Light Pollution - A Darker Side of Light

Acknowledgements President: James W. Caruana Social Policy Officer & Policy Paper Leader: Justin Cauchi S-Cubed Administrative Board: Mariah Zammit, Rachel Attard Chase, Rebekah Caruana & Francesca Camilleri S-Cubed Executive Board: Owen Cuschieri, Matteo Giorgino, Noelle Micallef, Stephanie Buttigieg, Gianni Ciappara, Martina Busuttil and Matthew Camilleri.

Design: Mariah Zammit

Table of Contents Introduction .............................................................................................................................................. 3 Effects on Human Health ......................................................................................................................... 5 Effects on the Natural Environment ........................................................................................................ 6 Conclusion ............................................................................................................................................... 8 References ................................................................................................................................................ 9

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Introduction While the term “pollution” typically brings to mind images of rubbish dumpsites, smog and islands of plastic debris floating in the middle of the ocean, many fail to realise that one of the most important technological milestones in human history, electricity, also brought with it a new and, more often than not, ignored form of pollution; light pollution. Light pollution can be defined as the increased nighttime lighting from natural, nocturnal light-levels as a result of artificial illumination (Cinzano , Falchi, Elvidge, & Baugh, 2000) (Falchi, et al., 2016). Some night time light does originate from natural sources such as the moon, stars, zodiacal lighting and airglow, however most night time illumination is the result of artificial lighting from the domestic and industrial sector as well as infrastructure and vehicles. It is the latter which is the primary cause of light pollution. While such sources contribute to light pollution directly via direct illumination of the immediate vicinity, the majority of light pollution is the result of indirect illumination via skyglow; whereby direct light is scattered and dispersed over a wider area by the atmosphere. The effect of this phenomenon is that light pollution not only affects urbanized areas, but neighbouring, non-urbanized areas as well.

Figure 1 - World map of artificial sky brightness showing artificial sky brightness as a ratio to natural sky brightness. Source - (Falchi, et al., 2016)

According to the most recent artificial night sky brightness atlas (Falchi, et al., 2016);

“…83% of the world’s population and more than 99% of the U.S. and European populations live under light-polluted skies (that is, where artificial sky brightness at the zenith is >14 mcd/m2). Due to light pollution, the Milky Way is not visible to more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world’s land surfaces between 75°N and 60°S, 88% of Europe, and almost half of the United States experience light- polluted nights.”

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With particular reference to Malta, this study also found that together with Singapore, Kuwait, Qatar and San Marino, Malta is one of the few countries where the Milky Way is not visible to the entire country’s population, as well as being the country with the third highest percentage of its land area from which the Milky Way is not visible at 89%, preceded only by Singapore and San Marino in which the Milky Way is not visible from any part of the country. Moreover, this study also found that 99.8% of the Maltese population and 88.5% of the country land area experienced light pollution of levels higher than 688 μcd/m2, and 41.5% of the population and 16.7% of the land area experienced light pollution greater than 3000 μcd/m2. All this points to Malta being one of the most heavily light polluted countries in the world both in per unit population and unit area.

Figure 2 – Graph showing the 20 most light polluted countries, which the legend on the right indicating the corresponding pollution level (μcd/m2) for each colour. Source - (Falchi, et al., 2016)

The aim of this paper is to compile the known detrimental side effects of light pollution and to explore possible ways to mitigate such pollution.

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Effects on Human Health Light pollution has a potentially strong impact on melatonin secretion in humans. Melatonin is a hormone secreted by the pineal gland and is secreted at night and serves as a biological signal for darkness. As a result, it is often depended upon by the body as a signal to induce and promote sleep.

This is supported by research which found that exogenous melatonin administered during daytime reduced sleep onset latency by decreasing core body temperature as well as affected sleep duration times (Hughes & Badia, 1997) (Reid, Van Den Heuvel, & Dawson, 1996). As stimulation of light receptors in the eyes suppress melatonin secretion (Lewy, Wehr, Goodwin, Newsome, & Markey, 1980), it is unsurprising that light pollution at night also delays melatonin secretion. In fact, a study by Gooley et al found that; “Compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min. Also, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50% in most (85%) trials.” (Gooley, et al., 2011) Moreover, due to being secreted only at night, daily melatonin cycles follow a circadian rhythm, together with the hormone cortisol which is secreted when melatonin levels are low; during the day.

Thus, light pollution can put daily melatonin/cortisol cycles, which are always constant (Selmaoui & Touitou, 2003), out of phase, with negative impacts on other physiological process which depend on the melatonin/cortisol cycles as a means of synchronisation with a circadian rhythm. All this may potential lead to problems with sleep, glucose homeostasis, blood pressure and thermoregulation (Arangino, et al., 1999) (Gooley, et al., 2011).

