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Assessment of Filter Subsampling and Extrapolation for Quantifying Microplastics in Marine Sediments using Raman Spectroscopy
Citation:
El Khatib, D., T. Langknecht, M. Cashman, R. Burgess, AND K. Ho. Assessment of Filter Subsampling and Extrapolation for Quantifying Microplastics in Marine Sediments using Raman Spectroscopy. SETAC North Atlantic Chapter, 28th Annual Meeting 2022, Groton, CT, June 27 - 28, 2022.
Impact/Purpose:
Microplastics (MPs), particles less than five mm, are widely reported in marine and estuarine environments including the sediments. Characterizing MPs in sediments involves isolating and extracting the particles from the sample and then identifying the specific polymers present. Raman spectroscopy is a standard vibrational spectroscopic method used to identify specific polymers through the characterization of their unique fingerprint spectra. However, performing Raman analysis can be extremely time intensive, requiring days to analyze a limited number of samples. This study investigates a subsampling method to expedite the Raman spectroscopic analysis of MPs present in sediments with sizes ranging between 45 and 1000 µm.
Description:
The process was tested using spiked MPs with the most common polymers (i.e., PE, PVC, PET) in different sizes and shapes in deionized water. This method was also validated using two environmentally contaminated sediments. Based on statistical analyses, our results found the analysis of a subfraction of 12.5% of the filter in a wedge form was optimal for estimating the entire filter count. Additionally, counting only a subfraction of the filter while extrapolating accurate estimates of the total MP present is critical for processing large numbers of samples necessary to understand the extent and type of MP contamination in sediments. Finally, applying the subsampling method, we assessed the presence of MPs in environmentally contaminated sediments from different marine regions of the United States. The average MP abundance in the sediment samples ranged from 570 ± 180 to 1218 ± 1260 particles/Kg wet sediment among all regions. The most abundant polymers found were polypropylene (PP), polyester (PES), and polyethylene (PE), while the most dominant shapes were fragments and fibers. Results of this component of the investigation provide a better understanding of MP distributions in coastal areas and uncovers information to identify sources of MP contamination.
