Role Of Ultraviolet Radiation Research Articles

Elevated risk for squamous cell carcinoma of the conjunctiva among adults with AIDS in the United States

Squamous cell carcinoma of the conjunctiva (SCCC) has been associated with HIV infection in equatorial Africa, but the evidence for association with HIV in developed countries, where SCCC is rarer, is controversial. We investigated the risk for SCCC and other eye cancers in the updated U.S. HIV/AIDS Cancer Match Registry Study. We calculated standardized incidence ratios (SIRs) to estimate excess risk for SCCC, primary ocular lymphoma, ocular Kaposi sarcoma (KS), and other eye tumors among 491, 048 adults (age > 15 years or older) with HIV/AIDS diagnosed from 1980 to 2004. We calculated relative proportions (per 105) to gain insight into risk factors. We identified 73 eye cancers (15 SCCC, 35 primary ocular lymphoma, 17 ocular KS, and 6 other). Overall SIRs were elevated for SCCC (SIR, 12.2, 95% CI 6.8 – 20.2), primary ocular lymphoma (21.7, 95% CI 15.1–30.2), and ocular KS (109, 95% CI 63.5–175). Risk for SCCC was elevated regardless of HIV acquisition category, CD4 lymphocyte count, and time-relative to AIDS-onset. Relative proportions of SCCC risk were highest with age ≥50 (8/105), Hispanic ethnicity (7/105), and residence in regions with high solar ultraviolet radiation (10/105). We show significantly increased incidence of SCCC among persons with HIV/AIDS in the United States. The associations with age and geography are in accord with etiological role for ultraviolet radiation in SCCC.

Bacterial diversity and morphology in deep ultraoligotrophic Andean lakes: The role of UVR on vertical distribution

We investigated the community composition and the relative size‐shape distribution of bacterial assemblages in deep transparent lakes, where bacteria may be affected by harmful ultraviolet radiation (UVR). Summer samples of the euphotic zones of nine ultraoligotrophic lakes located in different drainage basins between 40°27' and 42°49'S in the North Andean Patagonia were analyzed for relative diversity by denaturating gradient gel electrophoresis and the bacterial morphology (free‐living cocci and rods vs. filamentous forms) in relation to environmental factors (UVR, photosynthetically active radiation, temperature, nutrients, nanoflagellates, and ciliate abundances). The overall bacterial community composition was similar in all lakes and over depth in each lake. In contrast, the relative proportion of filaments to total bacterial biovolume was higher in the upper layers, which have higher UVR intensities (305‐340 nm). Lakes with lower Κd305 (diffuse extinction coefficient, 305 nm) showed a greater proportion of filaments. Filament mean length in the upper layers was also significantly greater than at deeper levels. There was a significant correlation between UVR and filament proportion, whereas neither nanopredator abundances (nanoflagellates and ciliates), nor predation pressure, nor resources (dissolved nutrients) could explain the high proportion of filamentation in the near‐surface layers. We propose that UVR plays a decisive role stimulating bacterial filamentation, particularly in lakes with high UVR penetration.

The role of ultraviolet radiation, photosensitizers, reactive oxygen species and ester groups in mechanisms of methane formation from pectin

Ultraviolet (UV) radiation has recently been demonstrated to drive an aerobic production of methane (CH(4)) from plant tissues and pectins, as do agents that generate reactive oxygen species (ROS) in vivo independently of UV. As the major building-blocks of pectin do not absorb solar UV found at the earth's surface (i.e. >280 nm), we explored the hypothesis that UV radiation affects pectin indirectly via generation of ROS which themselves release CH(4) from pectin. Decreasing the UV absorbance of commercial pectin by ethanol washing diminished UV-dependent CH(4) production, and this was restored by the addition of the UV photosensitizer tryptophan. Certain ROS scavengers [mannitol, a hydroxyl radical ((*)OH) scavenger; 1,4-diazabicyclo[2.2.2] octane; and iodide] strongly inhibited UV-induced CH(4) production from dry pectin. Furthermore, pectin solutions emitted CH(4) in darkness upon the addition of (*)OH, but not superoxide or H(2)O(2). Model carbohydrates reacted similarly if they possessed -CH(3) groups [e.g. methyl esters or (more weakly) acetyl esters but not rhamnose]. We conclude that UV evokes CH(4) production from pectic methyl groups by interacting with UV photosensitizers to generate (*)OH. We suggest that diverse processes generating (*)OH could contribute to CH(4) emissions independently of UV irradiation, and that environmental stresses and constitutive physiological processes generating ROS require careful evaluation in studies of CH(4) formation from foliage.

