ultraviolet-B Levels Research Articles

USDA UV-B monitoring system: An application of centralized architecture

In order to determine the spatial and temporal variations of solar ultraviolet-B (UV-B) radiation reaching the Earth's surface and their effects on agriculture and environment due to the depletion of atmospheric ozone, the U.S. Department of Agriculture (USDA) UV-B monitoring system has been established to provide essential information of ground UV-B levels, along with other variables, to research communities, decision makers, and the public. This monitoring network of 39 sites was designed as a centralized system covering the U.S. domain with collaborating sites in Canada and New Zealand. Programmed data loggers and a central data server are employed to automate the work. The centralized architecture allows centrally processing the data from all sites on a 3 min basis and making daily updates available for the users. The system architecture, algorithms for data collection and data flow in the data processing procedures are presented in this article. Statistics show that the system is rather reliable with an overall data completeness of 98.14% since it began running in 1994. Main damages to the instruments are caused by the static electricity associated with severe thunderstorms, which result in a lower data completeness in summer months than in the others. The drawbacks of the centralized architecture, the possible remedies for the network failures, and our experiences with the system are discussed.

Variation in UV sensitivity among common frog Rana temporaria populations along an altitudinal gradient

Solar ultraviolet-B (UV-B) radiation can be harmful for developing amphibians. As the UV-B dose increases with altitude, it has been suggested that high-altitude populations may have an increased tolerance to high levels of UV-B radiation as compared to lowland populations. We tested this hypothesis with the common frog ( Rana temporaria) by comparing populations from nine altitudes (from 333 to 2450 m above sea level). Eggs collected in the field were used for laboratory experiments, i.e., exposed to high levels of artificial UV-B radiation. Eggs were reared at 14±2 °C and exposed to UV treatments until hatching. Embryonic developmental rates increased strongly and linearly with increasing altitude, suggesting a genetic capacity for faster development in highland than lowland eggs. Body length at hatching varied significantly with UV-B treatments, being lower when eggs developed under direct UV-B exposure. Body length at hatching also increased as the altitude of populations increased, but UV-B exposure times were shorter as altitude of population increased. However, the body length difference between exposed and non-exposed individuals in each population decreased as altitude of populations increased, suggesting a costly effect of UV exposure on growth. Type of UV exposure did not influence the mean rates of embryonic mortality and deformity, but both mortality and deformity rates increased as the altitude of populations increased (while UV-B exposure duration decreased). The effect of UV-B on body length at hatching, mortality, and deformities suggests that the sensitivity to UV-B varied among populations along the altitudinal gradient. These results are discussed in evolutionary terms, specifically the potential of R. temporaria high-altitude populations to develop local genetic adaptation to high levels of UV-B.

Allelopathic Influence of Houndstongue (Cynoglossum officinale) and Its Modification By UV-B Radiation

Influence of aqueous leaf extracts, leaf residue, and leached-leaf residue of houndstongue, a noxious rangeland weed, on seedling emergence of forage grasses was studied. Ultraviolet-B (UV-B) effects during houndstongue growth on subsequent germination and growth-inhibitory activity of leaf extracts were investigated. Addition of glasshouse-grown houndstongue leaf extract to mineral soil decreased emergence of crested wheatgrass by 13% and prairie junegrass by 20% at 14 d after sowing. Idaho fescue emergence was unaffected. Incorporation of houndstongue leaf- and leached-leaf residue into soil (0.4 g residue : 20 g soil) delayed emergence of forage grasses. At 14 d after sowing, houndstongue leaf residue spread on the soil surface (0.2 g residue : 20 g soil) tended to inhibit seedling emergence more than leaf residues incorporated into soil. In separate experiments, houndstongue plants were grown at 0, 4, 7, and 11 kJ/m2/d biologically effective UV-B radiation for 6 wk, and leaf extracts (0.5, 1, 2, and 4% wt/v) were prepared. Exposure of houndstongue to increasing UV-B dose during plant growth generally increased the inhibitory activity of their leaf extract on prairie junegrass germination. Crested wheatgrass and Idaho fescue seedlings incubated in extracts of houndstongue leaves exposed to UV-B, compared with leaves grown in a UV-B–free environment, had decreased root lengths. Leaf extracts of plants exposed to elevated UV-B levels had higher absorbance at 300 nm, indicating greater concentration of UV-B–absorbing compounds. This study suggests houndstongue leaf extracts and residues inhibit seed germination and seedling emergence and that UV-B may enhance their allelopathic influence on some forage grasses. Field studies are needed to confirm the allelopathic influence of houndstongue under rangeland conditions.Nomenclature: Houndstongue, Cynoglossum officinale L. CYWOF, crested wheatgrass, Agropyron cristatum (L.) Gaertn., alternate binomial, Elymus wawawaiensis J. Carlson & Barkworth var. Secar, Idaho fescue, Festuca idahoensis Elmer var. Joseph, prairie junegrass, Koeleria macrantha (Ledeb.) J.A. Schultes

