Tackling the Challenge of Extracting Microplastics from Soils : A Protocol to Purify Soil Samples for Spectroscopic Analysis

Titelangaben

Möller, Julia N. ; Heisel, Ingrid ; Satzger, Anna ; Cseperke Vizsolyi, Eva ; Oster, Simon David Jakob ; Agarwal, Seema ; Laforsch, Christian ; Löder, Martin G. J.:
Tackling the Challenge of Extracting Microplastics from Soils : A Protocol to Purify Soil Samples for Spectroscopic Analysis.
In: Environmental Toxicology and Chemistry. (23 Februar 2021) .
ISSN 1552-8618
DOI der Verlagsversion: https://doi.org/10.1002/etc.5024

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Abstract

Microplastic pollution in soils is an emerging topic in the scientific community, with researchers striving to determine the occurrence and the impact of microplastics on the soil's health, ecology and functionality. However, information on the microplastic contamination of soils is limited, due to a lack of suitable analytical methods. As micro-Fourier-transform infrared spectroscopy (µ-FTIR), next to Raman spectroscopy, is one of the few methods that allow the determination of the number, polymer type, shape and size of microplastic particles, this study addresses the challenge of purifying soil samples sufficiently to allow a subsequent µ-FTIR analysis. A combination of freeze-drying, sieving, density separation and a sequential enzymatic-oxidative digestion protocol enables the removal of the mineral mass (>99.9% DW) and an average reduction of 77% DW of the remaining organic fraction. Additional to visual integrity, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) showed that polyamide, polyethylene, polyethylene terephthalate and polyvinyl chloride in the size range of 100-400µm were not affected by the approach. However, the biodegradable polylactic acid showed visible signs of degradation and reduced molecular weight distribution after the protease treatment. Nevertheless, the presented purification protocol is a reliable and robust method to purify relatively large soil samples of around 250 g DW for spectroscopic analysis in microplastic research, and has been shown to recover various microplastic fibers and fragments down to a size of 10 µm from natural soil samples.