Summer Sunlight Research Articles

Planning for the sun: urban forms as a Mesopotamian response to the sun

Urban forms create complex spatial environments which form, and are formed by, the lives of their inhabitants. Part of the construction of any urban environment is the formation of a light environment created by the interaction of the architecture with the changing natural light conditions through the day and over the year. This paper considers the construction of an appropriate and meaningful light environment to have been an essential factor in the development of urban form in ancient Mesopotamian cities, where strong summer sunlight constituted a serious limit to human activity and the sources of natural light held a high symbolic and religious value. The form and layout of ancient Mesopotamian cities is here examined in terms of the sort of light environments the architecture would have produced. Using the example of residential housing at ancient Ur, an analysis of the urban light environment demonstrates both functional and symbolic manipulation of sunlight through architectural form.

Photolysis of Chlortetracycline on a Clay Surface

Chlortetracycline, an antibiotic commonly used as a growth promoter in livestock, enters the environment primarily through application of animal waste to open fields. The photochemical loss of chlortetracycline in sunlight-exposed soils is a potentially important process in its environmental fate, especially because it is photochemically labile and sorbs strongly to mineral surfaces. In this study, photolysis on kaolinite clay under simulated sunlight was used as a model system to elucidate the mechanistic kinetics of chlortetracycline photolysis on soil surfaces. The results suggest that photolysis may be an important loss process for chlortetracycline sorbed to sunlight-exposed soils, as well as to suspended clays in surface waters. Under direct irradiation equivalent to noon-time, summer sunlight in the midwestern United States, chlortetracycline at the outer clay surface (before light attenuation) degraded with a rate constant of k(0)(p) = 0.65 +/- 0.30 h(-1). The depth at which photochemical action was reduced by 50% (z(0.5)), one of the parameters of the mechanistic model, was found to be 0.014 +/- 0.004 mm. The quantum yield on the clay surface was estimated to be (1.3 +/- 0.7) x 10(-4), an order of magnitude lower than the quantum yield of the aqueous chlortetracycline zwitterion [(1.3 +/- 0.3) x 10(-3); pH 5], although still significant.

Exudation and decomposition of chromophoric dissolved organic matter (CDOM) from some temperate macroalgae

The quantity of chromophoric or coloured dissolved organic matter (CDOM) released by eleven species of intertidal and sub-tidal macroalgae commonly found on UK shores was investigated. The subsequent breakdown of CDOM was also measured by exposing collected CDOM samples to light and dark conditions for over two weeks. CDOM absorption properties were compared at a fixed wavelength of 440 nm and across two integrated wave - bands; UV-A (400–315 nm) and UV-B (315–280 nm). Absorption spectra of macroalgal CDOM samples were typically characterized by peaks and shoulders in the UV bands, features which were species specific. The spectral slope, derived using the log-linear method, proved to be very specific to the species and to the effect of light. Slope measurements ranged from 0.010 to 0.027 nm −1, in the range of normal seawater values. Significantly more CDOM was produced by algae which were illuminated, providing evidence for a light driven exudation mechanism. Averaged across all species, exudation in the dark accounted for 63.7% of that in the light in the UV-B band. Interspecific differences in exudation rate encompassed an order of magnitude, with the highest absorption measurements attributable to brown algae. However, some brown algae produced considerably less CDOM (e.g. Pelvetia canaliculata), which were more comparable to the green and red species. Over an exposure time of 16 days, significant photochemical degradation of CDOM was observed using a natural summer sunlight regime, showing that natural solar radiation could be an important removal mechanism for newly produced algal CDOM. Though the most obvious effect was a decrease in absorption, photo-bleaching also caused a significant increase in the spectral slope parameter of 0.004 nm −1.

Photochemistry of Aqueous C60 Clusters: Evidence of 1O2 Formation and its Role in Mediating C60 Phototransformation

The expected rapid expansion of nanotechnology industries has raised concern over the environmental fate and effects of materials created by these industries, including carbon-based fullerenes. In this study, the reaction mechanism responsible for the photochemical transformation of aqueous C60 clusters (nC60) in sunlight has been examined. Evidence is presented that under lamps that emit light only within the solar spectrum, 1O2 is produced via aqueous nC60 suspensions, using furfuryl alcohol (FFA) as an indicator. In air-equilibrated suspensions, the losses of 0.2 mM FFA and 0.8 mg/L C60 were >90% and 70% after 15 h, while removing oxygen, the precursor of 1O2, stopped both reactions, indicating that 1O2 was produced and mediated nC60 phototransformation. Similar reactions performed in deuterium oxide and with added azide ion resulted in accelerated and slowed loss of FFA, respectively, as expected if 1O2 is a reaction intermediate. 1O2 production (as measured by FFA loss) increased with time as more water-soluble intermediate products accumulated in solution. In summer sunlight (West Lafayette, IN, 86 degrees 55' W, 40 degrees 26' N), suspensions of 5 mg/L nC60 produced 1O2 concentrations 1 order of magnitude higher thanthe average value typically found in natural waters containing the same mass of natural organic carbon.

