Review of the potential health effects of light and environmental exposures in underground workplaces
Introduction
Utilisation of underground (UG) spaces for various purposes has been a part of human civilization since it first evolved (Kaliampakos et al., 2016, Li et al., 2016). However, it is only during the last few decades that UG spaces have become a common feature of planning and development in many cities (Bobylev, 2016, Doyle, 2016). UG spaces have proven to be an effective solution for tackling pressing issues such as land shortage due to rapid population growth, increasing urbanisation, and environmental impacts of urban traffic (Romanova, 2016, Sterling et al., 2012a, Tengborg and Sturk, 2016, Wallace and Ng, 2016). Thus, many countries such as Sweden, Norway, Netherlands, Japan, US, Hong Kong, the United Kingdom, Turkey, Poland, Canada, Singapore and China have made UG space development part of their policy agenda (Broere, 2016, Kishii, 2016, Qihu, 2016, Shan et al., 2017, Sterling et al., 2012b, Tengborg and Sturk, 2016, Vähäaho, 2016, Wallace and Ng, 2016, Zhao et al., 2016, Zhou and Zhao, 2016). However it is challenging to obtain an estimate of the size of the global population which currently works UG, although it must number in the millions (Bobylev, 2016). About a million people reside in the network of bomb shelters under Beijing alone (Kim, 2016).
UG spaces may have environmental, social and economic benefits such as reduced air pollution and external noise, greater safety, reduced crowding, and saving of energy and natural resources (Asociación Española and de Túneles y Obras, 1996, Bhalla et al., 2005, Lee et al., 2017, Sellberg, 1996, Shan et al., 2017, Sterling et al., 2012b). Risks of working in UG spaces include the limited or lack of exposure of natural sunlight and sounds from the outside world (Carmody and Sterling, 1990, Carmody and Sterling, 1987, Küller and Wetterberg, 1996, Lee et al., 2017). To date, researchers have mostly focused on the engineering, and immediate physiological and psychological aspects of the UG working environments, (Carmody and Sterling, 1993, Carmody and Sterling, 1987, Lee et al., 2017, Lee et al., 2016, Nagy et al., 1995, Roberts et al., 2016) and very few have studied the long term health effects (Aries et al., 2010, Küller and Wetterberg, 1996, Soh et al., 2016). Some of the latter research has demonstrated that UG spaces appear to be less desirable to workers as they may be associated with darkness (the absence of daylight), coldness, dampness (mould and fungal growth), poor air quality due to insufficient ventilation or fear of confinement as well as other safety concerns (Küller and Wetterberg, 1996, Lee et al., 2017, Soh et al., 2016, Wada and Sakugawa, 1990). These disadvantages might in addition constitute risk factors for adverse health outcomes, and as a result in reduced productivity (Aries et al., 2010, Lowe et al., 2014, Manav, 2007). Therefore, it is crucial to investigate the potential risks as well as benefits of UG workplaces considering epidemiology, economics, environmental and occupational safety.
Aries et al. reported that in windowless aboveground (AG) workplaces, various factors such as lighting quality, cleanliness and external access are closely related to comfort, stress levels, health-related and psychological well-being, and sleep quality (Aries et al., 2010). Moreover, there may be other shortcomings in the UG environment such as high humidity, mould and fungal growth, poor air quality due to insufficient ventilation, and the absence of daylight (Küller and Wetterberg, 1996, Ree Joo et al., 1998). Shan et al. administered a questionnaire to 30 Singapore-based construction companies involved in UG projects and reported that limited access to natural light was regarded as the greatest disadvantage (Shan et al., 2017).
Despite the rapidly increasing usage of UG space internationally, there is an evidence gap in their potential health effects that needs to be filled. This paper aims to narratively review and summarize the actual and potential environmental exposures and plausible health effects of UG spaces.
