Title Information

Bayerische Akademie der Wissenschaften (editor):

Erhöhte UV-Strahlung:
Folgen und Maßnahmen

Rundgespräch am 9. Februar 2004

Inhalt

Lecturers and discussants

Baumer, Max, Dr., Bayerische Landesanstalt für Landwirtschaft, Institut für Pflanzenbau und Pflanzenzüchtung, Freising

Behn, Anita, Dr., Bayerische Landesanstalt für Landwirtschaft, Institut für Pflanzenbau und Pflanzenzüchtung, Freising

Braun-Falco, Otto, Prof. Dr. med., München

Caldwell, Martyn M., Prof. Dr., Utah State University, Ecology Center, USA

Elstner, Erich, Prof. Dr., Technische Universität München, Lehrstuhl für Phytopathologie, Freising

* Ernst, Dietrich, Dr. habil., GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Biochemische Pflanzenpathologie, Neuherberg

Fiedler, Franz, Prof. Dr., Universität Karlsruhe, Institut für Meteorologie und Klimaforschung, Karlsruhe

* Gaube, Sabine, Dr. med., Klinik und Poliklinik für Dermatologie und Allergologie, Ludwig-Maximilians-Universität München, München

Goppel, Thomas, Staatsminister Dr., Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst, München

* Hartl, Lorenz, Dr., Bayerische Landesanstalt für Landwirtschaft, Institut für Pflanzenbau und Pflanzenzüchtung, Freising

Heller, Werner, Dr., GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Biochemische Pflanzenpathologie, Neuherberg

Herm, Dietrich, Prof. Dr., Ludwig-Maximilians-Universität München, Institut für Paläontologie und Historische Geologie, München

Hoppe, Brigitte, Prof. Dr., c/o Ludwig-Maximilians-Universität München, Lehrstuhl für Geschichte der Naturwissenschaften, München

* Höppe, Peter, Prof. Dr., GeoRisikoForschung der Münchener Rückversicherung, München

Kleinschmidt, Jürgen, Prof. Dr. Dr., Ludwig-Maximilians-Universität München, Institut für Medizinische Balneologie und Klimatologie, München

* Knoche, Richard, Dr., Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung IMK-IFU, Bereich Atmosphärische Umweltforschung, Garmisch-Partenkirchen

* Kolb, Christiane, Dr., Universität Würzburg, Lehrstuhl für Botanik II, Würzburg

* Köpke, Peter, Dr., Ludwig-Maximilians-Universität München, Meteorologisches Institut, München

Kutzschenbach, Peter von, Dr. med., Vaterstetten

Magel, Elisabeth, Prof. Dr., Universität Hamburg, Zentrum Holzwirtschaft, Abt. Holzbiologie, Hamburg

* Nießner, Reinhard, Prof. Dr., Technische Universität München, Institut für Wasserchemie und Chemische Balneologie, München

Nöth, Heinrich, Prof. Dr., Präsident der Bayerischen Akademie der Wissenschaften, München

* Papen, Hans, PD Dr., Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung IMK-IFU, Bereich Atmosphärische Umweltforschung, Garmisch-Partenkirchen

* Pfündel, Erhard, PD Dr., Universität Würzburg, Lehrstuhl für Botanik II, Würzburg

* Placzek, Marianne, Dr. med., Klinik und Poliklinik für Dermatologie und Allergologie, Ludwig-Maximilians-Universität München, München

* Riederer, Markus, Prof. Dr., Universität Würzburg, Lehrstuhl für Botanik II, Würzburg

* Schnitzler, Jörg-Peter, PD Dr., Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung IMK-IFU, Bereich Atmosphärische Umweltforschung, Garmisch-Partenkirchen

* Schubert, Michael, Bayerische Landesanstalt für Landwirtschaft, Institut für Fischerei, Starnberg

Schuberth, Christian, MR, Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst, München

* Schween, Jan, Ludwig-Maximilians-Universität München, Meteorologisches Institut, München

* Seidlitz, Harald K., Dr., GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Bodenökologie, Abt. Experimentelle Umweltsimulation, Neuherberg

Steinmann, Alexander, Dr. med., Bayerisches Staatsministerium für Umwelt, Gesundheit und Verbraucherschutz, Ref. S-3.4, München

