Establishing freshwater sediment sample pretreatment methods for monitoring microplastics and its challenges

Microplastics (MPs) have been detected in various environmental matrices, drinking water, and food, and their presence is an ecological and human health concern. Most research on MPs has focused solely on their detection and analysis. However, sample pretreatment methods are critical for accurate MP analysis and must be properly established. In particular, freshwater sediment contains more impurities than other environment samples, thus requiring more elaborate sample pretreatment. Therefore, research on this media and corresponding pretreatment needs to be performed. Herein, we present a sample pretreatment method for analyzing MPs in freshwater sediments. Detailed factors in arriving at this pretreatment process were evaluated and discussed. Using this established pretreatment method, a total average recovery of six types of standard MPs (HDPE, LDPE, PS, PP, PET, and PVC) for sizes of ≥ 100 μm, 20-100 μm, and 1-20 μm was 94.0%, 90.2%, and 82.5%, respectively. After recovery validation, a modular pretreatment device was developed and combined with the established pretreatment method. The developed device performs density separation and organic matter removal, resulting in about 80% recovery of standard MPs. In addition, natural freshwater sediment samples were prepared using an established pretreatment method, and MPs in streams were analyzed using FTIR, TED-GC-MS, and Pyr-GC-MS. The device affords a low-cost, simple, efficient tool for sample pretreatment steps and easy MP recovery. Thus, it has great potential to simplify sample pretreatment steps for easy MP monitoring, especially for freshwater sediment samples.