Supplementing dairy steers and organically managed dairy cows with synthetic vitamin D3is unnecessary at pasture during exposure to summer sunlight

Use of synthetic feed additives, including synthetic vitamin D3 (D3) in the feed for cows and other ruminants, is not consistent with the international principles of organic farming. If dairy farmers wish to produce in accordance with the organic principles, production animals would be left with only their endogenous production of D3 from summer sunlight as a source of D3. To examine the impact of supplemental synthetic D3 from the feed on the D3 status of dairy cattle in organic production in Nordic countries, 20 high-yielding dairy cows and 30 dairy steers were divided into two groups: one supplemented with synthetic D3 in the feed and one not supplemented with synthetic D3. Vitamin D3 status of the animals was assessed by measuring the concentration of the liver-derived 25-hydroxyvitamin D3 (25OHD3) in plasma. Results showed that 25OHD3 concentration in plasma from dairy cattle as well as from steers decreased during winter for both supplemented and unsupplemented groups. Unsupplemented cows and steers had approximately 2 ng 25OHD3 per ml plasma during winter, whereas supplemented animals had between 10 (cows) and 30 (steers) ng/ml. During summer and autumn there was no additive effect of supplementing with synthetic D3 since unsupplemented and supplemented animals had the same D3 status at this time of year. In all cows summer concentrations of 25OHD3 were 20-25 ng/ml and in all steers 40-50 ng/ml plasma. The decrease in vitamin D3 status during winter indicates that cows and steers are able to store D3 only to a limited extent. The results also show that cows or steers fed supplemental D3 according to Swedish recommendation throughout the year are not able to maintain their summer value of 25OHD3 during winter.

Role of Nitric Oxide in the Visible Light-Induced Rapid Increase of Human Skin Microcirculation at the Local and Systemic Level: I. Diabetic Patients

This study aimed to reveal the effects of polychromatic visible (pVIS) or pVIS + near IR (nIR) light similar to some components of solar light on skin microcirculation and microvascular response to the vasodilatators acetylcholine (ACh) and nitroglycerine (NG), in the extremities of patients with diabetic microangiopathy. The mechanisms behind light-induced increases in microcirculation as well as extracellular effects of terrestrial pVIS and pVIS + nIR light remain unknown. In 24 subjects with type 2 diabetes mellitus local microcirculation was measured in the skin of the foot before and after exposure to both types of light. In another 26 patients systemic microcirculation was studied in the back of the hand before and after exposure of the lumbar-sacral area to light energy. Two different types of light therapy were performed by using two devises: Q-light, which delivers pVIP (385-750 nm) and pVIS nIR light (385-1700 nm) with a power density of 40 mW/cm2, which is similar to summer sunlight at noon in Central Europe. At 2 min after irradiation (12 J/cm2) of the forefoot with pVIS or pVIS + nIR light, a rise in local blood flow volume (Qas) was observed, on average by 39% and 31%, respectively. The maximal effect (+41-47%) had developed in all patients at 30 min, and it then decreased and disappeared completely 24 h post-irradiation. We obtained similar results after irradiation of the sacral area in Qas of the skin of the hand. Both types of microcirculation also increased following a second exposure to the light sources. Enhancement of microcirculation was accompanied by a decrease in the microvascular response to ACh and NG solutions administered intracutaneously by iontophoresis. Both types of irradiation stimulated microcirculation at the local and systemic levels through a mechanism of enhancement of endothelium-dependent and endothelium-independent vasodilation, in which nitric oxide plays a major role.

