Effects Of Intermittent Exposure Research Articles

A novel light source for post-harvest lettuce preservation based on chlorophyll absorption spectrum

With increased consumers’ demand for safe and healthy food, LED lighting for photobiology has received wider attention. In order to prolong the preservation time of the post-harvest lettuce, this paper documents a novel light source designed for preservation based on the chlorophyll absorption spectrum. Effects of intermittent exposure (35 μmol m−2 s−1) on sensory quality and chlorophyll content in fresh lettuce were investigated during 3 days storage at 20°C ± 1°C and 60% ± 1% humidity using dark as the control. The results show that the lighting reduced the colour difference value of lettuce by 23.5% compared with the dark. The content of chlorophyll was 19.7% more than in the dark. The lighting with the novel light source inhibited the decline in the colour difference value − a/ b of lettuce and delayed the degradation of chlorophyll.

Effect of elevated levels of CO2 on powdery mildew development in five cucurbit species

The environment is the key factor that influences the host-parasite relationship. Elevated CO2 levels resulting from various anthropogenic sources may directly affect the surroundings around pathogens and plants. It is hypothesized that plants may respond differently to pathogens in the environment containing an elevated concentration of CO2. To test the hypothesis an experiment was conducted to examine the effects of intermittent exposures of elevated levels of CO2viz., 400, 500 and 600 ppm (5 hr/day on alternate days) on the development of Sphaerotheca fuliginea causing powdery mildew disease on five cucurbits species using open-top chambers. The elevated levels of CO2 acted as a growth promoter and significantly enhanced the plant growth of all five cucurbit species. Inoculation with the fungus incited specific mildew symptoms on the leaves and decreased the plant growth and biomass production of the cucurbits tested except bitter gourd. The intermittent exposures with elevated levels of CO2 aggravated the disease development. As a result, severe mildew developed on all five cucurbits, including bitter gourd, which expressed tolerance to the pathogen. Fungus colonization in terms of the number of conidia/cm2 leaf surface was significantly greater on the plants exposed to 500 or 600 ppm CO2. The stomata and trichome density and stomatal pore width were increased in the leaves of CO2 exposed plants. The CO2 exposures also accelerated the photosynthesis rate, but transpiration, stomatal conductance, salicylic acid and total phenols were decreased; fungus inoculation caused the effects just reverse of CO2. Interaction between S. fuliginea and CO2 was found synergistic at 500 ppm, whereas with rest of the concentrations it was near to additive.

Effect of intermittent exposure to ethanol and MDMA during adolescence on learning and memory in adult mice

BackgroundHeavy binge drinking is increasingly frequent among adolescents, and consumption of 3,4-methylenedioxymethamphetamine (MDMA) is often combined with ethanol (EtOH). The long-lasting effects of intermittent exposure to EtOH and MDMA during adolescence on learning and memory were evaluated in adult mice using the Hebb-Williams maze.MethodsAdolescent OF1 mice were exposed to EtOH (1.25 g/kg) on two consecutive days at 48-h intervals over a 14-day period (from PD 29 to 42). MDMA (10 or 20 mg/kg) was injected twice daily at 4-h intervals over two consecutive days, and this schedule was repeated six days later (PD 33, 34, 41 and 42), resulting in a total of eight injections. Animals were initiated in the Hebb-Williams maze on PND 64. The concentration of brain monoamines in the striatum and hippocampus was then measured.ResultsAt the doses employed, both EtOH and MDMA, administered alone or together, impaired learning in the Hebb-Williams maze, as treated animals required more time to reach the goal than their saline-treated counterparts. The groups treated during adolescence with EtOH, alone or plus MDMA, also presented longer latency scores and needed more trials to reach the acquisition criterion score. MDMA induced a decrease in striatal DA concentration, an effect that was augmented by the co-administration of EtOH. All the treatment groups displayed an imbalance in the interaction DA/serotonin.ConclusionsThe present findings indicate that the developing brain is highly vulnerable to the damaging effects of EtOH and/or MDMA, since mice receiving these drugs in a binge pattern during adolescence exhibit impaired learning and memory in adulthood.

