High UV Doses Research Articles

Effects of nitrate on the UV photolysis of H2O2 for 2,4-dichlorophenol degradation in treated effluents

The major objective of this study was to delineate the effect of nitrate on the UV oxidation of 2,4-DCP by conducting a bench-scale operation at various reaction times, and initial concentrations of H2O2 and NO1 3. 2,4-DCP (20±5 μg/L) was oxidized in very limited amounts through direct UV photolysis, without additional oxidation by hydroxyl radicals. However, it was completely oxidized with an initial H2O2 concentration of 20 mg/L at a reaction time of 1.0 min under the operating conditions described below. The practical reaction time for 80% oxidation turned out to be 2.0 min (with a high UV dose) with an initial H2O2 concentration of 10 mg/L. Nitrate enhanced the 2,4-DCP oxidation by the hydroxyl radicals produced from nitrate photolysis with the relatively low initial H2O2 concentrations of 0.0 to 5 mg/L, but hindered the oxidation, when an initial H2O2 concentration in the reactor was less than or around about 10 mg/L. The adverse effect of nitrate on the 2,4-DCP oxidation was not observed with a rela...

Chromatin Organization and Radio Resistance in the Bacterium Gemmata obscuriglobus

The organization of chromatin has a major impact on cellular activities, such as gene expression. For bacteria, it was suggested that the spatial organization of the genetic material correlates with transcriptional levels, implying a specific architecture of the chromosome within the cytoplasm. Accordingly, recent technological advances have emphasized the organization of the genetic material within nucleoid structures. Gemmata obscuriglobus, a member of the phylum Planctomycetes, exhibits a distinctive nucleoid structure in which chromatin is encapsulated within a discrete membrane-bound compartment. Here, we show that this soil and freshwater bacterium tolerates high doses of UV and ionizing radiation. Cryoelectron tomography of frozen hydrated sections and electron microscopy of freeze-substituted cells have indicated a more highly ordered condensed-chromatin organization in actively dividing and stationary-phase G. obscuriglobus cells. These three-dimensional analyses revealed a complex network of double membranes that engulf the condensed DNA. Bioinformatics analysis has revealed the existence of a putative component involved in nonhomologous DNA end joining that presumably plays a role in maintaining chromatin integrity within the bacterium. Thus, our observations further support the notion that packed chromatin organization enhances radiation tolerance.

Submicron structural alteration of polycarbonate surface due to ArF laser irradiation at high doses and the subsequent electro-chemical etching treatment

Excimer lasers at short UV wavelengths create regular surface microstructure on polycarbonate (PC). The effect is strongly dependent on the laser properties such as pulse energy, laser wavelength and energy dose. Among those, the UV dose is dominant. Moreover, the PC microstructure consists of a network of micro cones, whose size and population change drastically at higher UV doses. The surface hardening at lower doses and the laser ablation at higher doses are investigated to explain the phenomenon. The conical microstructure was subsequently treated using an electro-chemical etching process which turns it into an array of micro holes due to the simultaneous chemical etching and electrical breakdown.

Retinyl palmitate is non-genotoxic in Chinese hamster ovary cells in the dark or after pre-irradiation or simultaneous irradiation with UV light

