WO2020161585A1

WO2020161585A1 - Characterization of plastic contamination of fluids using imagery of filter media

Info

Publication number: WO2020161585A1
Application number: PCT/IB2020/050803
Authority: WO
Inventors: Lauren Keira Marie SMITH; Nicole Elizabeth BALLISTON
Original assignee: Polygone Technologies Inc.
Priority date: 2019-02-08
Filing date: 2020-01-31
Publication date: 2020-08-13

Abstract

Systems and methods characterizing plastic contamination of a fluid are provided. An example system includes an imaging device to capture an image of a filter medium that contains plastic contaminants, the plastic contaminants captured by exposure of the filter medium to a sample of fluid. The example system includes a controller to apply a machine learning model to determine a characteristic of the plastic contaminants captured by the filter medium based on the image and to output the characteristic.

Description

CHARACTERIZATION OF PLASTIC CONTAMINATION OF FLUIDS USING IMAGERY OF FILTER MEDIA

FIELD

[0001] The present specification relates to fluid treatment, and in particular to the characterization of plastic contamination of fluids.

BACKGROUND

[0002] Plastic pollution is a widespread and pervasive problem. Microplastic contaminants have been detected in drinking water, beverages, foodstuffs, and in the environment. The source of such microplastic contamination is surprisingly benign, as it is believed to be caused by the household washing of synthetic textiles (i.e. laundering clothes), among other sources. Such plastic contamination puts humans at risk of increased exposure to harmful chemicals that collect on the surfaces of these plastics, such as polychlorinated biphenyl (BCP), bisphenol A (BPA), and other toxins. Evidence of bioaccumulation of such plastics in animal species has been discovered, leading organizations to investigate the extent, and the effects, of this contamination on humans.

SUMMARY

[0003] According to an aspect of the disclosure, a method for characterizing plastic contamination of a fluid is provided. The method involves capturing an image of a filter medium that contains plastic contaminants. The plastic contaminants are captured by exposure of the filter medium to a sample of fluid. The method further involves applying a machine learning model to determine a characteristic of the plastic contaminants captured by the filter medium based on the image and outputting the characteristic. [0004] According to another aspect of the disclosure, a system for characterizing plastic contamination of a fluid is provided. The system includes an imaging device to capture an image of a filter medium that contains plastic contaminants. The plastic contaminants are captured by exposure of the filter medium to a sample of fluid. The system further includes a controller to apply a machine learning model to determine a characteristic of the plastic

contaminants captured by the filter medium based on the image and to output the characteristic.

[0005] According to yet another aspect of the disclosure, a method for characterizing plastic contamination of a fluid is provided. The method involves obtaining a fluid source that contains plastic contaminants, adding a first amount of salt to the fluid source to cause the fluid source to reach a first density, separating a first sample of fluid from the fluid source, capturing a first amount of plastic contaminants onto a first filter medium by exposing the first filter medium to the first sample of fluid, and capturing a first image of the first filter medium. The method further involves adding a second amount of salt to the fluid source to cause the fluid source to reach a second density, separating a second sample of fluid from the fluid source, capturing a second amount of plastic contaminants onto a second filter medium by exposing the second filter medium to the second sample of fluid, and capturing a second image of the second filter medium. The method further involves applying a machine learning model to determine a characteristic of the plastic contaminants based on one or more of: the first image and the second image and outputting the characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a schematic diagram of an example system for

characterizing plastic contamination of a fluid.

[0007] FIG. 2 is a flowchart of an example method for characterizing plastic contamination of a fluid. [0008] FIG. 3 is a schematic diagram of an example system for

characterizing plastic contamination of a fluid using fluorescent dye.

[0009] FIG. 4 is a flowchart of an example method for characterizing plastic contamination of a fluid using a fluorescent dye.

[0010] FIG. 5 is a schematic diagram of an example system for

characterizing plastic contamination of a fluid using a salt separation process.

[0011] FIG. 6 is a flowchart of an example method for characterizing plastic contamination of a fluid using a group of images and a salt separation process.

[0012] FIG. 7 is a flowchart of an example method for separating a fluid containing plastic contaminants into sub-samples using salts.

DETAILED DESCRIPTION

[0013] The characterization of the plastic contamination of fluids is an important step toward resolving the problem of plastic pollution. However, existing methods for detecting plastic contamination in a fluid (let alone characterizing plastic contamination of a fluid) are underdeveloped. There currently exists no effective and standardized method for determining the concentration, or other characteristics of, microplastics in a fluid.

[0014] Existing methods of measurement, such as weighing the residual difference between contaminated samples and uncontaminated samples, do not produce reliable results, due to the small size and weight of microplastics. Other existing methods, such as the manual counting the number of microplastics in a fluid, is time-consuming and resource-intensive.

[0015] The present disclosure provides systems and methods for the characterization of plastic contamination of fluids by which the concentrations, size profiles, or other characteristics of the plastic contaminants therein may be accurately and economically ascertained. As described herein, samples of fluids which are contaminated with plastic contaminants are exposed to filter media which capture the plastic contaminants. Images of the filter media are analyzed by machine learning models to determine characteristics of the plastic contaminants.

