SOME FURTHER CONSIDERATIONS ON THE USE OF REPAIR-DEFECTIVE ORGANISMS AS BIOLOGICAL DOSIMETERS FOR BROAD-BAND ULTRAVIOLET RADIATION SOURCES

Abstract— The extreme variation in biological effectiveness of the various components of solar ultraviolet radiation (solar UV) which reaches the earth's surface, especially photons of wavelengths between 295 and 330 nm, makes the dosimetry of solar UV a complex and, as yet, unresolved problem. A proper weighting of the various components of solar UV would permit expression of expsoure as a single parameter (dose). Weighting could compensate for the variations in composition of solar UV which might occur during exposure or the differences in sources of UV radiations; weighting would permit comparison of exposures at various locations on the earth and extrapolation of laboratory observations to field situations where wavelength composition might be rather different. Various radiation-sensitive microorganisms have been proposed as biological dosimeters. Biological dosimeters automatically weight the subcomponents of solar UV differently than a purely physical irradiance meter. We have examined the available evidence regarding the weighting which repair-defective mutants provide in comparison with response of a number of wild-type organisms and would caution investigators that, for broad-band UV sources, especially those with significant biological actions through the range of 300–330 nm, repair-sensitive mutants may improperly weight the components, leading to errors of dosimetry and thus to possible errors of interpretation of results of solar UV exposure of wild-type organisms     

EFFECT OF IONIZING RADIATION UPON TOTAL DIFFUSE SPECTRAL REFLECTANCE OF ULTRAVIOLET LIGHT BY SKIN

Abstract— Irradiation of guinea-pig skin with X rays and beta particles resulted in decreased total diffuse reflectance (DSR) of 330–400 nm light. Qualitatively, this response resembled that seen after irradiation of the skin of normal guinea-pigs with ultraviolet (UV) radiation of wavelength shorter than 300 nm or that of photosensitized guinea pigs with UV wavelengths longer than 300 nm. We postulate that the transformations which depress the DSR result from energy-transfer processes, independent of the class of radiation. Moreover, they are intimately related to subsequent changes in vascular permeabilities (delayed erythema) which occur after the same radiation exposures that lower the 330–400 nm DSR of skin surfaces.     

PHOTOAGING EFFECTS ON SPECTRAL TRANSMITTANCE OF PLASTIC FILTERS

We examined the effects of ultraviolet (UV) radiation in combination with high levels of infrared (IR) radiation on the spectral transmittance of plastic filters. The biological action spectrum for damage to the human eye and skin changes dramatically in the 300-400 nm wavelength range. Cut-off filters used in this region to shape the spectrum of exposure sources are thus critical to the design of experiments which use broadband light sources. The changes in transmittance of three types of plastic filters were observed over an exposure period of 1000 h. One set of three filters was exposed mainly to UV radiation, while the other set was exposed to UV radiation plus IR radiation. Filters exposed to both UV and IR radiation showed spectral changes in their transmittance, while the filters exposed to UV only showed no measurable changes.     

COMPARATIVE POTENCY OF BROAD-BAND AND NARROW-BAND PHOTOTHERAPY SOURCES TO INDUCE EDEMA, SUNBURN CELLS AND UROCANIC ACID PHOTOISOMERIZATION IN HAIRLESS MOUSE SKIN

The Philips TL01 narrow-band (311–313 nm) fluorescent lamp provides effective phototherapy for psoriasis and atopic eczema while emitting less erythemogenic radiation than conventional broad-band ( e.g . Philips TL12; 270–350 nm) sources. We studied the potency of TL01 and TL12 radiation to induce edema and sunburn cells (SBC) and to photoisomerize naturally occumng trans- urocanic acid (UCA) to cis -UCA in hairless mouse skin. Cis -UCA has immunosuppressive properties and is a putative mediator of UV-induced suppression of immune responses. For each source, there was UV dose dependence for all three responses. Within the dose ranges used, the potency ratio of TL12: TL01 radiation to induce equivalent edema and SBC was about 6:1. However, the potency ratio to induce cis-IJCA was less than 2.3:1. Therefore, at a given level of edema or SBC induction, TL01 was more efficient than TL12 at UCA photoisomerization. The TL01 induction of immunomodulating cis -UCA, while causing minimal skin injury, may relate to the therapeutic efficacy of this source in skin conditions with an immunological component.     