Environmental Photochemistry of Tylosin: Efficient, Reversible Photoisomerization to a Less-Active Isomer, Followed by Photolysis

The environmental photochemical kinetics of tylosin, a common veterinary macrolide antibiotic and growth promoter, were investigated under simulated sunlight. An efficient, reversible photoisomerization was characterized using kinetic, mass spectrometry, and proton nuclear magnetic resonance data. The photoisomerization was confirmed to occur by a rotation about the distal alkene of the ketodiene functionality. Concurrent forward (quantum yield = 0.39 +/- 0.09) and back (quantum yield = 0.32 +/- 0.08) reactions lead to a photochemical equilibrium near a tylosin/photoisomer ratio of 50:50, completed in less than 2 min under a spectrum equivalent to noontime, summer sunlight. The activity of the isomer for the inhibition of Escherichia coli DH5alpha growth was observed to be less than that of tylosin. On a longer time scale than that of isomerization, the isomer mixture undergoes photolysis with a quantum yield of (1.4 +/- 0.3) x 10(-3). The observed quantum yields and UV-vis absorbance data allow for the prediction of the photochemical behavior of tylosin in most environmental systems. Indirect photosensitization was not a significant loss process in solutions of Suwannee River fulvic acid with concentrations from 1 to 20 mg L(-1).

Infrared irradiation has potential antidepressant effect

Purpose Light therapy was only partially effective in treatment of depression when compared with summer's sunlight. The antidepressant effect of infrared irradiation was evaluated using an experimental animal model. Methods Seventeen mice were randomly assigned to the exposure group ( n = 9) and the control group ( n = 8). The mice in the exposure group received infrared irradiation for 60 min daily during the study period of 4 weeks. The two groups were given forced swim test once a week to evaluate depression with the measurement of the immobility time. Results We found that the exposure group showed a tendency of less immobility time by the end of the 3rd week when compared with the control group, and at the end of 4th week the difference reached a statistical significance ( t 15 = 2.873; p = 0.012). Conclusions The result indicates that the immobility time in forced swim test, the sign of depression, can be reduced after prolonged (4 weeks) exposure to infrared irradiation in the animal model. The result suggests that a continuous application of infrared irradiation has antidepressant effect.

Ultraviolet Radiation Exposure and Risk of Non-Hodgkin's Lymphoma

Sun exposure has been suggested to increase the risk of non-Hodgkin's lymphoma. The authors analyzed data from a population-based, case-control study of Connecticut women between 1996 and 2000 to study the hypothesis. Women who reported having had a suntan experienced an increased risk of non-Hodgkin's lymphoma with increasing duration (p(trend) = 0.0062) compared with women who reported never having had a suntan. An almost threefold increased risk of non-Hodgkin's lymphoma was observed among women who reported having had a suntan for less than 3 months per year and a suntan history of more than 60 years (odds ratio = 2.8, 95% confidence interval: 1.6, 4.9) compared with those who reported never having had a suntan. For women who reported having spent time in strong sunlight between 9 a.m. and 3 p.m. during the summer, a 70% increased risk of non-Hodgkin's lymphoma was observed for the highest tertile of duration compared with the lowest (odds ratio = 1.7, 95% confidence interval: 1.2, 2.4). The risk increased with increasing duration of time spent in strong sunlight in summer (p(trend) = 0.0051). The risk appears to vary by non-Hodgkin's lymphoma subtypes. Further investigations of the role of ultraviolet radiation on the risk of non-Hodgkin's lymphoma are warranted.

Sunlight inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, in seawater and river water

The inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, was determined in 100 l chambers of seawater and river water located at an outdoor site. The chambers (paired with dark controls) were seeded with waste stabilization pond effluent and laboratory-cultured pathogens, and exposed to sunlight in summer and winter experiments. All sunlight inactivation (k(S)) rates, as a function of cumulative global solar radiation (insolation), were far higher than the corresponding dark (k(D)) rates, with a ranking (and average k(S) rates for seawater and river water, respectively) of: C. jejuni (3.23; 2.34)>S. enterica (0.51; 0.37)>E. coli (0.34; 0.26). All the T(90) (time to 90% inactivation) values were higher in winter than in summer, but there was far greater similarity between the summer and winter S(90) (insolation needed for 90% inactivation) values. The rapid inactivation of C. jejuni was attributed to a high susceptibility to photooxidative damage. The results suggest that, in sunlight-exposed waters, E. coli will be a more conservative indicator for C. jejuni than for S. enterica, and C. jejuni transmission as a pathogenic agent is less likely than for S. enterica.

