Separation, Identification, and Quantification Methods in Soil Microplastics Analysis: A Review
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Clc Number:

X830.2

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The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan), The Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research

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    Abstract:

    Microplastics (MPs) refer to plastic debris with a dimension <5 mm and possess high chemical stability, small particle size, and strong mobility. Once they enter the soil environment, MPs can exhibit long-term retention, act as a vector for soil contaminants, and even pass through the food chain by plant enrichment, causing serious damage to the environment and human health. Due to the complexity of soil substrates and the limitations of analytical techniques, there is still a big gap in the study of soil MPs. Research on soil MPs analysis technology is the basis for uncovering the migration and transformation mechanism in soils and to evaluate the ecological risks of MPs. In this study, worldwide research progress on the separation, extraction, and identification of MPs in environmental samples is reviewed. Moreover, the advantages and disadvantages of these methods and their applicability to soil samples are discussed. Finally, the development direction of future research on the analysis technology is suggested. The most common separation method, density separation, is simple and effective for extracting MPs, but it cannot remove organic matter or separate plastic debris <50 μm. Though it may damage MPs structures, the newly developed pressure fluid extraction (PFE) still has good application prospects because of its low cost, high automation and efficiency. Other alternative methods (e.g. oil extraction and magnetic separation) are rarely used, and their applicability to soil samples remains unclear. Also, digestion methods with different intensity are reported to cause different degrees of damage to the MPs structures, and the enhancement of organic matter digestion efficiency is usually at the cost of MPs recovery. The existing identification and quantification methods include (i) visual identification methods with the aid of a microscope, (ii) FTIR and Raman based spectral analysis methods, and (iii) the MS or chromatography coupled thermal analysis methods. When applied to soil MPs identification, these methods exhibited shortcomings such as time consumption, size and amount limitations of MPs sample, and damage to MPs structures. The combination of different technologies is expected to address these shortcomings. Importantly, due to the selection biases of researchers on available separation and analysis methods, the results of different studies were difficult to be compared horizontally. Considering the existing deficiencies in current analytical methods, the future research focus should be (1) to establish standard methods for soil MPs extraction, identification, and quantification; (2) to explore suitable analytical methods for small MPs (<50 μm); (3) to develop separation/identification/quantification methods that do not damage MPs structures and are less time-consuming.

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CHEN Yalan, SUN Ke, HAN Lanfang, GAO Bo. Separation, Identification, and Quantification Methods in Soil Microplastics Analysis: A Review[J]. Acta Pedologica Sinica,2022,59(2):364-380.

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History
  • Received:December 07,2020
  • Revised:March 22,2021
  • Adopted:March 25,2021
  • Online: March 27,2021
  • Published: February 11,2022