Impact of solar ultraviolet-B radiation on the antioxidant defense system in soybean lines differing in flavonoid contents

Exposure to ultraviolet-B (UV-B) radiation can lead to oxidative damage in plants. However, plants possess a number of UV-protection mechanisms including screening of potentially damaging UV-B and increased production or activities of antioxidants. The balance or trade-off between these two mechanisms has rarely been studied and is poorly understood. Two isolines of soybean ( Glycine max [L.] Merr.) Clark cultivar, the normal line with moderate levels of flavonoids and the magenta line with reduced flavonoids levels, were grown in the field with or without natural levels of UV-B. Leaflet blades of the first trifoliate leaf were harvested after 4–12 days of exposure to the experimental conditions for analysis of active oxygen species (AOS) and antioxidant levels. Solar UV-B radiation caused oxidative stress in both lines and altered AOS metabolism primarily by decreasing superoxide dismutase activity and increasing the activities of ascorbate peroxidase, catalase and glutathione reductase. This resulted in decreased ascorbic acid content and increased dehydroascorbate content. The magenta line had greater oxidative stress than the normal line in spite of its enhanced oxidative defense capacity as compared to the normal line, even under UV-B exclusion. These results indicate enhanced sensitivity in the magenta line, especially under UV-B exclusion that was likely due to the absence of flavonoid epidermal screening compounds and subsequent increased penetration of solar ultraviolet radiation into the leaf.

Impact of solar Ultraviolet-B on the proteome in soybean lines differing in flavonoid contents

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was used to systematically investigate the impact of solar ultraviolet-B (UV-B) radiation on the soybean leaf proteome. In order to investigate the protective role of flavonoids against UV-B, two isolines of the Clark cultivar (the standard line with moderate levels of flavonoids and the magenta line with reduced flavonoids) were grown in the field with or without natural levels of UV-B. The 12-day-old first trifoliates were harvested for proteomic analysis. More than 300 protein spots were reproducibly resolved and detected on each gel. Statistical analysis showed that 67 protein spots were significantly ( P < 0.05) affected by solar UV-B. Many more spots were altered by UV-B in the magenta line than in the standard line. Another 12 protein spots were not altered by UV-B but showed significantly ( P < 0.05) different accumulations between the two lines, and for most spots the line-specific differences were also observed under UV-B exclusion. Most of the differentially accumulated spots were identified by mass spectrometry. The proteins were quite diverse, and were involved in metabolism, energy, protein destination/storage, protein synthesis, disease/defense, transcription, and secondary metabolism. The results suggest that high levels of flavonoids lead to a reduction in UV-B sensitivity at the proteomic level.