[0016] In some examples, the fluids may be dyed with fluorescent dyes which enhance the images of the plastic contaminants, thereby improving analysis by the machine learning models. Further, samples of fluids may be divided into sub-samples by salt separation processes, and each of the sub samples may be exposed to one or more sizes of filter media so that an array of images may be captured to further improve the analysis by the machine learning models.

[0017] FIG. 1 is a schematic diagram of such an example system 100 for characterizing plastic contamination of a fluid. The system 100 includes an imaging device 110, such as a camera, to capture an image 112 of a filter medium 104, or filter substrate, that contains plastic contaminants 106. The plastic contaminants 106 were captured by exposing the filter medium 104 to the sample of fluid 102, such as by filtering the sample of fluid 102 through the filter medium 104.

[0018] The sample of fluid 102 may include a sample of water drawn from a body of water, a sample taken from a beverage product, or any other fluid source that is contaminated with plastic contaminants 106. The sample of fluid 102 may have been stored in a vessel that is convenient for exposure to the filter medium 104. For example, the sample of fluid 102 may have been stored in a separatory funnel, and the filter medium 104 may have been placed at the outlet of the separatory funnel, and then sample of fluid 102 may have been released through the outlet of the separatory funnel, through the filter medium 104, to expose the filter medium 104 to the sample of fluid 102, thereby allowing the plastic contaminants 106 to be captured by the filter medium 104. The sample of fluid 102 may have been allowed to settle before exposure (i.e.

filtering through) the filter medium 104. Filtering the sample of fluid 102 through the filter medium 104 may be accelerated by a vacuum pump. The filter medium 104 may have been dried (e.g. in a humidity-controlled environment with minimal interaction with air to prevent collection if additional airborne plastic contaminants) prior to the image 112 being captured.

[0019] The plastic contaminants 106 may include plastic particles or fibers with dimensions measured on the microscale (i.e. , microplastics) that may be captured by the filter medium 104. As described herein, microplastics may be understood to refer to plastic contaminants which are less than 5mm in any one dimension, and may include smaller plastic contaminants which have

dimensions measured on the nanoscale.

[0020] The filter medium 104 may include filter paper, such as cellulose filter paper (e.g. black cellulose), that is appropriately sized to capture the plastic contaminants 106. For example, the filter medium 104 may include a filter having filtration pore size of 333pm, 150pm, 20pm, 2pm, or 0.45pm. Further, a series of filter media 104 of different filtration pore sizes may be used, as described below with reference to FIG. 5. In some examples, the filter medium 104 may include glass fiber, stainless steel, or other material as appropriate for the suspected types of plastic contaminants 106, allowing analysis of varying aspects of the sample fluid composition. Thus, the filter medium 104 contains the plastic contaminants on or near an outer surface of the filter medium 104 where it is visible to be imaged by the imaging device 110. The imaging device 110 may include a structure, such as a retaining clip, stage, or imaging surface, to position the filter medium 104 a specified distance away from the imaging device 110 and in a specified position so that the imaging device 110 generates images 112 consistently.

[0021] The system 100 further includes a controller 120 to apply a machine learning model 122 to determine a characteristic 124 of the plastic contaminants 106 captured by the filter medium 104 based on the image 112. The controller 120 may include any quantity and combination of a computer, server, processor, central processing unit (CPU), microprocessor, microcontroller, field- programmable gate array (FPGA), and similar. In some examples, the controller 120 may be coupled to the imaging device 110 to receive the image 112 directly from the imaging device 110. In other examples, the imaging device 110 and controller 120 may be separated but in communication over one or more computing networks, such as the internet, through which the image 112 may be transmitted from the imaging device 110 to the controller 120. In still other examples, the imaging device 110 may be part of an apparatus, such as a microscope (e.g. dissecting scope) to be used in a laboratory environment, and the controller 120 may include a laboratory computer to which the image 112 is transmitted via any electrical connection, network connection, universal serial bus (USB) stick, CD-ROM, or any other way of transmitting information. In still further examples, the imaging device 110 may be part of a mobile device such a smartphone with a camera to capture the image 112 that is in communication with a remote server that runs the machine learning model 122. The controller 120 includes at least a processor and memory configured to carry out the actions described here, including running the machine learning model 122 to determine the characteristic 124 of the plastic contaminants 106.

[0022] The characteristic 124 that is determined may include a concentration of the plastic contaminants 106 in the sample of fluid 102, a number of plastic contaminants 106 on the filter medium 104, a size distribution profile of the plastic contaminants 106 in the sample of fluid 102 (which may include average lengths, volumes, or other dimensions of the plastic contaminants 106), shapes of the plastic contaminants 106, types of the plastic contaminants 106, or another characteristic of the plastic contaminants. The controller 120 may use the machine learning model 122 to determine a number of characteristics 124, such as a combination of the above characteristics 124.

