LAUSR

We describe a simple single-pot method for collection and preparation of natural water for microplastic (MP) analyses. The method prepares samples in the same vessel (Mason jars) that they are collected in right up until the MPs are transferred onto filters or spectroscopic windows for analyses. The method minimized contamination, degradation, and losses, while increasing recoveries and throughput when compared to conventional sieving. We applied it to surface grab samples collected from the Mississippi River and its major tributaries during and after historic flooding in 2019. Microplastics (>~30 µm) were quantified using Nile Red fluorescence detection, and a small subset of samples were identified by micro-Fourier Transform Infrared Imaging spectroscopy (µFTIR-Imaging). Concentrations were lower during the flooding, likely due to dilution. Concentrations (MPs/L) ranged from ~14 in the Tennessee River during flooding to ~83 in the Ohio River during low-flow (summer) conditions. Loads of MPs tended to increase down river and ranged from ~87 to ~129 trillion MPs/day near New Orleans. Most of the MPs (>60%) were in the lower size fraction (~30-90 µm), consisted primarily of fragments (~85%), followed by fibers (~8%) and beads (~7%), with polyester, polyethylene, polypropylene, and polyacrylate as the primary MP type. Overall, we demonstrate that the single-pot method is effective and versatile, and, because it uses relatively inexpensive and easily assembled materials, it can be adapted for MP surveys worldwide, especially those involving volunteers from the community and schools. This article is protected by copyright. All rights reserved.