Occupational Exposure to Ultraviolet Radiation and Risk of Non-Melanoma Skin Cancer in a Multinational European Study

Background

Studies suggest that ambient sunlight plays an important role in the pathogenesis of non-melanoma skin cancers (NMSC). However, there is ongoing controversy regarding the relevance of occupational exposure to natural and artificial ultraviolet radiation (UV) radiation.

Objectives

We investigated potential associations between natural and artificial UV radiation exposure at work with NMSC in a case-control study conducted in Hungary, Romania, and Slovakia.

Methods

Occupational exposures were classified by expert assessment for 527 controls and 618 NMSC cases (515 basal cell carcinoma, BCC). Covariate information was collected via interview and multiple logistic regression models were used to assess associations between UV exposure and NMSC.

Results

Lifetime prevalence of occupational exposure in the participants was 13% for natural UV radiation and 7% for artificial UV radiation. Significant negative associations between occupational exposure to natural UV radiation and NMSC were detected for all who had ever been exposed (odds ratio (OR) 0.47, 95% confidence interval (CI) 0.27–0.80); similar results were detected using a semi-quantitative metric of cumulative exposure. The effects were modified by skin complexion, with significantly decreased risks of BCC among participants with light skin complexion. No associations were observed in relation to occupational artificial UV radiation exposure.

Conclusions

The protective effect of occupational exposure to natural UV radiation was unexpected, but limited to light-skinned people, suggesting adequate sun-protection behaviors. Further investigations focusing on variations in the individual genetic susceptibility and potential interactions with environmental and other relevant factors are planned.     

Seasonal fluctuations in leaf phenolic composition under UV manipulations reflect contrasting strategies of alder and birch trees

Seasonal variation in leaf phenolic composition may be important for acclimation of plants to seasonal changes in their biotic and abiotic environment. For a realistic assessment of how plants respond to solar UV‐B (280–315 nm) and UV‐A (315–400 nm) radiation, seasonal variation in both environment and plant responses needs to be taken into account. This also has implications for studies concerning stratospheric ozone depletion and resulting increased UV‐B radiation, as other environmental variables and/or plant phenology could interact with UV radiation. To elucidate this, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds was measured during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees. Our results showed changes in concentration of, e.g. hydrolyzable tannins in birch that suggest an effect of UV‐A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV‐B irradiance and both linear and quadratic effect for UV‐A in second‐degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites; hence, the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation.     

Stress tolerance of soil fungal communities from native Atlantic forests,reforestations, and a sand mining degraded area

Microorganisms are essential to the functionality of the soil, particularly in organic matter decomposition and nutrient cycling, which regulate plant productivity and shape the soil structure. However, biotic and abiotic stresses greatly disrupt soil fungal communities and, thereby, disturb the ecosystem. This study quantified seasonal tolerances to UV-B radiation and heat of fungal communities, which could be cultured, found in soil from two native Atlantic forest fragments called F1 and F2, five reforested areas (RA) planted in 1994, 1997, 2004, 2007, and 2009 with native species of the Atlantic forest, and one sand mining degraded soil (SMDS). The cold activity of the soil fungal communities (FC) from the eight different areas was also studied. Higher tolerance to UV-B radiation and heat was found in the FC from the SMDS and the 2009RA, where the incidence of heat and UV radiation from sun was more intense, which caused selection for fungal taxa that were more UV-B and heat tolerant in those areas. Conversely, the FC from the native forests and older reforested sites were very susceptible to heat and UV-B radiation. The cold activity of the soil FC from different areas of the study showed an erratic pattern of responses among the sampling sites. Little difference in tolerance to UV-B radiation and heat was found among the FC of soil samples collected in different seasons; in general soil FC collected in winter were less tolerant to UV-B radiation, but not for heat. In conclusion, FC from SMDS soil that receive intense heat and UV radiation, as well as with low nutrient availability, were more tolerant to both UV-B radiation and heat.     