[0023] The machine learning model 122 may classify individual plastic contaminants 106 visible in the image 112 according to the borders, roughness, smoothness, density, colour, intensity, and/or other characteristic thereof, and thus, the characteristic 124 may include a list of the plastic contaminants 106 based on these classifications. For example, the machine learning model 122 may classify some of the plastic contaminants 106 as particles, some of the plastic contaminants 106 as fibers, and may further classify such plastic contaminants 106 based on size or other properties. The machine learning model 122 may further classify other debris on the filter medium 104 that is not plastic contamination. Thus, the controller 120 may determine a list of plastic contaminants 106 on the filter medium 104 and a list of non-plastic debris on the filter medium 104.

[0024] Where the characteristic 124 includes a number of plastic

contaminants 106 on the filter medium 104, an estimate of the concentration of plastic contaminants 106 present in the sample of fluid 102 may then be calculated given the volume of the sample of fluid 102.

[0025] The machine learning model 122 is trained to recognize these and other characteristics by analyzing imagery of filter media with plastic

contaminants. The machine learning model 122 may be trained with training data that correlates imagery of filter media containing plastic contaminants with known characteristics of the plastic contaminants in such imagery. Such training data may include a library of training images that includes images of filter media that contain plastic contaminants, the images being tagged or labelled with known characteristics of those plastic contaminants. For example, a training image may be an image of a filter medium that contains a visible amount of plastic contaminants, and the training image may be labelled with the actual number of plastic contaminants contained by the filter medium (having been determined by, for example, manual counting). Such labels or tags may be referred to as metadata.

[0026] The training images may be tagged or labelled with more rich information, such as the actual size distribution profile of the plastic

contaminants. A size distribution profile may include the number of plastic contaminants on the filter medium 104 which fall within a particular range of particle size (e.g., 271 particles below 333pm in length, 213 particles below 150pm in length, 38 particles below 20pm in length, 25 particles below 2pm in length). The size distribution profile may be based on the length, greatest dimension, surface area, or other factor relating to the size of the plastic contaminants. Information about the size distribution profile of plastic contaminants may be particularly useful where a particular size distribution profile may constitute evidence that the plastic contamination was a result of a particular source.

[0027] Such training images may also be tagged or labelled with information related to the capture of the plastic contaminants. For example, the training images may be labelled with the filtration pore size of the filter medium used to capture the plastic contaminants, or with the technique used to collect the sample of fluid (e.g. where and how the sample of fluid was collected), or with the technique used to capture the image (e.g. whether fluorescent dyes were used and at which stage in the process, whether excitation light was used, and whether emission filters were used, and the details about the use of these features and the properties thereof). Thus, the machine learning model 122 may be trained to recognize characteristics of plastic contaminants on filter media under various conditions, thereby allowing for flexibility in the application of the machine learning model 122 to a variety of samples of fluid.

[0028] Similarly, the controller 120 may tag the image 112 being analyzed with metadata with information related to the capture of the plastic contaminants 106 for processing by the machine learning model 122. The metadata may indicate a characteristic of the filter medium 104 (e.g. filtration pore size), a technique to collect the sample of fluid 102, and a technique to capture the image 112 (e.g. the use of a fluorescent dye, and other imaging techniques). Given information related to how the plastic contaminants 106 were captured (e.g. filter size, location of sample, dyes), the machine learning model 122 may be able to more accurately determine a particular characteristic 124 of the plastic contaminants.

[0029] The imaging device 110 may magnify the image 112 that is captured (e.g., 10x, 20x, 30x, 40x, or greater). In some examples, the imaging device 110 and/or controller 120 may stitch together a plurality of images 112 taken of different areas of the filter medium 104 to form a complete image of the filter medium 104. That is, the imaging device 110 may capture an image 112 that is only of a portion of the filter medium 104 (e.g. due to resolution or

magnification), and a plurality of images 112 may be combined to form a larger image that is ultimately processed by the machine learning model 122. In such examples, the imaging device 110 may include an automated XY stage to move the filter medium 104 and/or imaging device 110 through a series of positions so that a series of images 112 that cover an entire surface of the filter medium 104 may be obtained. That is, the filter medium 104 may be aligned to an XY stage, and the imaging device 110 may automatically pan over different sections of the XY stage to take a plurality of images 112 of the filter medium 104 that are ultimately stitched together into a composite image 112 of the filter medium 104 for analysis by the machine learning model 122.

[0030] The controller 120 also outputs the characteristic 124. The controller 120 may output the characteristic 124 to an output device (not shown), such as a display device (e.g. a computer screen or monitor), an audio device (e.g. speaker), or a communication interface (e.g. a network interface for

transmission to another device).

[0031] FIG. 2 is a flowchart of an example method 200 for characterizing plastic contamination of a fluid. For convenience, the method 200 is described with reference to the system 100 of FIG. 1 , but this is not limiting, and the method 200 may be applied to other systems.

