New Publication: Systematic development of extraction methods for quantitative microplastics analysis in soils using metal-doped plastics
Are you searching for a good way to extract microplastics from soils? We've developed a new approach suitable for a variety of soil textures, including those with high organic and lignocellose contents
Alissa Tophinke, Akshay Joshi, Urs Baier, Rudolf Hufenus, Denise M. Mitrano. Environmental Pollution. 211 (2022) 119933 external page Open access publication link here
This manuscript sets a few milestones: first, first author paper for Alissa and my 50th peer reviewed publication overall! :)
Highlights
1) Development of targeted extraction methods by systematically investigating soil subgroups (sand, silt, clay, non-lignified and lignified organic matter) to establish extraction chains for multi-component standard soils
2) New approach to degrade lignocellulose to isolate MPs, mimicking natural degradation processes in aerobic and anaerobic fungi
3) Quick and quantitative recovery measurements by using metal-doped PET MPs fragments and MPs fibers
4) Deep learning tool confirmed a clear filter with minimal organic and inorganic residues, aiding subsequent micro-FTIR analysis
5) Modular method design allows easy adaptation of the individual steps for other MPs polymer morphologies and compositions
Abstract
The inconsistency of available methods and the lack of harmonization in current microplastics (MPs) analysis in soils demand approaches for extraction and quantification which can be utilized across a wide variety of soil types. To enable robust and accurate assessment of extraction workflows, PET MPs with an inorganic tracer (Indium, 0.2% wt) were spiked into individual soil subgroups and standard soils with varying compositions. Due to the selectivity of the metal tracer, MPs recovery rates could be quickly and quantitatively assessed using ICP-MS. The evaluation of different methods specifically adapted to the soil properties were assessed by isolating MPs from complex soil matrices by systematically investigating specific subgroups (sand, silt, clay, non-lignified and lignified organic matter) before applying the workflow to standard soils. Removal of recalcitrant organic matter is one of the major hurdles in isolating MPs for further size and chemical characterization, requiring novel approaches to remove lignocellulosic structures. Therefore, a new biotechnological method (3-F-Ultra) was developed which mimics natural degradation processes occurring in aerobic (Fenton) and anaerobic fungi (CAZymes). Finally, a Nile Red staining protocol was developed to evaluate the suitability of the workflow for non-metal-doped MPs, which requires a filter with minimal background residues for further chemical identification, e.g. by µFTIR spectroscopy. Image analysis was performed using a Deep Learning tool, allowing for discrimination between the number of residues in bright-field and MPs counted in fluorescence mode to calculate a Filter Clearness Index (FCI). To validate the workflow, three well-characterized standard soils were analyzed applying the final method, with recoveries of 88% for MPs fragments and 74% for MPs fibers with an average FCI of 0.75. Collectively, this workflow improves our current understanding of how to adapt extraction protocols according to the target soil composition, allowing for improved MPs analysis in environmental sampling campaigns.