PVC-laponite nanocomposites: Enhanced resistance to UV radiation

Laponite, a clay mineral, was treated by intercalation of two different phthalocyanine amide polymers based on aliphatic amine (MF-PcAl) as well as an aromatic one (MF-PcAr). The intercalation of the amide polymers was followed by X-ray diffraction (XRD). The different forms of laponite even in its untreated form were incorporated into poly(vinyl chloride) (PVC) formulations via melt blending method to produce PVC-laponite nanocomposites of exfoliated type which was confirmed by XRD. The stabilization mode of the incorporated laponites against UV radiation is discussed based on scanning electron microscopy (SEM), XRD, UV-vis absorption and transmission spectra, electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and mechanical properties. Improved resistance to the UV degradative effect was explained on the light of the ability of the clay to scatter the light and to trap any growing radicals as well in addition to the sacrificing role of phthalocyanines by absorbing the incident light on the expense of the PVC and transmitting the rest of the light in another non-harmful form such as heat.     

UV radiation and skin cancer in Norway

A distinct increase in skin cancer incidences is observed since the registration started in Norway in the 1950s. As UV radiation is assumed to be the main risk factor for skin cancer, hourly values of the UV irradiance were reconstructed for the period 1957–2005 for 17 of the Norwegian counties (58–70°N). For reconstruction, a radiation transfer model is run with total ozone amount and cloud information as meteorological input. Reconstructed hourly erythemally weighted UV irradiances for about 5 years are compared to measurements at four stations, two stations representing the north–south extension of Norway, and two stations at about 60°N representing the eastern inland – Western coastal contrasts. The agreement between reconstructed and measured UV varies between 0% for the northernmost site to 10–15% overestimation for the other locations. For clear sky, a reasonable agreement between reconstructed and measured data was found for all stations, while for overcast, an overestimation of 10–20% was found for all but the northernmost station. Both the cancer incidences and the reconstructed UV values have a distinct north–south increase. The UV increase towards south is mostly due to increasing solar elevation. The west to east increase is much smaller, and differences in UV are due to differences in both cloud optical thickness and total cloud amount. One additional outcome from this work is that long-term UV-data are reconstructed for Norway, data that can be used in further biological and medical studies related to UV effects.     

Effects of UV radiation of cells

UV radiation interacts with mammalian cells in a very complex manner, although DNA appears to be the main chromophore. Recent literature within this field is reviewed. The review is concentrated on the following main topics: Chromophores for UV action, photoproducts in DNA, repair of UV-induced DNA damage, wavelength interactions, inactivation, mutagenesis, transformation and protection mechanisms against UV damage.     

Ozone and UV radiation over southern South America: climatology and anomalies

Ozone and UV radiation were analyzed at eight stations from tropical to sub-Antarctic regions in South America. Ground UV irradiances were measured by multichannel radiometers as part of the Inter American Institute for Global Change Radiation network. The irradiance channels used for this study were centered at 305 nm (for UV-B measurements) and 340 nm (for UV-A measurements). Results were presented as daily maximum irradiances, as monthly averaged, daily integrated irradiances and as the ratio of 305 nm to 340 nm. These findings are the first to be based on a long time series of semispectral data from the southern region of South America. As expected, the UV-B channel and total column ozone varied with latitude. The pattern of the UV-A channel was more complex because of local atmospheric conditions. Total column ozone levels of < 220 Dobson Units were observed at all sites. Analysis of autocorrelations showed a larger persistence of total column ozone level than irradiance. A decreasing cross-correlation coefficient between 305 and 340 nm and an increasing cross-correlation coefficient between 305 nm and ozone were observed at higher latitudes, indicating that factors such as cloud cover tend to dominate at northern sites and that ozone levels tend to dominate at southern sites. These results highlight the value of long-term monitoring of radiation with multichannel radiometers to determine climatological data and evaluate the combination of factors affecting ground UV radiation.     

UV index forecasts and measurements of health-effective radiation

While erythemal irradiance as a potentially damaging effect to the skin has been extensively studied and short-term forecasts have been issued to the public to reduce detrimental immediate and long-term effects such as sunburn and skin cancer by overexposure, beneficial effects to human health such as vitamin D(3) production by UV radiation and melatonin suppression by blue visible light have attained more and more attention, though both of them have not become part of forecasting yet. Using 4years of solar radiation data measured at the mid-latitude site Lindenberg (52°N), and forecast daily maximum UV index values, an overall good correspondence has been found. The data base of solar UV radiation and illuminance has also been used to analyze effects of clouds and aerosols on the effective irradiance. Optically thick clouds can strongly modify the ratios between erythemal and vitamin D(3) effective irradiance such that direct radiative transfer modeling of the latter in future UV forecasts should be preferably used. If parameterizations of vitamin D(3) effective irradiance from erythemal irradiance are used instead, the optical cloud depth would have to be taken into account to avoid an overestimation of vitamin D(3) with parameterizations neglecting cloud optical depth. Particular emphasis for the beneficial effects has been laid in our study on low exposure. Daily doses of solar irradiation for both vitamin D(3) and melatonin suppression do not reach minimum threshold doses even with clear sky and unobstructed horizon during the winter months.     

