Methods of soil sampling for microplastic analysis: a review

While microplastic analysis in aquatic systems is rather well standardized, the determination of microplastics in terrestrial samples has been less explored. Here, we review methods for microplastic analysis, with focus on sampling location and design, soil quantity, sampling depth and equipment, and sample handling and preservation. We found that the random sampling design can be used to collect a representative sample. Stainless steel shovels or soil augers were the most common tools for collecting topsoil, from 0 to 30 cm. Deep soil samples, of more than 100 cm depth, can only be obtained using a core drill. The number of soil samples collected in the field depends on the available budget and instruments for microplastic analysis. For example, if a micro-Fourier transform infrared microscope is used for analysis, soil samples as small as 15.0 g per point can be collected. Once the soils are collected, they can be stored in non-plastic containers, e.g., aluminum bags, to reduce contamination.