UV responses of Lolium perenne raised along a latitudinal gradient across Europe: a filtration study

Lolium perenne (cv. AberDart) was grown at 14 locations along a latitudinal gradient across Europe (37-68°N) to study the impact of ultraviolet radiation (UV) and climate on aboveground growth and foliar UV-B absorbing compounds. At each location, plants were grown outdoors for 5 weeks in a replicated UV-B filtration experiment consisting of open, UV-B transparent (cellulose diacetate) and UV-B opaque (polyester) environments. Fourier transform-infrared spectroscopy was used to compare plant metabolite profiles in relation to treatment and location. UV radiation and climatic parameters were determined for each location from online sources and the data were assessed using a combination of anova and multiple regression analyses. Most of the variation in growth between the locations was attributable to the combination of climatic parameters, with minimum temperature identified as an important growth constraint. However, no single environmental parameter could consistently account for the variability in plant growth. Concentrations of foliar UV-B absorbing compounds showed a positive trend with solar UV across the latitudinal gradient; however, this relationship was not consistent in all treatments. The most striking experimental outcome from this study was the effect of presence or absence of filtration frames on UV-absorbing compounds. Overall, the study demonstrates the value of an European approach in studying the impacts of natural UV across a large latitudinal gradient. We have shown the feasibility of coordinated UV filtration at multiple sites but have also highlighted the need for open controls and careful interpretation of plant responses.     

Response to challenging dose of X-rays as a predictive assay for molecular epidemiology

Human biomonitoring, as a tool to identify health risk from environmental exposures, has gained increasing interest especially in the areas of cancer risk assessment and response to therapy. Chromosome aberrations resulting from direct DNA breakage or from inhibition of DNA repair or synthesis, as measured in peripheral blood lymphocytes, have been used successfully in the assessment of environmental health. Susceptibility to the induction of genotoxicity has been evaluated by the use of an in vitro challenge dose of UV or X-rays. In this report, DNA damage was analyzed with the use of single cell gel electrophoresis (SCGE) assay in healthy donors and cancer patients. Studies have shown a good correlation between DNA damage induced in vivo or in vitro and cytogenetic measures. Results from studies on susceptibilities and repair competence in 475 controls, exposed workers and cancer patients are discussed. The possible effects of exposures and influence of the diet and other confounding factors are shown. The prospective use of a challenging dose of radiation combined with the SCGE assay as a predictive assay is suggested and the limitations are discussed.     

Who, what, where and when-influences on cutaneous vitamin D synthesis

The synthesis of vitamin D in skin is a two-stage process that begins with the production of previtamin D after irradiation of 7-dehydrocholesterol by ultraviolet (UV) radiation. A number of personal and environmental factors control the probability of a suitable UV photon reaching a molecule of 7-dehydrocholesterol in the skin. These are astronomical factors that govern the solar zenith angle (SZA), and the local state of the atmosphere, determining the available solar UV radiation; skin pigmentation and age, determining competing absorbers of UV radiation and available 7-dehydrocholesterol; individual behaviour in the local surroundings, determining exposure of unprotected skin to available UV radiation. The only one of these influences that can be determined unequivocally for any situation is the SZA. The other influences must be considered either as individual case studies, or be represented by "typical" and "idealised" situations for the weather, skin and behaviour. At large SZAs there is insufficient solar UV radiation to initiate significant vitamin D synthesis. At smaller SZAs assessment of solar exposure necessary for vitamin D synthesis can only be indicative and application of any such assessment necessarily requires awareness of both self- and the local environment.     

Ultraviolet radiation, toxic chemicals and amphibian population declines

Abstract. As part of an overall ‘biodiversity crisis’, many amphibian populations are in decline throughout the world. Numerous factors have contributed to these declines, including habitat destruction, pathogens, increasing ultraviolet (UV) radiation, introduced non‐native species and contaminants. In this paper we review the contribution of increasing UV radiation and environmental contamination to the global decline of amphibian populations. Both UV radiation and environmental contaminants can affect amphibians at all life stages. Exposure to UV radiation and to certain contaminants can kill amphibians and induce sublethal affects in embryos, larvae and adults. Moreover, UV radiation and contaminants may interact with one another synergistically. Synergistic interactions of UV radiation with contaminants can enhance the detrimental effects of the contaminant and UV radiation.     

