Carcinogenic potential of solar radiation and artificial sources of UV radiation

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1 Carcinogenic potential of solar radiation and artificial sources of UV radiation 1 Introduction Exposure of the eyes and skin to ultraviolet radiation may lead to both acute and long-term damage. Where exposure to UV radiation occurs at the workplace, suitable protective measures must therefore be taken in order to prevent such damage. The possible long-term damage includes the incidence of certain forms of skin cancer. A topical question is whether cases of skin cancer caused by exposure to UV radiation at the workplace should be recognized as an occupational disease. The differences between exposure to solar UV radiation and to artificial sources of UV radiation in terms of their causation of skin cancer is an issue relevant both to the prevention of occupational diseases and to the process of recognition of cases. 2 Optical radiation Optical radiation is a form of electromagnetic wave. Besides UV radiation, it includes visible radiation (which we experience as light) and infrared radiation. Optical radiation is characterized by its wavelength. Wavelengths are stated in nanometres (nm): one nanometre is equal to a billionth of a metre. Ultraviolet radiation lies in the wavelength range between 1 nm and 4 nm, visible radiation in that between 4 nm and 8 nm, and infrared radiation in that between 8 nm and 1,, nm. Ultraviolet radiation is subdivided further into UV-C (with a wavelength of between 1 nm and 28 nm), UV-B (28 nm to 315 nm) and UV-A (315 to 4 nm) radiation. Sources of optical radiation may emit radiation at a number of wavelengths. The radiation spectrum (also referred to as the spectral distribution) indicates the intensity of the radiation at particular wavelengths. Figures 1 and 2 (see Page 4) show, by way of example, the spectral distribution of solar radiation (blue, right-hand side) and that of a welding arc (red, across the full wavelength range) in the ultraviolet range. 2.1 Solar radiation Solar radiation spectra have the following characteristics: they begin in the ultraviolet range at around 29 nm; they peak in the visible range; and they extend into the infrared range [1]. At the earth's surface, however, a solar radiation spectrum possesses no components with a wavelength below 29 nm, since such radiation components are absorbed by the earth's atmosphere. There is not just one solar radiation spectrum, but a number of spectra. These differ according to the sun's height above the horizon (Figure 3, see Page 5). When the sun is very high above the horizon (in Germany, up to a maximum of approximately 62 ), the spectrum contains more ultraviolet and blue components. In the morning and evening, when the sun is only just above the horizon, strong ultraviolet and blue components are missing from the spectrum, and it exhibits greater red components, i.e. it is displaced towards longer wavelengths. The total intensity of the radiation is also much lower when the sun is low on the horizon than when it is high. In addition, the spectrum of solar radiation is influenced by the amount of cloud cover and by scatter of the solar radiation caused by air molecules. The scatter produces a blue sky with a high ultraviolet component. Carcinogenic potential of sources of optical radiation (June 211) Page 1 of 8