Toxicity to Melita plumulosa from intermittent and continuous exposures to dissolved copper

The concentrations of metal contaminants often fluctuate in estuarine waters; yet we have limited knowledge about the effects of intermittent exposures on estuarine organisms. Using 10-d lethality bioassays with the epibenthic amphipod Melita plumulosa, different combinations of intermittent (pulsed) dissolved Cu exposure were investigated, varying Cu concentration, pulse duration, and time between pulses. Negligible organism mortality was observed immediately after single 12- to 62-h duration pulsed exposures of 100 to 900 µg/L dissolved Cu. However, delayed mortality was observed in the subsequent 96-h nonexposure period, after which negligible additional mortality occurred during the remainder of the 240-h tests. For multiple pulsed exposures, increasing the time between pulses from 0 to 144 h did not result in significantly different mortality rates for 300 and 400 µg/L dissolved copper, indicating that the organisms did not recover between pulses. Organism mortality exhibited a strong relationship with the time-averaged concentration (TAC) resulting from the combination of exposure concentration and duration. The lethal concentration to 50 (LC50), 20 (LC20), and 10% (LC10) (95% confidence interval) of the test population for the combined TAC exposure-survival data were 86 (71-103), 44 (30-64), and 30 (18-49) µg Cu/L, respectively, which were similar to the respective values of 100 (87-114), 55 (43-70), and 39 (28-54) µg Cu/L determined for continuous exposure. The results from the current study support the use of analytical techniques capable of determining the time-averaged concentration of metals, because they will more accurately predict the effects of toxiciants on organisms than single time-point measurements.

Effects of shift work and intermittent noise exposure on hearing: Mechanisms and prophylactic potential

It is well established that intermittent noise exposure characteristically produces less hearing loss than equal energy/intensity continuous noise in animal models. Ongoing different shift work regimes open for direct studies on hearing effects of intermittent noise exposure in man without ethical concern. Amazingly, few such studies are reported. In one recent study in the present volume, noise-exposed employees working 12 hours a day for two consecutive days followed by two days off, the cycle then repeated, had significantly lower permanent hearing loss than employees working nine-hour shifts from 8 am to 5 pm Monday to Friday. This commentary refers to the few studies reported, gives a short overview of the mechanisms behind noise-induced hearing loss and the protective effect of intermittent exposure, and concludes that direct studies in man on the effects of different shift work regimes on occupational hearing loss under specified noise conditions represent a prophylactic potential that calls for increased research activity. Such studies might pave the way for direct use of more optimal intermittent noise exposure regimes in future design of the noise exposure workday/-week and make future hearing conservation programs more effective.

The theory underlying dose‐response models influences predictions for intermittent exposures

Prediction of pulsed or intermittent exposure effects on populations is emerging as an important issue in ecotoxicology. However, the underlying theory of the dose-response models has not been tested rigorously enough to provide a true understanding for predicting the effects of pulsed exposures. Since its introduction, the individual effective dose (IED) theory has remained the dominant explanation in the literature. The present study tested whether the IED theory is the dominant explanation for the probit model (or similar models) for both copper sulfate (CuSO4) and sodium pentachlorophenol (NaPCP). Three groups of amphipods (Hyalella azteca) were first exposed to lethal, sublethal, and zero concentrations of each toxicant. After recovery, all survivors were exposed to lethal concentrations, and their mortalities during a second exposure were compared. Under the specific concentrations and durations used, stochastic processes were dominant for CuSO4. Both stochasticity and IED appeared to be relevant for NaPCP, but stochasticity dominated the dynamics. Current ecotoxicology tests should include assessment of the underlying dynamics as one of the first steps of studying pulsed or intermittent exposure effects.

Refinement of risk assessment of dermally and intermittently exposed pesticide workers: A critique

The regulatory requirements for the registration of pesticides are mainly evolved from concern about dietary exposure and risk, i.e. chronic oral exposure. Pesticide workers, however, are predominantly exposed dermally and intermittently. The present critique provides suggestions for improvement of toxicity studies to refine the risk assessment of pesticide workers. In this respect it is considered of utmost importance that toxicity studies (either toxicokinetic or toxicodynamic) should be tuned towards the anticipated exposure scenario. Apart from suggestions for improvement of dermal toxicokinetic and dynamic studies, recommendations for further research and guidance are given, amongst which the request for information on the robustness of in vitro dermal absorption studies and guidance on how to use these data. With respect to the intermittent exposure of pesticide workers it is recognised that both information on the anticipated exposure scenario as well as knowledge on the effect of intermittent exposure on the toxicity are needed. From a toxicological point of view, the setting of more than one Acceptable Operator Exposure Level (AOEL), covering effects that may arise after different periods of exposure, as well as the development of more robust acute and short term studies are strongly recommended.

