Extracting microplastics from complex environmental samples - dos, don’ts, and validation

, Möller Julia, Heisel Ingrid, Satzger Anna, Oster Simon Jakob, Agarwal Seema, Löder Martin, Laforsch Christian.

Research on microplastics has been developing since 2004, with improved methods enabling the detection and characterization of ever-smaller microplastics. Initially, the field was limited to the marine environment, later expanding to freshwater systems and finally to the terrestrial environment. Soils are assumed to be a significant sink for microplastic pollution, but the extent of the contamination in soils is still widely unknown. This is mainly due to a lack of suitable methods capable of detecting a variety of small, particulate synthetic polymers in a complex particulate environmental matrix. We have developed a method for soil sample purification using a combination of sieving, density separation, and a novel sequential enzymatic digestion in order to purify soil samples of around 250g to such an extent that a particle analysis with focal plane array based µ-FTIR spectroscopy becomes possible. Overall, the protocol enables the removal of ¿99,9%(DW) of the bulk mineral mass and another average reduction of 77%(DW) of the lightweight organic fraction. Furthermore, the visual and molecular integrity of small particles in the size range of 100-400µm made of PE, PET, PA, PVC, and the biodegradable PLA were analyzed before and after undergoing the purification protocol. The presentation will also address the pitfalls we have encountered while developing the method. Furthermore, the importance of conducting validation for all methods and media used in microplastic research, as well as the significance of validating with chemically characterized spiking material, will be discussed. With this critical appraisal of how methods are developed, this talk aims to encourage a discussion targeted towards the final goal of devising harmonized procedures for more comparability within microplastic research.

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