Methods to optimize the collection, pretreatment, extraction, separation, and examination of microplastics in soil, groundwater, and human samples

Microplastics (MPs) in soil, groundwater, and human (SGH) present a significant global challenge due to their ecological and human health impacts. However, current protocols for detecting MPs in these environments and humans are limited, inconsistently applied, and vary significantly, particularly during the pretreatment stages of MP analysis. Moreover, no study has investigated the impact of methodological flaws on MP detection. This study conducted a thorough global assessment of the existing soil and groundwater (SG) pretreatment methods, using statistical tests to evaluate their effectiveness. It also reviewed filtration and analytical techniques for MPs in SGH samples. The analysis included research articles from PubMed, Google Scholar, Scopus, and Web of Science published between 2015 and 2024. Findings show that pretreatment using more than 100 g of soil can impact MP quantification, likely due to soil heterogeneity, while groundwater volume did not significantly affect MP quantification, likely due to the homogeneity of groundwater. During SGH pretreatment, various salts (e.g., ZnCl2 and NaCl) can be used for density flotation. Fenton's reagent was found to be a better choice than H2O2 for organic material removal because less heat was released. Post treatment MPs in SGH samples can be analyzed using various instruments and resolutions such as FTIR down to 1–5 µm, ATR-FTIR down to 2 µm, micro-Raman down to 500 nm, and LDIR down to 1 µm. This study lays the foundation for developing an effective MP analysis in SGH.