From Tap Water to Marine Organisms: a Micro-Spectroscopic Approach to Micro-Plastic Characterization The world leader in serving science Proprietary & Confidential
Micro-Plastics – What are they? • A micro-plastic is a small piece of plastic • How small? Name Abbreviation Expanded Polystyrene EPS • 5 mm to 1 micron Polypropylene PP • Common micro-plastics Polyethylene PE Acrylonitrile-butadiene-styrene ABS • PE, PP, PET Polystyrene PS • Sources Polyamide (Nylon) PA • Primary Polymethyl methacrylate PMMA Polycarbonate PC • Particles designed to be small (ie: cosmetic microbeads) Cellulose Acetate CA Polyvinyl chloride PVC • Secondary Polyethylene terephthalate PET • Formed from the breakdown of larger items Polytetrafluoroethylene PTFE 2
Where Does It Come From 1) Synthetic fibers in the wash 2) Tire dust 3) Paints 4) Secondary microplastics 5) Synthetic fibers in the air 6) Microbeads - primary https://orbmedia.org/stories/Invisibles_plastics/multimedia 3
Why the concern? • Ubiquitous • Found in so many places • Environmental Impact? • Aquatic life • Food Chain • Water Supply • 8 million tons of plastic makes it’s • Bottled Water way to the ocean • Fish & Seafood • 250K tons are micro-plastics • Consumer Products • Injectable pharmaceuticals 4
Where Is It Found EVERYWHERE! Studies have found micro-plastic in • Marine environment • Food grade salt • Bottled water • Tap water • Seafood and meat • Human stool • Blood contamination • Injectables • … 5
Characterization of Micro-Plastics • Common questions • Technique used to identify material depends on: • How much (Load)? • Particle Size • What type (Identity)? • Information Required • Which dimension/shape (sizing)? • Identity • Identity of plastic is related to: • Particle Size • Source • Size Distribution • Potential Toxicity • Number of particles to be analyzed • Some plastics contain endocrine disruptors • Others have the potential to be vectors for toxins (oleophilic polymers) 6
FTIR and Raman Spectroscopy IR Spectra of polyethylene and • FTIR and Raman are commonly used to identify polypropylene plastics • Both are non-destructive 1.0 Poly ethy lene 0.8 • Both can be used to identify microscopic particles 0.6 Abs 0.4 • The choice depends on the particle size and the 0.2 0.0 1.0 Poly propy lene information required 0.8 0.6 Abs • 5mm to 0.1mm (macro sampling techniques) 0.4 0.2 • 100 µ m to 10 µ m (both FTIR and Raman microscopy) 0.0 3500 3000 2500 2000 1500 1000 Wavenumbers (cm-1) • 10 µ m to 1 µ m (Raman microscopy is probably required) 7
Focus on Particles below 100 microns: Micro-Spectroscopy • Particle sizes below 100 microns require micro-spectroscopy • To visualize the sample • To focus the spectrometer beam to a suitably small size • Microscopy has two benefits • The ability to measure small particles • The ability measure multiple particles automatically • Both FTIR and Raman are available in microscope configurations 8
Data Collection Options • Single point • Only a single point is collected • Multiple-point • Many discrete particles are analyzed in sequence • Discrete point mapping • Imaging • Contiguous data points are acquired to provide a chemical map of an area 9
Single Point Analysis: Microbeads – Only Practical for a Small Number of Particles • Exfoliant microbeads obtained from person care formulation • Beads are 100-25 microns in size • Using and IR microscope equipped with an ATR objective, the particles were identified as polyethylene • Simple ‘point-and-shoot’ analysis 10
Generic Workflow for Sampling & Analysis of Micro-Plastics 11 Proprietary & Confidential
Sample Preparation for Micro-Spectroscopy Analysis • Typically after sampling and pre-treatment micro-plastics end up as suspensions • Particles are isolated by filtration • The choice of filters is important for subsequent spectroscopic analysis • Filter material should allow for direct analysis of the particles without significant interference • Typically many particles are observed but only a small fraction are micro-plastics • Minerals • Biological organic material • Etc. • Manually sorting through and isolating micro-plastic particles is time consuming 12 Proprietary & Confidential
Choice of Filters – Some Common Filter Types 13 Proprietary & Confidential
Example of Filtration Apparatus Using Silicon Filters silicone gasket PTFE gasket hole Si Filter Bottom Middle Top 14 Proprietary & Confidential
