The uniaxial array detector 32 has a plurality of photodetecting elements 33 arranged in a horizontal plane in a direction perpendicular to the axis A, and arranged so that the transmitted light transmitted in a linear manner can be widely received in the width direction of the flow path 11. has been done. Furthermore, the uniaxial array detector 32 is connected to the analysis device 40 and can output information regarding the intensity of the received transmitted light to the analysis device 40 as an electrical signal.

The analysis device 40 can obtain a spectrum at each position of the photodetector element 33 based on the output of the uniaxial array detector 32. In addition, by comparing the obtained spectrum with the spectrum of transmitted light obtained using a similar observation device using a plastic piece of a known resin type, it is possible to determine the type of resin constituting the microplastics floating in the water in the flow channel 11. can be determined. That is, the analysis device 40 is used as an analysis section of the observation device 1.

When comparing such spectra, for example, rather than measuring all the wavelengths under each wavelength condition in the spectrum range, it is easier to extract and measure the wavelength portion of the spectrum that has characteristics due to differences in resin type. This is preferable because the resin type can be determined based on time. An example of a method for selecting a wavelength portion having this characteristic is principal component analysis. Further, as a method for comparing spectra, for example, a method using a correlation coefficient can be mentioned.

Further, although the irradiated infrared rays have a certain wavelength width, the transmitted light received by the photodetecting element 33 may be separated into spectra in advance according to the wavelength width. Specifically, the photodetecting element 33 separates the infrared rays into wavelength portions that may be characteristic depending on the resin type, and outputs a spectral intensity corresponding to the wavelength width. In other words, the intensity of each of the separated wavelength parts is output. Then, based on this, the resin type is determined in the analysis device 40. This is also preferable because the resin type can be determined in a short time.

The analysis device 40 can also form an image of the shape of microplastics floating in water. That is, the resin type described above is continuously determined at predetermined time intervals, and a two-dimensional image based on time and the position of the photodetecting element 33 is created. For example, the product of the velocity of the flux of water flowing in the flow path 11 and the above-mentioned time interval corresponds to the distance in the direction along the axis A in the flow path 11, and the light detection lines are arranged in a row. The positions of the elements 33 are made to correspond to the distances in the width direction of the flow path 11. Then, by color-coding and creating an image based on the determination of the resin type described above, it is possible to form an image of the shape of the microplastic in the flow path 11 that passes over the photodetection element 33 together with the water. Note that the output from the photodetecting element 33 may be performed intermittently in accordance with the velocity of the flux, and the resin type may be determined each time the output is received to form an image in the same manner. That is, the analysis device 40 also functions as an image processing section of the observation device 1.

Note that known devices can be used as the uniaxial array detector 32 and the analysis device 40. For example, the analysis device 40 may be a personal computer equipped with spectrum analysis software.

[Verification test]
The results of observing plastic pieces of known resin types using the above-mentioned observation device 1 will be explained. The prepared plastic pieces were of four types: polymethyl methacrylate resin (acrylic), polystyrene resin, polyethylene resin, and polypropylene resin.

First, plastic pieces of each resin type were molded into approximately 5 mm square and 1 mm thick, and immersed in water. The width of the cell 10 is approximately 10 mm, and the vertical dimension is 3 mm. Since the water filled the flow path 11, the thickness of the water at the location where the plastic pieces were present was 2 mm.

As shown in FIG. 2(a), four types of plastic pieces can be observed externally, and as shown in FIG. 2(b), the same shape as the external appearance can be obtained in the two-dimensional image obtained by the observation device 1. It was observed that Note that the ranges surrounded by dotted lines correspond to each other in FIGS.

Further, this two-dimensional image is color-coded based on the determination of the resin type by the analysis device 40. The color coding based on this determination also corresponds to the resin type codes shown on the external appearance in Figure (a) (PMMA: polymethyl methacrylate resin (acrylic), PS: polystyrene resin, PE, polyethylene resin, PP: polypropylene resin). It turns out that there is. In this way, the two-dimensional image obtained by the observation device 1 was able to almost accurately represent at least the resin types and shapes of the four types of plastic pieces described above.