Steinmetz, Manfred, Dr., Bundesamt für Strahlenschutz, Institut für Strahlung und Gesundheit, Oberschleißheim

Tanner, Widmar, Prof. Dr., Universität Regensburg, Lehrstuhl für Zellbiologie, Regensburg

* Werle, Peter, Dr., Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung IMK-IFU, Bereich Atmosphärische Umweltforschung, Garmisch-Partenkirchen

Werner, Dietrich, Prof. Dr., Philipps-Universität Marburg, FG Zellbiologie und Angewandte Botanik, Marburg

Willenbrink, Johannes, Prof. Dr., Universität zu Köln, Institut für Botanik, Köln

* Winkler, Peter, Dr., Deutscher Wetterdienst, Meteorologisches Observatorium Hohenpeißenberg, Hohenpeißenberg

Ziegler, Hubert, Prof. Dr., Bayerische Akademie der Wissenschaften, Kommission für Ökologie, München

Ziegler, Irmgard, Dr., GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Klinische Molekularbiologie und Tumorgenetik, München

Zinkernagel, Volker, Prof. Dr., Technische Universität München, Lehrstuhl für Phytopathologie, Freising

Vorwort

Licht ist Leben – doch Veränderungen in der Zusammensetzung des auf die Erde einfallenden Sonnenlichtes gaben in den letzten Jahren Anlass zu Besorgnis. Aufgrund des Ozonabbaus in höheren Luftschichten nahm die Intensität der ultravioletten (UV) Strahlung auf der Erdoberfläche regional und zeitlich in unterschiedlichem Maße zu. Dies hat Auswirkungen auf den Menschen und die Umwelt. So kann erhöhte UV-Strahlung Hautkrebs begünstigen, pflanzliches Wachstum mindern und die chemische Zusammensetzung der Atmosphäre verändern.

Allerdings ist UV-Licht seit jeher ein natürlicher Bestandteil des Sonnenlichtes und für manche Lebensvorgänge unbedingt notwendig. Alle Lebewesen haben Schutzfunktionen und Reparaturmechanismen entwickelt, die sie vor Schäden durch UV-Strahlung bewahren. Es stellt sich also die Frage, ob diese natürlichen Schutzsysteme auch ausreichend gegen die erhöhte UV-Strahlung abschirmen.

Das vorliegende Buch soll über die Zunahme der UV-Strahlung und ihre Folgen informieren. Im Mittelpunkt stehen dabei Messung und Vorhersage der UV-Intensität, die Risiken erhöhter UV-Strahlung für Ökosysteme und für die Pflanzenproduktion, vor allem für Wein und Gerste, sowie Gefahren für die menschliche Gesundheit. Neben neuen Ergebnissen zur Wirkung von UV-Strahlen werden Maßnahmen zum Schutz vor Schäden durch UV-Strahlen diskutiert.

Die Beiträge dieses Berichtbandes wurden im Rahmen des Bayerischen Forschungsverbundes »Erhöhte UV-Strahlung in Bayern – Folgen und Maßnahmen« (BayFORUV) erstellt, der durch das Bayerische Staatsministerium für Wissenschaft, Forschung und Kunst sowie das Bayerische Staatsministerium für Umwelt, Gesundheit und Verbraucherschutz gefördert wurde. Mit dem Buch sollen die Problematik des Themas und die wesentlichen Ergebnisse der vierjährigen Arbeit des Forschungsverbundes einer breiten Öffentlichkeit zugänglich gemacht werden.

Abstracts

Peter KÖPKE, Joachim REUDER und Jan SCHWEEN: UV-Strahlung – gestern, heute und morgen

[p. 19-28]

The erythemally weighted solar UV radiation and its dependence on solar elevation and atmospheric para­meters are discussed. Besides ozone, UV radiation is affected by clouds, aerosols, ground albedo and the altitude of the observation site.

Compared to past conditions, represented by the 60s of the last century, average UV-B radiation has increased due to a reduction in total ozone content. For the next decades a recovery of the ozone layer can be expected. Consequently UV-B radiation will decrease for cloud free conditions. This change shows an annual course with a minimum reduction during spring, while the human skin is poorly adapted to solar radiation. The effect of ozone recovery is counteracted by a reduced cloud cover in central Europe during summer in a future climate. Since cloud effects will overcompensate for the ozone effect, under consideration of cloudiness average daily UV-B exposure will increase. For UV-A radiation even a disproportionate enhancement will occur, because the counterbalancing ozone effect is not active in this wavelength region.