[0032] At block 202, the image 112 of the filter medium 104 is captured. As described above with reference to FIG. 1 , the image 112 may be magnified. The filter medium 104 contains plastic contaminants 106. The plastic contaminants 106 were captured by exposure of the filter medium 104 to the sample of fluid 102, such as, for example, as described herein by flowing the sample of fluid 102 through the filter medium 104.

[0033] At block 204, the machine learning model 122 is applied to determine a characteristic 124 of the plastic contaminants 106 captured by the filter medium 104 based on the image 112. As discussed above, the characteristic 124 that is determined may include a concentration of plastic contaminants in the sample of fluids 102, a size distribution profile of the plastic contaminants 106 in the sample of fluid 102, or another characteristic. The plastic

contaminants may include microplastics.

[0034] In some examples, and as discussed above, the method 200 may further involve tagging the image 112 with metadata that indicates a

characteristic (e.g. filter size) of the filter medium 104, a technique to collect the sample of fluid 102, or a technique to capture the image 112. In such examples, application of the machine learning model 122 to determine the characteristic of the plastic contaminants 106 is further based on the metadata.

[0035] In some examples, as will be seen below in FIG. 3, the sample of fluid 102 may contain a fluorescent dye. In such examples, capturing the image 112 may involve directing excitation light to the filter medium 104 to cause the dye 105 to fluoresce. The image 112 may be captured directly by the imaging device 110, or the image 112 may be captured through an emission filter to capture fluorescence of the dye (in other words, a short-pass or band-pass filter may be used). In such examples, the image 112 may be tagged with metadata that indicates a type and/or amount of the fluorescent dye and/or solvent used, a range of wavelengths of the excitation light used and/or other characteristic of the excitation light emitter used, or a range of wavelengths passed by the emission filter and/or other characteristic of the type of emission filter used. Further, application of the machine learning model 122 to determine the characteristic 124 of plastic contaminants may be based on such metadata.

[0036] In some examples, as will be seen below in FIG. 5, the sample of fluid 102 may be a sub-sample extracted from a fluid source to which an amount of salt was added. The amount of salt was added to adjust a density of the fluid source prior to extraction of the sub-sample. As described in greater detail below with reference to FIG. 5, adjusting the density of the fluid source was to separate a portion of the plastic contaminants from the sub-sample based on density of the plastic contaminants. The different sub-samples may contain plastic contaminants of different average densities.

[0037] In such examples, the controller 120 may tag the image 112 with metadata that indicates a type of the salt, a density of the sub-sample, or a filtration size of the filter medium. Further, application of the machine learning model 122 to determine the characteristic of the plastic contaminants may be further based on such metadata.

[0038] At block 206, the characteristics 124 is outputted. As discussed above, the characteristic 124 may be outputted to an output device, such as a display device (e.g. a computer screen or monitor), an audio device (e.g.

speaker), or a communication interface (e.g. a network interface for

transmission to another device).

[0039] FIG. 3 is a schematic diagram of another example system 300 for characterizing plastic contamination of a fluid. The system 300 is similar to the system 100 of FIG. 1 , with like components numbered in the“300” series rather than the“100” series, and therefore includes a sample of fluid 302, filter medium 304, plastic contaminants 306, imaging device 310, image 312, controller 320, and machine learning model 322. For further description of the above components, reference may be had to the like components of the system 100 of FIG. 1.

[0040] However, in the system 300, the sample of fluid 302 contains a fluorescent dye 305, such as Nile Red, Nile Blue, Rose Bengal, or another synthetic polymer fluorescing compound, or other fluorescent dye. The fluorescent dye 305 may include any appropriate solvent, such as methanol, deionized water, to facilitate the fluorescence of plastic contaminants 306 (e.g. 1 mg Nile Red/L methanol or 10mg Nile Red/L acetone). The fluorescent dye 305 may be selected to adhere to the plastic contaminants 306. That is, where it is suspected that the sample of fluid 302 is contaminated with a particular type of plastic contaminant 306, a particular fluorescent dye 305 may be used to adhere to that particular type of plastic contaminant 306. In some examples, multiple fluorescent dyes 305 may be used, for example, to adhere to multiple types of plastic contaminants 306 in the sample of fluid 302. The fluorescent dye(s) 305 are to cause the plastic contaminants 306 to fluoresce under excitation light to enhance the visibility of the plastic contaminants 306 in the image 312 to improve analysis by the machine learning model 322.

[0041] The system 300 further includes an excitation light emitter 314 and an emission filter 316. These components may be part of, or otherwise coupled to, the imaging device 310, as shown. The excitation light emitter 314 may include one or more light-emitting diodes (LEDs) or other light sources, and is to direct excitation light at the filter medium 304 to excite the fluorescent dye 305 adhered to the plastic contaminants 306, thereby causing the fluorescent dye 305 and/or plastic contaminants 306 to fluoresce. The wavelengths of light emitted from the excitation light emitter 314 may be in the ultraviolet (UV) spectrum to cause the fluorescent dye 305 to fluoresce (e.g., for example, using wavelengths between about 365nm to about 395nm). The emission filter 316 may be fitted over a lens of the imaging device 310 so that light captured by the imaging device 310 passes through the emission filter 316. In the example where 1 pg Nile Red/L methanol is used, the excitation light may be in the approximately UV - blue wavelengths, and the emission filter 316 may pass through the green - orange wavelengths.

