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

Health effects of particulate matter air pollution in underground railway systems – A critical review of the evidence
Health effects of particulate matter air pollution in underground railway systems – A critical review of the evidence
Background
Exposure to ambient airborne particulate matter is a major risk factor for mortality and morbidity, associated with asthma, lung cancer, heart disease, myocardial infarction, and stroke, and more recently type 2 diabetes, dementia and loss of cognitive function. Less is understood about differential effects of particulate matter from different sources. Underground railways are used by millions of people on a daily basis in many cities. Poor air exchange with the outside environment means that underground railways often have an unusually high concentration of airborne particulate matter, while a high degree of railway-associated mechanical activity produces particulate matter which is physicochemically highly distinct from ambient particulate matter. The implications of this for the health of exposed commuters and employees is unclear.

Main body
A literature search found 27 publications directly assessing the potential health effects of underground particulate matter, including in vivo exposure studies, in vitro toxicology studies, and studies of particulate matter which might be similar to that found in underground railways. The methodology, findings, and conclusions of these studies were reviewed in depth, along with further publications directly relevant to the initial search results. In vitro studies suggest that  underground particulate matter may be more toxic than exposure to ambient/urban particulate matter, especially in terms of endpoints related to reactive oxygen species generation and oxidative stress. This appears to be predominantly a result of the metal-rich nature of underground particulate matter, which is suggestive of increased health risks. However, while there are measureable effects on a variety of endpoints following exposure in vivo, there is a lack of evidence for these effects being clinically significant as may be implied by the in vitro evidence

Conclusion
There is little direct evidence that underground railway PM exposure is more harmful than ambient PM exposure. This may be due to disparities between in vivo exposures and in vitro models, and differences in exposure doses, as well as statistical underpowering of in vivo studies of chronic exposure. Future research should focus on outcomes of chronic in vivo exposure, as well as further work to understand mechanisms and potential biomarkers of exposure.
underground railway, subway, particulate matter, transition metal, steel, iron, reactive oxygen species, oxidative stress, inflammation
1743-8977
Loxham, Matthew
8ef02171-9040-4c1d-8452-2ca34c56facb
Nieuwenhuijsen, Mark J.
49620224-0851-44e1-9361-4d601ef475cb
Loxham, Matthew
8ef02171-9040-4c1d-8452-2ca34c56facb
Nieuwenhuijsen, Mark J.
49620224-0851-44e1-9361-4d601ef475cb

Loxham, Matthew and Nieuwenhuijsen, Mark J. (2019) Health effects of particulate matter air pollution in underground railway systems – A critical review of the evidence. Particle and Fibre Toxicology, 16 (12). (doi:10.1186/s12989-019-0296-2).

Record type: Review

Abstract

Background
Exposure to ambient airborne particulate matter is a major risk factor for mortality and morbidity, associated with asthma, lung cancer, heart disease, myocardial infarction, and stroke, and more recently type 2 diabetes, dementia and loss of cognitive function. Less is understood about differential effects of particulate matter from different sources. Underground railways are used by millions of people on a daily basis in many cities. Poor air exchange with the outside environment means that underground railways often have an unusually high concentration of airborne particulate matter, while a high degree of railway-associated mechanical activity produces particulate matter which is physicochemically highly distinct from ambient particulate matter. The implications of this for the health of exposed commuters and employees is unclear.

Main body
A literature search found 27 publications directly assessing the potential health effects of underground particulate matter, including in vivo exposure studies, in vitro toxicology studies, and studies of particulate matter which might be similar to that found in underground railways. The methodology, findings, and conclusions of these studies were reviewed in depth, along with further publications directly relevant to the initial search results. In vitro studies suggest that  underground particulate matter may be more toxic than exposure to ambient/urban particulate matter, especially in terms of endpoints related to reactive oxygen species generation and oxidative stress. This appears to be predominantly a result of the metal-rich nature of underground particulate matter, which is suggestive of increased health risks. However, while there are measureable effects on a variety of endpoints following exposure in vivo, there is a lack of evidence for these effects being clinically significant as may be implied by the in vitro evidence

Conclusion
There is little direct evidence that underground railway PM exposure is more harmful than ambient PM exposure. This may be due to disparities between in vivo exposures and in vitro models, and differences in exposure doses, as well as statistical underpowering of in vivo studies of chronic exposure. Future research should focus on outcomes of chronic in vivo exposure, as well as further work to understand mechanisms and potential biomarkers of exposure.

Text
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More information

Accepted/In Press date: 19 February 2019
e-pub ahead of print date: 6 March 2019
Keywords: underground railway, subway, particulate matter, transition metal, steel, iron, reactive oxygen species, oxidative stress, inflammation

Identifiers

Local EPrints ID: 428554
URI: https://eprints.soton.ac.uk/id/eprint/428554
ISSN: 1743-8977
PURE UUID: 5fd72d55-e469-4d47-82ce-03db0439f4e2
ORCID for Matthew Loxham: ORCID iD orcid.org/0000-0001-6459-538X

Catalogue record

Date deposited: 01 Mar 2019 17:30
Last modified: 20 Jul 2019 04:01

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