AN EXAMINATION OF THE SPECTRAL RESPONSE CHARACTERISTICS OF SEVEN ROBERTSON-BERGER METERS AFTER LONG-TERM FIELD USE

Abstract— Seven Robertson-Berger ultraviolet meters located at National Weather Service stations were subjected to a laboratory analysis of their spectral response functions. The analysis revealed that all spectral response functions were similar in shape in the important erythematogenic wavelength region of 300–330 nm; however, a few of the spectral response function wavelength positions varied slightly. The average of the spectral response functions was compared to Robertson-Berger meter spectral response functions published in the 1970s. and they agreed within experimental error. This finding suggests that the shapes of the spectral response functions did not change or changed only slightly during the meters' long-term exposure in the network. To provide insight into the problems associated with measurement of ultraviolet radiation in the UV-B region (295–320 nm), examples of errors caused by wavelength band shifts and calibration procedures are given.     

Standard ultraviolet daylight for nonextreme exposure conditions

The skin is exposed to ultraviolet radiation (UVR) from natural or artificial sources on a daily basis. The effects of chronic low dose exposure merit investigation, even when these effects are neither conspicuous nor clinically assessable. The purpose of the present study was to define a relative spectral UV irradiance that is representative of frequent nonextreme sun exposure conditions and therefore more appropriate for studies of the long-term and daily effects of solar UV on the skin. Solar spectral UV irradiance values were calculated for different dates and locations by using a radiative transfer model. The spectral irradiance values obtained when the solar elevation is lower than 45 degrees were averaged. An important feature is the dUVA (320-400 nm) to dUVB (290-320 nm) irradiance values ratio, which was found to be 27.3 for the overall average. When the months corresponding to extreme irradiance values (low or high) were excluded from the calculations, the dUVA to dUVB ratio ranged from 27.2 to 27.5. The mean spectral irradiance of the model presented here represents environmental UV exposure conditions and can be used both as a standard to investigate the biological effects of a nonextreme UVR and to assess the effectiveness of products for daily skin protection.     

ULTRAVIOLET QUANTUM YIELDS OF PHOTOPHOSPHORYLATION IN Halobacterium halobium*

Quantum yields of photophosphorylation in Halobacterium halobium were determined for ultraviolet spectral bands between 276 and 365 nm, and at 565 nm wavelength, based on integral spectral cell absorptance, bacteriorhodopsin-specific cell absorptance and the corresponding quantum dose rates. In the ultraviolet, there is an almost linear decline of the quantum yields of photophosphorylation from 365 to 276 nm wavelength, despite the peak absorption of bacteriorhodopsin at 280 nm. The cycling quantum yield for 276 nm excitation of bacteriorhodopsin was determined as 4.5 ± 1.8%, which is about one fourth of the value of 19% for solubilized bacteriorhodopsin. Threshold energy fluence rates of 20 W m^?2 for UV-B radiation typify the photophosphorylation as three orders less sensitive than the sensory UV-B avoidance response that needs 0.02 W m^?2 as the threshold. Thus, UV-B avoidance appears as the dominating strategy for survival of the archaic bacterium H. halobium, rather than possible photoenergetic use of UV-B radiation and photorepair of UV-damage.     

MgZnO/ZnO p–n junction UV photodetector fabricated on sapphire substrate by plasma-assisted molecular beam epitaxy

We have investigated the spectral response of back- and front-surface-illumination MgZnO/ZnO p–n ultraviolet photodetector fabricated by plasma-assisted molecular beam epitaxy on sapphire substrate. The current–voltage measurements show that the device has a rectifying behavior with a turn-on voltage of 4.5 V. The detector exhibits a broad spectral response which covers the visible and UV spectra regions (from 275 to 375 nm) and has a maximum peak response at the wavelength of 330 nm. At a reverse bias of 5 V, the visible rejection (R330 nm/R500 nm) was more than two orders of magnitude. The peak responsivity at 330 nm for the device under back-illumination is about four times larger than that of the device under front-illumination under the same reverse bias. The response mechanisms of the device under back- and front-illumination are discussed.     