[0042] The emission filter 316 is complementary to the excitation light emitter 314 so that the fluorescence of the fluorescent dye 305 is visible at the imaging device 310. The imaging device 310 thus captures fluorescence of the plastic contaminants through the emission filter 316. For example, where the wavelengths of the excitation light are between about 365nm to about 395nm, the wavelengths passed through the emission filter 316 may be between about 500nm to about 550nm to remove unwanted light wavelengths and to capture only fluorescing wavelengths. Other combinations of wavelength ranges of excitation light and wavelength ranges passed through the emission filter 316 may be used. [0043] The controller 320 may tag the image 312 with information relating to the fluorescent dye 305 and excitation light. In particular, the controller 320 may tag the image 312 with metadata that indicates a type of the fluorescent dye 305, a range of wavelengths of the excitation light, or a range of wavelengths of the emission filter 316. The machine learning model 322 may thereby determine the characteristic 324 with the benefit of such metadata.

[0044] FIG. 4 is a flowchart of an example method 400 for characterizing plastic contamination of a fluid. For convenience, the method 400 is described with reference to the system 300 of FIG. 3, but this is not limiting, and the method 400 may be applied to other systems.

[0045] At block 402, the sample of fluid 302 is obtained. The sample of fluid 302 may include a sample of water drawn from a body of water, a sample taken from a beverage product, or any other fluid source which may contain plastic contaminants 306.

[0046] At block 404, the fluorescent dye 305 is added to the sample of fluid 302. As discussed above, the fluorescent dye 305 may be selected to adhere to the plastic contaminants 306. The sample of fluid 302 may be left to incubate (i.e. rest, mixing) with the fluorescent dye 305 for a period of time (e.g. 24 hours) before further use.

[0047] At block 406, plastic contaminants 306 are captured on the filter medium 304 by exposing the filter medium 304 to the sample of fluid 302.

[0048] In other examples, the fluorescent dye 305 may not be added to the sample of fluid 302, but rather applied to the filter medium 304 (e.g. sprayed onto the filter medium 304) after exposure to the sample of fluid 302. That is, block 404 may be omitted, and an additional block (e.g. between blocks 406 and 408) wherein the fluorescent dye 305 is applied to the filter medium 304, and therefore to the plastic contaminants 306 directly, may be added.

[0049] At block 408, the excitation light emitter 314 emits excitation light onto the filter medium 304. The excitation light is tuned to cause the fluorescent dye 305 to fluoresce, thereby causing the plastic contaminants 306, to which the fluorescent dye 305 is adhered, to fluoresce.

[0050] At block 410, the imaging device 310 captures the image 312 through the emission filter 316. As discussed above, the emission filter 316 is complementary to the excitation light emitter 314 so that the fluorescence is visible in the image 312, thereby enhancing the image 312.

[0051] At block 412, the controller 320 applies the machine learning model 322 to determine the characteristic 324 of the plastic contaminants 306, and at block 414, the controller 320 outputs the characteristic 324.

[0052] FIG. 5 is a schematic diagram of another example system 500 for characterizing plastic contamination of a fluid. The system 500 is similar to the system 100 of FIG. 1 , with like components numbered in the“500” series rather than the“100” series, and therefore includes a sample of fluid 502, filter medium 504, plastic contaminants 506, imaging device 510, controller 520, and machine learning model 522. For further description of the above components, reference may be had to like components of the system 100 of FIG. 1.

[0053] However, in the system 500, there are a plurality of samples of fluid 502, which are each sub-samples extracted from a fluid source 507, which may be a larger sample of the fluid. The fluid source 507 contains plastic

contaminants 506 which may be of different densities. Amounts of salt 503 are progressively added to the fluid source 507. After each addition of salt 503, a sample of fluid 502 is separated from the fluid source 507. The salt 503 increases the density of the fluid source 507, and thus, each sample of fluid 502 contains a different concentration of the salt 503 when it is separated from the fluid source 507.

[0054] As salt 503 is added to the fluid source 507, the density of the fluid source 507 increases, and plastic contaminants 506 having lower density float to the top of the fluid source 507. In some examples, the samples of fluid 502 may be separated from the fluid source 507 from the bottom of the fluid source 507. Thus, a sample of fluid 502 that is extracted from the fluid source 507 may contain plastic contaminants 506 of any density. However, the first sample of fluid 502 that is extracted from the fluid source 507 after the first amount of salt 503 is added will not contain any of the lowest density plastic contaminants 506. As each successive amount of salt 503 is added and each successive sample of fluid 502 is extracted, the samples of fluid 502 contain plastic contaminants 506 that are, on average, of higher and higher density. The last sample of fluid 502 contains plastic contaminants 506 that are, on average, of the highest density. Thus, the samples of fluid 502 each contain plastic contaminants 506 of different average densities. This process may be termed a salt separation process. The salt 503 that is used may include magnesium sulfate (Epsom salt), sodium chloride (table salt), or other type of salt.

