Solar radiation has played a fundamental role in the development of life on earth, and an adequate exposure is necessary for vitamin D production. On the other hand, overexposure is a major risk factor for several relevant adverse health effects, mainly on the eye and the skin. Moreover, the depletion of the stratospheric ozone layer currently ongoing is increasing ultraviolet (UV)-B component of solar radiation reaching the earth’s surface and, consequently, the potential for adverse health impact. High exposure to solar radiation, often well in excess of the recommended exposure limits, has been documented in several outdoor occupations, but we have to admit that sun protection is usually not considered a priority in outdoor work environments, and the vast majority of outdoor workers do not practice adequate sun safety, if any.

Exposure

Optical radiation emitted by the sun, including UV, light and infrared radiation, is filtered by the atmosphere. The infrared and visible components of the solar radiation comprise 95 % of the total radiation reaching the earth’s surface, but it is the UV component, i.e., the 5% only, responsible for most of the deleterious effects of solar exposure.

Terrestrial UV radiation is highly variable, depending upon the time of day, season, geographical latitude, stratospheric ozone, atmospheric pollutants, weather, ground reflectance and altitude and other factors. Furthermore, individual cumulative annual exposure can vary greatly due to several factors other than occupation, like cultural and social factors, outdoor activities, etc. In outdoor workers, high daily levels of UV exposure, often well in excess of recommended exposure limits, were documented in different studies, especially in agriculture (farmers, gardeners, etc), construction workers (as roofers and carpenters), roadworkers, fishers, sailors, instructors (ski instructors, mountain guides, etc), lifeguards, but also in many others. Artificial sources can also contribute to exposure, including occupations like electric arc welding, medical (as in the use of phototherapy equipment), and also lamps for cosmetic purposes.

Adverse health effects

Solar radiation exposure can induce both acute and chronic effects, largely related to the UV component.

Acute overexposure, not rare in an occupational setting, can cause various detrimental effects in the eye and skin, as photokeratitis and sunburn, as well as immunosuppression; some of the photochemical events that initiate acute effects can be also related to skin cancer.

However, in the field of occupational health and safety, the risk is usually more closely related to chronic excessive exposure. Again, the main target organs are the eye and skin.

UV exposure can induce photoaging in the skin, actinic keratoses, and cancer both in skin and eye, even if epidemiological evidence supports an association of excessive sunlight exposure with squamous cell and basal cell carcinoma (SCC and BCC respectively), and malignant melanoma, while evidence seems less conclusive for lip cancer, and ocular melanoma. Several epidemiological studies support the hypothesis that the development of SCC is related to the lifetime cumulative sun exposure, while less conclusive data are available for BCC, that seems related to both acute and chronic sun exposure, providing mixed effects of cumulative and intermittent sun exposure. High, intermittent exposure to solar UV is considered a significant risk factor for the development of malignant melanoma, and several epidemiological studies support a positive association with history of sunburn, particularly sunburn at an early age. Some very recent results show that regular sunscreen use may reduce melanoma risk. According to some data, the estimated proportion of skin melanomas related to UV exposure is 89 - 96% in males, 79 - 92 % in women. The risk of developing skin cancer (both non-melanoma skin cancer -NMSC- and melanoma) varies greatly with skin type, and is much higher in subjects with an high susceptibility to sunburn, and low tanning ability (melano-compromised). According to WHO, excessive solar UV exposure results in 60,000 premature deaths per year worldwide, 48,000 from malignant melanomas and 12,000 from skin carcinomas. Furthermore, the incidence of both NMSC and melanoma is increasing, but for melanoma data suggest an increase more rapid than any other cancer.

Concerning the eye, epidemiological data support a correlation between chronic exposure to UV and pterygium, pinguecula and droplet keratitis, but the most relevant chronic effect of UV exposure is certainly cataracts, in particular in its cortical localization. The estimated number of blind people worldwide, based on 2001 data, is 40 to 45 million: about 50% are currently blind as a result of cataracts. Of these, WHO estimates that as many as 20 % (i.e., about 4 to 5 millions) is due to UV exposure. Moreover, it is estimated that each 1% decrease in stratospheric ozone would result in a 0.5% increase in the number of cataracts related to solar UV.

A possible role of UV exposure was also hypothesized in the development of age-related macular degeneration, i.e., the leading cause of blindness among people aged 55 years and older in the U.S. and other Western countries, but overall results are still scarcely conclusive.

Protection

For an adequate protection of outdoor workers, different measures can be applied, including engineering measures, as shading structures, personal protection items, such as hats, sunglasses, protective clothing, use of sunscreens, and sun-safety training. The results of some studies on interventions to promote sun-safe practices and environments provide encouraging results. A specific problem is that of sun-sensitive workers, as may be difficult, or impossible, achieving an adequate reduction of solar UV exposure, possibly leading these individuals not to choose outdoor occupations.

Conclusions

In conclusion, epidemiological data clearly show that excessive exposure to UV solar radiation currently induce a relevant number of adverse health effects in outdoor workers, including cancer and cataracts. Apparently, this risk is largely underestimated. Outdoor workers clearly need a more adequate sun protection: the development of effective policies and interventions programs is urgently needed.

KEY WORDS

Solar radiation, ultraviolet radiation (UV), occupational exposure; acute effects; cancer, carcinoma, melanoma, cataract

Relevant references

 Lucas R, McMichael T, Smith W, Armstrong B

Solar Ultraviolet Radiation. Global burden of disease from solar ultraviolet radiation

World Health Organization (WHO) Environmental Burden of Disease Series, No. 13. Geneva, 2007

Available at the web page:  http://www.who.int/uv/health/solaruvradfull_180706.pdf

Vecchia P, Hietanen M, Stuck BE, van Deventer E, Niu S

Protecting Workers from Ultraviolet Radiation

International Commission on Non-Ionizing Radiation Protection (ICNIRP): Germany, 2007.

Available at the web page: http://www.who.int/uv/publications/Protecting_Workers_UV_pub.pdf

International Commission on Non-Ionizing Radiation Protection (ICNIRP)

ICNIRP STATEMENT—PROTECTION OF WORKERS AGAINST ULTRAVIOLET RADIATION

Health Phys 2010;99:66-87

Available at the web page: http://www.icnirp.de/documents/UVWorkersHP.pdf

International Commission on Non-Ionizing Radiation Protection (ICNIRP)

GUIDELINES ON LIMITS OF EXPOSURE TO ULTRAVIOLET RADIATION OF WAVELENGTHS BETWEEN 180 NM AND 400 NM (INCOHERENT OPTICAL RADIATION)

Health Phys 2004;87:171-86

Available at the web page: http://www.icnirp.de/documents/UV2004.pdf

 Glanz K, Buller DB, Saraiya M

Reducing ultraviolet radiation exposure among outdoor workers: State of the evidence and recommendations

Environmental Health 2007, 6:22

Available at the web page: http://www.ehjournal.net/content/6/1/22