Hazardous air pollutants, Iron, Underground railway, Public Health/Gesundheitswesen, Bioavailability, Epidemiology, Subway, Health Informatics & Health Administration, Medicine & Public Health, Metro, Chromium, Dose-response, Steel dust, transit workers, Manganese, Dust - analysis, Manganese - blood, Steel - toxicity, Air Pollutants - analysis, Chromium - ur...