A substantial amount of literature also points to light pollution being a potential carcinogen due to its effect on melatonin levels. Melatonin has been found to have oncostatic properties (Blask, et al., 2005) and, in fact, a study by Schernhammer et al found that female night shift workers had a moderately highly chance of contracting breast cancer after working for an extended period of time (Schernhammer, et al., 2001). This is further supported by another study by Hahn et al which found that blind women, which have as a result higher melatonin levels, were half as likely to contract breast cancer (Hahn, 1991). This same study also found that this effect lessens with age and although this may be correlated to the fact that melatonin levels decrease with age as well, further cementing the link between melatonin levels and breast cancer risk, other research has found that the drop in melatonin levels occurs in early adulthood and melatonin levels remain constant thereafter (Kennaway, et al., 1999). Hence, the increase in breast cancer risk with age may be due to another risk factor which increases with age and annuls the contribution to cancer risk by melatonin levels. The International Agency of Research on Cancer (IARC) found in a review study that, on the effect of increased light exposure duration; “The experimental data from animal studies in several inter-related physiological systems are strongly suggestive of a causal link between circadian disruption and all its consequences and the development of malignant tumours. Human studies are suggestive of physiological effects that are possibly relevant to carcinogenesis.” and as a consequence, classified shift work (due to its increased light exposure and consequent lower melatonin levels) as a Group 2A carcinogen (International Agency for Research on Cancer, 2010).

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Effects on the Natural Environment Being a recent product of human invention, most organisms which have adapted to the natural day/night cycle and have come to depend on it are unsurprisingly negatively impacted by artificial light at night.

Most negatively impacted are nocturnal invertebrates such as moths. It is well known that moths, like many other nocturnal insects are drawn to light sources. However, what is less known is the fact that such an attraction has fatal consequences on moth population. Aggregating in small, well-lit areas makes them easier targets for predators. Moreover, moths swarming around nocturnal artificial light sources were found to spend less time feeding and, are thus more prone to higher fatality rates (van Langevelde, van Grunsven, Veenendaal, & Fijen, 2017). Studies have shown that certain families are more attracted to artificial light at night, with the consequence that such families experience a sharper decline population, which in turn may upset ecosystem balance (Merckx & Slade, 2014). Other studies have shown that light negatively impacts the life-cycles of moths, retarding pupal diapause in both sexes as well as inhibiting growth in male caterpillars (van Geffen, van Grunsven, van Ruijven, Berendse, & Veenendaal, 2014). Apart from affecting moth populations directly, light pollution also causes a decrease in pollination efficiency in moths with the consequent implications on dependent plant populations (Macgregor, Evans, Fox, & Pocock, 2016) as well as gives fast-flying bat species a competitive edge on slow- flying bat species, the latter of which tend to avoid exploiting moth aggregations at artificial lights (Rydell, 1992).

Turtle hatchlings are also negatively affected by light pollution. Turtle hatchlings typically orient themselves towards the sea by exploiting the fact that the sea is more reflective than the land and thus is the brighter part of the hatchlings’ field of vision (Rich & Longcore, 2006) (Bourgeois, GilotFromont, Viallefont, Boussamba, & Deem, 2009). The presence of light pollution which is usually found in the onshore direction, hence, obviously has a disorienting effect on the hatchlings, causing them to crawl inland and be more prone to predation, death as a result of human activities (such as being killed by cars on roads nearby) or death due to dehydration by still being on land when the sun rises.

Apart from affecting hatchling land crawl, light pollution also affects orientation whilst swimming offshore both if the hatchling crawled landward prior to entering the sea (Lorne & Salmon, 2007) as well as when exposure to light occurred only when the hatchlings were already seaborne (Thums, et al., 2016). Light near nesting beaches also deters female turtles from nesting on those same beaches (Chepesiuk, 2009).

Another group affected by light pollution are members of the Procellariforms order or tubenose seabirds.

In Malta, such species would include Yelkouan Shearwater (Puffinus yelkouan), the Scopoli’s Shearwater (Calonectris diomedea) and the European Storm-petrel (Hydrobates pelagicus). All these species are nocturnal seabirds which are known to have breeding colonies in Malta. Several studies have shown that colonies on the Azores, Réunion, Kuai and Tenerife of tubenose species experience lightinduced mortalities as a result of a phenomenon known as fallout. This occurs when fledglings of such species on their first flight are attracted to bright lights at night and are consequently disoriented and grounded as a result of exhaustion. Such grounded fledglings are then more prone to die as a result of predation or accidental damage by human activity (being run over by cars for example). Thus, colonies near light-polluted areas are more likely to have higher mortality rates of young induced by artificial light at night, with potentially negative effects on the colonies’ populations. Research has not shown

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any negative effects on adult birds. (Fontaine, Gimenez, & Bried, 2011) (Le Corre, Ollivier, Ribes, & Jouventin, 2002) (Podolsky, Ainley, Spencer, Deforest, & Nur, 1998) (RodrĂ­guez & RodrĂ­guez , 2009).

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Conclusion It is clear that light pollution is a concern both for biodiversity conservation as well as for human health and, therefore, curbing the extent of its damaging effects should be a top priority for any country. The best solution for managing light pollution is to directly decrease lighting at night. However, this is not always feasible due to economic and social reasons and other alternatives need to be exploited. Light at night could be automated to become dimmer or switched off completely at times where the demand of light is not that necessary. Research has also shown that shorter wavelength light sources attract more moths than longer wavelength light sources, and thus the effect of such light sources could be mitigated by modifying their spectral composition (Somers-Yeates, Hodgson, McGregor, Spalding, & ffrenchConstant, 2013). Other solutions include designing lighting apparatus in such a way so as to lessen the amount of indirect lighting which occurs and using fluorescent or reflective lighting alternatives (Gaston, Davies, Bennie, & Hopkins, 2012).

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