Retinyl palmitate (RP), an ingredient of cosmetic and medical skin-care preparations, has been reported to be photo-genotoxic/photo-clastogenic in mouse lymphoma cells ( Tk locus) as well as in human Jurkat T-cells, as measured by use of the comet assay. Given that these results were obtained under exploratory conditions, we re-investigated the photo-genotoxicity of RP following a protocol consistent with current recommendations for photo-genotoxicity testing of drugs and chemicals. We tested RP in Chinese hamster ovary (CHO) cells in the dark (standard chromosome aberration test), under pre-irradiation (UVA irradiation of cells and subsequent treatment with RP) or simultaneous irradiation (irradiation of cells and RP together, standard photo-genotoxicity protocol) conditions. UVA irradiation was applied at 350 and 700 mJ/cm 2 with the high UV dose targeted to produce a small increase in the incidence of structural chromosome aberrations (CA) in cells not treated with RP. RP was tested up to and above its limit of solubility in the culture medium (20–40 μg/mL). There was no overt cytotoxicity under dark or different irradiation conditions. Treatment of cells with RP in the dark, as well as treatment under pre- or simultaneous irradiation conditions failed to produce biologically significant increases in the incidence of CA, whereas the positive control substances 4-nitroquinolone and 8-methoxypsoralene produced significantly positive effects in the dark or under simultaneous irradiation, respectively. Overall, our results failed to confirm the reported positive photo-genotoxic effects, and suggest that they may have been due to the test conditions, i.e. high irradiation doses, high cytotoxicity or re-irradiation of photo-products. In conclusion, our data suggest that, under standard conditions for testing photo-genotoxicity, RP had no in vitro genotoxic or photo-genotoxic potential and is therefore unlikely to pose a local or systemic genotoxic or photo-genotoxic risk.

Recent Developments in Phototherapy: Treatment Methods and Devices

We review recently patented methods and devices that allow for more effectively targeted phototherapy with fewer side effects. Among the new devices and methods reviewed here are narrow-band UVB (311- 313 nm) with a flat-type light source and the new xenon chloride excimer light (308 nm), both of which allow for targeted spot irradiation, limiting the unnecessary exposure of healthy skin to UV light. Some new devices are designed to selectively irradiate targeted nasal and oral mucosal tissue and to deliver controlled doses of UV light. Devices that provide targeted phototherapy attenuate treatment-induced increases in skin temperature, thereby reducing tissue damage and increasing skin tolerance to high UV doses. Other recently patented methods include the use of irradiation efficacy enhancers, such as topical formulations of provitamin D and its analogs, followed by irradiation with UV and/or blue light. Combined phototherapy and electrotherapy therapy can also be used to treat selected skin areas. These new methods and devices are aimed at improving the safety and efficacy of phototherapy, especially targeted phototherapy.

EFFECTS OF NITRATE ON THE UV PHOTOLYSIS OF H2O2 FOR VOCs DEGRADATION IN AN AQUEOUS SOLUTION

ABSTRACT The major objective of this study was to delineate the effect of nitrate on the UV oxidation of benzene and toluene, dissolved in less than 100 μg l−1, by conducting a bench‐scale operation at various reaction times and with various initial concentrations of H2O2 and NO3 −. The oxidation of benzene and toluene can be expected to be only about 10% and 18%, respectively, through the photolysis of H2O2 (initial conc. of 50 mg l−1), where the reactor was operated at a reaction time of 2 min, with an initial NO3 −‐N concentration of 5 mg l−1. Nitrate clearly hindered UV oxidation when the initial H2O2 concentration in the reactor was less than 50 mg l−1. Even if approximately 40% removal could be achieved under the conditions mentioned above (an initial H2O2 concentration of 200 mg l−1 at a reaction time of 9 min, with a high UV dose), the operating conditions for the 40% removal might be beyond the practical limits applied for effluents discharged from wastewater treatment plants. The results of the experiment also indicate that benzene and toluene can be oxidized in very limited amounts through direct photolysis, without additional oxidation by hydroxyl radicals.