Peter WINKLER und Sebastian TREPTE: Einfluss veränderter Bewölkung auf die UV-Strahlung

[p. 31-38]

UV influences many biological and air chemical systems which emphasises the necessity to know long-term changes of UV. The seasonally dependent ozone decline and the trend of the thickness of the ozone layer determine the peak values of UV while clouds and their seasonally different long-term trends influence the UV-dose. In order to study the resulting long-term changes in the UV exposure a procedure was developed by which the UV radiation could be reconstructed from observed data of total ozone and global radiation, normalised to a pure Raleigh scattering atmosphere. The cloud influence is accounted for by a cloud modification factor. From the period 1990-1998 the relevant correlations are derived and applied to the period 1968-1990, where no direct UV observations are available. The method allows to explain 97 % of the UV variance which could be confirmed by independent observations. The reconstruction has been performed for the stations Hohenpeissenberg (Southern Bavaria) and Würzburg (Northern Bavaria).

Day-to-day changes of total ozone can make up –30 % resulting in a UV increase of 40 %. Clouds, especially high cirrus clouds have increased in frequency (and optical thickness) in spring and fall but decreased in summer. On a long-term basis this has enhanced the UV dose in summer and attenuated it in spring and fall.

Richard KNOCHE und Renate FORKEL: Regionale Klimaänderung und ihr Einfluss auf UV-Strahlung und Photosmog

[p. 39-46]

The changes of the global climate expected for the near future will also have an effect on the UV radiation and on tropospheric photochemistry, and therefore on the photo-smog situation in Bavaria. In order to give a quantitative estimate of the possible future development, regional simulations with the coupled climate-chemistry model MCCM were performed. Based on results of the global climate model ECHAM4, present day conditions and conditions to be expected within the next 30 to 40 years were simulated. Comparison of the two time periods shows an increase of the summer temperatures by almost 2 degrees and a significant decrease of cloudiness. Simultaneously an increase of the UV-B radiation and the emission of biogenic hydrocarbons is simulated. As a result, for Bavaria the mean daily maximum of the near surface ozone concentration will increase by nearly 10 % and this will lead to a significantly higher number of days with threshold value exceedances.

Peter WERLE, Stephan SCHERLE und Eva FALGE: Strahlungsvariabilität in einem Gerstenbestand

[p. 47-55]

Mathematical models are increasingly being used in the field of ecosystem research to describe the interactions between physiological processes and morphological structures in plant stands of different architecture. In this context, light interaction with plants is an important aspect. The spatial and temporal variability of the solar radiation has been measured in the UV and visible spectral range within and above a barley field. The probability density functions of the radiation intensity in light spots, penumbra and umbra have been investigated. Based upon plant specific (phytometric) data a 3-dimensional radiation transfer model has been applied to compare theoretical and experimental results.

Jan SCHWEEN und Peter KÖPKE: Modellierung der UV-Dosis im Gerstenbestand

[p. 57-62]

Within the Bavarian research project BayFORUV a model has been developed to calculate UV exposure within plant stands for longer periods. This model enables the calculation of the variation of irradiance due to different sun positions, and to the variability of all atmospheric parameters like total ozone content, aerosol amount and properties and also clouds. Especially the way to model cloud influence by use of the "Cloud Free Line Of Sight" concept is new. The model takes into account the growth of the plants, with its change of leaf area, the spatial distribution and the orientation of the leaves. This is important for annual plants like barley for which, as an example, the UV exposition has been calculated for the growing season in the year 2002. The plant weighted UV irradiances where calculated for ten levels within the canopy and from this the UV exposition as the cumulative UV radiation of all preceding days. Since plants have repair mechanisms for UV radiation additionally a virtual impact of UV radiation, considering especially the last days, was modeled. It was calculated under the assumption that the effect of UV radiation of the preceding days fades away exponentially.

