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

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 soil health, ecology, and functionality. However, information on the microplastic contamination of soils is limited because of a...

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Bibliographic Details
Published in:Environmental toxicology and chemistry 2022-04, Vol.41 (4), p.844-857
Main Authors: Möller, Julia N., Heisel, Ingrid, Satzger, Anna, Vizsolyi, Eva C., Oster, S.D. Jakob, Agarwal, Seema, Laforsch, Christian, Löder, Martin G.J.
Format: Article
Language:English
Subjects:
Analytical chemistry
Analytical methods
Biodegradability
Biodegradation
Calorimetry
Contamination
Differential scanning calorimetry
Dry weight
Drying
Environmental Monitoring - methods
Enzymatic‐oxidative digestion
Fibers
Fourier transforms
Infrared analysis
Infrared spectroscopy
Liquid chromatography
Microplastics
Molecular weight
Molecular weight distribution
Plastic debris
Plastic pollution
Plastics - analysis
Polyamide resins
Polyamides
Polyethylene
Polyethylene terephthalate
Polylactic acid
Polymers
Polyvinyl chloride
Purification protocol
Raman spectroscopy
Sediment pollution
Soil
Soil contamination
Soil pollution
Soils
Spectroscopic analysis
Spectroscopy, Fourier Transform Infrared
Toxicology
Water Pollutants, Chemical - analysis
Weight reduction
µ‐FTIR
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Summary: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 soil health, ecology, and functionality. However, information on the microplastic contamination of soils is limited because of a lack of suitable analytical methods. Because micro‐Fourier‐transform infrared spectroscopy (µ‐FTIR), next to Raman spectroscopy, is one of the few methods that allows the determination of the number, polymer type, shape, and size of microplastic particles, the present 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 removal of the mineral mass (>99.9% dry wt) and an average reduction of 77% dry weight of the remaining organic fraction. In addition to visual integrity, attenuated total reflectance FTIR, gel permeation chromatography, and differential scanning calorimetry showed that polyamide, polyethylene, polyethylene terephthalate, and polyvinyl chloride in the size range of 100 to 400 µm were not affected by the approach. However, biodegradable polylactic acid showed visible signs of degradation and reduced molecular weight distribution after protease treatment. Nevertheless, the presented purification protocol is a reliable and robust method to purify relatively large soil samples of approximately 250 g dry weight 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. Environ Toxicol Chem 2022;41:844–857. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. A novel purification sequence for natural soil samples undergoing microplastic analysis.
ISSN:0730-7268
1552-8618
DOI:10.1002/etc.5024