Metal content of settled railway dust: factors affecting iron (Fe) content of dust in railway stations in England and implications for human health exposure assessments.

Railway infrastructure generates metal-containing particles enriched in elements with known health impacts, which are released into the environment and may expose railway users and workers. This study aimed to characterise the metal composition of settled dust in railway stations, estimate deposition rates, and identify station characteristics associated with elevated exposure. Settled dust samples were collected using dust wipes from undisturbed surfaces in nine English railway stations, which enabled opportunistic metals analysis. Metal concentrations were quantified using Inductively Coupled Plasma Mass Spectrometry. Deposition rates (ng cm-2 month-1) were calculated, and associations between iron (Fe) deposition and environmental and station characteristics were examined. An ordinal logistic regression model was developed to identify predictors of elevated Fe deposition rates. Fe showed the highest deposition rates, with a geometric mean of 325 ng cm-2 month-1, while zinc and copper were consistently detected. Higher Fe deposition was associated with darker sample colour, higher annual station footfall, and greater train movements. Fe deposition rates were higher in winter than in summer and in enclosed stations compared with more open environments. In multivariate analysis, sample solution colour, station openness, and annual footfall were the strongest predictors of Fe deposition. The relative ranking of metals (Fe > Al > Zn > Cu) was consistent with previous studies of railway dust. Other station characteristics, including train numbers, diesel fleet proportion, local deprivation, and Fe concentrations in surrounding soil, were not associated with Fe deposition. Future work should assess how metal concentrations in railway dust contribute to environmental and occupational exposures and associated health risks.