Joint Effects of Elevated Levels of Ultraviolet-B Radiation, Carbon Dioxide and Ozone on Plants¶†

There is growing interest regarding the joint effects of elevated levels of surface ultraviolet B (UV-B) radiation, carbon dioxide (CO2) and ozone (O3) on plants. Our current knowledge of this subject is too limited to draw any specific conclusions, although one might state that such effects are likely to be highly species dependent and may be more than additive, additive or less than additive. There are a number of uncertainties associated with the experimental protocols used and the conclusions reached in many studies. Nevertheless, in North America, there appear to be genotypes of three monocot crop species (Avena sativa L., Oryza sativa L. and Sorghum vulgare L.); six dicot crops (Cucumis sativus L., Lactuca sativa L., Lycopersicon esculentum Mill., Phaseolus vulgaris L., Pisum sativum L. and Solanum tuberosum L.) and two conifer species (Pinus ponderosa Dougl. and Pinus taeda L.) that may be considered sensitive to the joint effects of elevated levels of UV-B, CO2 and O3. However, to provide a more reliable assessment or validation of the predictions, future research must consider the concept of plant response surfaces and describe them more fully in numerical terms. Achieving that objective will require close cooperation among a number of scientists representing geographic locations with known spatial and temporal differences in UV-B, CO2 and O3 to conduct experiments under their site-specific conditions, using common plant materials and experimental protocols.

THE COST OF TOLERANCE: SENSITIVITY OF STREAM BENTHIC COMMUNITIES TO UV-B AND METALS

The ability to tolerate disturbance is a defense strategy that minimizes the effects of damage to fitness and is essential for sustainability of populations, communities, and ecosystems. Despite the apparent benefits of tolerance, there may be an associated cost that results in a deficiency of a system to respond to additional disturbances. Aquatic ecosystems are often exposed to a variety of natural and anthropogenic disturbances, and the effects of these compound perturbations are not well known. In this investigation, we examine whether tolerance to one stressor, metals, results in a cost of increased sensitivity to an additional stressor, ultraviolet-B (UV-B) radiation. Heavy metal pollution is recognized as a major environmental problem in Rocky Mountain streams. These high-elevation, typically clear streams may be at particular risk to elevated UV-B levels associated with reduced levels of ozone. Microcosm experiments were conducted using natural stream benthic communities collected from a reference site and a site with a long-term history of heavy-metal pollution. Direct and interactive effects of heavy metals and UV-B radiation on structural and functional characteristics of benthic communities were evaluated among four treatments: control, UV-B, metals, and metal and UV-B. Communities from the metal-polluted site were more tolerant of metals but less tolerant to UV-B compared to reference communities. Increased mayfly drift and reduced metabolism in response to metal exposure were observed in reference communities but not in the metal-polluted communities. In contrast to these results, UV-B radiation significantly reduced community metabolism, total macroinvertebrate abundance, and abundances of mayflies, caddisflies, and dipterans from the metal-polluted site, but had no effects on benthic communities from the reference site. ANOSIM results demonstrated that community responses differed among treatments at both sites. Metals had the largest impact on community differences at both sites, while UV-B had greater impacts at the metal-polluted site. This research demonstrates the need to account for potential costs associated with tolerance and that these costs can result in behavioral, structural, and functional impacts to benthic communities.

Do low-ethylene-producing transgenic canola (Brassica napus) plants expressing the ACC deaminase gene differ from wild-type plants in response to UVB radiation?

Few studies have considered ethylene involvement in plant responses to ultraviolet-B (UVB) radiation. We studied the responses to UVB radiation of one wild-type (WT, ‘Westar’) canola (Brassica napus L.) with normal ethylene evolution and two transgenic (C1, C2) lines with lower ethylene evolution. Canola plants were grown under biologically effective levels of UVB (UVBBE) radiation: 0.03 (low), 4.88 (medium), and 9.78 (high) kJ·m–2·d–1 in controlled-environment growth chambers. The growth and physiological parameters of the plants were measured. Of the two transgenic lines, C1 demonstrated higher ethylene evolution than C2 but lower than WT. The lowest aboveground and belowground biomass was found with exposure to high UVB radiation. WT produced more biomass than C2. Net CO2 assimilation and transpiration did not vary among plant lines or UVB treatments. Water-use efficiency was lower under high UVB radiation than under low UVB. The quantum yield of photosystem II was higher for C2 than for either WT or C1. WT did not differ from transgenic plants in respect to photosynthetic pigments and UV-screening compounds. Photosynthetic pigment concentration decreased, but concentration of UV-screening compounds, thickness of epicuticular wax, and the rate of root hydraulic conductance were increased by exposure to UVB radiation. While there appears to be a lack of ethylene involvement in some of the measured physiological parameters, the transgenic plants exhibited differential sensitivity to UVB in a few key measured parameters.