Melanoma: What Are the Gaps in Our Knowledge?

Cutaneous malignant melanoma (MM) falls into two main groups, based on aetiology [1–3]. First, a small minority of patients have acral MM, in which the disease occurs on the palms and soles. The incidence of acral MM is similar in people with widely different skin colours (and hence with different amounts of skin melanin), and at different latitudes. The palms and soles have a thick epidermis, and so few harmful photons of ultraviolet radiation (UVR) will penetrate to the germinative layers. Acral melanomas are therefore not believed to be causally related to UVR, and their aetiology remains a mystery. They will not be discussed further in this article. By contrast, more than 90% of MM occurs on non-acral sites and is thought to be caused by UVR [2,4]. The evidence for such causality comes from a variety of fields. MM is most common in those with pale skin, which has a relative lack of melanin, a substance that blocks photons from penetrating deeply into skin [2]. African people with very dark skin are hundreds of times less sensitive to the harmful effects of UVR than white Northern Europeans. Even within white Northern European populations, MM rates vary in relation to more subtle degrees of difference in sun sensitivity. Those with red hair, pale skin, and a tendency to freckle are about three times more likely to develop MM than those without these three features [2,5]. The dramatically elevated rate of MM in those with European ancestry in Australia is therefore what we would expect: susceptibility of the host coupled with enhanced environmental exposure leads to a high disease risk [4]. Linked Research Article This Research in Translation discusses the following new study published in PLoS Medicine: Viros A, Fridlyand J, Bauer J, Lasithiotakis K, Garbe C, et al. (2008) Improving melanoma classification by integrating genetic and morphologic features. PLoS Med 5(6): e120. doi:10.1371/journal.pmed.0050120 Boris Bastian and colleagues present a refined morphological classification of primary melanomas that can be used to improve existing melanoma classifications by defining genetically homogeneous subgroups. However, it is not just epidemiology that implicates a key role for UVR. Patients with the rare Mendelian disorder xeroderma pigmentosa (see http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=278700) have a dramatically increased risk of most types of skin cancer, including MM. This disorder is characterised acutely by sun-burn in response to tiny amounts of UVR, and both this sun-burn and the elevated cancer rates are a result of an inability to repair the DNA damage induced by UVR. The lesson is quite clear: it is not sunlight per se, but the highly mutagenic UVR part of the electromagnetic spectrum that is important for skin carcinogenesis. Given that we know the major host and environmental factors that lead to non-acral melanomas, one might think that we know enough to reduce the incidence of MM. But our ability to change people's behaviour so that they reduce their exposure to UVR remains limited. In addition, as our knowledge of MM has increased, so has the incidence of disease. Puzzling gaps therefore remain in our knowledge of the aetiology of non-acral melanomas. So what important things do we not know?

The role of ultraviolet radiation during ultralow k films curing: Strengthening mechanisms and sacrificial porogen removal