Harald K. SEIDLITZ, Dietrich ERNST, Andreas KRINS und Werner HELLER: Erhöhte UV-Strahlung – Simulation und Risikobewertung

[p. 65-71]

Spectral biological weighting functions play a key role for the risk assessment of the detrimental potential of elevated UV-B radiation on plants. The GSF sun simulators provide an optimal environment for the determination of biological weighting functions. We show that various technical lamps can be combined in a way that the resulting spectrum is very close to the spectral composition of natural sun light. In addition diurnal and seasonal changes can also be simulated. The second part gives an introduction to biological action spectroscopy and outlines the difference between monochromatic and polychromatic weighting functions. We present a new biological weighting function for the induction of the UV screening pigment quercetin in Arabidopsis. Final conclusions are drawn by valuating our findings compared to other biological weighting functions from the literature.

Jörg-Peter SCHNITZLER, Martina ZAHN und Christa OSCHINSKI: Schäden in der Gerstenpflanze durch Sonnenstrahlung

[p. 73-80]

Experiments were carried out in order to identify the biochemical-physiological background of the non parasitic leaf spotting disease in spring barley cultivars. The data show that leaves of sensitive cultivars contain higher concentrations of O2^2–· radicals than resistant lines and that this effect is often correlated with lower activities of Cu/Zn superoxide dismutase. In addition, studies of gene expression revealed that a gene coding for a Cu/Zn SOD showed enhanced expression rates in the resistant line IPZ 24727 compared to the sensitive cultivar cv. Ricarda. Formation of O2^2–· radicals was more pronounced in light exposed parts of the leaves indicating an enhanced oxidative stress in this tissue. Microscopic analysis demonstrated the abiotic nature of the disease complex. High light intensity in general, rather than UV-B radiation, seems to be major cause for the induction of non parasitic leaf spotting.

Dietrich ERNST, Michael GÖTZ, Bernd HEIDENREICH, Werner HELLER, Andreas KRINS und Harald K. SEIDLITZ: Spektrale Abhängigkeit der Regulation von pflanzlichen Schutzpigmenten

[p. 81-87]

Spectral biological weighting functions play a key role for the risk assessment of the detrimental potential of elevated UV-B radiation on crop plants (e.g., barley). The GSF sun simulators provide an optimal environment for the determination of biological weighting functions. As a first step towards this goal the expression patterns of selected genes of the model plant Arabidopsis thaliana were analysed by using DNA microarray technology. The list of genes included: biosynthesis of aromatic compounds, antioxidative metabolism and photosynthesis. Up- as well as down-regulated genes were grouped into clusters. Based on the results obtained with Arabidopsis an experiment with barley was designed. The spectral dependency of the induction of lutonarin was very similar to that of the corresponding quercetin derivatives in Arabidopsis. The level of this type of metabolites also showed a strong increase if the plant was exposed to shortwave UV-B components. Preliminary expression data of selected homologous probes indicated an increased expression of some phenylpropanoid genes similar to Arabidopsis.

Lorenz HARTL, Anita BEHN, Günther SCHWEIZER und Max BAUMER: Resistenzzüchtung gegen die nichtparasitäre Blattverbräunung bei Gerste

[p. 89-96]

Non-parasitic leaf spots (NPLS) cause considerable yield and quality losses in barley. The spots appear just after heading date. UV-B is not exclusively responsible to trigger NPLS. For genetic characterization of NPLS resistance two anther culture-derived double haploid populations descending from the resistant breeding line IPZ 24727 were evaluated in field trials in several environments. After genotyping and construction of a molecular map QTLs (quantitative trait loci) responsible for NPLS resistance were determined. The main resistance QTL was localized on chromosome 4H. The susceptibility allel is in coupling phase near by or identical to the mlo powdery mildew resistance gene. Therefore it is arguable whether the mlo powdery mildew resistance gene is further useful under Bavarian conditions or should be replaced. The identified QTLs are the basis for the development of a marker assisted breeding program.

Erhard E. PFÜNDEL: Wirkung von UV-Strahlung auf Lebewesen

[p. 99-107]

The UV-B spectral band (280-315 nm) includes the short-wavelength part of ultraviolet radiation on Earth. Natural UV-B radiation exhibits relatively low intensities. Because of the high energy of its photons together with significant absorbance of lipids, proteins and nucleotides, UV-B has the potential to damage living matter severely. Formation of dimers of pyrimidine nucleotides due to UV radiation affects DNA-encoded information and, hence, represents central deleterious action of UV. For normal cell function, repair of DNA damage is indispensable and is carried out by specific enzymes. In addition to repair, UV avoidance and UV screening by various UV absorbing compounds are of prime importance for life on Earth. Also, UV-B radiation stimulates the synthesis of UV screening compounds in many organisms.