[0055] The samples of fluid 502 may be separated from the bottom of the fluid source 507 using a separatory funnel. That is, the fluid source 507 is held in the separatory funnel, amounts of salt 503 are added to the separatory funnel, and samples of fluid 502 are drawn from the bottom of the separatory funnel so that the portion of the fluid source 507 that is drained as the sample of fluid 502 is the portion of the fluid source 507 of highest density. In some examples, the sample of fluid 502 may be collected in a separate container for exposure to a filter medium 504 or for the further addition of salt prior to exposure to a filter medium 504. In other examples, the sample of fluid 502 may be extracted through a filter medium 504 directly so that exposure of the sample of fluid 502 to the filter medium 504 occurs simultaneously with extraction of the sample of fluid 502. Other equipment that is capable of separating the samples of fluid 502 from the bottom of the fluid source 507 are contemplated.

[0056] In other examples, the samples of fluid 502 may be separated from the top of the fluid source 507. Rather than being drawn from the bottom of the fluid source 507, the samples of fluid 502 may be skimmed, decanted, or otherwise extracted from the top of the fluid source 507. In such examples, as each successive amount of salt 503 is added and each successive sample of fluid 502 is extracted, the samples of fluid 502 contain plastic contaminants 506 that are, on average, of lower and lower density.

[0057] Following the salt separation process described above, each sample of fluid 502 is exposed (e.g. passed through) a filter medium 504 that captures the plastic contaminants 506. Thus, a series of filter media 504 having plastic contaminants 506 of different average density is obtained. A series of images 512 may be captured of the series of filter media 504 for analysis by the machine learning model 522 to determine a characteristic 524 of the plastic contaminants 506. Each image 512 may be labelled with metadata, such as the density to which the sample of fluid 502 to which the filter media 504 was exposed, so that the machine learning model 522 can interpret the image 512 with reference to the density of the sample of fluid 502. Further, the machine learning model 522 may be more accurately able to determine characteristics 524 of the plastic contaminants 506 based on a series of images 512 rather than a single image 512.

[0058] In some examples, each sample of fluid 502 may be exposed to a series of filter media 504 of different filtration sizes. For example, each sample of fluid 502 may be exposed to a filter media 504 having filtration size 333pm, 150pm, 20pm, and 2pm. Thus, an array of images 513 may be obtained of filter media 504 of different filtration size and different density of samples of fluid 502. For example, as shown, the array of images 513 includes images 512 of filter media 504 that captured plastic contaminants 506 from samples of fluid 502 of densities 1.0 g/mL, 1.1 g/mL, and 1.3 g/mL, using filter media 504 of filtration sizes 333pm, 150pm, 20pm, and 2pm. In some examples, the samples of fluid 502 are of densities 1.0 g/mL, 1.1 g/mL, 1.3 g/mL, 1.35 g/mL, and 2.13 g/mL.

[0059] In still further examples, in addition to adding salt 503 to the fluid source 507, oil may be added to the fluid source 507 to further separate portions of the plastic contaminants 506 from one another based on density. When oil is used in a separation process, a portion of the plastic contaminants 506 may be separated into the oil phase, and this portion of the plastic contaminants 506 may be exposed to a filter medium 504 for imaging analysis. The water phase may be drained and discarded. The addition of oil to the fluid source 507 may be particularly useful to separate plastic contaminants 506 from the samples of fluid 502 with relatively higher densities. In an example separation process, a series of samples of fluid 502 may be of densities 1.0 g/mL, 1.1 g/mL, 1.3 g/mL, 1.35 g/mL with oil, 2.13 g/mL, and 2.13 g/mL with oil. The oil that is used may include mineral oil. After a sample of fluid 502 is filtered through a filter medium 504, the filter medium 504 may be rid of oily residue prior to imaging. For example, a filter medium 504 collected from an oily sample of fluid 502 may be rinsed with soap and deionized water to remove oil from the sample but maintain the plastic contaminants 506 on the filter medium 504.

[0060] As with the series of images 512, the array of images 513 may be captured of the series of filter media 504 for analysis by the machine learning model 522 to determine a characteristic 524 of the plastic contaminants 506. Each image 512 may be labelled with metadata, such as the density to which the sample of fluid 502 to which the filter media 504 was exposed, and the filtration size of the filter media 504 used, so that the machine learning model 522 can interpret the image 512 with reference to the density of the sample of fluid 502 and the size of the filter media 504. The machine learning model 522 may be more accurately able to determine characteristics 524 of the plastic contaminants 506 based on such an array of images 512 rather than a single image 512.