This work proposes a fundamental understanding of structural transformation occurring during porogen extraction from as-deposited ultralow k (ULK) materials when exposed to ultraviolet (UV) radiation during thermal curing. Specific explanations are provided for as deposited films at high temperature (T>250 °C). This temperature range is sufficient to assess thin-film stability. Two distinguished regimes were identified in the curing process. During the first stage, the film shrinks strongly in similar proportion to SiCH3 break. Preferential impact of UV radiation on hydrocarbon porogen bonds leads also to a break of SiCH3 structures. In this work, 5 min of curing is enough to remove the porogen and create the max of porosity (33%). After the porogen removal step, the porous film shrinks under UV radiation leading to an increase of SiOSi bond concentration. A structural rearrangement of the bulk is initiated since the porogen is totally evacuated from the film. The increase of normalized infrared SiOSi peak during UV curing (related in literature to an improvement of mechanical properties) is mainly due to film densification (a few SiOSi bonds creation). The origin of shrinkage is explained by the breaking of SiCH3 which could turn into a SiH bond leading to a free volume reduction within the film. In this case, a correlation is found between shrinkage and elastic modulus. The resulting SiOSi structure densification drives, at first order, the improvement of the mechanical properties. UV radiation exposure shows no effect in silanol condensation and acts mainly on the porogen decomposition and bulk densification. Si-CH2-Si structure formation, pointed out in the literature as a possible reaction way to enhance film crosslinking, is identified in the nuclear magnetic resonance (NMR) broadband spectrum of the ULK film. However, resulted NMR and infrared peaks intensities suggest its formation as a minor. This study gives a full understanding of UV curing impact on ULK films (k≤2.5) where structure densification is identified as a main process to enhance the film strength in addition to the crosslinking.

The squamous variant of eccrine porocarcinoma: a clinicopathological study of 21 cases

Aim:Squamous differentiation in eccrine porocarcinoma (EPC) is an unusual phenomenon that has rarely been reported in the literature. This study describes the clinical and pathological findings in a series of...

Effects of ultraviolet radiation on litter decomposition depend on precipitation and litter chemistry in a shortgrass steppe ecosystem

AbstractWe examined the effect of altered levels of ultraviolet (UV) radiation (280–400 nm) and different amounts of precipitation on the decomposition rates of litter of contrasting carbon to nitrogen ratio (C : N) in a 3‐year field experiment in a shortgrass steppe (SGS) ecosystem. UV radiation was either blocked or passed under clear plastic tents where precipitation was applied to simulate a very dry or very wet year. These treatments minimized or maximized the abiotic component (UV) or the biotic component (biological activity of decomposer organisms) of decomposition to assess potential interactions between the two. Initial litter chemistry varied in response to having been grown under ambient or elevated atmospheric CO2 concentrations. While precipitation and litter chemistry were the most important drivers in decomposition in this system, UV radiation increased decomposition rates under dry conditions in litter with higher C : N ratios. Exposure to UV radiation slightly increased the amount of holocellulose that was lost from the litter. UV exposure did not affect the decomposition of the lignin fraction. Increased decomposition with UV radiation was accompanied by a decrease in N immobilization over the summer months. These results suggest that the effects of UV radiation on decomposition rates may be primarily abiotic, caused by direct photochemical degradation of the litter. Our results demonstrate that the role of UV radiation in litter decomposition in semiarid systems depends on the aridity of the system and the chemistry of the litter.

Climate Impacts on Arctic Freshwater Ecosystems and Fisheries: Background, Rationale and Approach of the Arctic Climate Impact Assessment (ACIA)

Changes in climate and ultraviolet radiation levels in the Arctic will have far-reaching impacts, affecting aquatic species at various trophic levels, the physical and chemical environment that makes up their habitat, and the processes that act on and within freshwater ecosystems. Interactions of climatic variables, such as temperature and precipitation, with freshwater ecosystems are highly complex and can propagate through the ecosystem in ways that are difficult to project. This is partly due to a poor understanding of arctic freshwater systems and their basic interrelationships with climate and other environmental variables, and partly due to a paucity of long-term freshwater monitoring sites and integrated hydro-ecological research programs in the Arctic. The papers in this special issue are an abstraction of the analyses performed by 25 international experts and their associated networks on Arctic freshwater hydrology and related aquatic ecosystems that was initially published by the Arctic Climate Impact Assessment (ACIA) in 2005 as "Chapter 8--Freshwater Ecosystems and Fisheries". The papers provide a broad overview of the general hydrological and ecological features of the various freshwater ecosystems in the Arctic, including descriptions of each ACIA region, followed by a review of historical changes in freshwater systems during the Holocene. This is followed by an assessment of the effects of climate change on broad-scale hydro-ecology; aquatic biota and ecosystem structure and function; and arctic fish and fisheries. Potential synergistic and cumulative effects are also discussed, as are the roles of ultraviolet radiation and contaminants. The nature and complexity of many of the effects are illustrated using case studies from around the circumpolar north, together with a discussion of important threshold responses (i.e., those that produce stepwise and/or nonlinear effects). The issue concludes with summary the key findings, a list of gaps in scientific understanding, and policy-related recommendations.