Christiane A. KOLB, Markus RIEDERER und Erhard E. PFÜNDEL: Sonnenbrand bei Weinbeeren

[p. 111-116]

The role of phenolics in UV-screening was investigated in berries of a white grape cultivar (Vitis vinifera L. cv. Bacchus). Flavonols and hydroxycinnamic acids were identified as the main groups of UV-absorbing phenolics. Relationships between natural radiation and the synthesis of phenolics were studied in plants that were cultivated in the absence of UV radiation in a greenhouse prior to outdoor exposure to three different light regimes: (1) the entire solar spectrum, (2) the solar spectrum minus UV-B radiation and (3) only visible radiation. During six days of exposure, flavonol synthesis was significantly stimulated by natural UV, in particular UV-B, but concentrations of hydroxycinnamic acids decreased under all conditions. While increased flavonol levels resulted in efficient UV-A shielding, UV-B shielding was incomplete probably due to decreased levels of the UV-B-absorbing hydroxycinnamic acids during exposure. Decreased UV-B-shielding might be involved in severe sunburn damage in the presence of UV-B radiation.

Michael SCHUBERT: Auswirkung der UV-Strahlung auf Fischbrut

[p. 117-123]

The influence of UV-B radiation on larval and juvenile stages of different rheophilous fish species was investigated. Fish fry showed a strong thermophilous behaviour as well as optimized growth at elevated water temperatures; that explains the use of shallow inshore habitats of running waters as nursery habitats. UV-B radiation in spring and summer is assessed to be harmful for fish fry at these habitats. The UV-B transparency differed widely between several Bavarian rivers.

For single species both solar and artificial UV-B radiation caused increased mortality, reduction of number and size of goblet cells (mucus secreting cells) in the dorsal epidermis, and proliferation of dorsal epidermis. Also an increased expression of heatshock proteins (Hsp's) was detected. A direct connection of artificial UV-B radiation with DNA damage as well as with activity of genes participating in DNA repair systems was found and also an influence of artificial UV-B radiation on swimming behaviour was ascertained.

Hans PAPEN, Thomas HEUSER, Robert J. FISCHBACH und Wolfgang ZIMMERT: Folgen der UV-Strahlung für Mikroorganismen auf Pflanzenblättern

[p. 125-132]

Leaf surfaces of plants are colonised by microorganisms, which might influence the health of the leaves they are living on in a positive or negative way. In the next years and decades the UV-B level on earth is supposed to be different from today, which might have influence on plants and microorganisms. The objective of the project was, therefore, to determine the influence of UV-B radiation on epiphytic microorganisms on leaf surfaces of English oak (Quercus robur L.), an important tree in Germany. Neither by classical microbiological techniques nor by molecular biological methods an influence of UV-B radiation on epiphytic microorganisms on leaves of English oak could be detected. On the other hand, the colonisation density was clearly influenced by the experimental site: the amounts of epiphytes decreased with increasing altitude of the exposition sites. Furthermore, a large variability in colonisation density from leaf to leaf was observed.

Sabine GAUBE und Marianne PLACZEK: UV-Strahlung und menschliche Gesundheit

[p. 135-146]

The skin as contact and border organ is notably exposed to environmental factors, especially to sunlight. The solar radiation consists of UV-B, UV-A, visible light and infrared. Radiation with shorter wavelengths is absorbed by the atmosphere. The knowledge about certain wavelengths causing special damage by UV-B (280-315 nm) or UV-A (315-400 nm) is important for protective measures. This is of special interest for territories with great differences in geographic heights and therefore different UV intensities and different UV spectra (e.g. like in Bavaria). Passing an individually different threshold dose of sun radiation leads necessarily to dermatitis solaris (sunburn reaction) and – without any prior visible redness – to pigmentation (bronzing). Dermatolo­gically, sunlight reactions that are based on photosensitization are particularly interesting: specific substances, that are externally applied on the skin or internally taken in as drugs, result in increased radiation sensitivity. The underlying process may be toxic or allergic (phototoxicity or photoallergy). Porphyria is due to endogenous photosensitizing substances that are augmented. The frequent clinical picture polymorphus light eruption and more seldom diseases like light urticaria are presumably based on photosensitization on unknown substances, as well; they develop rapidly after sun radiation. Reactions with latency over years or decades must be looked at separately. Long-time UV radiation leads to premature skin aging (photoaging) that can be accounted as a harmless cosmetic damage. UV radiation is the major etiologic factor for the development of skin tumors that have grave consequences for the human skin. The locally destructive basal cell carcinoma and the squamous cell carcinoma, that is able to metastasise, are very frequent. Because it is rapidly metastasising, the malignant melanoma has to be considered as the most dangerous skin cancer. As a consequence, it is of utmost importance to develop effective preventive measures, which can be implemented easily.