2 2.2 Artificial sources of radiation Artificial sources of radiation may emit different spectra. They exhibit either radiation at a single wavelength only (e.g. HeNe laser pointers with a characteristic red colour), a wide wavelength distribution (a light-bulb which appears white), or a superposition of individual radiation lines (fluorescent lamps). A number of radiation sources which radiate in the ultraviolet range exist at workplaces: welding arcs, gas burners for glass treatment, UV lamps for testing for microcracks, UV lamps for the drying of printing ink and adhesives, UV lamps for sterilization, etc. Their spectra may encompass a wide range of wavelengths (e.g. arcs arising during arc welding, gas burners), or they may be limited to particular areas (e.g. the use of UV-A radiation for microcrack testing, or of UV-C radiation for sterilization) (see Figures 4 to 9, pp. 5 to 8). They may vary strongly in their intensity, from a low intensity (as in the case of UV lamps used to check banknotes for forgeries) to an extremely high intensity (as in the case of UV web printing). Arc-welding methods may give rise to a UV radiation intensity as high as 1,5 times that of the strongest UV radiation intensity caused by the sun. 3 The effects of UV radiation upon the skin The effects of optical radiation upon unprotected human skin depend upon factors including the level and duration of the radiation intensity, and also its spectral distribution. Different wavelengths may differ in the strength of a particular effect. A particular effect is described in this context as the action spectrum. For example, the erythemal action spectrum s er ( )[2] is frequently used in dermatology to describe the causation of skin erythema (sunburn) by radiation. A different action spectrum is used to describe the causation of skin cancer, namely the NMSC action spectrum, s nmsc ( ). NMSC stands for non-melanoma skin cancer, and covers the action of squamous cell carcinoma and basal-cell carcinoma. The s nmsc ( ) action spectrum for non-melanoma skin cancer was published by the International Commission on Illumination (CIE) in document CIE S 19 [3]. This action spectrum is based upon the results of animal tests which were then recalculated for human skin. A substantial contribution was made by co-operation between dermatologists in Utrecht and experts in Philadelphia; for this reason, the identified action spectra are also known as SCUP-m (Skin Cancer Utrecht Philadelphia) for mice, and SCUP-h [4] for human beings. The CIE action spectrum s nmsc ( ), which now enjoys international recognition, was derived from the SCUP-h action spectrum. The s nmsc ( ) action spectrum is shown in Figures 1 and 2 (green curve in the middle of the graph). Its values range from to 1; its maximum equates to a wavelength of = 299 nm. It is located primarily within the UV-B range, and to a small degree also in the UV-A range. This is consistent with current findings: skin cancer is known to be caused primarily by UV-B radiation, and to a small degree by UV-A radiation. The precise characteristic of an action spectrum for human skin cancer remains unknown; the standardized action spectrum s nmsc ( ) to CIE S 19 is however regarded as a close approximation for this purpose. In order for the carcinogenic action of an instance of radiation to be determined, the value of a radiation spectrum at each wavelength is multiplied by the associated value of the action spectrum s nmsc ( ). The results for all wavelengths are then summated. The result is the NMSC effective irradiance E nmsc. This describes the carcinogenic potential of an instance of radiation. If the NMSC effective irradiance E nmsc is multiplied by the duration t exp of exposure of the skin to the radiation, the result is the effective NMSC radiation exposure H nmsc. This is also referred to as the UV radiation dose or simply as the UV dose. Together with other factors, the effective NMSC radiation exposure H nmsc determines the probability of non-melanoma skin cancer occurring following years of exposure of the skin to UV radiation. Carcinogenic potential of sources of optical radiation (June 211) Page 2 of 8

3 4 Carcinogenic action of solar radiation and of artificial sources of UV radiation How high is the carcinogenic potential of artificial sources of UV radiation at workplaces, compared to solar radiation? This depends, among other things, upon the level of the radiation component in the range of the action spectrum s nmsc ( ), i.e. how much radiation intensity falls within the range marked in green in the middle of Figure 1. This is equally true for solar radiation and radiation from artificial sources. In order to illustrate this more clearly, the solar radiation spectrum is shown in Figure 2 magnified by a factor of 15. The UV radiation from a high sun under low-cloud conditions has a correspondingly high carcinogenic potential. Morning and evening sunshine contains far fewer UV radiation components (Figure 3). Accordingly, its carcinogenic potential is low to zero. Arcs arising during arc welding exhibit radiation components in the UV-C, UV-B and UV-A range, fall within the area of the action spectrum s nmsc ( ) marked in green in the middle of Figure 1, and therefore have a carcinogenic potential. Where other artificial sources of radiation are concerned, the presence of carcinogenic components is dependent upon the emitted spectrum. Crack testing by means of UV-A radiation (Figure 5) and the use of a hand-held lamp for glass bonding (Figure 8) give rise only to a very low carcinogenic potential. Conversely, the UV dryers studied on a printing machine (Figure 4), the UV drying of adhesives (Figure 6), MAG welding (Figure 7) and the gas flame used for glass treatment (Figure 9) present a high carcinogenic potential. 5 Conclusion In addition to solar radiation, workplace exposure to optical radiation from artificial UV sources may cause skin cancer when a relevant radiation component within the range of the s nmsc ( ) action spectrum is present and the person exposed is unprotected. 6 Bibliography [1] Leitfaden Nichtionisierende Strahlung Sonnenstrahlung. FS-6-13/2-AKNIR. Published by: Fachverband für Strahlenschutz, 26 [2] ISO 17166:1999/CIE S7-1998: Erythema Reference Action Spectrum and Standard Erythema Dose [3] ISO 2877:26 (CIE S19/E:26): Photocarcinogenesis action spectrum (nonmelanoma skin cancers) [4] de Gruijl, F.R.; van der Leun, J.C.: Estimate of the wavelength dependency of ultraviolet carcinogenesis in humans and its relevance to the risk assessment of a stratospheric ozone depletion. Health Phys. Vol. 67 (1994), pp Author: Dr. Harald Siekmann, Institut für Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung (IFA), Sankt Augustin Carcinogenic potential of sources of optical radiation (June 211) Page 3 of 8