Fluorescence spectral imaging of dihydroxyacetone on skin in vivo

Dihydroxyacetone (DHA) has been proposed as a potential alternative to dansyl chloride for use as a fluorescence marker on skin to assess stratum corneum turnover time in vivo. However, the fluorescence from DHA on skin has not been adequately studied. To address this void, a noninvasive, noncontact spectral imaging system is used to characterize the fluorescence spectrum of DHA on skin in vivo and to determine the optimal wavelengths over which to collect the DHA signal that minimizes the contributions from skin autofluorescence. The DHA-skin fluorescence signal dominates the 580-680 nm region of the visible spectrum when excited with ultraviolet radiation in the 320-400 nm wavelength region (UVA). An explanation of the time-dependent spectral features is proposed in terms of DHA polymerization and binding to skin.     

Ovariectomy accelerates photoaging of rat skin

We have previously reported the formation of wrinkles, a decrease in skin elasticity and a loss in the linearity of dermal elastic fibers in rat hind limb skin irradiated with ultraviolet radiation in wavelength ranging 290-320 nm (UVB) at a suberythemal dose for 6 weeks. Estrogens are considered effective in preventing photoaging in postmenopausal females, but the role of estrogen in the skin remains unclear. In this study we have evaluated the influence of short-term chronic UVB irradiation at a suberythemal dose on the skin of ovariectomized rats. An ovariectomy or a sham operation was performed on each 3 week-old female Sprague-Dawley rat. Starting 1 week after the operation the hind limb skin of each rat was irradiated with UVB at a suberythemal dose (130 mJ/cm2) three times a week for 3 or 6 weeks. Decreases in elasticity and wrinkle formation in the skins of ovariectomized animals were induced more quickly than in the skins of sham-operated animals following UVB irradiation. The linearity of elastic fibers in the ovariectomy group decreased significantly compared with the sham-operation group, but erythema in the ovariectomy group was induced more readily than in the sham-operation group following UVB irradiation. These findings suggest that decreases in the estrogen levels after ovariectomy accelerate photoaging in terms of the morphology and physical properties of the skin surface and the three-dimensional structure of elastic fibers.     

SKIN OPTICS AND PHOTOTHERAPY OF JAUNDICE

Abstract The Kubelka–Munk theory of radiation transfer is applied to determine the influence of skin optical losses on the efficiency of phototherapy of jaundice. Using a multi-layer model of the skin the photon absorption rate of bilirubin molecules is calculated for spectrally Gaussian light sources and fluorescent lamps used in phototherapy. Light absorption and scattering processes in the skin layers shift the optimum value of the peak excitation wavelength from λ= 453 nm (absorption maximum of bilirubin in vitro ) to λ= 480 nm. This suggests the clinical investigation of narrow-spectrum lamps emitting in the blue-green region of the spectrum.     

A NEW DOSIMETER FOR ULTRAVIOLET-B RADIATION

Abstract— A type of polycarbonate plastic was found to be sensitive to ultraviolet (UV) radiation. The damage to the material due to UV exposure was revealed by etching in a strong alkaline solution. The latent effect can be retained in the material for a period of at least 30 days. The material was tested for use as a detector of ultraviolet-B (UV-B 280–320 nm) radiation.
The response of the detector in the wavelength region between 254 and 365 nm was determined using a set of narrow-band filters and a 200 W UV xenon-mercury lamp. The maximum UV effect in the detector was observed at a wavelength of 290 nm. The spectral response curve was found to be similar to the human erythema action spectrum.
The detector may be miniaturized for dosimetric applications. The dose response curve is linear in the region up to an erythemal dose of 300 mJcm⁻². Laboratory and field tests showed that the dosimeter response to UV exposure was additive and was independent of dose rate. Further experiments suggested that the dosimeter was stable against changes in temperature and humidity.     

Assessing the optical changes in dissolved organic matter in humic lakes by spectral slope distributions

The impact of photodegradation and mixing processes on the optical properties of dissolved organic matter (DOM) was examined using a distribution of absorption spectral slopes and fluorescence measurements in two Argentine lakes. By examining the variability of the absorption spectral slopes throughout the ultraviolet and visible wavelengths, it was possible to determine which wavelength intervals were most sensitive to dominant loss processes. For DOM photodegradation, results show that increases in the absorption spectral slope between 265 and 305 nm were highly sensitive to increased exposure to solar ultraviolet radiation. A slightly larger wavelength range (265-340 nm) was found to be influenced when both mixing and photodegradation processes were considered, in terms DOM residence time, DOM absorption and UV diffuse attenuation coefficients. This same interval of spectral slopes (265-340 nm) was found to highly correlate with changes in fluorescence emission/excitation in wavelengths that are typically associated with terrestrial humic-like DOM. The identification of specific wavelength intervals, rather than the use of standard wavelength intervals or ratios, improved our ability to identify the dominant dissolved organic matter (humic-like) and major loss mechanisms (photodegradation) in these lakes.     