Physiological Effects of Solar Ultraviolet-B Exclusion on Two Cultivars ofVitis viniferaL. from La Rioja, Spain

The response of two cultivars of <i>Vitis vinifera</i> (Tempranillo and Viura) typical of La Rioja to current levels of ultraviolet-B (UV-B) radiation was evaluated. Plants were exposed to near ambient radiation (PAR + UV-A + UV-B) or near ambient radiation 95% depleted in UV-B. At the end of the 16-day exposure, diurnal variations in photosynthetic pigment composition, soil-plant-analysis-development (SPAD) values, variables of chlorophyll fluorescence, methanol-extractable UV-absorbing compounds (MEUVAC), and sclerophylly were analyzed. The responses of the two grapevine cultivars to the reduction of solar UV-B were somewhat different. The only significant response of Viura was a decrease in MEUVAC. This response was also found in Tempranillo, together with a reduced action of the xanthophyll cycle and an increase in the concentrations of chlorophyll and carotenoids and in SPAD values. Thus, solar UV-B seems to cause slight damage in Tempranillo grapevines. This damage as compared to the almost unaltered Viura grapevines could be related to the lower capacity of Tempranillo to produce MEUVAC under solar UV-B. Given that the exclusion of solar UV-B causes only modest physiological effects, at least in the short term, both cultivars seem to be adapted to the high solar radiation typical of the Mediterranean climate, and their photosynthetic performance (derived from chlorophyll fluorescence variables) does not appear to be at risk from current levels of UV-B.

Solar ultraviolet-B exposure and cancer incidence and mortality in the United States, 1993–2002

BackgroundAn inverse relationship between solar ultraviolet-B (UV-B) exposure and non-skin cancer mortality has long been reported. Vitamin D, acquired primarily through exposure to the sun via the skin, is believed to inhibit tumor development and growth and reduce mortality for certain cancers.MethodsWe extend the analysis of this relationship to include cancer incidence as well as mortality, using higher quality and higher resolution data sets than have typically been available. Over three million incident cancer cases between 1998 and 2002 and three million cancer deaths between 1993 and 2002 in the continental United States were regressed against daily satellite-measured solar UV-B levels, adjusting for numerous confounders. Relative risks of reduced solar UV-B exposure were calculated for thirty-two different cancer sites.ResultsFor non-Hispanic whites, an inverse relationship between solar UV-B exposure and cancer incidence and mortality was observed for ten sites: bladder, colon, Hodgkin lymphoma, myeloma, other biliary, prostate, rectum, stomach, uterus, and vulva. Weaker evidence of an inverse relationship was observed for six sites: breast, kidney, leukemia, non-Hodgkin lymphoma, pancreas, and small intestine. For three sites, inverse relationships were seen that varied markedly by sex: esophagus (stronger in males than females), gallbladder (stronger in females than males), and thyroid (only seen in females). No association was found for bone and joint, brain, larynx, liver, nasal cavity, ovary, soft tissue, male thyroid, and miscellaneous cancers. A positive association between solar UV-B exposure and cancer mortality and incidence was found for anus, cervix, oral cavity, melanoma, and other non-epithelial skin cancer.ConclusionThis paper adds to the mounting evidence for the influential role of solar UV-B exposure on cancer, particularly for some of the less-well studied digestive cancers. The relative risks for cancer incidence are similar to those for cancer mortality for most sites. For several sites (breast, colon, rectum, esophagus, other biliary, vulva), the relative risks of mortality are higher, possibly suggesting that the maintenance of adequate vitamin D levels is more critical for limiting tumor progression than for preventing tumor onset. Our findings are generally consistent with the published literature, and include three cancer sites not previously linked with solar UV-B exposure, to our knowledge: leukemia, small intestine, and vulva.