Sensitised decomposition of microcystin-LR using UV radiation

UV radiation was applied to degrade cyanobacterial hepatotoxin, microcystin-LR in the presence of phycocyanin as a model natural sensitiser. The concentrations of both the toxin and the pigment used in the experiments were higher by several orders of magnitude than found in the environment. The photoreaction parameters were optimised. The process was found to be of limited use for water treatment due to its low efficacy. Additionally, pronounced UV-induced bleaching of the pigment significantly reducing the photoreaction rates of the toxin was observed for the highest UV radiation intensities applied.     

Photoimmunology: the mechanisms involved in immune modulation by UV radiation

Ultraviolet radiation (UVR) may be the most prevalent agent that man encounters in his environment. As a result, certain biological adaptations take advantage of the beneficial effects of UVR exposure, e.g. the photoactivation steps involved in vitamin D metabolism. In this regard, UVR plays an important role in maintaining our good health; however, it must be noted that UVR is potentially the most harmful naturally occurring agent in our environment. Thus, it appears that several mechanisms have evolved to protect us against the detrimental effects of UVR overexposure. Although epidermal melaninization or "tanning" may be the most obvious example of these processes, we would argue that adoptive mechanisms within the immune system also provide protection against UVR-induced skin damage. It is now known that UVR affects the distribution and functional activities of various immunocompetent cells within the skin, as well as modifying the production of inflammatory and hematopoietically active cytokines. This review will focus on the known mechanisms involved in the immune modulatory effects of UVR and how adoptive immune responses to UVR-induced skin damage contribute to specific pathological processes.     

Influence of UV radiation on four freshwater invertebrates

Laboratory tests confirmed a negative and variable response of the following four species to artificial UV radiation: Cypridopsis vidua, an ostracode; Chironomus riparius, a midge larvae; Hyalella azteca, an amphipod; and Daphnia magna, a daphnid. Severe damage occurred at UV-B irradiance ranging from 50 to 80% of incident summer values. Under constant exposure to UV and photosynthetically active radiation (PAR) the acute lethal response was recorded at 0.3, 0.8, 0.8 and 4.9 W m-2 UV-B for D. magna, H. azteca, C. riparius and C. vidua, respectively. Sublethal UV-B damage to invertebrates included impaired movement, partial paralysis, changes in pigmentation and altered water balance (bloating). A series of UV-B, UV-A and PAR treatments, applied separately and in combination, revealed a positive role for both UV-A and PAR in slowing down UV-B damage. Mean lethal concentration values of the species typically more tolerant to UV and PAR (Cypridopsis, Chironomus) decreased conspicuously when both UV-A and PAR were eliminated. For UV-B-sensitive species (Hyalella, Daphnia) these differences were notably smaller. We suggest that this gradation of sensitivity among the tested species demonstrates potential differences in repairing mechanisms which seem to work more efficiently for ostracodes and chironomids than for amphipods and daphnids. Manipulations with a cellulose acetate filter showed that lower range UV-B (280-290 nm), produced by FS-40 lamps, may cause excessive UV damage to invertebrates.     

The influence of UV radiation on silk fibroin

An investigation into the influence of UV-irradiation on regenerated silk fibroin dissolved in water was carried out using UV-Vis and fluorescence spectroscopy. It was found that the absorption of regenerated silk fibroin in solution increased during UV-irradiation of the sample, most notably between 250 and 400 nm. Moreover, after UV-irradiation a wide peak emerged between 290 and 340 nm with maximum at about 305 nm. The new peak suggests that new photoproducts are formed during UV-irradiation of regenerated silk fibroin.The fluorescence of regenerated silk fibroin was observed at 305 nm, at 480 nm and at 601 nm after excitation at 275 nm. UV-irradiation caused fluorescence fading at 305 nm and at 601 nm. The increase of fluorescence was observed at 480 nm, probably due to formation of new photoproducts. After excitation at 305 nm the fluorescence of regenerated silk fibroin was observed at 340 nm and at 400 nm. UV-irradiation caused fluorescence fading at 340 nm. FTIR spectroscopy showed that primary structure of regenerated silk fibroin was not significantly affected by UV radiation. SDS-PAGE chromatography showed alterations of molecular weight of silk after UV exposure.     