The effect of UV irradiation on uracil thin layer measured by optical waveguide lightmode spectroscopy

The polycrystalline uracil thin-layer dosimeter is a well-established method to monitor the biological effects of the environmental ultraviolet (UV) radiation. It is based on the optical density (OD) decrease of the uracil layer in the UV absorption band due to photodimerization of the crystal caused by UV irradiation. In the present study, we report measurements made with optical waveguide lightmode spectroscopy (OWLS) to characterize the changes in the optogeometrical parameters of the uracil layer caused by an artificial UV source. It is shown that UV irradiation causes a decrease in the refractive index and an increase of the optical anisotropy. The determined kinetic parameters of the UV dose-sensor response curves correlate well with results of OD measurements, but the sensitivity of OWLS is about ten times higher. The results show that OWLS is capable of analyzing the UV response of the uracil layer and opens the way for dosimetrical applications.     

On-line sterilization of cheese whey using ultraviolet radiation

The effectiveness of ultraviolet radiation for on-line sterilization of cheese whey was investigated. The effects of flow rate and residence time on the performance of three UV reactors having different gap sizes (18, 13, and 6 mm) were studied. Six flow rates and six residence times were tested with the three UV reactors. The cheese whey used in this study had a very high turbidity (4317 NTU), very poor transmittance in the UV radiation germicidal range ( approximately 0%), and high percentage of large solid particles ( approximately 20% > 100 microm). Although the cheese whey physical characteristics showed low probability of sterilization using UV radiation, the study showed that UV radiation can be used on-line to sterilize cheese whey if the proper reactor gap size and the appropriate residence time are used. There were combined effects of the flow rate and gap size. The cell removal efficiency increased with increases in residence time and decreases in the UV reactor gap size. Removal efficiency of 100% was not achieved in this study with the first UV reactor (18-mm gap size), whereas 100% removal efficiency was achieved with the second (13-mm gap size) and third (6-mm gap size) UV reactors at residence times of 2.0 and 0.5 h, respectively. The microbial decay rates achieved in this study were 4.94, 7.62, and 20.9 h(-)(1) using the first, second, and third UV reactor, respectively. Residence times of 3.3, 2.1, and 0.8 h would be required to completely destruct a microbial population of 5.95 x 10(6) cells/mL using the first, second, and third UV reactors, respectively. Although cheese whey sterilization using UV radiation seems to be a good alternative to pasteurization, increases in cheese whey temperature resulted in lamp fouling. If online sterilization is to be used, the fouling problem should be investigated and a maintenance scheme for the UV reactor should be developed.     

The lizard Psammodromus algirus (Squamata: Lacertidae) is darker at high altitudes

Altitudinal gradients offer a good opportunity to study organisms' adaptations to clinal environmental variables. Regarding altitude, the most influential variables on organisms are temperature and ultraviolet (UV) solar radiation, the first decreasing and the second increasing with altitude. Both variables affect ectotherms' biology, as ectotherms depend on environmental temperature for thermoregulation, frequently being heliotherms. Here, we studied dorsal coloration in the lizard Psammodromus algirus (Linnaeus, 1758) along a wide altitudinal gradient (2200 m) in Sierra Nevada (south‐east Spain). We hypothesize that the skin will be darker with altitude, i.e. in environments with lower temperatures and higher UV radiation intensity. Results show that individual dorsal colorations became darker at high altitude. We propose two non‐mutually exclusive explanations for this result: (1) darker dorsal surface would favour faster warming at high altitudes, where temperature is lower, and (2) darker dorsal surface would protect against UV radiation, stronger at high altitudes. We found significant relationships between both temperature and UV radiation and population dorsal darkness, giving mixed support for the two explanations. Moreover, dorsal hue was positively correlated with substrate hue, suggesting that hue evolved to maximize crypsis. Our study therefore suggests that geographical variation in dorsal coloration in this lizard is adaptive, and darkness coloration might have evolved in response to adverse conditions (low temperature and high UV radiation) at high altitudes. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 132–141.     