[0061] FIG. 6 is a flowchart of an example method 600 for characterizing plastic contamination of a fluid using a group of images (e.g. series or array) and a salt separation process. For convenience, the method 600 is described with reference to the system 500 of FIG. 5, but this is not limiting, and the method 600 may be applied to other systems.

[0062] At block 602, the fluid source 507 is obtained. The fluid source 507 contains plastic contaminants. A sample of fluid 502 may be separated from the fluid source 507 prior to the addition of any salt 503. At block 604, an amount of salt 503 is added to the fluid source 507 to cause the fluid source 507 to reach a first density. At block 606, a sample of fluid 502 is separated from the fluid source 507. At block 608, an amount of plastic contaminants is captured onto a filter medium 504 by exposing the filter medium 504 to the sample of fluid 502. At block 610, the imaging device 510 captures an image 512 of the filter medium 504. The sample of fluid 502 may be exposed to several filter media 504, and an image 512 of each filter media may be captured, if an array of images 513 is to be used, as described above.

[0063] At block 612, it is determined whether the series of images 512 or array of images 513 is complete, as the case may be. If not complete, the method 600 returns to block 604, and thus a second amount of salt 503 is added to the fluid source 507 to cause the fluid source 507 to reach a second density, and a second sample of fluid 502 is separated, from which an amount of plastic contaminants 506 is captured by a second filter medium 504, and an image 512 of the second filter medium 504 is captured.

[0064] If complete, at block 614, the controller 520 applies the machine learning model 522 to determine a characteristic 524 of the plastic contaminants 506. The characteristic 524 may be of the first amount of plastic contaminants 506, the second amount of plastic contaminants 506, or the plastic

contaminants 506 as a whole. In some examples, the method 600 may further involve tagging each images 512 with a metadata tags that indicate a type of the salt 503, a density of the sample of fluid 502 from which the image 512 is captured, and a filtration size of the filter medium 504. In such examples, applying the machine learning model 522 to determine the characteristic 524 is further based the first metadata tag or the second metadata tag.

[0065] In some examples, the method 600 may involve the use of a fluorescent dye, such as described in FIGs. 3 and 4.

[0066] A salt separation processed as described above may be applied to the separation of fluids containing plastic contaminants into smaller sub samples containing plastic contaminants of different average densities for purposes other than image analysis. Thus, a method 700 for separating a fluid containing plastic contaminants into sub-samples based on density of the plastic contaminants is shown in FIG. 7. For convenience, the method 700 is described with reference to the system 500 of FIG. 5, but this is not limiting, and the method 700 may be applied to other systems.

[0067] At block 702, the fluid source 507 is obtained. The fluid source 507 contains plastic contaminants. A sample of fluid 502 may be separated from the fluid source 507 prior to the addition of any salt 503. At block 704, an amount of salt 503 is added to the fluid source 507 to cause the fluid source 507 to increase the density of the fluid source 507. At block 706, a sample of fluid 502 is separated from the fluid source 507.

[0068] At block 708, it is determined whether a group of the samples of fluid 502 is complete. If not complete, the method 700 returns to block 704, and additional salt 503 is added to the fluid source 507 to cause the density of the fluid source 507 to increase further, and another sample of fluid 502 is separated. As discussed above, the samples of fluid 502 contain plastic contaminants 506 that are, on average, of higher and higher density. Each sample of fluid 502 may be exposed to a filter medium 504 for the capture of plastic contaminants 506 thereon, and may be used for image analysis, as described herein, or for other purposes.

[0069] Thus, the plastic contamination of fluids may be analyzed and characterized by exposing the fluids to filter media and analyzing images of the filter media using machine learning. The machine learning analysis of the images may be enhanced by the use of fluorescent dyes and arrays of images obtained via salt separation processes. The techniques described herein may allow the accurate and economic analysis of fluids, including drinking water, beverages, foodstuffs, and water in the environment, for plastic contaminants, particularly microplastics, and the characteristics thereof.

[0070] It should be recognized that features and aspects of the various examples provided above can be combined into further examples that also fall within the scope of the present disclosure. The scope of the claims should not be limited by the above examples but should be given the broadest interpretation consistent with the description as a whole.

Claims

1. A method for characterizing plastic contamination of a fluid, the method comprising: capturing an image of a filter medium that contains plastic contaminants, the plastic contaminants captured by exposure of the filter medium to a sample of fluid; applying a machine learning model to determine a characteristic of the plastic contaminants captured by the filter medium based on the image; and outputting the characteristic.

2. The method of claim 1 , further comprising: tagging the image with metadata that indicates one or more of: a filtration pore size of the filter medium, a technique to collect the sample of fluid, and a technique to capture the image; wherein application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

3. The method of claim 1 , wherein the characteristic comprises a size distribution profile of plastic contaminants in the sample of fluid or a

concentration of plastic contaminants in the sample of fluid.

4. The method of claim 1 , wherein: the sample of fluid contains a fluorescent dye, the fluorescent dye to adhere to the plastic contaminants; and capturing the image comprises directing excitation light to the filter medium with excitation light to cause the dye to fluoresce, and capturing the image further comprises capturing the image through an emission filter to capture fluorescence of the dye.