Silver doped titanium dioxide nanomaterials for enhanced visible light photocatalysis

This paper presents a systematic study on two different preparation methods for titanium dioxide with silver. The silver can be incorporated by irradiating the reaction mixture during preparation to reduce silver ion to silver metal or by direct calcination of the sol–gel material to decompose silver nitrate to silver. Of the two methods, we found the latter produces a more effective photocatalytic material (6–50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material. The efficiency of the materials were examined using a Q-Sun solar simulator (visible light) and in Dublin summer sunlight (latitude 54°N). In both cases, the addition of increasing amounts of silver, for both batches of samples, significantly increases the rate of degradation of a model dye, rhodamine 6G (R6G), increasing the rate of degradation from 0.06 min −1 for TiO 2 to 0.34 min −1 for 5 mol% Ag–TiO 2. This is attributed to the increasing visible absorption capacity due to the presence of silver nanoparticles.

Run, Dad!

Run, Dad! Kim Aeran (bio) Translated by Kevin O'Rourke (bio) I cried a lot when I was a fetus. I cried because I was scared of the tiny darkness within my seed-small womb. I was diminutive; I had miniscule wrinkles, a small, rapidly beating heart and a body that didn't know what language was. I'm talking about a time without yesterdays or tomorrows. I came like something in the mail, my arrival announced by mom, a parcel of flesh without language. Mom gave birth to me in a semi-basement room where summer sunlight rough as sandpaper shone relentlessly. She flailed around with only a shirt to cover her. And with no hand to hold onto, she simply grabbed a scissors. Outside the window she could see the feet of people walking by. Every time she felt she wanted to die, she stabbed the floor with the scissors. This went on for hours. In the end, she didn't kill herself; instead she cut my umbilical cord. Here I was, newly arrived in the world, and I couldn't hear mom's heart beating. The silence made me think I was deaf! The first light I saw as a newborn was window-sized. I knew it existed outside of me. I don't remember where my dad was. He was always someplace else, or he was late, or he didn't come at all. Mom and I held onto each other, heart against rapidly beating heart. Mom, naked, looked down at my solemn face and wiped it several times with her big hand. I liked my mom, but I didn't know how to tell her; I just frowned all [End Page 227] the time. I discovered that mom laughed a lot when my face puckered with wrinkles. I think I concluded that love was not so much two people laughing together as one looking funny to the other. Mom fell asleep and I was left on my own. The world was quiet; the sunlight lay over there on the floor like a polite "Dear John" letter, the first unpleasant note I received in this world. I had no pockets. So I clenched my fists. When I picture dad, it's always against the same background: he's running resolutely somewhere. He's wearing luminous pink shorts and has thin, hairy legs, and he's running straight-backed with a high knee action. He looks like a referee who's enforcing rules no one cares about. So he cuts a comical figure. I guess he's been running for twenty years, his posture and face always the same: a laughing red countenance sporting a row of yellow teeth like a bad painting someone stuck on him. It's not just dad, though. Everyone playing the exercise game looks funny. It embarrasses me when I see middle-aged men in the park bouncing their bellies off the trunks of pine trees, or middle-aged women clapping their hands as they walk. They're always so serious about what they're doing and so enthusiastic. As if getting healthy entails looking more and more ridiculous. I've never really seen dad running, but as far as I'm concerned he's been running all his life. I may have gotten this idea from something mom told me long ago. When she first told me this story, she had a washboard stuck in the V between her legs. She was scrubbing laundry in a welter of soapy suds and breathing so hard she looked very angry. Mom says dad never ran to her. He wasn't the kind of man to come running: not when she said they should break up, not when she said she missed him, not even when I was born. People called him a gentleman; mom thought he was a fool. If mom made up her [End Page 228] mind to wait for him on a certain day, he'd show up the next. And when he arrived late, he looked haggard. She always had a joke to greet her diffident lover—with his inevitable late-schoolboy look. He made no excuses, used no big...

Sunlight induced degradation of E133 in a commercial beverage

The degradation pathway of E133 dye was investigated, when a commercial beverage containing the dye was subjected to summer sunlight and temperature. The study employed HPLC-DAD and HPLC–MS n analyses, conducted on both the beverage and model solutions subjected to sunlight irradiation. The results indicate that E133 was not present in the beverage after 16 days of irradiation and that the degradation products are formed only after long exposure times. Possible structures are proposed but their identification was made difficult by the formation of adducts with other ingredients present. Solid Phase Extraction (SPE) was developed to lower the matrix interferences.