Photolysis and advanced oxidation treatment of pharmaceuticals in tap water and treated sewage

The aim of this study was to investigate the removal efficiency of six phannaceuticals byphoto-degradation and the advanced oxidation process (AOP), UV/H2O2. The sixphannaceuticals were the four NSAIDs ibuprofen, diclofenac, naproxen and ketoprofen, thepharmacological active metabolite of the lipid lowering agent, clofibrin, clofibric acid, and theanticonvulsant and mood stabilizing drug, carbamazepine.Treatment experiments were perfom1ed using a UV lamp optimized for photochemicaltreatment in a flow through set-up. For the AOP experiments 60 mg/L H2O2 was added to thewater before treatment. The treatment effectiveness is evaluated based on the ElectricalEnergy per Order (EEO) (unit kWh!m\ which is defined as the electrical energy consumedper unit volume of water treated required for 90% removal of the investigated compound.It was found that four of the six phannaceuticals were completely removed in tap water byboth UV treatment and the AOP. The exceptions were ibuprofen and carbamazepine, whichexhibited a relationship between UV dose and removal. The electrical energy per order, EEOwas detennined to 8.2 kWh/ml (UV) and 3. 7 kWh/ml (UV /H2O2 ) for ibuprofen.In the wastewater effluent the removal by UV irradiation was almost complete for ketoprofen,while the other compounds show dependency of flow rate/UV dose. Ibuprofen was thecompound that needed the highest UV dose to remove 90% (EEO = 33.4 kWh/ml) wherenaproxen and clofibric acid required 9.6 kWh/ml and 5.5 kWh/ml, respectively. Ketoprofenand diclofenac needed considerable less energy than clofibric acid. Ibuprofen and naproxen isbiodegradable and will be removed in biologically treated wastewater. Therefore, the relevantestimate of the needed treatment is the energy use for removal of clofibric acid which required5.5 kWh/ml for 90% removal.

The Effect of Chronic Ultraviolet Radiation on the Human Immune System†

A single or a limited number of UVR exposures is recognized to suppress cell-mediated immunity in human subjects. The complex pathway leading from the absorption of photons by chromophores in the skin to the generation of T regulatory cells has been, at least partially, elucidated. However, the effect of repeated UV exposures on immune responses and associated mediators is not well studied, particularly to assess whether they lead, first, to the development of photoprotection so that these immune changes are reduced or no longer occur, and, secondly, to the development of photoprotection against the normal downregulation of immunity induced by a high UV dose. For almost all the parameters evaluated in this review--epidermal DNA damage/erythema, urocanic acid, Langerhans and dendritic cells, natural killer cells, macrophages, mast cells, contact and delayed hypersensitivity responses--none, aside from epidermal DNA damage/erythema and macrophage phagocytic activity, show convincing evidence of photoadaptation or, where appropriate, photoprotection. It is concluded that repeatedly irradiating individuals with UVR is likely to continue to result in downregulation of immunity.

Prebiotic chemistry: chemical evolution of organics on the primitive Earth under simulated prebiotic conditions

A series of prebiotic mixtures of simple molecules, sources of C, H, N, and O, were examined under conditions that may have prevailed during the Hadean eon (4.6-3.8 billion years), namely an oxygen-free atmosphere and a significant UV radiation flux over a large wavelength range due to the absence of an ozone layer. Mixtures contained a C source (methanol, acetone or other ketones), a N source (ammonia or methylamine), and an O source (water) at various molar ratios of C : H : N : O. When subjected to UV light or heated for periods of 7 to 45 days under an argon atmosphere, they yielded a narrow product distribution of a few principal compounds. Different initial conditions produced different distributions. The nature of the products was ascertained by gas chromatographic-mass spectral analysis (GC-MS). UVC irradiation of an aqueous methanol-ammonia-water prebiotic mixture for 14 days under low UV dose (6 x 10(-2) Einstein) produced methylisourea, hexamethylenetetramine (HMT), methyl-HMT and hydroxy-HMT, whereas under high UV dose (45 days; 1.9 x 10(-1) Einstein) yielded only HMT. By contrast, the prebiotic mixture composed of acetone-ammonia-water produced five principal species with acetamide as the major component; thermally the same mixture produced a different product distribution of four principal species. UVC irradiation of the CH(3)CN-NH(3)-H(2)O prebiotic mixture for 7 days gave mostly trimethyl-s-triazine, whereas in the presence of two metal oxides (TiO(2) or Fe(2)O(3)) also produced some HMT; the thermal process yielded only acetamide.