The role of ultraviolet radiation in litter decomposition in arid ecosystems

In arid ecosystems, as much as 75% of solar radiation that penetrates the atmosphere hits the surface of the soil. The combination of high irradiance, high temperature, and low moisture puts constraints on the activity and organization of microbial communities. To separate the direct effects of UV absorbance on litter decomposition from the indirect effects of microbial selection, we placed mixed cohorts of senescent piñon ( Pinus edulis) and juniper ( Juniperus monosperma) litter into triplicate microcosms assigned to four treatments: UV irradiated (0.6 mW/cm 2 UV-A and UV-B for 12 h/day), with and without water additions, and non-irradiated with and without water additions. After 26 weeks, mass loss rates did not differ significantly among treatments with 90% organic matter remaining for piñon litter and 60% for juniper. The distribution and abundance of functional groups as assessed by FTIR spectra did not reveal any differences in relation to treatment, but differences were observed in the quantity and quality of dissolved organic carbon (DOC) extracted from the samples. The amount of DOC extracted increased by 56% for piñon litter and decreased by 32% for juniper in the UV-only treatment compared to initial values. Litter treated with UV and water had the lowest concentration of DOC with a decrease of 69% for juniper litter and 28% for piñon. The largest concentration of reactive phenols was found in the UV-only treatment with a 309% increase for piñon litter and a 10% reduction for juniper when compared to initial values. The treatments receiving water in the presence or absence of UV showed a similar response for both litter types, a reduction of 20–30% in phenolic concentration. Five extracellular enzyme activities, used, as indicators of microbial activity, were higher in the treatments that received water, but activities did not show an interaction with UV irradiation. The results suggest that UV radiation alone, or in combination with microbial activity, was as effective at decomposing litter as microbial activity alone. Thus, solar radiation can be an important contributor to litter degradation in arid systems.

The role of ultraviolet radiation in structuring epilithic algal communities in Rocky Mountain montane lakes: evidence from pigments and taxonomy

We investigated changes in the community structure of epilithic (rock-dwelling) algae brought about by ultraviolet-A and -B radiation (UV-A and UV-B, respectively), using measurements of biovolume of individual taxa, and taxonomically diagnostic photosynthetic pigments. We undertook our study in four Canadian Rocky Mountain montane lakes, where downwelling ultraviolet radiation (UVR) can be intense. Although taxonomic counts revealed significant decreases in algal community diversity under UV-A and UV-B exposure, they revealed no other significant trends in algal community composition. Instead, redundancy analysis using these counts suggested that variations in nutrient concentrations were most important in structuring these communities. Photosynthetic pigments decreased significantly under UV-A and UV-B exposure. This decrease was much more striking for carotenoid than for chlorophyll concentrations, despite the photoprotective properties of many carotenoid pigments. Grazed carotenoids have been shown to be more resistant to degradation than grazed chlorophylls. We suggest that an observed increase in grazing pressure in our UVR-shielded communities counteracted increases in algal growth, but that increased algal growth rates were reflected by increased concentrations of slowly degrading carotenoids. Our study suggests that other factors, such as nutrients and grazers, are more important than UVR for structuring epilithic algal communities in our study lakes.

Surface avoidance by freshwater zooplankton: Field evidence on the role of ultraviolet radiation

The avoidance of surface waters by crustacean zooplankton is a common phenomenon both in marine and freshwaters. The contemporary paradigm interprets such behavior as an antipredator strategy. However, the phenomenon has also been reported in predator‐free environments, which suggests that other variables may contribute to this depth‐selection behavior. We investigated the possibility that ultraviolet radiation (UVR) could influence the avoidance of surface waters in three interconnected lakes differing in their transparency. Each lake was sampled 17 or 18 times. In the two most transparent lakes, the percentage of the population occurring in the surface layer decreased during spring and summer, but this pattern was not observed in the less transparent lake. Such differences in the patterns of surface‐water avoidance were unrelated to the abundance and vertical distribution of the dominant planktivores (early stages of galaxiid fishes) as well as to temperature and food availability. They were inversely related, however, to the average UVR levels within the surface layer. A UV avoidance strategy was predicted for the copepod Boeckella gracilipes, on account of its low UV tolerance and lack of photoprotective compounds. Our results support this prediction and strongly suggest that surface avoidance by freshwater Patagonian zooplankton is not just a byproduct benefit of an antipredator behavior but is a direct response to high UVR levels.