Measurement of UV radiation using suspensions of microorganisms

The measurement of solar UV radiation is usually performed using physical devices like photodiodes or photomultipliers or with chemical substances (actinometry). The application of biological material such as microorganisms for this purpose has gained increasing importance in the last few years. The microorganisms may be dried and spread on a flat surface or they may be in aqueous suspensions contained in UV-transparent vessels. If the measurements are done on flat surfaces, the irradiance weighted by the action spectrum of the dried microorganism used is the result of the measurement. If aqueous suspensions of microorganisms are used, contained for instance in spherical vessels, the fluence weighted by the action spectrum of the microorganisms in the aqueous suspension is the result. A problem of this method of measurement can be that inside the vessel the distribution of UV radiation is usually not homogeneous, causing distributions of fluences among the irradiated microorganisms, which may result in variation of the results depending on the mixing characteristics of the suspension during irradiation.     

Degradation of ROMP-based bio-renewable polymers by UV radiation

The degradation of a bio-renewable polymer under UV exposure was studied using various methods. Degradation of the bio-renewable polymer increased with increasing exposure time. Enhanced cross-link density in the early stage of degradation was confirmed by Soxhlet extraction. Tensile testing showed a transition from ductile failure to brittle fracture. Surface cracks and embrittlement were primary reasons for most reductions in mechanical properties, such as tensile strength and breaking strain. The effects of degradation were confined to the surface of thick bio-based polymer specimens, confirmed by both SEM and PAS-FTIR. Depth profile studies of degraded samples showed that the concentration of oxidation products, such as hydroxyl and carbonyl groups, varied with depth depending on the diffusion of oxygen.     

Photoprotection of the eye - UV radiation and sunglasses.

Although most health scientists now agree that health risks to the skin (e.g., skin cancer) exist from exposure to the ultraviolet radiation in sunlight, a scientific consensus has not really been achieved vis-à-vis sunlight and ocular health. A growing number of scientists warn of hazards to the eye if ultraviolet radiation - and perhaps even shorter wavelength visible radiation also - is not filtered by lenses. Despite a substantial literature on the adverse effects of ultraviolet radiation (UVR) and intense light upon ocular structures, particularly upon the retina, controversy still surrounds the question of whether the levels of natural and man-made light sources are damaging when encountered under normal viewing conditions. Although scientific evidence accumulates to indicate that chronic exposure conditions may accelerate ageing processes in ocular tissues, the quantitative question of "How much is safe?" remains to be answered conclusively.     

Accidental exposure to UV radiation produced by germicidal lamp: case report and risk assessment

Ultraviolet radiation is known to cause both benefits and harmful effects on humans. The adverse effects mainly involve two target organs, skin and eye, and can be further divided into short- and long-term effects. The present case report describes an accidental exposure of two health-care workers to ultraviolet radiation produced by a germicidal lamp in a hospital pharmacy. The germicidal lamp presented a spectrum with an intense UV-C component as well as a modest UV-B contribution. Overexposure to UV-C radiation was over 100 times as large as the ICNIRP exposure limits. A few hours after the exposure, the two subjects reported symptoms of acute UV injury and both of them continued having significant clinical signs for over 2 years. In this study, we describe acute and potentially irreversible effects caused by high UV exposure. In addition, we present the results of risk assessment by occupational exposure to germicidal lamps.     

Photosensitizing mechanism and identification of levofloxacin photoproducts at ambient UV radiation

Levofloxacin (LVFX) is a broad spectrum third generation fluoroquinolone antibiotic, used in the treatment of severe or life-threatening bacterial infections. Photosensitizing mechanism of LVFX was investigated under the ambient environmental intensities of UV-A, UV-B and sunlight exposure. Phototoxic effects of LVFX were assessed on NIH-3T3 and HaCaT cell lines. Results identified first time three photoproducts of LVFX at ambient levels of UV-R by LC-MS/MS. The generation of reactive oxygen species (ROS) was investigated photochemically as well as intracellularly in HaCaT cell line. ROS were significantly quenched by specific quenchers like DABCO, NaN(3), D-mannitol and NAC. Photosensitized LVFX caused lipid peroxidation at different concentrations. Quenching study with superoxide dismutase confirms the LVFX-induced lipid photoperoxidation. Further, photocytotoxicity of LVFX showed significant reduction in cell viability by MTT and neutral red uptake assays. LVFX caused cell arrest in G2/M phases as well as induced apoptosis through ROS-dependent pathway. In addition, photosensitized LVFX also induced upregulation of p21 and Bax/Bcl-2 genes ratio. India is a tropical country and most of the human activities such as agriculture, commerce, sports, etc. take place in bright sunlight; therefore, photosensitive LVFX may lead to skin/ocular disorders and immune suppression. Information is needed regarding the phototoxicity of LVFX for human safety.     