Ambient levels of UV-B in Hawaii combined with nutrient deficiency decrease photosynthesis in near-isogenic maize lines varying in leaf flavonoids: Flavonoids decrease photoinhibition in plants exposed to UV-B

Near-isogenic lines of maize varying in their genes for flavonoid biosynthesis were utilized to examine the effects of foliar flavonoids and nutrient deficiency on maximum net photosynthetic rate (P N) and chlorophyll (Chl) fluorescence (Fv/Fm) in response to ultraviolet-B (UV-B) radiation. Plants with deficient (30 to 70 % lower N, K, Mn, Fe, and Zn) and sufficient nutrients were exposed to four irradiation regimes: (1) no UV-B with solar photosynthetically active radiation (PAR), (2) two day shift to ambient artificial UV-B, 8.2-9.5 kJ m-2 d-1 (21-25 mmol m-2 d-1); (3) continuous ambient artificial UV-B; (4) continuous solar UV-B in Hawaii 12-18 kJ m-2 d-1 (32-47 mmol m-2 d-1). The natural ratio of UVB: PAR (0.25-0.40) was maintained in the UV-B treatments. In the adequately fertilized plants, lines b and lc had higher contents of flavonoids and anthocyanins than did lines hi27 and dta. UV-B induced the accumulation of foliar flavonoids in lines hi27 and b, but not in the low flavonoid line dta or in the high flavonoid line lc. In plants grown on deficient relative to adequate nutrients, flavonoid and anthocyanin contents decreased by 30-40 and 40-50 %, respectively, and Chl a and Chl b contents decreased by 30 and 70 %, respectively. The UV-B treatments did not significantly affect P N and Fv/Fm in plants grown on sufficient nutrients, except in the low flavonoid lines dta and hi27 in which P N and Fv/Fm decreased by ∼15 %. P N, Fv/Fm, and stomatal conductance decreased markedly (20-30 %) in all lines exposed to UV-B when grown on low nutrients. The decrease in Fv/Fm was 10 % less in higher flavonoid lines b and lc. The photosynthetic apparatus of maize readily tolerated ambient UV-B in the tropics when plants were adequately fertilized. In contrast, ambient UV-B combined with nutrient deficiency significantly reduced photosynthesis in this C4 plant. Nutrient deficiency increased the susceptibility of maize to UV-B-induced photoinhibition in part by decreasing the contents of photoprotective compounds.

Different sensitivity of carp ( Cyprinus carpio) and rainbow trout ( Oncorhynchus mykiss) to the immunomodulatory effects of UVB irradiation

In order to study the sensitivity of two fish species, carp ( Cyprinus carpio) and rainbow trout ( Oncorhynchus mykiss), to the immunomodulatory effects of ultraviolet B (UVB) radiation, the fish were exposed to a single UVB dose of 50, 250, 500 or 1000 mJ cm −2. These species represent different phylogenetic groups of fish, and they differ also in their behaviour inhabitating often dark and turbid (carp) or clear and transparent waters (salmonids). Immune responses were studied on day 1 post-irradiation. Unexposed fish, and fish exposed to radiation depleted of UV wavelengths served as controls. UVB irradiation markedly enhanced the blood respiratory burst and cytotoxic activity in carp, but in the head kidney these parameters were significantly suppressed. Rainbow trout respiratory burst was affected only after exposure with the highest dose of UVB. Lymphopenia and granulophilia were noted in both fish blood after exposure. This study indicates that UVB irradiation modulates immune functions in both fish species studied, and that rainbow trout is more tolerant than carp against UVB. Fish are clearly adapted to the environmental UVB levels prevailing in their usual living habitats, but are also a target of undesired effects of UVB on immune functions whenever exposed to increased radiation levels.