Photodegradation of strong copper-complexing ligands in organic-rich estuarine waters

Exposure to solar radiation substantially decreased the strong copper-complexing capacity of samples collected from the organic-rich Cape Fear estuary, North Carolina. Samples exposed to natural sunlight for 1-2 d experienced a loss of strong Cu ligand (modeled at fixed K‘CuL = 1013.5) ranging from 15-33%, and >90% using long-term exposures under controlled conditions with a Xe arc solar simulator light (14 d summer sunlight). Pseudo firstorder rate constants of strong Cu ligand photodegradation averaged 0.28 d-1 for two separate Cape Fear samples exposed to simulated solar radiation, much higher than corresponding dissolved organic carbon photooxidation rate constants (<0.01 d-1). Degradation rates measured in solar simulator experiments predicted ligand concentrations in separate samples exposed to natural sunlight within 30% after rates were normalized to the ultraviolet (UV) light absorption coefficient at 300 nm. UV light is not solely responsible for photodegradation because exposure to photosynthetically active radiation also decreased strong Cu ligand levels, but with a smaller rate constant (0.06 d-1). Although photodegradation appears to be a relatively minor sink within the Cape Fear estuary because of a shallow light penetration depth (<2% of water column) and short residence times (<1 week), strong Cu ligand levels in optically clearer South Atlantic Bight (SAB) surface waters are likely to be substantially reduced by photodegradation. Ligand degradation may be especially important to Cu-sensitive ecosystems where large increases in bioavailable and potentially toxic levels of free Cu2+ ions are possible.

Determinants of vitamin D status in adult Crohn's disease patients, with particular emphasis on supplemental vitamin D use

To investigate determinants (pathophysiologic and physiologic, behavioural and lifestyle) of vitamin D status in Irish Crohn's disease (CD) patients. A cross-sectional observational study. Cork City, Ireland (52 degrees N). Crohn's Disease patients (n=58; mean age 38.1 years) were recruited from Cork University Hospital. Fifty and nineteen percent of Irish CD patients were vitamin D deficient (defined by serum 25 hydroxyvitamin (OH) D levels <50 nmol/l) during winter and summer, respectively. Multiple regression analysis showed that summer-time serum 25 (OH) D levels were positively associated with use of vitamin D supplements (P=0.033) and negatively associated with smoking (P=0.006) and being male (P=0.063). During winter-time, use of vitamin D supplements (P=0.041) and sun habits (P=0.066) were positively associated, whereas small intestinal involvement (P=0.005) and body mass index (BMI) (P=0.083) were negatively associated with serum 25 (OH) D levels. There was no significant association between other non-pathophysiologic (age, dietary calcium or vitamin D) or pathophysiologic factors (steroid use, resection), and serum 25 (OH) D levels, at either season. Approximately 41 and 60% of the total variation in summer- and winter-time serum 25 (OH) D, respectively, was explained by this model. A high proportion of Irish CD patents had some level of vitamin D deficiency (<50 nmol/l) during late-wintertime. Use of regular low-dose supplemental vitamin D, particularly by patients with small intestinal involvement, cessation of smoking and adequate, but responsible, exposure to summer sunlight as well as maintaining BMI in the normal range could help maintain adequate vitamin D levels during wintertime.

Why do Polytrichaceae have lamellae?

Light-response curves of chlorophyll-fluorescence parameters from 12 species of Polytrichaceae show photosynthetic electron flow giving a good fit to negative-exponential saturation curves up to high irradiances; 95%-saturation irradiances for the species of unshaded habitats approached or exceeded noon summer sunlight. The species showed little or no indication of the non-saturating electron flow at high irradiances, or the very high values of non-photochemical quenching, seen in many other mosses of dry, sun-exposed habitats. Calculation of CO2 diffusion rates from first principles on a cell-area basis indicates that photosynthesis of mosses with unistratose leaves is likely to be limited by CO2 diffusion resistance at high irradiances. In Polytrichaceae the area for CO2 uptake is often >6 times the projected leaf area. By lowering the whole-leaf resistance to CO2 uptake, the lamellae remove the CO2-diffusion constraint that limits mosses with unistratose leaves and allow Polytrichaceae to utilize efficiently the high irradiance of direct sunlight.

