Preservation, storage, and sample preparation methods for freshwater microplastics – a comprehensive review

Due to their long-lasting negative effects on the environment and detrimental impact on the health of living organisms, microplastics (MPs), found in both water and sediment matrices, have attracted researchers' attention recently. Although various research and reviews have been conducted about MP occurrence and abundance in aqueous environments, less attention has been paid to freshwater matrices through which MPs enter oceans and seas. Freshwater is a vital source of drinking water supply, irrigation systems, and animal feeding systems, and it directly or indirectly affects human health. Thereby, it becomes important to study the occurrence of MPs in freshwater reserves, such as lakes and set up standardized methods for sample collection, storage, and preparation for analysis. Several recent studies have established best-practice in MP characterization and analysis. However, only a few studies have depicted the importance of the pre-analysis phase, including sampling methods, storage, preservation, and preparation strategies. Therefore, this review delineates different sampling methods from freshwater compartments – the surface and column of water and sediments, followed by storage and preservation of obtained samples. Finally, preparation (pre-treatment and extraction) methods have been elaborated, which are necessary to purify MP samples before further investigations. This review aims to provide a clear understanding of the analytical steps and tools, leading to accurate investigations regarding MP's occurrence in future studies.