Finding Microplastics in Soils: A Review of Analytical Methods

Research on microplastics in soils is still uncommon, and the existing publications are often incomparable due to the use of different sampling, processing, and analytical methods. Given the complex nature of soils, a suitable and efficient method for standardized microplastic analysis in the soil matrix has yet to be found. This paper proposes a critical review on the different published methods for sampling, extraction, purification, and identification/quantification of microplastics in complex environmental matrices, with the main focus on their applicability for soil samples. While large microplastic particles can be manually sorted out and verified with chemical analysis, sample preparation for smaller microplastic analysis is usually more difficult. Of the analytical approaches proposed in the literature, some are established, whereas others are a proof of principle and have not yet been applied to environmental samples. For the sake of development, all approaches are discussed and assessed for their potential applicability for soil samples. So far, none of the published methods seems ideally suitable for the analysis of smaller microplastics in soil samples, but slight modifications and combinations of methods may prove promising and need to be explored.