Wavelength sensitivity of acrylonitrile–butadiene–styrene

The wavelength sensitivity of unpigmented 100 mil thick ABS exposed to sunlight and filtered xenon are radiation was determined by the sharp cut filter technique based on three types of photochemical changes: bleaching, yellowing and loss in impact strength. Bleaching of the yellow-colored species formed in the processed material is caused by wavelengths between 380 and 525 nm with maximum color change by the 475–485 nm region. Photochemical yellowing is due to wavelengths between 300 and 380 nm with all wavelengths being almost equally effective. The spectral sensitivity based on change in impact strength shifts from the UV to the visible region as photochemical yellowing progresses. Addition of two stabilizers, a benzotriazole ultraviolet absorber and a hindered amine stabilizer, shifts the wavelength sensitivity based on yellowing to wavelengths shorter than 330 nm, but has no influence on the spectral effects based on impact strength. It is postulated that the rate of yellowing is reduced mainly by the ultraviolet absorber and stabilization against loss in impact strength is due largely to the hindered amine. Differences in rates and spectral response of the three types of photochemical changes indicate that they are due to different initiating mechanisms and thus require different types of stabilization. The significance to stability testing is discussed.     

UVA exposure affects UVB and cis-urocanic acid-induced systemic suppression of immune responses in Listeria monocytogenes-infected Balb/c mice

Ultraviolet radiation can inhibit immune responses locally as well as systemically. Such effects have been measured in animals and humans exposed to ultraviolet B (wavelength 280-315 nm) (UVB) and ultraviolet A (315-400 nm) (UVA). The precise wavelength dependence is important for the identification of possible molecular targets and for assessments of risk of different artificial UV sources and solar UV. In such analyses, it is commonly assumed that radiation energy from each wavelength contributes to the effect independent of the other wavelengths. Here we show that this assumption does not hold good. In the present study, it was investigated whether exposure to broadband UVA or longwave ultraviolet A 1 (340-400 nm) (UVA 1) prior to the standard immunosuppressive UVB protocol might modulate the immunosuppressive effects induced by UVB. Preexposure to broadband UVA or longwave UVA 1, 1 day prior to the standard immunosuppressive UVB protocol, inhibited the UVB-induced suppression of delayed type hypersensitivity (DTH) to Listeria monocytogenes significantly. This effect was not associated with restoring the number of interleukin (IL-12)-positive cells in the spleen. Since isomerization of trans-urocanic acid (UCA) into the immunosuppressive cis-UCA isomer plays a crucial role in UVB-induced immunomodulation, in a second set of experiments it was investigated whether immunosuppression induced by cis-UCA might also be downregulated by preexposure to UVA. Animals were exposed to broad-band UVA or longwave UVA 1 prior to application of an immunosuppressive dose of cis- or trans-UCA as a control. Both UVA and UVA 1 appear to inhibit the cis-UCA-induced systemic immunosuppression (DTH and IL-12) to L. monocytogenes. These studies clearly show that UVA radiation modulates both UVB and cis-UCA-induced immunomodulation. In general, our studies indicate that both broadband UVA and longwave UVA 1 could induce modulation of UVB and cis-UCA-induced immunomodulation. As sunlight contains both UVA and UVB radiation the balance between these two radiations apparently determines the net immunomodulatory effect.     