UV disinfection of RBC-treated light greywater effluent: Kinetics, survival and regrowth of selected microorganisms

The microbial quality of raw greywater was found to be much better than that of municipal wastewater, with 1.6×10 7 cfu ml −1 heterotrophic plate count (HPC), and 3.8×10 4, 9.9×10 3, 3.3×10 3 and 4.6×10 0 cfu 100 ml −1 faecal coliforms (FC), Staphylococcus aureus sp., Pseudomonas aeruginosa sp. and Clostridium perfringes sp., respectively. Further, three viral indicators monitored (somatic phage, host: Escherichia coli CN 13 and F-RNA phages, hosts: E. coli F + amp, E. coli K 12) were not present in raw greywater. The greywater was treated by an RBC followed by sedimentation. The treatment removed two orders of magnitude of all bacteria. UV disinfection kinetics, survival and regrowth of HPC, FC, P. aeruginosa sp. and S. aureus sp. were examined. At doses up to 69 mW s cm −2 FC were found to be the most resistant bacteria, followed by HPC, P. aeruginosa sp. and S. aureus sp. (inactivation rate coefficients: 0.0687, 0.113, 0.129 and 0.201 cm 2 mW −1 s −1, respectively). At higher doses (69–439 mW s cm −2) all but HPC (which exhibited a tailing curve) were completely eliminated. Microscopic examination showed that FC self-aggregate in the greywater effluent. This provides FC an advantage at low doses, since the concentration of suspended matter (that can provide shelter from UV radiation) in the effluent was very low. FC, P. aeruginosa sp. and S. aureus sp. did not exhibit regrowth up to 6 h after exposure to increasing UV doses (19–439 mW s cm −2). HPC regrowth was proven to be statistically significant in un-disinfected effluent and after irradiation with high UV doses (147 and 439 mW s cm −2). At these doses regrowth resulted from growth of UV-resistant bacteria due to decreased competition with other bacteria eliminated by the irradiation.

Preapoptotic chromatin changes induced by ultraviolet B irradiation in human erythroleukemia K562 cells

Exponentially growing human erythroleukemia K562 cells were permeabilized and the dose dependent decrease of DNA synthesis rate was measured after ultraviolet (UV B, 290 nm) irradiation. Cells were able to overcome 2 and 5 J/m2 UV doses, partial recovery was observed at 15 J/m2, while at high (25 J/m2) UV dose replicative DNA synthesis remained suppressed. K562 cells were subjected to synchronization prior to and after UV irradiation (24 J/m2) and 18 fractions were collected by centrifugal elutriation. Cell cycle analysis by flow cytometry did not show early apoptotic cells after UV irradiation. The gradual increase in DNA content typical for non-irradiated cells was contrasted by an early S phase block between 2.2 and 2.4 C-values after UV irradiation. Cell cycle dependent chromatin changes after ultraviolet irradiation were seen as a fine fibrillary network covering the mainly fibrous chromatin structures and incompletely folded primitive chromosomes. Based on observations after UV irradiation and on earlier results with cadmium treatment and gamma irradiation, we confirm that typical chromatin changes characteristic to genotoxic agents can be recognized and classified.

INVESTIGATION OF BY-PRODUCT FORMATION DURING THE IRRADIATION OF DRINKING WATER WITH A MEDIUM PRESSURE LAMP

The goal of this study was to determine the effect of UV irradiation with a polychromatic spectrum on natural organic matter. Several irradiation tests were carried out with or without cut-off of wavelengths lower than 240 nm on water samples coming from different drinking water plants. DOC, BDOC, SEC analyses, chlorine demand, nitrate and nitrite concentration measurements were made. Changes were noticed as regarding SEC and chlorine demand analyses. Indeed a consistent trend of breaking-up NOM molecules into smaller fragments was observed. Moreover, the chlorine demand increased with the dose when the cut-off filter was not applied, whereas a maximum value resulted when the cut-off filter was applied. Most of these results were obtained at high UV doses (40000 J. m-2), suggesting that UV irradiation would not have a noticeable effect on the water samples tested at doses usually used for drinking water treatment.

