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Table 1 Studies investigating the health effects of exposure to underground railway air pollution in vivo

From: Health effects of particulate matter air pollution in underground railway systems – a critical review of the evidence

First Author Publication Year (Study Dates) Underground [Airborne PM] (μg/m3 unless stated) PM Composition Exposure Period Sample Size Effects of Underground Exposure
Klepczynska Nystrom [15] 2010 (October 2006–March 2007) Stockholm, Sweden PM10 = 242 ± 40; PM2.5 = 77 ± 10;
PM0.1 PNC = 8283 ± 1716/cm3
PM10: Fe = 58.6 ± 21.0%; Ba = 1.0 ± 0.4%; Cu = 0.8 ± 0.4%; Mn = 0.5 ± 0.2% 2 h, afternoon rush hour 20 healthy non-smoking volunteers (13 M 7F), mean age 27 y (range 18–46) No change in lung function or airway cellular parameters, increased plasma fibrinogen, increased blood Treg count.
Bigert [20] 2011 (November 2004–March 2005) Stockholm, Sweden PM10–1 DataRAM and PM2.5 ticket office = 13 ± 3, 10 ± 3; train drivers = 33 ± 12, 19 ± 3; platform workers = 182 ± 57, 63 ± 12 Not stated ~ 8 h working day 81 non-smoking workers (55 M 26F), mean age 38 y (range 25–50) No changes in FENO or lung function over working day.
Klepczynska Nystrom [21] 2012 (mid November-early April, year not stated) Stockholm, Sweden PM10 = 232 ± 51; PM2.5 = 71 ± 13;
PM0.1 PNC = 8960 ± 660/cm3
PM10: Fe = 49.3 ± 7.3%; Ba0.7 ± 0.1%; Cu = ND; Mn = 0.4 ± 0.1 2 h, afternoon rush hour 16 mild asthmatic non-smoking volunteers (5 M 11F), mean age 26 y (range 18–52) Increased activated T cells in BALF, no effect on blood T cell counts or coagulation markers.
Bigert [27] 2008 (November 2004–March 2005) Stockholm, Sweden PM10–1 DataRAM and PM2.5 ticket sellers = 13 ± 3, 10 ± 3; train drivers = 33 ± 12, 19 ± 3; platform cleaners = 256 ± 97, 79 ± 17; platform ticket collectors = 108 ± 26, 50 ± 8 Not stated 48 h (over 2 working days) 79 non-smoking workers (54 M, 25F), mean age 38 y (range 25–50) Increased PAI-1 in ticket sellers, increased fibrinogen in train drivers. More exposed platform workers had higher baseline PAI-1 and hsCRP, but no effect over exposure period. No obvious PM effect.
Lundstrom [28] 2011 (mid November-early April, year not stated) Stockholm, Sweden Not stated – see [15, 21] Not stated – see [15, 21] 2 h, afternoon rush hour 18 healthy, 15 mild intermittent asthmatic non-smoking volunteers (17 M, 16F), mean age 26 y (range 18–52) 9/64 oxylipins assayed in BALF increased in healthy vs. asthmatic, volunteers, principally 15-lipoxygenase-generated derivatives of linoleic and α-linolenic acids.
Liu [30] 2015 Taipei, Taiwan PM10, PM2.5 underground = 32 ± 12, 22 ± 7; bus = 40 ± 16, 32 ± 12; car = 34 ± 13, 29 ± 11; walking = 50 ± 21, 42 ± 18 Not stated 1 h morning commute 120 healthy volunteers (58 M, 62F), mean age 21 y (range 19–24) Underground commute showed lowest PM2.5 exposure and lowest effect on heart rate variability vs. bus, car, or walk.
Bigert [33] 2007 (data from 1976 to 1996) Stockholm, Sweden Not stated Not stated Chronic workplace exposure 131,496 M (250 underground drivers), 22,311 myocardial infarction cases (54 underground drivers) No increased risk of myocardial infarction in underground drivers (RR = 0.92 [95% CI 0.68–1.25] vs. manual workers, 1.06 [95% CI 0.78–1.43] vs. other employed males).
Gustavsson [34] 2008 (subjects followed from 1970 to 1989) Stockholm, Sweden Not stated Not stated Chronic workplace exposure 319,979 M (348 underground drivers), 4731 lung cancer cases (9 underground drivers) No increased risk of lung cancer in underground drivers (standardised incidence ratio 0.82 [95% CI 0.38–1.56]).
Grass [35] 2010 (November 2004–February 2005) New York City, USA PM2.5 exposure median across all subway roles = 27 (5th–95th %ile = 8–112) PM2.5: median Fe = 27% Chronic workplace exposure 39 M underground drivers (median age 48 y, IQR 38–53), 11 M bus drivers (45 y, 41–48), 25 M office workers (44 (37–51)) Across a wide range of chemical and biomarker assays in blood and urine, only urinary 8-isoprostate was associated with (cumulative) underground exposure.
Mehrdad [36] 2015 (September–October 2012) Tehran, Iran Not stated Not stated Chronic workplace exposure 81 M healthy underground workers, mean age 32 ± 7 y Increased urinary 8-OHdG in underground tunnel workers vs. underground non-tunnel workers.