DETECTION OF MICROPLASTIC CONTAMINANTS IN THE MARINE ENVIRONMENT. Michelle Nguy

Transcription

1 DETECTION OF MICROPLASTIC CONTAMINANTS IN THE MARINE ENVIRONMENT Michelle Nguy

2 Outline Introduction to microplastics (types of microplastics) Impacts: How can microplastics affect the biological systems of aquatic animals? Methods of detection: Fourier Transform Infrared (FTIR) Spectroscopy and Raman Spectroscopy Comparison between FTIR and Raman Spectroscopy Methods to remove MP from marine animals using ATR-FTIR Conclusion Michelle Nguy 2

3 Introduction to Microplastics Types of microplastics (MP) (1) Primary Microplastics Manufactured in the size range of 1nm to 5mm Found in personal care ( i.e. toothpaste, shower gel, scrubs, and cosmetics) (2) Secondary Microplastics Resulting from the breakdown of large plastic items into smaller pieces (i.e. fishing gears, ships, aquaculture and recreational activities. Formation of MPs Greatly influenced by a combination of environmental factors: (a) Solar Ultra-Violet Radiation that facilitates oxidative degradation (b) Weathering: Mechanical abrasion such as wind, wave, ocean current, and human activity. O.O. Solomon, T. Palanisami, Microplastics in the Marine Environment: Current Status, Assessment Methodologies, Impacts and Solutions, Journal of Pollution Effects & Control. 04 (2016). doi: /

4 Importance and Impacts Plastic products are composed of monomers joined to make the polymer structure and additive chemicals -Additives account for approx. 4% of the weight of MP. Once created, plastic polymers= Non-toxic because they are not reactive and cannot easily transport across biological membranes due to size. Non-polymeric substances = hazardous to human health and environment when they leach from the plastic polymer matrix. Surface area to volume ration increases Smith, M.; Love, D. C.; Rochman, C. M.; Neff, R. A. Microplastics in Seafood and the Implications for Human Health. Current Environmental Health Reports2018, 5(3),

5 Microplastics can cause physical harm to aquatic mammals Internal abrasions Intestinal blockage affecting the digestive system to starvation, debilitation and ultimately, death. Indigestible particles fill the stomach and reduce the feeling of hunger which leads to starvation Microplastics can also cause chemical harm to aquatic mammals: many plastics contain flame retardants Additives can be transferred into the tissues of animals that have consumed plastics, with potential effects on the physiology and health of the organism Critchell, K.; Hoogenboom, M. O. Effects of Microplastic Exposure on the Body Condition and Behaviour of Planktivorous Reef Fish (Acanthochromis Polyacanthus). Plos One2018, 13(3). 5

6 Microplastic Sampling and Sample Processing Microplastic is widely considered as under-researched components of marine debris. Three main Sampling techniques: 1) Selective Sampling -Identification with naked eye -Can be extracted directly from environmental matrices. 2) Bulk Sampling -Collecting the entire sample without reducing its volume during the sampling process. 3) Volume-Reduced Sampling -Reducing entire volume of a bulk sample by fast filtration during sampling and preserving only a small fraction of the sample for subsequent analysis. Wang, W.; Wang, J. Investigation of Microplastics in Aquatic Environments: An Overview of the Methods Used, from Field Sampling to Laboratory Analysis. TrAC Trends in Analytical Chemistry2018, 108,

7 Separation Separate from both organic and inorganic non-plastic particles Density principles Using salt solutions with varying densities (NaCl, NaI, Na 6 O 39 W 12 Sediment is mixed with NaCl solution and vigorously shaken Supernatant is filtered with a filtration unit and a vacuum pump. Filter (usually nitro- ceullose 0.45 micron-meter) is dried and sealed in petri-dish *Use of NaCl is cheap and eco-friendly O.O. Solomon, T. Palanisami, Microplastics in the Marine Environment: Current Status, Assessment Methodologies, Impacts and Solutions, Journal of Pollution Effects & Control. 04 (2016). doi: / Ivleva, N. P.; Wiesheu, A. C.; Niessner, R. Microplastic in Aquatic Ecosystems. Angewandte Chemie International Edition2016, 56(7),

8 Purification & Identification Two different methods have been applied for purification: Chemical Degradation MP samples are treated with different chemicals 30% hydrogen peroxide (H 2 O 2 ) solution or Mixtures of H 2 O 2 and Sulfuric acid (H 2 SO 4 ). Enzymatic Degradation of organic matrix. MP samples are treated with a mixture of enzymes (lipase, amylase, proteinase, chitinase and cellulase) Two different methods have been applied for Identification: Visual Sorting Naked eye or dissecting microscope ( The obtained values for MP occurrence are not reliable and strongly depend on observer performing the separation) For better visual identification, Rose Bengal can stain natural organic particles ( cellulose fibers). Non-stained material= Microplastic Spectroscopic analysis (FTIR or RM) = Best Method! Ivleva, N. P.; Wiesheu, A. C.; Niessner, R. Microplastic in Aquatic Ecosystems. Angewandte Chemie International Edition2016, 56(7),