Replicated mesocosm study on the role of natural ultraviolet radiation in high CDOM, shallow lakes.

The role of ultraviolet radiation on shallow, high CDOM (colored dissolved organic matter) lakes was investigated during two consecutive summers (1999 and 2000) in replicated mesocosms (rectangular fiberglass tanks). Each tank (volume: 300 L; depth: 40 cm) was covered with a layer (approximately 3 cm) of sediment from lake El Toro (40 degrees 14' S; 70 degrees 22' W) and filled with filtered water. The experimental design consisted of two treatments: full natural radiation (UV-exposed) and natural radiation without ultraviolet radiation (UV-shielded). UV-exposed and UV-shielded treatments differed in most studied variables as revealed by repeated measures ANOVA. UV-exposed tanks displayed lower CDOM levels (dissolved absorbance) of lower average molecular size (absorbance ratio between 250 and 365 nm), higher bacterial biomass, and lower chlorophyll a concentration. The effect on consumers (rotifers and crustaceans) was less noticeable. The results are consistent with UV stimulation of bacteria production mediated by higher rates of CDOM photobleaching, and the photoinhibition of planktonic algae. Thus, a major effect of UVR in shallow, high CDOM ecosystems appears to be the stimulation of heterotrophic pathways and a simultaneous inhibition of photoautotrophs.

Role of Ultraviolet Radiation in Accumulation of Anthocyanin in Berries of 'Gros Colman' Grapes (Vitis vinifera L.)

The role of UV radiation in the accumulation of anthocyanin in 'Gros Colman' (Vitis vinifera L.), a light-sensitive cultivar, was examined by using berry sections prepared from the softened green berries at veraison. The sections were exposed to diffuse sunlight under covering materials such as glass plate, polyolefin film (PO), poly vinyl chloride film (PVC), UV-proof PVC, ethylenetetrafluoroethylene (ETFE), polycarbonate resin plate (PC), fiber-reinforced acrylic resin plate (FRA) for 72 hr. The accumulation of anthocyanin in the berry skins under diffuse sunlight was greatly reduced with the covering materials which prevent the penetration of UV light. Artificial irradiation with an UV lamp (peak wavelength: 352 nm) greatly promoted the accumulation of anthocyanin. With increasing light intensity in the UV-A region (320-400 nm) up to 0.4 W·m-2, the anthocyanin content markedly increased, reached a plateau and then levelled off at 2.3 W·m-2. Increasing the intensity of white light up to 8.5 W·m-2 induced a gradual accumulation of anthocyanin. When UV irradiation was combined with white light at about 4.1 W·m-2, the accumulation of anthocyanin was further enhanced. These results suggest that UV light is involved in the accumulation of anthocyanin in 'Gros Colman' grapes. Hence, UV permeability of covering materials in the protected culture should be considered.

Photobiological uncertainties in the Archaean and post-Archaean world

The notion that ultraviolet (UV) fluxes, and thus biologically weighted irradiances, were higher on Archaean Earth than on present-day Earth has been a pervasive influence on thinking concerning the nature of early Earth. It directly influences calculations concerning protection strategies that may or may not have been required by early life. Our knowledge of the Earth's changing UV radiation climate over time depends upon our knowledge of a diversity of factors, the magnitudes of which are uncertain. Here these uncertainties are explored. During the Archaean Era, calculations of the surface photobiological environment span a three order of magnitude difference in DNA-damage weighted irradiances with consequences for our assumptions concerning the environment for exposed surface life and the role of UV radiation as a mutagen. These differences are primarily caused by uncertainties in the concentrations of trace gases and the partial pressures of carbon dioxide and nitrogen that affect scattering in the atmosphere. To a lesser extent, the luminosity of the Sun in the UV region is also a factor. During the Proterozoic and Phanerozoic, when we know that an ozone column existed, these uncertainties drop to two orders of magnitude and are primarily caused by poor knowledge about the frequency and atmospheric effects of potentially ozone-depleting agents such as volcanism, impact events and supernovae explosions as well as the effects of global temperatures on ozone concentrations and thus surface UV irradiance. Changes in other atmospheric constituents during this time have less of an effect on photobiological consequences, which include a Palaeozoic oxygen pulse. Understanding the cause of photobiological uncertainties and their consequences constitutes a current challenge for atmospheric chemists and photobiologists.

