Quantitative assessment of human exposure UVA radiation

Transcription

1 Environmental Exposure and Health 329 Quantitative assessment of human exposure UVA radiation M. G. Kimlin 1, A. V. Parisi 2, J. M. Macaranas 1 & D. J. Turnbull 1,2 1 Centre for Health Research, School of Public Health, Queensland University of Technology, Brisbane, Queensland, Australia 2 Centre for Astronomy, Solar Radiation and Climate, Faculty of Sciences, University of Southern Queensland, Toowoomba, Australia Abstract Humans are exposed to ultraviolet radiation in their normal day-to-day lives. Much research has been conducted into the impact of exposure to UVB radiation ( nm), whist research into impact of exposures to UVA radiation ( nm) is gaining momentum. Exposure to UVA radiation has been linked to increasing the risk of skin cancer, DNA damage, ocular diseases and immunosuppression. Unlike UVB radiation, UVA radiation is transmitted through material such as window glass found in offices and homes. Accordingly, humans are exposed to this radiation in environments where UV exposure is not normally associated (indoors). This paper describes a prototype UVA dosimeter that is responsive to the UVA wavelengths only and does not respond to the UVB wavelengths and how this dosimeter can be used to assess personal UVA exposure. Keywords: UVA radiation, solar UV, dosimetry. 1 Introduction Most acute responses of humans to UV exposure occur as a result of UVB exposures (280nm to 320nm), as these wavelengths are highly sensitive in creating a human biological response. However, of the solar UV radiation reaching the surface of the earth, only 5% of it comes from UVB while at least 95% of the remaining comes from UVA (320 to 400nm). This high proportion of UVA reaching the earth s surface has prompted an awareness of its likely

2 330 Environmental Exposure and Health damaging effects in our everyday life rather than in exceptional exposure conditions. It has now been clearly established that UVA plays an important role in skin photoageing, skin cancer, DNA damage, ocular diseases and immunosuppression. Unlike UVB radiation, UVA is not reduced by the ozone layer surrounding the earth and are transmitted through clouds and glass [1]. Furthermore, while 90% of UVB is blocked by the substratum corneum of the skin, over 50% of the UVA radiation received is capable of penetrating deep into the cutaneous structure as far as the papillary and reticular derma [2]. A recent study using laser capture microdissection of human skin squamous cell carcinomas and solar keratoses has revealed that UVA fingerprint mutations were detectable in the basal germinative layer in contrast with the suprabasal localization of UVB fingerprint mutations [3]. This implies that UVA is an important carcinogen in the stem cell compartment of the skin. Even if the exact mechanisms still need to be understood, photoageing, photoimmunosuppression and skin cancer involve the impact of wavelengths from 320 to 400 nm [4]. The involvement of lipid peroxidation in UVA-induced activation of matrix metalloproteinases has been demonstrated [5], which plays a role in the degradation of dermal collagen and malfunction of the connective tissue remodeling process. During challenge of normal skin with environmentally relevant doses of UVA, bioactive nitric oxide which is known to play a pivotal role in cutaneous physiology, is formed due to photodecomposition of nitrite and S-nitrosothiols. Nitrite and S-nitrosothiols could be quantified for the first time and found at concentrations times those found in the plasma levels of healthy volunteers [6]. This represents the primary basis for nitric oxide formation during UVA exposure and strengthens its role in skin aging, immunosuppression and carcinogenesis. In the light of the above impacts on human UVA exposure, the development of a UVA dosimeter becomes more imperative. A study estimating human UVA exposures from ambient UVA measurements has employed the anatomical UV exposure ratios determined for erythemal UV due to the unavailability of a suitable UVA dosimeter at the time [7]. Population exposure will be subject to a wide range of variability owing to differences in ambient UVA with latitude, in the fraction of UVA received at different anatomical sites, and in individual lifeand work-styles [7,8]. With the development of a suitable UVA dosimeter and the capacity for characterising these for the measurement of UV radiation, this variability can be quantified and analysed. In the current study we address the issue of the unavailability of a suitable UVA dosimeter for human exposure assessment by presenting results from a preliminary study developing such a tool. We also investigate the reproducibility of this tool and discuss challenges facing our group in the development of a reliable measurement tool for exposure risk assessment. We have chosen unique polymers that are responsive only to UVA radiation and the results presented provide a more detailed view on the characteristics of these polymers.

3 Environmental Exposure and Health Methods 2.1 Polymers The polymer, phenothiazine (Sigma Aldrich Chemicals), was used as the active UV sensitive film for this project. However, phenothiazine is sensitive to the entire UV spectrum (both the UVA and UVB wavelengths). Phenothiazine itself cannot be cast into a thin sheet polymer as its tensile properties cause any such casting to produce a rigid, unusable thin film sheet that disintegrates when handled. In order to create a useable polymer sheet with appropriate flexibility and tensile strength, phenothiazine was mixed with PVC to act as a substrate. Since the goal of this research is to produce a thin film dosimeter that is sensitive only to the UVA wavebands of the UV spectrum, we needed to filter out the unwanted UVB radiation. To compensate for phenothiazine s sensitivity to all UV, we used Mylar (DuPont) film to filter the UVB wavebands of the UV spectrum. Mylar has characteristics that we have carefully defined, included in this list is filtering of UVB radiation and long-term photostability. Using the Mylar/phenothiazine combination, we are able to create a spectrally sensitive dosimeter that responds only to the UVA wavebands. However, for the research presented in this paper, we are investigating the phenothiazine-pvc combination only. 2.2 UV irradiance A dual beam UV-Visible Spectrophotometer (Shimadzu Model 1700) measured the response of the phenothiazine-pvc thin film. Measurements were taken from 250nm to 700nm. For this project we used an artificial sunlight source, a solar simulator (Solar Light Co.) to irradiate the sample with UVA radiation. Careful monitoring of the output spectra allowed us to titrate a specific dose to our samples that was highly repeatable. In order to investigate the characteristics of varying experimental methodology, we conducted several variants of the time and sequence of chemical mixing. The four variants in the methodology are presented below. Method 1: g Phenothiazine and 5 g PVC were mixed together in 50 ml tetrahydrofluran (THF) and left to stand inside a fume cabinet until completely dissolved. Thin film casting and air drying for one hour. Method 2: g PH and 4 g PVC were mixed together in 50 ml THF and left to stand inside a fume cupboard until completely dissolved. Thin film casting and air drying took 1 hour. Method 3: 5 g PVC was left to dissolve in 50 ml THF inside a fume cupboard and g PH was added just before casting. The sheet was lifted from the glass after one hour. Method 4: 5 g PVC was left to dissolve in 50 ml THF inside a fume cupboard and g PH was added just before casting. The sheet was lifted after one hour.

