Assessing the Lost Fraction: Diversity, Abundance, and Mass of Microplastics (1-300 µm) in Aquatic Systems

The protocol presented here enables the quantification of microplastics (MPs) as small as ~1 µm in diameter, accurate identification of polymer types, and estimation of particle volume, critically allowing for the calculation of MP mass. Representative results from samples collected in the Great South Bay (GSB), NY, showed that particles within the 1-6 µm equivalent spherical diameter (ESD) range were the most abundant, with approximately 75% of particles measuring less than 5 µm. Notably, the pre-sieving step failed to yield any particles larger than 60 µm, suggesting that large MPs were rare at the coastal sites sampled. Prior to filtration, a chemical oxidation step was used to remove organic debris, which facilitated the filtration of larger water volumes (>1 L) from discrete bottle-collected samples and reduced filter clogging. While this approach significantly improved filtration efficiency, aspects of the methodology still require refinement to reduce the total time required for sample preparation and data analysis. Raman microspectroscopy and associated data processing remain time-intensive, particularly for accurately analyzing particles smaller than 10 µm in complex environmental matrices. Ongoing efforts are focused on minimizing analytical uncertainties, optimizing the trade-off between particle counting accuracy and processing time, and reducing artifacts in the detection workflow.