Marion LACKHOFF und Reinhard NIESSNER: Schadstoffabbau durch UV-Strahlung

[p. 149-154]

During photocatalysis natural UV radiation is used to degrade harmful substances and pollutants. Hereby irradiation energy of the sun is first absorbed by very small particles and afterwards carried to active sides, which degrade even persistent pollutants. The question of this project was which particles are capable of eliminating persistent pollutants. Therefore solutions of the herbicide atrazine were mixed with different particles and irradiated by simulated sunlight. Atrazine degradation by model catalysts like the white pigment powder titanium dioxide was very fast, whereas with environmental particle samples (different soil particles or aerosols like soot, fly ash and road dust) no significant photocatalytic activity was observed. Thus photocatalysis by aerosol or soil particles appears not to enhance atrazine degradation in the environment. However, the degradation of harmful substances by photocatalysis could be used by exposing the most active particles to natural sunlight in the environment. As a result of this project it could be shown that the irradiation of titanium dioxide containing cement samples increases atrazine degradation significantly.

Peter HÖPPE, Andreas OPPENRIEDER, Peter KÖPKE, Jochen REUDER, Meinhard SEEFELDNER und Dennis NOWAK: Auf den Menschen bezogene Messung von UV-Strahlung

[p. 155-162]

Intensities of UV radiation are usually measured for horizontal surfaces, as e. g. the internationally used UV index. To specify the relevant UV exposure for the human body or parts of its surface the characterization of irradiances on inclined surfaces typical for the human body is needed. Therefore a measuring system was designed and built three times to record erythemally weighted irradiances in 27 directions within two minutes and simultaneously on a horizontal surface. By the end of this study more than 3000 measuring days at five different locations could be completed. The data provide a statistical base for the calculation of average UVI values on inclined surfaces at five locations in Bavaria. The UV-irradiance of the inclined compared to the horizontal surface at most was 60 % higher on the mountain Zugspitze in winter and 40 % higher in Munich. The UVI data also were combined with a virtual surface model of the human body and by this the UV exposure of the human body could be visualized.

GAUBE, Sabine, Urs KERKMANN, Bernhard PRZYBILLA und Marianne PLACZEK: Schutz vor UV-Strahlung durch Antioxidantien

[p. 163-171]

Ultraviolet (UV) radiation from the sun is the main etiologic factor in the genesis of malignant skin tumors, which have become extremely frequent. Therefore, it is important to develop implementable and effective preventive measures. In a former study we had shown that oral intake of the antioxidants ascorbic acid (vitamin C) and d-alpha-tocopherol (vitamin E) for 8 days reduced sunburn sensitivity significantly. Now we found that blood levels of ascorbic acid and d-alpha-tocopherol increased significantly after the 3 months’ intake of these antioxidants. This was again associated with a significant reduction of sunburn sensitivity, and this effect after longer intake of antioxidants was more pronounced than in the previous study. Further indicators of a UV-protective effect of antioxidants were – compared to baseline – a reduction of cyclooxygenase-2-expression (parameter for inflammatory reactions), of thymine dimers (DNA damage) and of cell proliferation (extended repair time) in UV-B-irradiated skin biopsies. In tests with cultured melanoma cells we found in cells treated with ascorbic acid and trolox (vitamin-E-analogue) an enhancement of UV-induced cell cycle blocks, which are necessary for DNA repair. On the other hand UV-induced direct DNA damage was only marginally reduced with antioxidant treatment. The UV-protective effect of ascorbic acid and d-alpha-tocopherol seems to depend mainly on an enhancement of UV-induced cell cycle blocks, which are important for DNA repair. It has to be investigated in clinical trials, whether antioxidants can inhibit photocarcinogenesis in humans.