Errors and recommended practices that should be identified to reduce suspected concentrations of microplastics in soil and groundwater: A review

Abstract

Over the last decade, many studies on microplastics (MPs) have only focused on the marine environment, and scientist have recently begun to document soil and groundwater MP contamination. However, many of these studies have included errors that should be addressed. Therefore, the aim of this study is to identify multiple errors in internationally reported soil and groundwater MPs studies and to provide recommendations. Over 185 original research papers on soil and groundwater MPs published between 2017 and 2022 from seven database categories in the Web of Science were sorted. These papers were manually sorted to identify errors in (i) sample quantity, (ii) quality assurance and equipment used, (iii) microplastic identification, and (iv) microplastic classification. The majority of studies were found not to use blank samples, classified MPs incorrectly by mixing MP shapes and forms, used filters with either larger pore sizes, or materials that could be potential sources of MP. In some of these studies, the statistical package or law used for statistical analysis was not specified, with some other studies using problematic MP analysis procedures. As a remediation method to address these errors, MP studies should consider using blank soil samples and metallic filters. Statistical software packages should be used, and the statistical prerequisite laws should be verified prior to analysis. Stereo microscopes should be used simultaneously with Raman or Fourier transform infrared (FTIR) spectroscopy to identify MPs in soils and groundwater. • It is essential plastic kits are not used for storing soil and groundwater after sampling. • Accurate microplastic analysis requires at least one trip and a device blank sample each time. • Film and fragment should be classified as the same microplastics shape, not separate shapes. • A glass filter is preferable to a cellulose filter for accurate microplastics analysis. • It is critical to collect soil weight in the range of 200–1000 g for accurate microplastic analysis.