Microplastics in Settled Dust from Indian Long-Distance Railway Coaches: Baseline Occurrence, Relative Load, and Scenario-Based Ingestion Estimates

Microplastics (MPs) in long-distance trains remain undercharacterized despite prolonged exposure of passengers and staff in confined environments. In this study, settled dust was collected from four distinct coach classes on an Indian railway to establish baseline MPs occurrence, morphology, polymer composition, relative load, and exposure-relevant particle intake. Samples were processed via oxidative digestion, density separation, and stereomicroscopy for particle quantification and morphological characterization. Polymer identity was assessed using micro-Raman spectroscopy, and human exposure was evaluated using estimated trip (EDITrip) and annual (EAI) intake models. MPs were detected in all four sampled coach composites, with coach-level concentrations ranging from 925 to 3755 MPs/g. Among the four sampled coaches, the 1AC (first-class sleeper air-conditioned) coach had the highest measured concentration. Fibers (72%), transparent particles (61%), and polyester dominated, suggesting mixed textile and interior sources. The Relative Load Ratio (RLR) reached 4.06 in 1AC, compared to the lowest-abundance general unreserved coach (GL). Deterministic EDITrip ranged from 5.78 to 388.35 particles/trip, with maximum intake observed for toddlers on full-route 1AC journeys. Monte Carlo simulations confirmed intake increases with travel duration and frequency. These findings highlight long-distance railway coaches as overlooked MPs reservoirs, emphasize the need for improved dust control, ventilation management, and lower-shedding interior materials.