4 Spektrenvergleich Schweißen Sonnenstrahlung nmsc-wirkung relative Einheiten Wellenlänge [nm] Figure 1: Radiation spectrum of the sun at the zenith (blue, bottom right) and of a welding arc (red, throughout the range). For interpretation, the action spectrum s nmsc ( ) (green, middle of the graph) for causation of nonmelanoma skin cancer is shown. UV radiation range shown: 2 to 4 nm. Spektrenvergleich 14 Schweißen Sonnenstrahlung nmsc-wirkung 12 1 relative Einheiten Wellenlänge [nm] Figure 2: The same spectra as shown in Figure 1. The solar spectrum (blue, right) is however shown here at 15 times the magnitude, in order to illustrate more clearly what component of it falls within the range of the action spectrum s nmsc ( ) (green, centre). Carcinogenic potential of sources of optical radiation (June 211) Page 4 of 8

5 Sonnenspektren am in Sankt Augustin 5 Stunden davor Sonnenhöchststand 4 Stunden danach 1,8 1,6 1,4 1,2 E in W/(m² nm) 1,8,6,4, Figure 3: Solar spectra with the sun at its highest point (blue, top), four hours later (green, centre), and five hours earlier (orange, bottom). The spectra in the ultraviolet and visible wavelength ranges from 2 to 8 nm are shown. Solar spectra contain components in the UV range of varying level, according to the sun's position. 4 3 E in mw/(m²nm) Figure 4: Radiation spectrum of a UV dryer on a printing machine (wavelength range from 2 to 8 nm) Carcinogenic potential of sources of optical radiation (June 211) Page 5 of 8

6 ,6,5 E in W/(m² nm),4,3,2, Figure 5: Radiation spectrum of a UV lamp for fluorescence analysis of workpieces for microcracks (wavelength range from 2 to 8 nm),14,12,1 E in W/(m² nm),8,6,4, Figure 6: Spectrum of a lamp for the drying of adhesive bonds with UV radiation (wavelength range from 2 to 8 nm) Carcinogenic potential of sources of optical radiation (June 211) Page 6 of 8

7 ,5,4 E in W/(m²nm),3,2, Figure 7: Spectrum of a MAG welding arc (wavelength range from 2 to 8 nm) E in mw/(m² nm) Figure 8: Spectrum of a hand-held lamp for the curing of glass bonds (wavelength range from 2 to 8 nm) Carcinogenic potential of sources of optical radiation (June 211) Page 7 of 8

8 1 8 E in mw/(m² nm) Figure 9: Spectrum of the flame of a gas burner for the treatment of glass workpieces (wavelength range from 2 to 8 nm) Carcinogenic potential of sources of optical radiation (June 211) Page 8 of 8