FTIR Talk Letter Vol. 46

Significance of the Topic

Microplastics (MPs) are ubiquitous environmental particles (<5 mm) arising from primary production and secondary fragmentation of larger plastics. Beyond ecological damage, inhalation of airborne MPs—especially particles in the micrometer to sub-micrometer range—has emerged as a potential human health hazard affecting the respiratory system. Understanding deposition, persistence, and biological effects of MPs in lung tissue is essential for risk assessment, clinical research into respiratory disease and cancer modulation, and for forming evidence-based public-health recommendations.

Study Objectives and Overview

This collection of articles and application notes describes (1) clinical and experimental investigations into pulmonary microplastic accumulation and its biological effects by the Nagasaki University group, (2) analytical workflows and software for infrared and infrared‑Raman particle analysis (Shimadzu), and (3) practical guidance for infrared spectral interpretation of amide-containing materials (e.g., nylons, proteins). The combined goal is to move beyond presence/absence detection to reliable localization, chemical identification, quantification and mechanistic studies linking MPs to inflammation, fibrosis and potentially tumor promotion.

Methodology and Analytical Workflow

• Human sample analysis: surplus lung resection tissue and bronchoalveolar lavage fluid (BAL) analyzed by micro‑Raman spectroscopy to detect common polymers (polystyrene, polypropylene, polyethylene).
• Animal models: intratracheal administration of fluorescent or non‑fluorescent polystyrene beads (3 μm and 6 μm); development of a reliable endotracheal delivery technique using a laryngoscope, guidewire and Surflo needle to ensure uniform lung distribution.
• Sample preparation: adoption of frozen sections and fluorescently labeled MPs to avoid particle loss during FFPE processing; frozen sections preserve hydrophobic particles that are otherwise removed by organic solvents (xylene, alcohol).
• High‑throughput detection: combined wide‑area 3D laser reflectance imaging (OLS5100) for rapid morphological screening and coordinate extraction, followed by pointwise chemical identification using infrared‑Raman microscopy (AIRsight) for unambiguous polymer identification.
• Software‑assisted analysis: AMsolution particle analysis function to auto‑detect particles in mapping datasets, compute geometric parameters (major/minor axis, Feret diameters, area) and estimate mass/volume using established geometric relationships; high‑speed mapping mode to skip background regions and drastically reduce acquisition time while preserving spectral quality for regions containing particles.

Used Instrumentation

• OLS5100 3D measuring laser microscope (large‑area, submicron resolution reflectance and topography imaging).
• AIRsight infrared‑Raman microscope (combined infrared and Raman identification at point locations).
• AIMsight and AIM‑9000 infrared microscopes controlled via AMsolution software for mapping and particle analysis.
• Standard FTIR and Raman systems and ancillary pathology equipment for frozen sectioning and fluorescent microscopy.

Main Results and Discussion

• Demonstrated deposition: Micro‑Raman analysis detected MPs in human lung tissue, validating inhalation-to‑lung deposition pathways and showing that airborne MPs can reach deep lung regions.
• Methodological insight: FFPE histological workflows often cause loss or displacement of hydrophobic MPs, leaving voids rather than intact particles. Frozen sections combined with fluorescent labeling preserve particle‑tissue associations and allow direct visualization of particle localization and macrophage interactions.
• Analytical throughput: The two‑step workflow—wide‑area OLS5100 scanning for morphological candidates followed by AIRsight chemical confirmation—significantly reduces time required to locate and identify micrometer‑scale MPs in large tissue sections while minimizing false positives (e.g., lipids) that affect staining methods like Nile Red.
• Biological effects (preliminary): Intratracheal MP exposure in mice indicates enhanced fibrotic responses (Masson’s trichrome and collagen‑I staining) and activation of oxidative stress and Wnt/β‑catenin signaling in some studies. Planned transcriptomic profiling aims to map pathways involved in inflammation, senescence, impaired repair, and cell death.
• Analytical software performance: AMsolution particle analysis computes particle counts, sizes and estimated mass/volume; high‑speed mapping uses an initial accumulation spectrum to classify background vs sample points, accelerating mapping of filters and tissue sections without compromising identification accuracy.

Benefits and Practical Applications

• Robust detection workflow: Combining morphological pre‑screening with spectral confirmation produces high‑confidence identification and localization of MPs in clinical and experimental specimens.
• Improved sample preservation: Frozen section protocols enable direct study of particle‑cell interactions, reducing false negatives caused by conventional histopathology solvents.
• Scalable clinical research: High‑speed mapping and automated particle analysis make larger epidemiological and clinicopathological studies feasible, enabling correlations with residential, occupational, smoking status and tumor adjacency.
• Regulatory and translational relevance: Data generated by these workflows can inform exposure guidelines, risk assessments, and the design of mitigation strategies or therapeutic interventions where MPs exacerbate pulmonary disease.

Future Trends and Opportunities

• Mechanistic studies: Integration of intratracheal exposure in disease models (COPD, bleomycin fibrosis, ovalbumin asthma) with transcriptomics and proteomics to define pathways by which MPs exacerbate inflammation, fibrosis and potentially tumor promotion.
• Nanoplastic focus: Extending detection and toxicology work toward submicron and nanoscale plastics, which may penetrate deeper into alveoli and have distinct cellular responses.
• Standardization and clinical databases: Large‑scale, multi‑center datasets linking MP burden to clinical variables, aided by standardized sample handling and analytical pipelines, will be critical for risk quantification and policy guidance.
• Instrument and software evolution: Continued advances in high‑throughput spectral imaging, machine‑learning classification, and rapid mass/volume estimation will further streamline MP analysis across environmental and biomedical matrices.

Conclusion

Detectable, persistent microplastics are present in human and experimental lung tissues. Methodological refinements—avoiding solvent‑based histology, using fluorescent tracers and frozen sections, and pairing wide‑area laser imaging with infrared‑Raman chemical confirmation—yield reliable spatial and chemical evidence of MPs in lung parenchyma. These advances permit more efficient, rigorous studies of how MPs influence inflammation, fibrosis and cancer biology, and set the stage for evidence‑based public‑health recommendations and therapeutic strategies.

Reference

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3. Sobue K. High‑Speed Measurement of Microplastics Smaller than 100 μm Collected on a Filter—Using a High‑Speed Mapping Program and Particle Analysis Program—. Shimadzu Application News 01‑00994.
4. Tange Y. Analyzing Microscopic Contaminants Embedded in Recycled Plastic. Shimadzu Application News 01‑01001.
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