Ultraviolet-B Wavelengths Regulate Changes in UV Absorption of Cleaner Fish Labroides dimidiatus Mucus

High-energy wavelengths in the ultraviolet-B (UVB, 280-315 nm) and the UVA (315-400-nm) portion of the spectrum are harmful to terrestrial and aquatic organisms. Interestingly, UVA is also involved in the repair of UV induced damage. Organisms living in shallow coral reef environments possess UV absorbing compounds, such as mycosporine-like amino acids, to protect them from UV radiation. While it has been demonstrated that exposure to UV (280-400 nm) affects the UV absorbance of fish mucus, whether the effects of UV exposure vary between UVB and UVA wavelengths is not known. Therefore, we investigated whether the UVB, UVA, or photosynthetically active radiation (PAR, 400-700 nm) portions of the spectrum affected the UV absorbance of epithelial mucus and Fulton’s body condition index of the cleaner fish Labroides dimidiatus. We also compared field-measured UV absorbance with laboratory based high-performance liquid chromatography measurements of mycosporine-like amino acid concentrations. After 1 week, we found that the UV absorbance of epithelial mucus was higher in the UVB+UVA+PAR treatment compared with the UVA+PAR and PAR only treatments; after 2 and 3 weeks, however, differences between treatments were not detected. After 3 weeks, Fulton’s body condition index was lower for fish in the UVB+UVA+PAR compared with PAR and UVA+PAR treatments; furthermore, all experimentally treated fish had a lower Fulton’s body condition index than did freshly caught fish. Finally, we found a decrease with depth in the UV absorbance of mucus of wild-caught fish. This study suggests that the increase in UV absorbance of fish mucus in response to increased overall UV levels is a function of the UVB portion of the spectrum. This has important implications for the ability of cleaner fish and other fishes to adjust their mucus UV protection in response to variations in environmental UV exposure.     

The solar UV radiation level needed for cutaneous production of vitamin D3 in the face. A study conducted among subjects living at a high latitude (68 degrees N).

Populations at high latitudes experience several winter months with insufficient UV solar radiation to induce a significant cutaneous production of vitamin D. This unique study was designed to pursue an in vivo threshold of UV radiation needed for cutaneous production of vitamin D to take place if only the face was exposed to UV radiation. The vitamin D status were measured by analyzing blood samples weekly from a study group of 15 subjects over a period of 2 months during late winter, when UV radiation can be expected to increase substantially from rising solar elevations. Statistical analysis showed no significant positive association between the mean UV radiation dose and the mean 25(OH)D (25-hydroxy vitamin D) for the group. On an individual basis, however, we found indications that subjects with very low initial concentration of 25(OH)D (<30 nmol l(-1)) seemed to respond to UV radiation as early as in the beginning of March. For other individuals diet seemed to be the dominant controlling factor for 25(OH)D levels.     