Polymer-based triphenyl tetrazolium chloride films for ultraviolet radiation monitoring

Ultraviolet (UV) radiation monitoring films were prepared from solutions of polymers (polyvinyl, alcohol, PVA, or polyvinyl butyral, PVB), containing triphenyl tetrazolium chloride dye (TTC). These films have a pronounced response to the main UV radiation spectral regions [UV-A (400–320 nm), UV-B (320–280 nm), and UV-C (280–180 nm)] showing different sensitivities. PVA/TTC film has its maximum sensitivity in the UV-A region, while PVB/TTC film has its maximum sensitivity in the UV-C region. Both films have almost the same sensitivity in the UV-B region. The radiation-induced colour change is analysed spectrophotometrically at the maximum of the visible absorption band peaking at 492 nm wavelength. The measurement uncertainty of estimating ultraviolet radiation energy incident per unit area on the films is found to be about 3.5% (1 σ). The study of the effect of radiance exposure, incident wavelength, and storage conditions have been carried out to characterise the use of these films for actinometric monitoring artificial ultraviolet radiation sources which are used for medical and industrial applications.     

Impact of Long‐Wavelength Ultraviolet A1 and Visible Light on Light‐Skinned Individuals

Solar radiation is known to be a major contributor to the development of skin cancer. Most sunscreen formulations, including those with broad spectrum, offer minimal protection in long‐wavelength ultraviolet A1 (UVA1; 370–400 nm) and visible light (VL; 400–700 nm) domain. There is limited information regarding the impact of this broad waveband (VL + UVA1, 370–700 nm) on those with light skin. In this study, ten healthy adult subjects with Fitzpatrick skin phototypes I–III were enrolled. On day 0, subjects' lower back was exposed to a VL + UVA1 dose of 480 J cm^?2. A statistically significant increase in erythema immediately after irradiation compared with subjects' baseline nonirradiated skin was observed. Clinically perceptible erythema with VL + UVA1 is a novel finding since the erythemogenic spectrum of sunlight has primarily been attributed to ultraviolet B and short‐wavelength ultraviolet A (320–340 nm). The results emphasize the need for protection against this part of the solar spectra and warrant further investigation.     

Compact fiber-optic fluorosensor employing light-emitting ultraviolet diodes as excitation sources

A compact fluorosensor using three different ultraviolet light-emission diodes as excitation sources for fiber-optic recording of fluorescence spectra from samples is described. A compact integrated spectrometer with linear array wavelength recording is used, yielding a spectral resolution of about 8 nm. In two system implementations ultraviolet light-emitting diodes at 300, 340 and 395 nm, or at 360, 385 and 410 nm were used as excitation sources with typical emission halfwidths of 12 nm, each combined with a matching long-path colored-glass filter automatically brought into the fluorescence light flow for suppression of reflected light. Spectra from measurements on vegetation, human skin tumors and a rare-earth ion-based thermographic phosphor were recorded to illustrate the system performance.     

IMMEDIATE PIGMENT DARKENING: VISUAL AND REFLECTANCE SPECTROPHOTOMETRIC ANALYSIS OF ACTION SPECTRUM

Immediate pigment darkening (IPD) occurs in human skin upon exposure to ultraviolet-A and visible radiation. The spectral changes that occur during IPD were measured with a rapid scanning reflectance spectrophotometer (RS) which employs optical fiber bundles for delivery and detection of light between 400 and 750 nm. The radiation dose dependence and wavelength dependence (334-549 nm irradiation) of IPD were studied by both the classical visual grading method and by spectrophotometric scoring using the RS system. The spectral changes that occur at long wavelengths with IPD mimic the natural absorption spectrum of melanin. Therefore, the IPD was scored in terms of the apparent change in melanin optical density, using the method Kollias and Baqer [Photochem. Photobiol. 43, 49-54 (1986)], based on reflectance in the 620-720 nm range. The nonlinearity of the visual grading method is demonstrated. The degree of IPD is first-order with respect to delivered dose and saturates after high doses. The maximum amount of IPD attained at saturation is greater for shorter wavelengths. Extrapolation of the reflectance data suggests the longest wavelength capable of eliciting IPD is about 470 nm.     

TUMORIGENESIS BY A LONG WAVELENGTH UV-A SOURCE

Albino hairless mice (Skh-hr1) were exposed daily to radiation from a high-power long wavelength UV-A source (wavelengths longer than 340 nm). The irradiations lasted 2 h per day. The daily dose was 220 kJ/m2. Heavy scratching marks were observed in 13 out of 48 animals. However during the experiment 31 of the animals developed tumors of 1 mm or larger before any scratching was observed. The median induction time was 265 days for 1 mm tumors.