Effects of intermittent exposures of aflatoxin B1 on hepatic and testicular glutathione S‐transferase in rats

Effects of intermittent exposures of aflatoxin B1 on hepatic and testicular glutathione S‐transferase in rats

Effects of intermittent ozone exposures on powdery mildew of cucumber

Exposure of plants to O 3 may influence foliar diseases caused by fungi. It is hypothesized that concentrations of O 3 at or below economic threshold may enhance severity of the fungal disease, whereas higher levels may decrease the severity. To test this hypothesis, effects of intermittent exposures at 50, 100 and 200 ppb O 3 and powdery mildew infection by Sphaerotheca fuliginea, using pre-, post- and concomitant-inoculation exposures were investigated on cucumber in closed-top exposure chambers. For impact assessment, plant growth, flowering, fruit-setting, foliar ozone injury, fungal colonization, conidia size and their germination were considered. Ozone (except 50 ppb) caused necrotic lesions on leaves and reduced the plant growth and fruit-setting of cucumber. Plants inoculated with S. fuliginea conidia developed powdery colonies in the intercostal region of leaves. Ozone injury was relatively moderate on fungus-inoculated plants. Powdery mildew development was, however, severe on the plants exposed to 50 ppb O 3, but at higher concentrations there was significant decline in fungus colonization. Conidia examined from such plants (exposed to 100 or 200 ppb) were smaller in size and contained fewer fibrosin bodies and showed poor germination. Ozone exposures at 50 ppb, however, stimulated the conidial germination. In an in–vitro experiment, the conidia directly exposed to ozone on glass slides showed more or less similar response to the gas. Ozone at 50 ppb and S. fuliginea interacted synergistically and caused significantly greater decrease in the number of fruits/plant. At 200 ppb O 3, the mutual effects were antagonistic. Fungus infection provided partial protection to plants against 200 ppb ozone, and mildew infection was also mild.

Effects of Intermittent Exposure to Therapeutic Levels of Formalin on Growth Characteristics and Body Condition of Juvenile Rainbow Trout

Abstract The effects of twice weekly exposure to formalin (200 mg/L in a 1-h static bath) on juvenile rainbow trout Oncorhynchus mykiss (57.4 g initial weight) were assessed in a completely random, matched-pairs, 12-week growth trial. Growth rates, appetite, feed conversion, and body condition index of the fish were not significantly affected by formalin treatment after 6 and 12 weeks. There was also no evidence of a cumulative effect of formalin treatments over time, because the similarities between treated and untreated groups of fish persisted over the 12-week trial. Formalin-treated fish had significantly better fin condition and a lower incidence of corneal opacity than did untreated fish. This study showed that formalin, in a 1-h static bath at 200 mg/L repeated twice weekly, can be used as a disease prophylaxis regime with no negative effects on growth.

Development of Tolerance Against Ozone Effects on Drinking and Eating Behaviors in Rats by Intermittent Exposures

AbstractThis study exammed the effects of intermittent exposures to 0.4–0.8 ppm ozone (O3) on drinking and eating behaviors in rats to evaluate the development of tolerance to O3 exposure. When rats were exposed to 0.4 ppm (787 μg/m3) O3 for 23 h the first time, the drinking activity was reduced to 29% of the control value and the eating activity to 44%. A decrease in body weight (mean decrease 11 g) was also noted. However, the magnitude of these changes was attenuated when the rats were exposed to 0.4 ppm O3 on day 2, 4, or 7 after the first exposure. When rats were exposed to 0.4 ppm O3 and then to 0.8 ppm (1577 μg/m3) O3 7 days later, the magnitude of decrease in the drinking activity was considerably smaller during the second exposure compared with that of a single exposure to 0.8 ppm O3. The lowered drinking activity by O3 exposure did not produce a postexposure compensatory increase of water intake. Moreover, deprivation of food and water prior to O3 exposure scarcely affected decrease in drinking ...

Acute mountain sickness and physiological stress during intermittent exposure to high altitude.

