Assessment of Indoor Microplastics in Settled Dust at a High-Traffic Transit Building: Characterization, Abundance, Polymer Profiling, and Ingestion Exposure

High-traffic public buildings are significant yet understudied sources of indoor microplastics (MPs) pollution. This descriptive study characterizes the abundance, morphological distribution, and polymer composition of MPs in settled dust from a high-traffic railway station in Rajkot, India. It provides an initial estimate of human exposure via dust ingestion. Dust samples were collected from diverse microenvironments, such as air-conditioned/non-AC waiting rooms, offices, and parcel offices, processed via density separation, and analyzed using stereomicroscopy for morphological characterization and Micro-Raman spectroscopy for polymer identification. The results revealed high MP contamination of 4,464.11 ± 481.60 MPs/g, dominated by polyethylene terephthalate. Overall, fibers were the dominant morphology (67.15%), with the 200–500 μm size dominating across all particles (37.04%). Principal Component Analysis identified microenvironment specific patterns linked to human activity (e.g., textile shedding), with non-AC waiting rooms showing 30% higher abundance than AC areas, attributed to elevated passenger flow (300 vs. 150 daily visitors) and open ventilation. The parcel office exhibited fragment-enriched and red-colored MPs signatures, mechanistically linked to institutional packaging practices. Estimated daily intake via dust ingestion was highest for toddlers (38.17 MPs/kg body weight/day), substantially exceeding residential exposure levels. These findings provide baseline data on MPs abundance in a major railway station and may be indicative of conditions in similar public transport hubs, highlighting it as a potential site of MPs accumulation and human exposure. This contributes to the limited literature on indoor MPs in high-traffic public buildings and suggests avenues for future multi-site, multi-season research to inform evidence-based mitigation strategies.