4 332 Environmental Exposure and Health Two primary questions have guided this research into the phenothazine UVA dosimeter. First, is this polymer combination sensitive to UVA wavelengths only? Secondly, how does experimental procedure during the construction of the phenothiazine film affect its spectral and excitation properties? 3 Results and discussion Figure 1: Experimental methods 1 and UV induced response of the polymer Output absorption spectra of the experimental procedures 1 through 4 are shown in Figures 1 and 2. Data is also included in this figure showing the impact of

5 Environmental Exposure and Health 333 irradiation of various doses of UVA radiation (5 Jcm-2, 10Jcm-2, 50Jcm-2) which was provided by the solar simulator. Figure 2: Experimental procedures 3 and 4. Figures 3 and 4 present the same data, but, as a function of change in absorbancy of various irradiations compared to no irradiation. From the abovementioned figures, Methods 1, 2 and 3 produced absorption spectra of similar spectral shape and distribution, whilst Method 4 produced a spectrum that has differing properties to the other methods.

6 334 Environmental Exposure and Health Figure 3: Experimental procedures 1 and 2. It was determined that experimental Methods 1 and 2 produced films with most similar spectral properties. Method 2 had a decreased concentration of PVC, implying that PVC concentration may play a minor role in contributing to variability. Higher absorptivities of the film were observed when the same amount of phenothiazine was introduced to the mixture just before casting (Method 3), giving proportional increases in the absorbance and excitation spectra but still similar to methods 1 and 2.

7 Environmental Exposure and Health 335 Figure 4: Experimental procedures 3 and 4. This suggests that long time standing of phenothiazine solution prior to thin film casting hastens the photosensitisation process, resulting in decreased absorbance. Decreasing the phenothiazine concentration (method 4) produced quite different results from methods 1 to 3, implying that a threshold level of phenothiazine exists below which consistency of results becomes a problem. While casting and air drying procedures have been standardised, more trials on the time and sequence of mixing the chemical ingredients have to be made.

8 336 Environmental Exposure and Health 4 Discussion These data indicate that a small variation in the preparation of the phenothiazine- PVC solution has significant impacts on the spectral properties of the thin film. The data provides support for the hypothesis that we have created a material that can be sensitive to the UVA wavelengths, although this analysis suggests that the reproducibility of such thin film polymers is still questionable. It appears that the association between the phenothiazine-pvc solution concentrations is a very important consideration when casting such thin film sheets. Other factors that our group are in the process of investigating that may also influence the thin film casting include, the impact of drying time, humidity and the time taken to dissolve the phenothiazine-pvc solution. Preliminary data (unpublished) collected suggests that careful control of these environmental factors must also be considers when constructing this film. We also must be aware that for this work, we used a simulated solar spectrum, we are currently in the process of undertaking a field trial using the sun as the UV source, which may again alter the outcomes of this work. The results that we have presented in this paper suggests to that researchers need to be fully aware of the challenges facing them when undertaking such work, and the significant impact small experimental procedure changes have on the spectral sensitivity of such UV sensitive films. Acknowledgement This project is supported by a US National Institute of Health Grant, from the National Cancer Institute, number R01 CA A2. References [1] Parisi, A. V., Sabburg, J. and Kimlin, M. G. (2004) Scattered and Filtered Solar UV Measurements, Kluwer Academic Publishers, London. [2] Rougier, A. (1998) In Protection of the Skin against Ultraviolet Radiations (Eds, Rougier, A. and Scaefer, h.) John Libbey Eurotext, Paris. [3] Agar, N. S., Halliday, G. M., Barnetson, R. S. C., Ananthaswamy, H. N., Wheeler, M. and Jones, A. M. (2004) Proceedings of the National Academy of Sciences of the United States of America, 101, Marrot, L., Belaidi, J.-P. and Meunier, J.-R. (2005) Mutation Research, 571, [4] Marrot, L., Belaidi, J.-P. and Meunier, J.-R. (2005) Mutation Research, 571, [5] Polte, T. and Tyrrell, R. M. (2004) Free Radical Biology and Medicine, 36, [6] Paunel, A. N., Dejam, A., Thelen, S., Kirsch, M., Horstjann, M., Gharini, P., Murtz, M., Kelm, M., De Groot, H., Kolb-Bachofen, V. and Suschek, C. V. (2005) Free Radical Biology and Medicine, 38,

9 Environmental Exposure and Health 337 [7] Kimlin, M., Parisi, A. V. and Downs, N. D. (2003) Photochem. Photobiol. Sci., 2, [8] Kimlin, M. G., Parisi, A. V., Sabburg, J. and Downs, N. D. (2002) Photochem. Photobiol. Sci., 1,