UV/H2O2 Treatment: A Practical Solution for Organic Contaminant Control and Primary Disinfection

PWN's water treatment plant Andijk was commissioned almost 40 years ago. It services water from the IJssel Lake by conventional surface water treatment. In view of taste and odor problems the plant was retrofitted with GAC filtration 25 years ago. The finished water quality still complies with all E.C. and Dutch drinking water standards. Nevertheless an upgrade is desired to avoid the use of chlorine and to extend the barriers against pathogenic micro-organisms and a broad range of organic micropollutants such as pesticides, rocket fuel by-products (NDMA), fuel oxygenates (MTBE), solvents (dioxane), endocrine disruptors, algae toxins, pharmaceuticals, etc. UV/H2O2 treatment was selected for both primary disinfection and organic contaminant control. The disinfection requirements were based on a 10−4 health risk. The required 3 log inactivation for Giardia and Cryptosporidium was achieved by an UV dose lower than 20 mJ/cm2. The highest UV dose, 105 mJ/cm2, was needed for the inactivation of spores of Sulphite Reducing Clostridia. Reactivation of protozoa was established for UV doses up to 25 mJ/cm2, for doses higher than 45 mJ/cm2 no reactivation was observed. In view of the raw water concentrations the required organic contaminant degradation was set at 80%. Collimated beam and pilot-plant work showed that the required degradation can be achieved by the proper combination of electric energy and H2O2. In a UV reactor optimized for organic contaminant control, UV dose of 540 mJ/cm2 (about 0.5 kWh/m3) and 6 mg/L H2O2 were needed. Under those conditions pesticides (atrazine), NDMA, MTBE, dioxane, endocrine disruptors (bisphenol A), microcystine and pharmaceuticals (diclofenac, ibuprofen) could be removed up to the required 80%. Bromate formation was absent while formation of primary metabolites was insignificant. The UV dose for organic contaminant control is about five times higher than the dose needed for disinfection. The UV/H2O2 process was implemented into the existing treatment train between the sand and GAC filters. In the GAC filters excess H2O2 is degraded, nitrite is converted into nitrate and biodegradable reaction products are consumed by bacteria. The full-scale installation with 3 streets of 4 Trojan Swift 16L30 reactors has been in operation since October 2004. Disinfection and organic contaminant control are as expected.

Bcl-2 is the target of a UV-inducible apoptosis switch and a node for UV signaling

Sunlight's UVB radiation triggers cell signaling at multiple sites to induce apoptosis. The integration of these signal entry sites is not understood. Here we show that P53 and E2f1 constitute a UV-inducible apoptosis switch. At low-UV doses, wild-type cells resemble the OFF state of an siP53-treated cell, whereas at high-UV doses, the apoptosis frequency transitions to the fully ON behavior of an siE2f1-treated cell. The switch's target is Bcl-2: Rapid Bcl-2 down-regulation in response to UVB-induced DNA photoproducts is lost in P53-deficient cells, but, as for apoptosis, is restored when both P53 and its inhibited target E2f1 are absent. P53's down-regulation of Bcl-2 is mediated entirely through E2f1. Bcl-2 is also down-regulated by a separate pathway triggered by DNA photoproducts in the absence of P53 and E2f1. Four UV pathways terminating on Bcl-2 contribute to apoptosis after UVB irradiation. The apoptosis lost in p53(-/-) is completely restored by siBcl-2, implying that Bcl-2 is a rate-limiting member of this network. These results identify Bcl-2 as an integrator of several UV-induced proapoptotic signals and show that it, in turn, suppresses a direct UV-apoptosis pathway. UV-induced apoptosis requires both UV activation of the direct pathway and a separate UV disinhibition of this pathway through P53-E2f1-Bcl-2.