Section snippets
Methods
In this review we have attempted to answer the question: what are the known or possible health effects of UG workplaces? Because of the wide range of exposures involved it was not feasible to conduct a single systematic review. We carried out this narrative review using the following search terms “underground spaces”, “subsurface space”, “subterranean workplaces”, “working underground”, together with “health impact”, “health implications”, “underground and health”, and as well as terms such as
Results
As our focus is on UG workplaces, we first discuss the very limited evidence base comparing UG and AG environments. As lighting and sunlight exposure is an evident difference between UG and most AG spaces (Lee et al., 2017), we then report the major known effects of light on health through circadian rhythm disruption and effects on sleep quality and mental health, as well as vitamin D deficiency as health consequences of lack of sunlight, or an appropriate artificial alternative. We also
Circadian disruptions
A characteristic of UG workplaces is exposure to artificial electric lighting rather than sunlight. Regular exposure to adequate sunlight (or similar artificial light), and day-night contrasts, are important for human health and wellbeing (Bonmati-Carrion et al., 2014, Martinez-Nicolas et al., 2014). These exposures are mediated by the suprachiasmatic nucleus (SCN), a brain area which acts as central pacemaker for the human circadian system (Arendt, 2006, Brainard and Hanifin, 2014, Brown, 1994
Shift working
About 20% of the working population in developed countries work some late or nightshifts. Shift working, like working UG, involves increased exposure to artificial lighting and decreased exposure to sunlight, and so could be seen as a paradigm for UG workspaces, while taking into account sleep loss, which is common in shift workers. Epidemiologic research on shift working has converged with biological research to demonstrate effects on human health. A systematic review (SR) of studies linking
Light at night (LAN)
Any consideration of the health effects of light in UG workplaces needs to take into account light in the home environment of workers. There is now a hypothesis linking LAN and increased disease risks, which postulates a linkage through MLT. Most indolamines like MLT can act as scavengers of oxygen radicals, which damage DNA, and DNA damage can cause cancer (Stevens, 2009). There is growing epidemiologic evidence of an association between LAN and cancer risk (Haim and Portnov, 2013, Haim and
Light wavelengths on circadian rhythms
In the comparative studies above neither Küller and Wetterberg nor Leger et al measured wavelengths of light, only light intensity (illuminance). It has only recently become clear that different wavelengths have different effects on human circadian rhythmicity (Stevens et al., 2014). Circadian phase resetting and MLT suppression in response to bright monochromatic light is most sensitive to short-wavelength (blue) light, indicating that melanopsin has a primary role in human circadian
Vitamin D deficiency
Vitamin D is a hormone essential for a number of functions in the body including calcium absorption, cell proliferation and differentiation, and regulation of immuno- and neuromuscular system (Aranow, 2011, Wintermeyer et al., 2016). The skin is the major site for synthesis of vitamin D, where ultraviolet rays from sunlight penetrate into the epidermis and activate the cycle of reactions triggering the production of Vitamin D. Vitamin D levels in the skin are affected by many factors including
Indoor air quality and sick building syndrome (SBS)
In developed countries most people spend most of their lives in indoors, so the impact of indoor environmental parameters are very important (Ooi et al., 1998, Sahlberg et al., 2013). Due to inadequate ventilation systems and influx of outdoor pollutants, many hazardous components can remain in indoor air such as gaseous pollutants (SO2, NOx, CO, ozone), volatile organic compounds (VOCs), biological threats, pesticides, radon and particulate matter, all of which may increase the susceptibility
Excessive noise
In a work environment, noise can be caused by occupational or environmental factors. Occupational noise refers to workplace-specific noise generated by machines, telephones and conversations, and environmental noise includes external traffic, industrial activity and public works (Hansell et al., 2013, NIOSH, 1998, Schomer, 2005). Building UG spaces could be a protective factor, because environmental noise levels can be reduced (Broere, 2016, Durmisevic, 1999, Godard, 2004). However, in some
Radon
UG facilities may lead to increased radon exposures. Radon is an odourless and invisible, naturally-occurring radioactive gas which can permeate surrounding soil and rocks and enter buildings through cracks or gaps in the floors and walls. Radon and its decay products (known as radon “daughters” or “progeny”) emit highly ionizing alpha-radiation. Radon concentration is low AG due to dilution, however there is a significant level in UG structures, and highest levels UG spaces in contact with the
Comparative studies of health effects of AG and UG working (including windowless environments)
Our searches revealed only five studies (Küller and Wetterberg, 1996, Leger et al., 2011), (Ree Joo et al., 1998, Wada and Sakugawa, 1990, Xueyuan and Yu, 1988) comparing objective health effects in people in modern-day UG working environments and those working in AG spaces, and one of windowed vs windowless environments (Boubekri et al., 2014). They measured different components of circadian rhythm disruption and employed very different experimental methods. In 1996, Küller and Wetterberg
Discussion
Globally the number of people working UG spaces is increasing and therefore identifying the populations at risk and quantifying any specific health effects should be a priority. In this narrative review, we have summarized and discussed some of the actual and hypothetical wide-ranging health impacts of UG environments. We found a few studies investigating the actual effects and mainly observational research literature on the hypothetical health effects. This included the lack of exposure to
Strengths and limitations
This review has important strengths including comprehensive searches of published and unpublished literature over the past 37 years. However, several limitations should be kept in mind when interpreting results of this review. First and foremost, we did not apply any specific exclusion criteria for deciding which studies to exclude from the review. Secondly, no formal validity/risk of bias assessments were planned and performed. Thirdly, from the conceptual perspective, many of the health
Conclusions
We need to expand our knowledge on the actual health effects of working in UG environments. Although five observational studies have reported predominantly, detrimental health effects of UG environments compared with AG spaces, these were mainly short-term, mostly based on self-reported data, and the findings were not conclusive. Larger experimental studies examining the medium- and long-term health effects of working in diverse UG locations; with a range of environmental measures, periods of
Disclaimer
This article was prepared while Nang Ei Ei Khaing was employed at Nanyang Technological University. The opinions expressed in this article are the author's own and do not reflect the view of the National Institutes of Health, the Department of Health and Human Services, or the United States government.
Acknowledgements
This material is based on research/work supported by the Land and Livability National Innovation Challenge (L2 NIC) award number L2NICCFP1-2013-2 and a Lee Kong Chian School of Medicine, Nanyang Technological University Start-Up Grant. The study funder and sponsors had no role in the study design, collection, analysis and interpretation of the data, writing of the report, and the decision to submit the paper for publication.
Competing interests
None of the investigators involved in the study have a conflict of interest. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of L2NIC.
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