Photo-degradation of PADC by UV radiation at various wavelengths

The effects of ultraviolet (UV) photons at different wavelengths (namely UVA, UVA + B and UVC) on PADC (polyallyl diglycol carbonate) were investigated in this study. The chemical modifications were studied by Fourier Transform Infrared (FTIR) spectrometry and the corresponding nano-mechanical properties were also determined. The scission process could be revealed by the decreasing net absorbance at particular wavelengths in the infrared (IR) spectra. On the other hand, the cross-linking was indicated by the increased hardness and reduced modulus determined with a nanoindenter. UVA caused no chemical modifications as most of the UV photons in this range were not absorbed by PADC. Both UVA + B and UVC irradiation caused scission of the chemical bonds, which was also manifested by the faster chemical etching rates. The bulk etch rate increased from 1.37 to 5.73 μm/h for 60 h of UVA + B exposure for 3 h of chemical etching, and increased to 5.13 μm/h for 60 h of UVC exposure. For 3 h of etching, the bulk etch rate remained unchanged for UVC exposures longer than 20 h. The saturation of the bulk etch rate was due to formation of cross-linked structures on the surface of the PADC samples. It was also observed that a UVC exposure caused a comparatively higher bulk etch rate at the beginning of etching. However, the bulk etch rate decreased with the depth of the PADC sample due to the lower rate of oxygen diffusion into deeper regions.     

Diffuse solar UV radiation and implications for preventing human eye damage

Ocular UV exposure is a function of both the direct and diffuse components of solar radiation. Broadband global and diffuse UV measurements were made in the morning, noon and afternoon. Thirty sets of measurements were made in summer and 50 in each of the other seasons at each of the periods in full sun. Corresponding sets were made in the shade of Australian evergreen trees: 42 trees in summer and 50 in each of the other seasons. The percentage diffuse UV was higher for the shorter 320-400 nm range (UVB) than for 280-320 nm (UVA). The percentage diffuse UVB ranged from 23 to 59%, whereas the percentage diffuse UVA ranged from 17 to 31%. The percentage diffuse UV was lower at noon than in the morning and afternoon with the difference more pronounced for the UVB. The average percentage diffuse UVB over all the measurements in the tree shade for the morning, noon and afternoon was 62, 58 and 71%, respectively, and the average percentage diffuse UVA was 52, 51 and 59%, respectively.     

UV radiation effects on pathogens and insect pests of greenhouse-grown crops

Production of high-value crops is often performed under protected cultivation. In recent years various spectral modifications have been made in greenhouse covers. Two of the main reasons to modify the spectral characteristics of greenhouse covers have been to suppress the proliferation of several foliar diseases and to protect crops from insects and insect-borne virus diseases of greenhouse-grown crops. These goals were achieved by complete or partial absorption of solar UV radiation, which interrupts the life cycle of several fungal pathogens and alters the visual behavior of many insects. Examples of these management strategies are described in this article.     

Evaluating radiation risks and resource opportunities associated with phosphogypsum in the Philippines

Journal of Radioanalytical and Nuclear Chemistry - Phosphogypsum (PG) accumulates during wet-phosphoric acid production for fertilizers. In the Philippines, PG is partly (40%) utilized to produce...     

Oxidation of guanine in cellular DNA by solar UV radiation: biological role.

The formation of cyclobutane pyrimidine dimers (CPD) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) was investigated in Chinese hamster ovary cells upon exposure to either UVC, UVB, UVA or simulated sunlight (SSL). Two cell lines were used, namely AT3-2 and UVL9, the latter being deficient in nucleotide excision repair and consequently UV sensitive. For all types of radiation, including UVA, CPD were found to be the predominant lesions quantitatively. At the biologically relevant doses used, UVC, UVB and SSL irradiation yielded 8-oxodGuo at a rather low level, whereas UVA radiation produced relatively higher amounts. The formation of CPD was 10(2) and 10(5) more effective upon UVC than UVB and UVA exposure. These yields of formation followed DNA absorption, even in the UVA range. The calculated relative spectral effectiveness in the production of the two lesions showed that efficient induction of 8-oxodGuo upon UVA irradiation was shifted toward longer wavelengths, in comparison with those for CPD formation, in agreement with a photosensitization mechanism. In addition, after exposure to SSL, about 19% and 20% of 8-oxodGuo were produced between 290-320 nm and 320-340 nm, respectively, whereas CPD were essentially (90%) induced in the UVB region. However, the ratio of CPD to 8-oxodGuo greatly differed from one source of light to the other: it was over 100 for UVB but only a few units for UVA source. The extent of 8-oxodGuo and CPD was also compared to the lethality for the different types of radiation. The involvement of 8-oxodGuo in cell killing by solar UV radiation was clearly ruled out. In addition, our previously reported mutation spectra demonstrated that the contribution of 8-oxodGuo in the overall solar UV mutagenic process is very minor.