Overexposure to ultraviolet (UV) radiation is considered to be a health risk, causing skin and eye damage, alongside effects on the immune system comment that ultimately compromise health. The primary protection against solar UV radiation is the stratospheric ozone layer.
The ozone layer absorbs high-energy UV rays preventing them from reaching the earth's surface. Catalytic destruction of the ozone layer, therefore, increases the amount of UV radiation act the earth's surface, exacerbating the risk-averse health effects. Therefore, the protection and restoration of the ozone layer are of the utmost importance to human health.
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What is the Ozone Layer?
The ozone layer is a region of the atmosphere located between 15 and 30 kilometers above the earth's surface. Its main function is to provide a barrier to ultraviolet radiation by filtering out these rays from the sunlight, therefore, preventing that travel to the earth's surface, protecting the atmosphere.
It is formed naturally in the topmost of the atmosphere as a consequence of the sun's UV rays. Here, ozone molecules absorb the UV, resulting in an increased temperature of the stratosphere. Vertical mixing of the layers above the atmosphere is prevented; consequently, a stable stratospheric layer is formed. Some UV does reach the ground, however. It is between 290 and 320 nm in length and is known as UV-B. It provides some health benefits, stimulating the formation of vitamin D.
Evidence for Protecting the Ozone Layer
In a seminal paper published in 1974, Molinda and Rowland described efficient catalytic destruction of the ozone as a consequence of human-made chlorofluoromethanes. These chlorofluoromethanes remain in the troposphere, however, released chlorine atoms open reaching the stratosphere; these chlorine atoms catalyze the destruction of the ozone.
In 1985, this concern of catalytic ozone destruction was increased following the discovery of the Antarctic ozone hole. Subsequent research over the next decade demonstrated that heterogeneous chlorine chemistry was capable of depleting more ozone relative to gas-phase processes alone as observed following the eruption of mountain Pinatubo.
In the 1980s, health impacts of ozone-depleting substances (ODS)-induced changes in the stratospheric ozone on the US population were studied by the United States Environmental Protection Agency (EPA). These health effects induced by exposure to ultraviolet radiation predominantly affect the eyes, skin, and immune systems. Differential health effects were observed with different wavelengths in the UV-A (400–315nm) and UV-B (315–280 nm) ranges
The Effect of UV Radiation on the Skin
The effects of ultraviolet radiation include erythema, also known as sunburn, skin aging, and increased risk of several types of cancer. These cancers include cutaneous malignant melanoma and keratinocyte cancer. Among keratinocyte cancer, the most common forms include squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Melanoma is more prevalent in those with reduced pigmentation and thinner skin. There is a correlative relationship between melanoma and exposure to the sun, as well as sunburn history.
The Effect of UV Radiation on the Eyes
UV radiation can cause cataracts to appear in the eyes, SCC to develop in the cornea or conjunctivitis, as well as other damage to the eye surface. Cataracts caused clouding of the eye’s clear lens, subsequently leading to vision impairment and blindness.
Cataracts related to age are caused by several potential factors, however, exposure to UV radiation, particularly UV-B is known to play a significant causative role. In addition, the lens of the eye can be damaged by oxidative agents. UV radiation causes the formation of such oxidative species, which can result in damaged cornea and lens.
The Effect of UV Radiation on the Immune System
The body's immunological defenses can be reduced in response to UV radiation overexposure, this can subsequently result in reactivation of latent viral infections, the increased voracity of skin cancers mediated by viruses, and an increased risk of infection. This is also known as immunosuppression.
Immunosuppression Is particularly problematic concerning infections that occur in the skin, for example, leprosy and malaria. The herpes simplex virus can be triggered by sun exposure and exemplifies an infection caused by UV-induced immunosuppression.
However, melanoma is considered to be the most lethal human health effect resulting from sun exposure; melanoma causes over 7100 deaths annually in the United States.
UV radiation can also alter organic molecules in the body, causing the formation of novel antigens; these could serve as potential triggers for the immune system.
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The Indirect Effects of UV Radiation in the Body
UV-B radiation is known to contribute to the formation of photochemical smog. This subsequently increases the concentration of ozone at the earth's surface, therefore aggravating respiratory illnesses. Moreover, a decrease in food production as a result of stratospheric ozone depletion Is likely to produce indirect health effects on humans as a result of reduced food supply. However, these effects are indirect and difficult to quantify.
International agreements to phase out ozone-depleting substances, to reduce depletion of the ozone have been in play since the Montreal protocol of 1987. Consequently, the thickness of the stratospheric ozone map is projected to reach a minimum. Most recently, a review of the effectiveness of the Montreal Protocol has hailed the protocol“been hailed as the most successful environmental treaty ever”.
In this study, long-term UV index (UVI) data taken from spectroradiometer measurements have demonstrated its success in preventing continuous increases in UV radiation. It is predicted, that in the absence of this agreement, UVI values would have increased by ~20% over the period 1900-today in mid-latitude locations, with subsequent quadrupling by the year 2100.
Due to the protocol, analysis of UVI data has demonstrated that UVI values have remained constant over the past two decades, in all seasons, with a slight decrease in the southern hemisphere (most predominantly in Antarctica where ozone depletion effects were greater).
Consequently, there is some improvement in the ozone damage, suggesting the Monreal protocol’s relative success. Continuous compliance with international agreements is essential to prevent the degradation of the stratospheric ozone – crucial to protecting human health.
References:
- McKenzie R, Bernhard G, Liley B, et al. (2019) Success of Montreal Protocol Demonstrated by Comparing High-Quality UV Measurements with "World Avoided" Calculations from Two Chemistry-Climate Models. Sci Rep. doi:10.1038/s41598-019-48625-z.
- de Gruijl FR, van der Leun JC. (2000) Environment and health: 3. Ozone depletion and ultraviolet radiation. CMAJ.
- United Nations Environment Programme, Environmental Effects Assessment Panel. Environmental effects of ozone depletion and its interactions with climate change: Progress report, 2016. (2017) Photochem Photobiol Sci. doi:10.1039/c7pp90001e.
- Barnes PW, Williamson CE, Lucas RM, et al. (2019) Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future. Nat Sustain. doi:10.1038/s41893-019-0314-2.
- Bais AF , Lucas RM , Bornman JF, et al. (2018) Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017. Photochem Photobiol Sci. doi:10.1039/c7pp90043k.
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