着生藻类和浮游藻类在三峡库区河流健康评价中的适宜性比较研究

藻类对水体环境变化敏感,其种类和数量与环境因素有密切联系并因环境的变化而发生变化,因此藻类常作为河流健康评价的指示生物。水体中的藻类根据生活习性不同分为着生藻类和浮游藻类,在河流健康评价中,以往的工作中有的采用浮游藻类用于河流健康评价,有的采用着生藻类用于评价,但浮游藻类和着生藻类究竟何者用于河流健康评价更适宜,抑或是二者在用于评价的适宜性上没有明显差别,迄今为止未开展过深入研究。选择三峡库区内的两条河流嘉陵江和乌江作为研究对象,于2015年9月,在两条河流上共布设11个研究断面,对嘉陵江、乌江的水环境理化因子、着生藻类和浮游藻类群落进行调查研究,应用着生藻类生物完整性指数(Periphytic algal index of biological integrity,Pe-IBI)和浮游藻类生物完整性指数(Phytoplankton index of biological integrity,Ph-IBI),并结合水体综合污染指数(Comprehensive pollution index,CPI),对嘉陵江、乌江的健康状况进行评价。研究结果表明,采用着生藻类生物完整性评价(Pe-IBI)能筛选出7个核心生物参数(藻类总分类单元数、蓝藻总分类单元数、绿藻总分类单元数、菱形藻比例、优势分类单元比例、香农多样性指数、均匀度)用于河流健康评价,着生藻类生物完整性指数(Pe-IBI)与水体综合污染指数(CPI)具有极显著的负相关关系,并且与水体中总氮、铅含量也有极显著的负相关关系,表明水环境质量越低则着生藻类的生物完整性越差;当采用浮游藻类生物完整性(Ph-IBI)用于河流健康评价时却只能筛选出1个核心生物参数(藻类密度),而且浮游藻类生物完整性指数(Ph-IBI)与水体综合污染指数(CPI)及12个水体环境指标并无明显的相关性。本研究表明,在河流水体中,与浮游藻类相比,着生藻类更能反映水体环境的状况,对河流水体环境的反映更为准确。因此,在以流动水体为特征的河流的健康评价中,采用着生藻类比采用浮游藻类更为适宜。     

Life cycle assessment in green chemistry

Background, Aims and Scope Using renewable feedstock and introducing biocatalysts in the chemical industry have been suggested as the key strategies to reduce the environmental impact of chemicals. The Swedish interdisciplinary programme ‘Greenchem’, is aiming to develop these strategies. One target group of chemicals for Greenchem are wax esters which can be used in wood surface coatings for wood furniture, etc. The aim of this study was to conduct a life cycle assessment of four different wood surface coatings, two wax-based coatings and two lacquers using ultra violet light for hardening (UV lacquers). One of the two wax-based coatings is based on a renewable wax ester produced with biocatalysts from rapeseed oil, denoted ‘green wax’, while the other is based on fossil feedstock and is denoted ‘fossil wax’. The two UV lacquers consist of one ‘100% UV’ coating and one ‘water-based UV’ coating. The scope was to compare the environmental performance of the new ‘green’ coating with the three coatings which are on the market today. Methods The study has a cradle-to-grave perspective and the functional unit is ‘decoration and protection of 1 m² wood table surface for 20 years’. Extensive data collection and calculations have been performed for the two wax-based coatings, whereas mainly existing LCI data have been used to characterise the production of the two UV lacquers. Results For all impact categories studied, the ‘100% UV’ lacquer is the most environmentally benign alternative. The ‘water-based UV’ is the second best alternative for all impact categories except EP, where the ‘fossil wax’ is slightly better. For GWP the ‘fossil wax’ has the highest contribution followed by the ‘green wax’. For AP and EP it is the ‘green wax’ that makes the highest environmental impact due to the contribution from the cultivation of the rapeseed and the production of the rapeseed oil. For POCP the ‘fossil wax’ makes the highest contribution, slightly higher than the contribution from the ‘green wax’. Also the energy requirements for the ‘100% UV’ lacquer is much lower than for the other coatings. The results from the toxicological evaluation conducted in this study, which was restricted to include only the UV lacquers, are inconclusive, giving different results depending on the model chosen, EDIP97 or USES. Discussion The result in this study shows that the environmental benefits of using revewable feedstock and processes based on biocatalysis in the production of wax esters used in wood surface coatings are rather limited. This is due to the high environmental impact from other steps in the life cycle of the coating. Conclusions Overall the ‘100% UV’ lacquer seems to be the best alternative from an environmental point of view. This study shows that the hot spots of the life cycle of the coatings are the production of the ingredients, but also the application and drying of the coatings. The toxicity assessment shows the need for the development of a new model, a model which finds common ground in order to overcome the current situation of diverging results of toxicity assessments. The results in this study also point to the importance of investigating the environmental performance of a product based on fossil or renewable feedstock from a life cycle perspective. Recommendations and Perspectives The results in this study show that an efficient way to improve the wood coating industry environmentally is to increase the utilization of UV lacquers that are 100% UV-based. These coatings can also be even further improved by introducing biocatalytic processes and producing epoxides and diacrylates from renewable raw material instead of the fossil-based ones produced with conventional chemical methods in use today. In doing this, however, choosing a vegetable oil with good environmental performance is important. An alternative application of the ‘green wax’ analysed in this study may be as an ingredient in health care products, for example, which may result in greater environmental benefits than when the wax is used inwood coating products. The results in this study illustrate the importance of investigating the environmental performance of a product from cradle-to-grave perspective and not consider it ‘green’ because it is based on renewable resources.     