Next, the plastic pieces of each resin type are molded to about 1 mm square and 1 mm thick, and the vertical dimension of the cell 10 is changed to 2 mm, that is, the thickness of the water where the plastic pieces are located is 1 mm. Similar observations were made with different

As shown in FIG. 3(a), four types of plastic pieces can be observed externally, and as shown in FIG. 3(b), a shape similar to the external appearance can be obtained in the two-dimensional image obtained by the observation device 1. It was observed that

It was also found that the color classification based on the determination of the resin type corresponded to the resin type code shown on the external appearance in FIG. It has been found that the two-dimensional image obtained by the observation device 1 can almost accurately represent the resin type and shape of a plastic piece having a size of at least 1 mm square.

As described above, according to the observation device 1, microplastics in water can be observed using infrared rays. In particular, the irradiation side optical system 20 focuses the infrared rays on a straight line to reduce the irradiation area, and the light intensity per area can be increased even with the same light source. Therefore, even infrared rays, which are highly absorbed underwater, can be observed without increasing the size of the light source, making it possible to use a compact observation device. According to such an observation device 1, it becomes easy to observe microplastics in seawater, for example, on a ship.

Although typical embodiments according to the present invention have been described above, the present invention is not necessarily limited thereto, and those skilled in the art can easily understand the invention without departing from the spirit of the present invention or the scope of the appended claims. , various alternative embodiments and modifications may be found.

1 Observation device 10 Flow cell 11 Channel 20 Irradiation side optical system 30 Light receiving side optical system 40 Analysis device A Axis

Claims (13)

A method for observing microplastics in water using infrared rays, the method comprising:
After the water flows so as to form a flux flowing at a constant speed along the axis, infrared rays from a light source are linearly irradiated on a straight line perpendicular to the axis, and the transmitted light is transmitted. A method for observing microplastics characterized by detecting light by guiding it onto a uniaxial array detector in which photodetecting elements are arranged in a row. 2. The method for observing microplastics according to claim 1, wherein the output from the uniaxial array detector is made to correspond to the velocity of the flux to form an image of the shape of the microplastics. The infrared rays are emitted from a wavelength tunable light source and have a wavelength width, and the photodetection element of the uniaxial array detector outputs a spectral intensity corresponding to the wavelength width to indicate the type of resin constituting the microplastic. The method for observing microplastics according to claim 1, characterized in that: 4. The method for observing microplastics according to claim 1, wherein the infrared rays are within a range of 1 to 10 μm. 2. The method for observing microplastics according to claim 1, wherein the water is flowed to fill a channel provided along the axis. 6. The microplastic observation method according to claim 5, wherein the flow path has a rectangular cross section perpendicular to the axis. A device for observing microplastics in water using infrared rays,
a flow cell in which the water flows so as to form a flux flowing at a constant speed along an axis;
an optical system that linearly irradiates infrared rays from a light source on a straight line perpendicular to the axis and guides the transmitted light onto a uniaxial array detector in which photodetecting elements are arranged in a row to detect light; A microplastic observation device comprising: 8. The microplastic observation device according to claim 7, wherein the optical system includes a cylindrical lens that focuses the infrared rays into a linear shape. 8. The microplastic observation device according to claim 7, further comprising an image processing unit that forms an image of the shape of the microplastic by making the output from the uniaxial array detector correspond to the velocity of the flux. . The infrared rays are emitted from a wavelength tunable light source and have a wavelength width, and the photodetection element of the uniaxial array detector outputs a spectral intensity corresponding to the wavelength width to indicate the type of resin constituting the microplastic. 8. The microplastic observation device according to claim 7, further comprising an analysis section. The microplastic observation device according to claim 7, wherein the infrared rays are within a range of 1 to 10 μm. 8. The microplastic observation device according to claim 7, wherein the flow cell allows the water to flow so as to fill a channel provided along the axis. 13. The microplastic observation device according to claim 12, wherein the flow path has a rectangular cross section perpendicular to the axis.

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