Sensitivity of Two Salamander (Ambystoma) Species to Ultraviolet Radiation

Increased ultraviolet-B (UV-B) radiation reaching the Earth's surface has been implicated in amphibian declines. Recent studies have shown that many amphibian species have differences in sensitivity depending on developmental stage. Embryos and larvae of Ambystoma maculatum (Spotted Salamander) and larvae of Ambystoma talpoideum (Mole Salamander) were exposed to five simulated UV-B treatments in controlled laboratory experiments to determine the relative sensitivity of different lifestages. Hatching success of the embryos exceeded 95% in all treatments; however, the larvae of both species exhibited greater sensitivity to UV-B exposure. Older larvae of A. maculatum that were not exposed to UV-B as embryos were more sensitive than larvae that had hatched during exposure to UV-B. Growth of surviving larvae of A. maculatum was significantly reduced as UV-B intensity increased, whereas growth of A. talpoideum was unaffected. These results were compared to ambient UV-B conditions in natural environments. It appears that the embryo stage is relatively unaffected by UV-B levels observed in natural habitats, probably because of protection from vegetation, organic matter in the water column, oviposition depth, and egg jelly. The larval stage of these species may be at greater risk, particularly if there is an increase in UV-B radiation exposure caused by increases in water clarity and/or decreases in dissolved organic carbon.

Genomic Mutation in Lines ofArabidopsis thalianaExposed to Ultraviolet-B Radiation

Studies that have attempted to estimate the rate of deleterious mutation have typically been conducted under low levels of ultraviolet-B (UV-B) radiation, a naturally occurring mutagen. We conducted experiments to test whether the inclusion of natural levels of UV-B radiation in mutation-accumulation (MA) experiments influences the rate and effects of mildly deleterious mutation in the plant Arabidopsis thaliana. Ten generations of MA proved insufficient to observe significant changes in means or among-line variances in experimental lines maintained either with or without supplemental UV-B radiation. Maximum-likelihood estimates of mutation rate for total flower number revealed a small but significant rate of mutation for MA lines propagated under supplemental UV-B exposure, but not for those in which supplemental UV-B was omitted. A fraction of the flower number mutations under UV-B (approximately 25-30%) are estimated to increase flower number. Results from the application of transposon display to plant materials obtained after MA, in both the presence and absence of supplemental UV-B, suggest that the average rate of transposition for the class I and II transposable elements (TEs) surveyed was no more than 10(-4). Overall, the estimates of mutation parameters are qualitatively similar to what has been observed in other MA experiments with this species in which supplemental UV-B levels have not been used. As well, it appears that naturally occurring levels of UV-B do not lead to detectable increases in levels of transposable element activity.

Distribution Patterns of Lentic-Breeding Amphibians in Relation to Ultraviolet Radiation Exposure in Western North America

An increase in ultraviolet-B (UV-B) radiation has been posited to be a potential factor in the decline of some amphibian population. This hypothesis has received support from laboratory and field experiments showing that current levels of UV-B can cause embryo mortality in some species, but little research has addressed whether UV-B is influencing the distribution of amphibian populations. We compared patterns of amphibian presence to sitespecific estimates of UV-B dose at 683 ponds and lakes in Glacier, Olympic, and Sequoia‐Kings Canyon National Parks. All three parks are located in western North America, a region with a concentration of documented amphibian declines. Sitespecific daily UV-B dose was estimated using modeled and field-collected data to incorporate the effects of elevation, landscape, and water-column dissolved organic carbon. Of the eight species we examined (Ambystoma gracile, Ambystoma macrodactylum, Bufo boreas, Pseudacris regilla, Rana cascadae, Rana leuteiventris, Rana muscosa, Taricha granulosa), two species (T. granulosa and A. macrodactylum) had quadratic relationships with UV-B that could have resulted from negative UV-B effects. Both species were most likely to occur at moderate UV-B levels. Ambystoma macrodactylum showed this pattern only in Glacier National Park. Occurrence of A. macrodactylum increased as UV-B increased in Olympic National Park despite UV-B levels similar to those recorded in Glacier. We also found marginal support for a negative association with UV-B for P. regilla in one of the two parks where it occurred. We did not find evidence of a negative UV-B effect for any other species. Much more work is still needed to determine whether UV-B, either alone or in concert with other factors, is causing widespread population losses in amphibians.