The effect of melatonin on eye lens of rats exposed to ultraviolet radiation

We investigated the influence of exogenously administered melatonin on adult rats eye lenses exposed to ultraviolet radiation (UV) A and B ranging from 356-254 nm irradiation at 8 microW/cm(2). Rats exposed to this range of UV for 15 min for one week showed a significant (P<0.05) reduction in antioxidant enzymes activities; superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and elevated (P<0.001) lipid peroxidation served as an index of cellular damage by free radicals. UV-radiation significantly (P<0.001) elevated calcium ions (Ca(2+)) and lactate dehydrogenase (LDH) activity in lenses. Depleting animals of their stores of important intracellular antioxidant and elevating lenticular Ca(2+) by UV irradiation, may be the main cause of lens opacification. Melatonin injection with radiation significantly reduced (P<0.05) lipid peroxidation, Ca(2+) and (P<0.001) for LDH. When melatonin was injected after radiation, SOD and GSH-Px enzyme activities increased significantly (P<0.01), and lipid peroxidation, Ca(2+) levels and LDH activities were reduced significantly. Melatonin injection after UV radiation was as effective as melatonin treatment concurrent with UV irradiation. We conclude that melatonin may protect the eye lens from the damaging effects of UV exposure, and its actions protect lens from oxidative stress, elevating Ca(2+) levels, which are considered as an important causes of cataractogenesis.     

Evaluation of the environmental stress index (ESI) for the southern hemisphere

The environmental stress index (ESI), constructed from ambient temperature, relative humidity, and solar radiation, was further evaluated from databases collected in Israel and New Zealand. High correlations were found between ESI and WBGT (R²=0.959 and R²=0.973 for Israel and New Zealand, respectively). However, for the New Zealand database, residuals were not distributed symmetrically around the zero line, which might be due to the difference in the global radiation spectrum. The ultraviolet radiation measurements were significantly higher in New Zealand than in Israel. As a consequence, a correction factor might be needed for ESI to be used in the southern hemisphere.     

Natural agents: cellular and molecular mechanisms of photoprotection

The skin is the largest organ of the body that produces a flexible and self-repairing barrier and protects the body from most common potentially harmful physical, environmental, and biological insults. Solar ultraviolet (UV) radiation is one of the major environmental insults to the skin and causes multi-tiered cellular and molecular events eventually leading to skin cancer. The past decade has seen a surge in the incidence of skin cancer due to changes in life style patterns that have led to a significant increase in the amount of UV radiation that people receive. Reducing excessive exposure to UV radiation is desirable; nevertheless this approach is not easy to implement. Therefore, there is an urgent need to develop novel strategies to reduce the adverse biological effects of UV radiation on the skin. A wide variety of natural agents have been reported to possess substantial skin photoprotective effects. Numerous preclinical and clinical studies have elucidated that natural agents act by several cellular and molecular mechanisms to delay or prevent skin cancer. In this review article, we have summarized and discussed some of the selected natural agents for skin photoprotection.     