9 Fourier Transform Infrared (FTIR) Spectroscopy - Analytical technique used to identify polymeric materials -Measures the absorption of infrared radiation by the sample material versus wavelength -Infrared absorption bands identify molecular components and structures. 1. Sending source energy through an interferometer and through the sample. 2. The light passes through a beam splitter, which sends the light in two directions at right angles 3. One beam goes to a stationary mirror then back to the beam splitter; The other goes to a moving mirror 4. Speed of the moving mirror is controlled by using a helium-neon laser beam 5. Two beams meet up at the beam splitter and recombine 6. The difference in path lengths creates constructive and destructive interference: an interferogram 7. The recombined beam passes through the sample 8. The sample absorbs all the different wavelengths characteristic of its spectrum 9. The detector reports variation in energy versus time for all wavelengths simultaneously **The longer the path of the moving mirror, the higher the resolution. Michelle Nguy 9

10 A mathematical function called a Fourier transform can convert an intensity-vs.-time spectrum into an intensity-vs.-frequency spectrum. The Fourier transform: Michelle Nguy 10

11 ARTICLE 1 Prevalence of microplastics in Singapore s coastal marine environment K.L. Ng, J.P. Obbard Ng, K.; Obbard, J. Prevalence of Microplastics in Singapore s Coastal Marine Environment. Marine Pollution Bulletin2006, 52(7),

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13 Article 1: Conclusion Synthetic polymer microplastics including polyethylene, polypropylene and polystyrene are prevalent in both seawater and sediment in the Asian marine environment. It is likely that these microplastics are derived from the physical and chemical fragmentation of larger plastic debris in the coastal environment. Both polystyrene and polyethylene were found to be common, where polystyrene was most readily detected in sediments. Polyethylene was more prevalent in subsurface waters. Michelle Nguy 13

14 Raman Spectroscopy (RS) Used to observe vibrational, rotational, and other low-frequency modes in a system Used to provide structural fingerprint by which molecules can be identified Relies on inelastic scattering of monochromatic light from a laser in the visible, near infrared or near ultraviolet range. The laser light interacts with molecular vibrations, photons or other excitations in the system, resulting in energy of laser photos being shifted up or down. Shift in energy provides information about vibrational modes in the system. RS can easily be coupled to a standard optical microscope = Raman Microspectrscopy (RM) RM has been applied in a number of MP studies in the marine and freshwater ecosystem Ivleva, N. P.; Wiesheu, A. C.; Niessner, R. Microplastic in Aquatic Ecosystems. Angewandte Chemie International Edition2016, 56(7),

15 ARTICLE 2 A critical assessment of visual identification of marine microplastic using Raman spectroscopy for analysis improvement Robin Lenz, Kristina Enders, Colin A. Stedmon, David M.A. Mackenzie, Torkel Gissel Nielsen Wang, W.; Wang, J. Investigation of Microplastics in Aquatic Environments: An Overview of the Methods Used, from Field Sampling to Laboratory Analysis. TrAC Trends in Analytical Chemistry2018, 108,

16 Future Research needs to account for factors including: sampling locations, sampling techniques and number of replicates Extraction efficiency depends heavily on the extraction solution. It is recommended to re-utilize some heavy salts (e.g. ZnCl2) 452 Fibers and 827 Particles were visually identified as plastic of which 75% and 64% were confirmed by Raman spectroscopy. Comparing with chemical digestants, the use of enzymes can not only effectively digest the interfering organic mater, it will do little harm to microplastics. Michelle Nguy 16

17 Methods to remove MP from fish stomachs using ATR-FTIR Sample is first placed on ATR crystal Surface is irradiated with evanescent wave Enabling an FTIR analysis of larger MP. What are the advantages of ATR? Minimal sample preparation place the sample on the crystal and collect data Fast and easy cleanup simply remove the sample and clean the surface of the crystal Analysis of samples in their natural states no need to heat, press into pellets, or grind in order to collect spectra Excellent for thick or strongly absorbing samples ideal for difficult samples like black rubber FTIR Sample Techniques: Attenuated Total Reflection (ATR) 17

18 Comparison between FTIR and Raman Spectroscopy -Both are based on molecular vibrations FTIR: Uses absorption of light Depends on a change in dipole movement Good identification of organic materials A lot more extensive databases than Raman Less expensive than Raman counterparts. Raman: Focuses on scattering of light Change in polarizability of a molecule Can detect the presence of amorphous carbon, which can be indicative of thermal degradation Michelle Nguy 18

19 Conclusion These techniques have different advantages and disadvantages. Exemplarily, Raman has a better size resolution (detects particles down to a size of 1 μm), In contrast, FTIR has a less precise size resolution (detects particles down to a size of μm) Raman: No sample prep is required, smaller sampling ( 1 micron or less is possible), non-destructive method FTIR limitations: Molecules must be active in IR region Recycle your plastics so they don t end up in the aquatic environment! Michelle Nguy 19

20 Thank you! Any questions? 20

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22 O.O. Solomon, T. Palanisami, Microplastics in the Marine Environment: Current Status, Assessment Methodologies, Impacts and Solutions, Journal of Pollution Effects & Control. 04 (2016). doi: /