Cotton responses to ultraviolet-B radiation: experimentation and algorithm development

The potential impact of an increase in solar ultraviolet-B (UV-B) radiation due to human activity on higher plants has been the subject of many studies. Little work has been carried out so far on cotton responses to enhanced UV-B radiation. The objective of this study was to determine whether or not the current and projected increases in UV-B levels affect cotton growth and development, and to quantify and develop UV-B radiation functional algorithms that can be used in simulation models. Two experiments were conducted during the summer of 2001 using sunlit plant growth chambers in a wide range of UV-B radiations under optimal growing conditions. Leaves exposed to UV-B radiation developed chlorotic and necrotic patches depending on the intensity and length of exposure. Along with changes in visible morphology, cotton canopy photosynthesis declined with increased UV-B radiation. The decline in canopy photosynthesis was partly due to loss of photosynthetic pigments and UV-B-induced decay of leaf-level photosynthetic efficiency (maximum photosynthesis) and capacity (quantum yield) as the leaves aged. The total leaf area was less due to smaller leaves and fewer leaves per plant. Less plant height was closely related to a shorter average internode length rather than a fewer mainstem nodes. The UV-B did not affect cotton major developmental events such as time taken to square, time to flower, and leaf addition rates on the mainstem. Lower biomass was closely related to both smaller leaf area and lower photosynthesis. The critical limit, defined as 90% of optimum or the control, for stem elongation was lower (8.7 kJ m −2 per day UV-B) than the critical limit for leaf expansion (11.2 kJ m −2 per day UV-B), indicating that stem elongation was more sensitive to UV-B than leaf expansion. The critical limits for canopy photosynthesis and total dry weight were 7 and 7.3 kJ m −2 per day, respectively. The identified UV-B-specific indices for stem and leaf growth and photosynthesis parameters may be incorporated into cotton simulation models such as GOSSYM to predict yields under present and future climatic conditions.

COMBINED EFFECTS OF UV-B RADIATION AND NITRATE FERTILIZER ON LARVAL AMPHIBIANS

As part of a global loss of biodiversity, amphibian populations are declining worldwide. Numerous factors may be involved in these declines, including environmental changes and the spread of contaminants. Ultraviolet-B (UV-B) radiation (280–315 nm) and chemical pollution are two factors that have become increasingly important as contributing to amphibian mortality and, perhaps, to amphibian population declines. Therefore, we studied the combined effects of ambient UV-B radiation and nitrate fertilizer pollution on larval amphibians in outdoor experiments at low and high elevation sites in Oregon. Recent studies have shown that UV-B radiation and nitrate fertilizer pollution have differential effects on amphibians. Some species are more susceptible than others when exposed to either UV-B or to nitrate. Moreover, depending upon other environmental conditions, UV-B levels are often greater in intensity at higher elevation sites compared to lower elevation sites. Therefore, our experiments were designed to include amphibians from both low and high elevations. Very little is known about interpopulational variation regarding the effects of environmental stressors. We tested the combined effects of UV-B and nitrate on larval survival, mass, and length in Pacific treefrogs (Hyla regilla) and long-toed salamanders (Ambystoma macrodactylum). In the low elevation experiment, we found that UV-B and nitrate together reduced the mass of larval H. regilla. In the high elevation experiment, we found that UV-B and nitrate together reduced the survival of larval H. regilla. In both the low elevation and the high elevation experiment, nitrate increased the mass of larval A. macrodactylum. However, in the high elevation experiment, this result occurred only when UV-B was blocked. This result indicates that the effects of nitrate addition could depend upon the presence of other factors such as UV-B. Results emphasize the importance of considering the effects of multiple stressors.

Geographical correlation between ambient UVB level and mortality risk of leukemia in Japan

As a preliminary epidemiological study, we evaluated the geographical correlation between estimated ambient ultraviolet B (UVB) levels and the mortality risk of leukemia in Japan. Ambient UVB levels were estimated from meteorological data for several successive periods. The standardized mortality ratio (SMR) was calculated for the 11 regions or 38 large cities and different times for nine types of leukemia [the International Classification of Diseases, ninth revision (ICD-9), ICD 200–208]. The ecological relationship was assessed by calculating Spearman’s correlation coefficient. Among the nine types of leukemia, geographical correlation was found for two types of leukemia: “other malignant neoplasms of lymphoid and histiocytic tissue” (ICD 202) and “lymphoid leukemia” (ICD 204). The correlation coefficients between the SMR and UVB levels were statistically significant and ranged from 0.4 to 0.7 for the former and from 0.3 to 0.6 for the latter type of leukemia. This ecological study generated the hypothesis that UVB exposure may increase the risk of leukemias of lymphatic origin.