Microorganism repair after UV-disinfection of secondary-level effluent for agricultural irrigation

A pilot study of microorganism repair after UV disinfection was performed for agricultural reuse of secondary-level effluent in paddy rice fields in Korea. Effluent from the bio-filter of a 16-unit apartment was used in a flow-through type UV-disinfection system. The average concentration of suspended solids (SS) and biochemical oxygen demand (BOD) were 3.4 and 5.9 mg L−1, respectively. The mean total coliform level was in the range of 1.5 × 104 MPN 100 mL−1. Photoreactivation and dark repair were apparent at a low UV dose (6 mW s cm−2). In low-dose UV disinfection, microorganisms increased within 12 h by approximately 5 and 1% due to photoreactivation and dark repair, respectively. This increase was not significant at a high UV dose (16 mW s cm−2). The repaired microorganisms were further inactivated, rather than reactivated, by solar irradiation, and numbers decreased to non-detectible levels after 4 h of exposure to solar irradiation. Based on UV disinfection and repair studies, a UV dose of 30 mW s cm−2 is recommended as sufficient to produce reclaimed water virtually free of pathogens and may be adequate for disinfection of secondary effluent for agricultural irrigation in paddy rice culture.

UV inactivation of humic-coated bacteriophages MS2 and T4 in water

This bench-scale study investigated the hypothesis that humic acids may thinly coat the surfaces of viruses (bacteriophages MS2 and T4) and thereby protect them from inactivation by UV light (254 nm). The model viruses were mixed in buffered water (pH 5.5) that contained Aldrich® humic acid (AHA) concentrations of 0, 10, 50, and 150 mg/L and were exposed to UV light at 40 and 80 mJ/cm2 for bacteriophage MS2 and 2 and 7 mJ/cm2 for bacteriophage T4 using a low pressure UV collimated beam. No steps were taken to form particles (i.e., no coagulant was added). The UV inactivation of both bacteriophages decreased to a statistically significant degree (based on 95% confidence level, Student's t test) at a humic acid concentration of 150 mg/L at the higher UV doses for each phage. This was despite the increased UV absorbance at 254 nm (UV254) caused by the humic acid being taken into account in the UV dose calculation. It was therefore hypothesized that the humic acid was coating the phage surfaces with a thin UV-shielding layer. As a further investigation of this hypothesis, samples containing humic acid, both with and without phage, were pelletized by ultracentrifugation and re-suspended in pure Milli-Q® water and the resulting UV254 values were compared. It was anticipated that the re-suspended pellets from the solutions containing humic acid and phage would exhibit higher UV254 than those of the pellets from solutions containing either phage or humic acid, due to the coating interaction. While there were statistically significant differences in UV254 among some of the re-suspended pellets, the results were inconsistent due to limitations of the experiment. As such, while some supporting evidence for the humic coating hypothesis was provided by this initial proof of concept study, further research is needed to more fully understand this phenomenon. Key words: ultraviolet light, disinfection, humic acid, bacteriophage, MS2, T4.

UV irradiation induces a postreplication DNA damage checkpoint

Eukaryotic cells irradiated with high doses of UV exhibit cell-cycle responses referred to as G(1)/S, intraS, and G(2)/M checkpoints. After a moderate UV dose that approximates sunlight exposure and is lethal to fission yeast checkpoint mutants, we found unexpectedly that these cell-cycle responses do not occur. Instead, cells at all stages of the cell cycle carry lesions into S phase and delay cell-cycle progression for hours after the completion of bulk DNA synthesis. Both DNA replication and the checkpoint kinase, Chk1, are required to generate this cell-cycle response. UV-irradiation of Deltachk1 cells causes chromosome damage and loss of viability only after cells have replicated irradiated DNA and entered mitosis. These data suggest that an important physiological role of the cell-cycle response to UV is to provide time for postreplication repair.

