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

Over the last decade, many studies on microplastics (MPs) have only focused on the ma-rine 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.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Many studies on microplastics have focused on marine environment, but studies on soil and groundwater microplastic contamination are recently emerging. However, a number of errors have been found in these studies, including sample quantity, quality assurance and equipment used, microplastic identification, and microplastic classification. Recommendations are provided to address these errors, such as using blank soil samples and metallic filters, using statistical software packages and verifying statistical prerequisite laws, and using stereo microscopes in conjunction with Raman or FTIR spectroscopy for microplastic identification in soils and groundwater.