After Particles Have Been Isolated on a Suitable Filter Proceed to Spectroscopic Analysis: Discrete Particle Analysis or Spectroscopic Imaging 15 Proprietary & Confidential
Discrete Particle Analysis First Step – Collect a Visual Image of the Filter and Particles • Sample: Filtered bottled water 500 ml • Silicon filter • 8 mm diameter circular area (defined by gasket) • Visual mosaic image constructed from many individual fields of view • Visible Image (contrast) is important because visible image is used to select particles and determine particle size 16 Proprietary & Confidential
Defining Particles for Analysis – Remember Only a Small Fraction are Micro-Plastics • Visual Contrast is used to define particles for analysis • Adjustments to the sensitivity defines what is selected as a particle • Size parameters limits the size of the particles considered for analysis • Proceed to automated collection of spectral data from all the selected particles to identify particle material types • FTIR and Raman Microscopy Size Sensitivity 17 Proprietary & Confidential
Spectral Data Collection: Identifying Particles - Workflows for FTIR and Raman •FTIR Microscopy •Raman Microscopy •Collect spectra from selected particles •Collect Raman spectra from selected particles •Transmission or Reflection •Filter contributions can be subtracted out as •Automatically adjusts aperture to fit with required particle size •Search libraries to identify particles •Collect a series of backgrounds with corresponding apertures •Report particle identities along with size and shape information derived from the visual •Generate infrared spectra from all the image analysis particles •Search libraries to identify particles •Report particle identities along with size and shape information derived from the visual image analysis Proprietary & Confidential 18
Example of Identified Micro-Plastic Particle # Spectrum Position X,Y (µm) Identified Component Name Area (µm^2) Length (µm) Width (µm) 994 #0994 X,Y=1162,7289 Polypropylene, Isotactic 1032 78 16 60 55 50 45 40 35 30 Int 25 Particle # 994 20 15 10 5 0 -5 Library spectrum of polypropylene 3000 2500 2000 1500 1000 Raman shift (cm-1) Proprietary & Confidential 19
Example: Tabulated Results of the Particle Analysis (Raman) Spectrum Position X,Y (µm) Identified Component Name Area (µm 2 ) Length (µm) Width (µm) #0349 X,Y=4075,1656 Polyethylene 1727 56 39.3 #0823 X,Y=1406,5406 Poly(Ethylene Terephthalate) 229 16.6 16.6 #0833 X,Y=2197,5672 Poly(Ethylene Terephthalate) 25403 316.8 102.1 #0957 X,Y=1422,7059 Poly(Ethylene Terephthalate) 390 22.1 22.1 #0036 X,Y=118,218 Poly(Tetrafluoroethylene) 10424 199.1 66.6 #0246 X,Y=2957,1103 Poly(Tetrafluoroethylene) 673 30.4 28.2 #0304 X,Y=7914,1476 Poly(Tetrafluoroethylene) 275 19.4 18.1 #0481 X,Y=8702,2555 Poly(Tetrafluoroethylene) 1551 57.5 34.3 #0534 X,Y=365,3010 Poly(Tetrafluoroethylene) 405 22.3 22.3 #0810 X,Y=6955,5268 Poly(Tetrafluoroethylene) 329 27.6 15.1 #0925 X,Y=40,6827 Poly(Tetrafluoroethylene) 306 22.1 17.6 #0976 X,Y=924,7129 Poly(Tetrafluoroethylene) 734 33.2 28.2 #1063 X,Y=6737,7969 Poly(Tetrafluoroethylene) 222 19.4 14.6 #0477 X,Y=760,2542 Polyisoprene 22560 355 80.9 #0555 X,Y=8396,3093 Polypropylene, Isotactic 168 16.6 12.9 #0750 X,Y=6687,4717 Polypropylene, Isotactic 604 35.9 21.4 #0994 X,Y=1162,7289 Polypropylene, Isotactic 1032 77.9 16.9 #0646 X,Y=1593,3709 Polystyrene 12997 156.4 105.8 #0365 X,Y=3193,1743 Polystyrene 275 19.4 18.1 #0580 X,Y=6208,3224 Polystyrene 390 22.3 22.3 20 Proprietary & Confidential
Summary of Micro-Plastics Identified from Bottled Drinking Water Type of Micro-Plastic FTIR (total particles – 801) Raman (total particles 1065) PTFE 5 9 Polyester (PET) 3 3 Polystyrene Not observed 3 Polypropylene 3 3 Long chain hydrocarbon material (search result not 2 1 sufficient for positive identification) Polyethylene 2 1 • A majority of the particles present were not micro-plastics • Some micro-plastics are better identified by Raman and some are better identified by FTIR • Selection rule differences (dipole moment vs. polarization), fluorescence issues with Raman, particle size considerations, etc. • Some of the features selected as particles were just features on the surface of the filter (scratches, etc.) • Some of the particles were not Raman or FTIR active materials • There were particles present other than micro-plastics • Protein, cellulose, beta carotene, talc, silica, calcium carbonate, etc. Proprietary & Confidential 21
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