Joint effects of elevated levels of ultraviolet-B radiation, carbon dioxide and ozone on plants.

There is growing interest regarding the joint effects of elevated levels of surface ultraviolet B (UV-B) radiation, carbon dioxide (CO2) and ozone (O3) on plants. Our current knowledge of this subject is too limited to draw any specific conclusions, although one might state that such effects are likely to be highly species dependent and may be more than additive, additive or less than additive. There are a number of uncertainties associated with the experimental protocols used and the conclusions reached in many studies. Nevertheless, in North America, there appear to be genotypes of three monocot crop species (Avena sativa L., Oryza sativa L. and Sorghum vulgare L.); six dicot crops (Cucumis sativus L., Lactuca sativa L., Lycopersicon esculentum Mill., Phaseolus vulgaris L., Pisum sativum L. and Solanum tuberosum L.) and two conifer species (Pinus ponderosa Dougl. and Pinus taeda L.) that may be considered sensitive to the joint effects of elevated levels of UV-B, CO2 and O3. However, to provide a more reliable assessment or validation of the predictions, future research must consider the concept of plant response surfaces and describe them more fully in numerical terms. Achieving that objective will require close cooperation among a number of scientists representing geographic locations with known spatial and temporal differences in UV-B, CO2 and O3 to conduct experiments under their site-specific conditions, using common plant materials and experimental protocols.

Skin cancer and ultraviolet-B radiation under the Antarctic ozone hole: southern Chile, 1987-2000.

Punta Arenas, Chile, the southernmost city in the world (53 degrees S), with a population of 154,000, is located near the Antarctic ozone hole (AOH) and has been regularly affected by high levels of ultraviolet-B (UV-B) radiation each spring for the last 20 years. Large increases in UV-B associated with the AOH have been measured with increases in UV-B at 297 nm of up to 38 times those of similar days with normal ozone. Recently we reported significant increases in sunburns during the spring of 1999 on days with low ozone because of the AOH. A surveillance of skin cancers occurring from 1987 to 2000 was performed. Age, sex, location, type of skin cancer and skin phototype were recorded. A Brewer Spectrophotometer was used in order to obtain in situ measurements of ozone and UV-B. Total Ozone Mapping Spectrometer (TOMS) data from National Aeronautics and Space Administration (NASA) was used in order to establish pre-ozone hole climatology. Ozone levels as low as 145 DU (Dobson Units) were recorded, a 56% decrease in ozone, and UV-B levels up to 4.947 J/m2. These levels are close to summertime levels at mid latitudes. For the 14-year period--from 1987 to 2000--173 cases of skin cancer were diagnosed, 65 during the first 7 years, 108 during the second, an increase of 66%. Cutaneous malignant melanoma (CMM), 19% of the cases, increased by 56%, raising the rate from 1.22 to 1.91 per 100,000. Non-melanoma skin cancer (NMSC), 81% of the total, increased the rate from 5.43 to 7.94 per 100 000 (P < 0.05), a 46% increase. Patients with CMM and NMSC had skin phototypes I-II in 59% and 54% of cases, respectively. Days with more than 25% ozone loss occurred in 143 days during the last 20 springs. Significant increases of UV-B were observed under ozone hole conditions, especially around 300 nm, the most carcinogenic wavelengths. Highly unusual ozone loss and UV-B increases have occurred in the Punta Arenas area over the past two decades resulting in the non-photoadapted population being repeatedly exposed to an altered solar UV spectrum with a greater effectiveness for erythema and photocarcinogenesis. This phenomenon has not previously been reported over other populated areas and an additional increase in the skin cancer rate attributable to the AOH may be occurring. Research on the clinical and subclinical impact of these abnormalities is urgently needed.