5. The method of claim 4, further comprising: tagging the image with metadata that indicates one or more of: a type of the fluorescent dye, a range of wavelengths of the excitation light, and a range of wavelengths of the emission filter; wherein application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

6. The method of claim 1 , wherein the sample of fluid comprises a sub-sample extracted from a fluid source to which an amount of salt was added to adjust a density of the fluid source prior to extraction of the sub-sample to separate a portion of the plastic contaminants from the sub-sample based on density of the plastic contaminants.

7. The method of claim 6, wherein an amount of oil was added to the sub sample to separate a portion of the plastic contaminants into an oil phase.

8. The method of claim 7, further comprising: tagging the image with metadata that indicates one or more of: a type of the salt, a density of the sub-sample, and a filtration pore size of the filter medium; wherein application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

9. The method of claim 1 , wherein the plastic contaminants comprise microplastics.

10. A system for characterizing plastic contamination of a fluid, the system comprising: an imaging device to capture an image of a filter medium that contains plastic contaminants, the plastic contaminants captured by exposure of the filter medium to a sample of fluid; and a controller to apply a machine learning model to determine a

characteristic of the plastic contaminants captured by the filter medium based on the image, and to output the characteristic.

11. The system of claim 10, wherein the controller is further to: tag the image with metadata that indicates one or more of: a filtration pore size of the filter medium, a technique to collect the sample of fluid, and a technique to capture the image; wherein application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

12. The system of claim 10, wherein: the sample of fluid contains a fluorescent dye, the fluorescent dye to adhere to the plastic contaminants; the system further comprises an excitation light emitter to direct excitation light to the filter medium to cause the plastic contaminants to fluoresce; the system further comprises an emission filter through which the imaging device is to capture fluorescence of the dye; the controller is further to tag the image with metadata that indicates one or more of: a type of the fluorescent dye, a range of wavelengths of the excitation light, and a range of wavelengths of the emission filter; and application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

13. The system of claim 10, wherein: the sample of fluid comprises a sub-sample extracted from a fluid source to which an amount of salt was added to adjust a density of the fluid source prior to extraction of the sub-sample to separate a portion of the plastic contaminants from the sub-sample based on density of the plastic contaminants; and the controller is further to tag the image with metadata that indicates one or more of: a type of the salt, a density of the sub-sample, and a filtration pore size of the filter medium; wherein application of the machine learning model to determine the characteristic of the plastic contaminants is further based on the metadata.

14. The system of claim 10, wherein the filter medium comprises filter paper.

15. The system of claim 10, wherein the plastic contaminants comprise microplastics.

16. A method for characterizing plastic contamination of a fluid, the method comprising: obtaining a fluid source that contains plastic contaminants; adding a first amount of salt to the fluid source to cause the fluid source to reach a first density; separating a first sample of fluid from the fluid source; capturing a first amount of plastic contaminants onto a first filter medium by exposing the first filter medium to the first sample of fluid; capturing a first image of the first filter medium; adding a second amount of salt to the fluid source to cause the fluid source to reach a second density; separating a second sample of fluid from the fluid source; capturing a second amount of plastic contaminants onto a second filter medium by exposing the second filter medium to the second sample of fluid; capturing a second image of the second filter medium; applying a machine learning model to determine a characteristic of the plastic contaminants based on one or more of: the first image and the second image; and outputting the characteristic.

17. The method of claim 16, further comprising: tagging the first image with a first metadata tag that indicates one or more of: a type of the first amount of salt, a density of the first sample at exposure of the first filter medium to the first sample; and a filtration pore size of the first filter medium; and tagging the second image with a second metadata tag that indicates one or more of: a type of the second amount of salt, a quantity of the second amount of salt, and a filtration pore size of the second filter medium; wherein applying the machine learning model to determine the characteristic is further based on one or more of: the first metadata tag and the second metadata tag.

18. The method of claim 17, further comprising: capturing a third amount of plastic contaminants onto a third filter medium by exposing the third filter medium to the first sample of fluid, the third filter medium having a different filtration pore size than the first filter medium; capturing a third image of the third filter medium; and tagging the third image with a third metadata tag that indicates the filtration pore size of the third filter medium; wherein application of the machine learning model to determine the characteristic is further based on one or more of: the third image and the third metadata tag.

19. The method of claim 16, wherein: the method further comprises adding a fluorescent dye to the fluid source, the fluorescent dye to adhere to the plastic contaminants; capturing the first image comprises directing excitation light to the first filter medium with to cause the fluorescent dye to fluoresce, and capturing the first image through an emission filter to capture fluorescence of the dye; the method further comprises tagging the first image with a third metadata tag that indicates one or more of: a type of the fluorescent dye, a range of wavelengths of the excitation light, and a range of wavelengths of the emission filter; and application of the machine learning model to determine the characteristic is further based on the third metadata tag.

20. The method of claim 16, wherein the plastic contaminants comprise microplastics.