Aqueous photochemistry of triclosan: Formation of 2,4‐dichlorophenol, 2,8‐dichlorodibenzo‐p‐dioxin, and oligomerization products

The photochemical fate of the antimicrobial agent triclosan is presented. Experiments performed in both natural and buffered deionized water show that triclosan rapidly photodegrades by direct photolysis (t(1/2) = 5 h, pH 8, noon summer sunlight, 45 degrees N latitude). Both 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) and 2,4-dichlorophenol (2,4-DCP) are produced. The 2,8-DCDD and 2,4-DCP also are photolabile and, thus, are intermediates. The yields for 2,8-DCDD and 2,4-DCP ranged from 3 to 12% depending on the conditions employed. When triclosan is photolyzed in the presence of Suwannee River (GA, USA) fulvic acid, a portion of the initial mass is recovered as insoluble material. Based on experiments in which the formation of insoluble material was monitored with photolysis time, it is postulated that photolysis in natural waters leads to some of the triclosan being coupled to humic matter. Triclosan also reacts rapidly with both singlet oxygen (k(rxn) = 1.07 +/- 0.03 x 10(8) M(-1) s(-1) in water of pH 10) and hydroxyl radical (k(*OH) = 5.4 +/- 0.3 X 10(9) M(-1)(s-1). Indirect photolysis pathways, however, are not expected to be important because of low steady-state concentrations of reactive oxygen species in natural waters and the efficiency of the direct photolysis of triclosan.

Inter‐relation between variables determining constitutional UV sensitivity in Caucasian children

Sensitivity to ultraviolet (UV) light is associated with phenotypic variables like iris or hair colour or freckling, which are all strongly inter-related. We assessed the pattern of association among these factors to construct a summary measure reflecting constitutional UV sensitivity in a simple one-dimensional score with sufficient discriminating power. Information on iris and hair colour (3 and 4 categories, respectively), freckling (none vs. any) and the reaction to mid-day summer sunlight as an outcome (dichotomized into 'burn' and 'tan') was collected in a cross-sectional study among children at school enrollment in 1999 and 2000 in Göttingen, Germany (n=3765 with complete data). Chi-squared automatic interaction detector (CHAID) analysis and log-linear modelling was used to assess the pattern of mutual inter-relations. Hair colour turned out to be the factor most strongly associated with UV sensitivity. In case of blonde or brown hair (the most common phenotypes in our sample), the consideration of freckling further refined the classification system, whereas iris colour did not contribute additional information. The results of the CHAID and log-linear analyses suggest a simple five-point score capturing constitutional UV sensitivity. The discriminating power of this score was high in our sample, with the proportion of persons who burned ranging from 7.7 (lowest category) to 73% (highest category). The new scoring system summarized efficiently relevant information on individual constitutional UV sensitivity in our sample. Its further validation in independent studies comprising Caucasian children or adults is necessary to assess objectively its properties for future applications.

PORTAL ORIENTATION AND ARCHITECTURE OF BURROWS IN TYMPANOCTOMYS BARRERAE (RODENTIA, OCTODONTIDAE)

The red viscacha rat, Tympanoctomys barrerae, is an octodontid rodent endemic to the Monte and Patagonian deserts of Argentina. It lives in burrows with numerous portals facing different directions. We studied climatic factors as possible determinants of burrow architecture and portal orientation, in 2 populations. Climatic factors examined were sunlight, direction of sun's rays, and wind frequency and intensity. Variables analyzed for burrow architecture were portal orientation, slope, and depth at the 1st turn. Mean number of portals per burrow was significantly different between populations. Burrows had few portals oriented toward predominantly cold and intense winds. More portals faced direct solar light in winter. Burrows are so constructed as to allow openings to receive direct sunlight in winter and indirect sunlight in summer.

Sunlight inactivation of human enteric viruses and fecal bacteria

Three human enteric viruses (poliovirus, echovirus, coxsackievirus) suspended in seawater or buffer were stable for 6 hr in the absence of sunlight but were inactivated at the same rate in the presence of sunlight. Under summer sunlight conditions, at least 3 logs of these viruses were inactivated by one-hit kinetics while under winter sunlight conditions only 1 log of these viruses was inactivated by two-hit kinetics. Under these same conditions, 6 logs of E. coli were inactivated within 1 hr by one-hit kinetics under summer and winter conditions. In comparison, E. faecalis was inactivated by two-hit kinetics and only 2.5 logs of inactivation were observed after 4 hr of exposure to winter sunlight. Since human enteric viruses are considerably more resistant to sunlight inactivation than E. coli and moderately more resistant than E. faecalis, marine recreational water quality standards should be based on concentrations of enterococci and not on coliform bacteria. Since the mechanism and rate of inactivation of coliphage and human enteric viruses are similar, coliphages appear to be the best indicator for the presence of human enteric viruses in recreational waters, especially coastal waters where abundant sunshine is available.