On non-metric multidimensional scaling ordination and interpretation of the matorral vegetation in lowland Murcía

The plant-environment relationships in a range of matorral communities, having different rainfall conditions in semi-arid lowland habitats in Murcía, S.E. Spain, were examined using the non-metric multidimensional scaling ordination technique. Hypotheses on floristic variations were derived based on an interpretative strategy which involved a site configuration rotation, followed by stepwise multiple regression analysis. An environmental data set was used to isolate variables associated with site co-ordinate trends. Results showed that floristic variation in these communities was mainly determined by aspect induced radiation receipt. Besides, most environmental trends in the study areas were found to be oblique to original site ordination axes and configuration rotation seemed to be a prerequisite in quantitative interpretation. The interpretative strategy introduced in this study was effective. It enhanced straightforward, quantitative and objective interpretation whereby inductive inferences on environmental trends could be readily formulated.Abbreviations ARAD radiation receipt surrogate - DEPTH soil depth - DISTURB disturbance index - NMDS non-metric multidimensional scaling - NUT nutrient scalar - SLOPE slope angle - TEXTIN texture index     

A biological spectral weighting function for ozone depletion research with higher plants

Biological spectral weighting functions (BSWF) play a key role in assessing implications of stratospheric ozone reduction. They are used to calculate the increase in biologically effective solar UV radiation due to ozone reduction (radiation amplification factor, RAF), assess current latitudinal gradients of solar UV radiation, and compare solar UV radiation with that from lamps and filters used in experiments. As a basis for a BSWF, we developed an action spectrum for growth responses of light-grown oat ( Avena sativa L. cv. Otana) seedlings exposed to narrowband UV radiation from a large double water-prism monochromator. Five UV wavelength peaks were used (275, 297, 302, 313 and 366 nm) in the absence of any visible radiation. Growth responses were measured from 1 to 10 days after the treatments. At all these wavelengths, the UV radiation inhibited height growth, including the height at which the first leaf separated from the stem. Radiation at all wavelengths used, except the one UV-A wavelength, promoted the length of the second leaf. The resulting action spectrum closely resembles the commonly used generalized plant response function except that it indicates continued sensitivity into the UV-A region. When used as a BSWF for the ozone depletion problem, this new function for plant growth would suggest substantially less impact of ozone depletion because it results in only a modest increment of biologically effective UV for a given level of ozone depletion (a lower RAF). Yet this new BSWF also suggests that experimental treatments based on previous BSWF with less emphasis on the UV-A may have resulted in simulations of less pronounced ozone depletion than intended. The validity of this new BSWF with UV-A sensitivity, designated the UV plant growth weighting function, was verified in field experiments as described in the companion paper.     

Leaf surface wax is a source of plant methane formation under UV radiation and in the presence of oxygen

The terrestrial vegetation is a source of UV radiation‐induced aerobic methane (CH₄) release to the atmosphere. Hitherto pectin, a plant structural component, has been considered as the most likely precursor for this CH₄ release. However, most of the leaf pectin is situated below the surface wax layer, and UV transmittance of the cuticle differs among plant species. In some species, the cuticle effectively absorbs and/or reflects UV radiation. Thus, pectin may not necessarily contribute substantially to the UV radiation‐induced CH₄ emission measured at surface level in all species. Here, we investigated the potential of the leaf surface wax itself as a source of UV radiation‐induced leaf aerobic CH₄ formation. Isolated leaf surface wax emitted CH₄ at substantial rates in response to UV radiation. This discovery has implications for how the phenomenon should be scaled to global levels. In relation to this, we demonstrated that the UV radiation‐induced CH₄ emission is independent of leaf area index above unity. Further, we observed that the presence of O₂ in the atmosphere was necessary for achieving the highest rates of CH₄ emission. Methane formation from leaf surface wax is supposedly a two‐step process initiated by a photolytic rearrangement reaction of the major component followed by an α‐cleavage of the generated ketone.