Penetration of solar radiation into the water column of the central subtropical Atlantic Ocean—optical properties and possible biological consequences

The optical properties of the waters as well as the penetration of both solar ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) were analyzed at different stations of the central subtropical Atlantic Ocean during the AZORES II cruise of the research vessel ‘‘Hesperides’’ in April 1999 to assess the impact of solar UVR on microorganisms populating highly transparent oceanic waters. The investigation was based on direct spectral measurements of the scalar and downward-solar irradiance between 290 and 750 nm at different depths using a temperature-stabilized double monochromator spectroradiometer (Optronic, type 754) with a highly sensitive 4p sensor connected to the entrance slit by a 20-m quartz fiber cable. In addition, the Secchi depth was measured, and water samples of different depths at each station were analyzed to determine the concentration and optical properties of phytoplankton as well as attenuating substances such as seston and gelbstoff in the column. Using the spectral irradiance data at different depths as well as the vertical irradiance profiles at different wavelengths, the following parameters were calculated: the spectral attenuation coefficients, the spectral depths of penetration to 1% of the subsurface value (‘‘1% depths’’), the 1% depths for the ranges UV-B, UV-A and PAR, as well as the water type in the Jerlov system of optical classification. The optical properties of the waters investigated can be classified into the oceanic types OI–OII in the Jerlov system, which are characterized by very small concentrations of seston and of gelbstoff, which are the main absorbers for UV radiation in natural waters. The Secchi depths varied between about 15 m (type OII) to about 45 m (type OI) showing ratios to the 1% depths of PAR of about 0.21 to about 0.31. Values of the same order were found for the depths of the maximal concentration of chlorophyll a, which varied between 45 and 100 m during midnight and between 70 and 110 m during noon, showing also significant increases with increasing transparency of the waters. In contrast, the 1% depths for the penetration of solar UV irradiance were found between 12 and 19 m (type OII) and between 26 and 31 m (type OI) for UV-B whereas their values ranged for UV-A between 29 and 65 m (type OII) and between 55 and 93 m (type OI). Thus, solar UV-B penetrates up to about 25% of the photic zone in these waters whereas for UV-A about 75–93% were found. So, solar UVR may significantly affect both the photosynthetic activity by photoinhibition as well as the composition of the kind of species populating different depths of the column by further effects such as DNA damage and inhibition of motility. The role of UVR as a selection factor is shown by a strong absorption peak in the UV range of the water samples, which occurred only when the organisms

Crises and extinction in the fossil record—a role for ultraviolet radiation?

AbstractA number of natural events can cause ozone depletion, including asteroid and comet impacts, large-scale volcanism involving the stratospheric injection of chlorine, and close cosmic events such as supernovae. These events have previously been postulated to have been sole or contributory causes of mass extinctions. Following such events, UV-B radiation would have been elevated at the surface of the earth. The possibilities for detecting elevated UV-B as a kill mechanism in the fossil record are discussed. In the case of impact events and large-scale volcanism, the taxa affected by increases in UV-B radiation are likely to be similar to those affected by cooling and by the initial drop in irradiance caused by stratospheric dust injection. Thus UV-B may synergistically exacerbate the effects of these other environmental changes and contribute to stress in the biosphere, although UV-B alone is unlikely to cause a mass extinction. By the same token, however, this similarity in affected taxa is likely to make delineating the involvement of UV-B radiation in the fossil record more difficult. Cosmic events such as supernovae may produce smaller extinction events, but ones that are “cleaner” UV catastrophes without the involvement of other environmental changes.