UV Induces p21 Rapid Turnover Independently of Ubiquitin and Skp2

It was previously reported that low doses, but not high doses, of UV trigger the Skp2-mediated proteasomal degradation of the cyclin-dependent kinase inhibitor p21 in mammalian cells. Here we show that both UV-C and UV-B lead to decrease of p21 protein, but not mRNA, level in a dose-dependent fashion in all of six human cell lines and five mouse cell lines tested. Also, high doses of UV reduce the half-life of p21. High doses, but not low doses, of UV induced p21 degradation in both skp2-proficient and -deficient murine embryonic fibroblast cells. UV-induced p21 reduction was rescued by proteasome inhibitors in all human and mouse cell lines tested. Neither a caspase inhibitor nor small interfering RNA against skp2 had an effect on the UV-induced p21 decrease, suggesting that this p21 degradation pathway may not involve caspases, or Skp2. Finally, UV did not induce p21 ubiquitination but still induced its degradation when the E1-activating enzyme was inactivated in an E1 temperature-sensitive mouse embryonic fibroblast cell line. Altogether, these results demonstrate that UV induces p21 degradation through an Skp2 and ubiquitin-independent pathway.

Alternative recombination pathways in UV-irradiated XP variant cells

XP variant (XP-V) cells lack the damage-specific polymerase eta and exhibit prolonged replication arrest after UV irradiation due to impaired bypass of UV photoproducts. To analyse the outcome of the arrested replication forks, homologous recombination (HR, Rad51 events) and fork breakage (Rad50 events) were assayed by immunofluorescent detection of foci-positive cells. Within 1 h of irradiation, XP-V cells showed more Rad51-positive cells than normal cells, while neither cell type showed an increase in Rad50 foci. Beyond 1 h, the frequency of Rad51-positive cells reached similar levels in both cell types, then declined at higher UV doses. At these later times, Rad50-positive cells increased with dose and to a greater extent in XP-V cells. Few cells were simultaneously positive for both sets of foci, suggesting a mutually exclusive recruitment of recombination proteins, or that these pathways operate at different stages during S phase. Analysis of cells containing a vector of tandemly arranged enhanced green fluorescent protein genes also showed that UV-induced HR was higher in XP-V cells. These results suggest that cells make an early commitment to HR, and that at later times a subset of arrested forks degrade into double-strand breaks, two alternative pathways that are greater in XP-V cells.

UV Dose Determines Key Characteristics of Nonmelanoma Skin Cancer

Abstract Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), known as nonmelanoma skin cancer (NMSC), are the most common cancers worldwide. Although many factors are involved in the pathogenesis of NMSC, UV radiation is an important risk factor. A fundamental question in skin cancer research is whether varying doses of total UV radiation influence key characteristics of NMSC. The hypothesis that differences in UV doses influence the BCC/SCC ratio, number of tumors, and anatomic location of the tumor was investigated in 311 participants having 326 tumors and with exposure to a broad range of UV doses. An epidemiologic questionnaire was given to each participant soliciting detailed information on exposure to solar radiation. Environmental UVA and UVB doses were measured continually for 6 years at a permanent UV monitoring station. The total ratio of BCC/SCC was 3.5. Participants who received low and high UV doses had a BCC/SCC ratio of 4.2. Those who received very high UV doses had a ratio of 2.1. A very high UV dose was also associated with the doubling of the total number of tumors per person and a significantly increased risk of having SCC, a more aggressive malignancy. Tumors in sun-exposed areas (on the body) were more common in participants who received high and very high UV doses. The tumors in sun-protected areas were associated with exposure to lower levels of UV. This large-scale population study provides evidence that varying doses of UV radiation have a profound influence on key characteristics of NMSC.