Role of ultraviolet radiation on phytoplankton extracellular release and its subsequent utilization by marine bacterioplankton

The influence of ultraviolet (UV) radiation on the production rate and percentage of photosynthetic extracellular release (PER) to total production (PER + particulate) was investigated in the laboratory using the diatom species Chaetoceros muelleri grown under different nutrient and radiation conditions. Only when growing on higher nutrient concentrations (f/2 and f/4 media), were both specific particulate production and PER rates (production per unit chl a) were significantly lower in the presence of photosynthetic active radiation (PhAR) + UV as compared to the treatments receiving only PhAR. When growing on lower nutrient concentrations (f/16 medium), UV radiation had no sigmficant effect on the production rates. The percentage of PER to the total amount of carbon fixed was sirmlar for the PhAR + UV and the PhAR treatments. However, PER produced by C. muelleri during PhAR + UV exposure was taken up by bacterioplankton in the dark at significantly lower rates than PER produced in the absence of UV. This indicates that PER, considered as an important component of the dissolved organic carbon pool, becomes more resistant to bacterial utilization upon UV exposure. Whether this reduced PER-uptake by bacterioplankton is caused by changes in the macromolecular composition of the PER and/or is due to a subsequent photochemically induced alteration of the molecules during UV-exposure remains to be investigated.

Mechanisms of induction of skin cancer by UV radiation.

Ultraviolet (UV) radiation is the carcinogenic factor in sunlight; damage to skin cells from repeated exposure can lead to the development of cancer. UV radiation has been mainly implicated as the cause of non-melanoma skin cancer, although some role for UV in malignant melanoma has been suggested. The induction of skin cancer is mainly caused by the accumulation of mutations caused by UV damage. Cellular mechanisms exist to repair the DNA damage, or to induce apoptosis to remove severely damaged cells; however, the additive effects of mutations in genes involved in these mechanisms, or in control of the cell cycle, can lead to abnormal cell proliferation and tumor development. The molecular events in the induction of skin cancer are being actively investigated, and recent research has added to the understanding of the roles of tumor suppressor and oncogenes in skin cancer. UV radiation has been shown to induce the expression of the p53 tumor suppressor gene, and is known to produce "signature" mutations in p53 in human and mouse skin cancers and in the tumor suppressor gene patched in human basal cell carcinoma. The role of UV radiation in suppression of immune surveillance in the skin, which is an important protection against skin tumor development, is also being investigated. The knowledge gained will help to better understand the ways in which skin cancer arises from UV exposure, which will in turn allow development of better methods of treatment and prevention.

A Clinical Review of the Evidence for the Role of Ultraviolet Radiation in the Etiology of Cutaneous Melanoma

INTRODUCTION The incidence of cutaneous melanoma is increasing at a greater rate than any other malignancy in men and is second only to lung cancer in women (1). In the United States the incidence of melanoma has been increasing 4% each year over the period 1973-1991 (2). There is strong epidemiological evidence that solar radiation is an important underlying cause of melanoma and is playing a role in the striking increase in incidence noted recently. It has been estimated that solar radiation is responsible for 96% and 92% of melanoma in Caucasian men and women in the United States, respectively (3). This review will outline the epidemiological evidence for the role of ultraviolet radiation in causing melanoma and emphasize the public health implications.

Cutaneous malignancies in renal transplant recipients from Nova Scotia, Canada.

Four hundred and seventy-four Nova Scotian renal transplant recipients were screened, using the records of the Nova Scotia Cancer Registry and the Victoria General Hospital, in a retrospective study, for the development of cutaneous malignancies. Sixteen patients developed a total of 60 squamous cell carcinomas (SCC) and 14 developed 28 basal cell carcinomas (BCC). The survival curve shows that within 10 years of transplant, less than 10% will develop SCC. This is a 16-fold increase above the rate of SCC in the general population of Nova Scotia, Canada. Age at time of transplantation appears to be a significant determinant of subsequent skin cancer risk. None of the previously reported HLA associations was found to hold in this small study. The role of ultraviolet radiation, due to both geographic and lifestyle exposure, is discussed when comparing to other transplant studies.