The effect of intermittent exposure to high altitude (4200 m) hypoxia on symptomatology of acute mountain sickness (AMS) was observed, and the relationship between AMS and stress hormone excretion was examined among shift workers at the United Kingdom Infrared Telescope (UKIRT) facility and a control group of sea level residents. Some of the shift workers experienced AMS during their first day at altitude, but had recovered after 5 days residence at altitude. Upon acute exposure to altitude, none of the shift workers reported severe cases of AMS after 5 days residence at sea level, but some reported severe cases after 45 residence at sea level, thus providing some evidence for a 'carry over' of acclimatization for a 5 day period. Reported symptomatology at sea level was predictive of 24 h. excretion rates of adrenaline and 17-hydroxycorticosteroids at high altitude. No good predictors of symptomatology of AMS at high altitude were found using sea level measures alone.

Role of time as a factor in the toxicity of chemical compounds in intermittent and continuous exposures. Part II. Effects of intermittent exposure.

Because of fluctuations in levels of industrial air pollution linked to weather and other factors, a joint U.S.‐Soviet research team studied differences in the effect of time in exposures of air‐breathing animals to controlled varied concentrations of air pollutants. An experimental model environment was used to investigate the effects of nitrogen dixoide (NO2), sulfur dioxide (SO2), and benzene (C6H6) in the air environment of laboratory animals, with both continuous and intermittent exposures. For intermittent exposures the investigators used amounts of toxic gases whose cumulative total equaled the total in the continuous exposures, and intercalated the intermittent exposures with periods of nonpolluted air. To equal the cumulative total concentration of the single continuous exposures over an equal time period, the concentrations of toxic gases were necessarily greater in the intermittent exposures. Part I of this work deals with the effects of continuous exposure to C6 H6 on the central nervous system and blood. Toxic effects of continuous exposure to various concentrations of C6H6 were found involving the central nervous system and blood. The time‐effect relationships could be approximated on a log‐log scale by straight lines. Similar results were obtained with SO2. Using different parameters to measure toxicity, similar results were obtained with NO2 —namely, concentration‐time relationships that when plotted on a log‐log scale gave straight lines. Part II concerns the toxicities of Intermittent exposures to C 6 H 6 and NO2; three parameters were used. The toxic effects of NO2 with intermittent exposure were not reduced as was the case with C6H6. Data are presented to show that intermittent exposure to NO2 may be more toxic than continuous exposure when short‐term peaks of NO2 concentrations are involved.

The effect of intermittent exposure to risk on failure time distributions

The relation is investigated between the distributions of the total time until failure and the time of exposure to risk until failure, for individuals who are at risk only intermittently during their lifetimes. A specific example is considered in the case of computer failures.

Light-sensitive papers as controls for testing textile colorfastness and stability of materials under arc lamp exposure

A simple method of control of the integrated exposure of the fluctuating arc lamps used in the textile and other industries for testing lightfastness of textile dyeings and stability toward light of materials in general, is described. A piece of light-sensitive paper is placed in lamps along with materials to be tested, and the exposure is terminated when a match with a standard, observable with the unaided eye, is obtained. The standard is a strip of the same batch of paper that has been exposed in a master lamp to a definite light dosage. The method is based upon standard light quantities and is thus largely independent of variation between batches of light-sensitive paper. The variations among fading lamps used in the textile industry and the causes, such as differences in lamp models, and line voltage, are discussed. A 4-percent difference in line voltage leads to a difference in radiant output of 11 percent in the waveband from 300 to 480 millimicrons, the region probably causing most of the fading of dyed textiles. Variations in line voltage considerably larger than 4 percent are probable in many communities. The papers were made in batches of 20 to 30 thousand test pieces by dip-dyeing special cotton-rag or wood-fibers papers with aqueous solutions of Niagara Blue G, or with Victoria Blue B in aqueous ethanol. One paper was made by beater-dyeing wood fibers with Niagara Blue G to give a nonleaching paper and was sized with melamine resin to impart high wet strength, making the paper suitable for lamps with water spray. Other paper-dye combinations were studied. Data are presented indicating the visual sensitivity of the various types of papers from 1 to 100 hours of usual arc exposure, the permanence of the papers during storage in the dark, the uniformity throughout each batch, and the effect of nonuniformity, temperature effect, lasting qualities of the standard strips during use, correlation with textile dyeings, and the effect of intermittent exposure. The master lamp used for standardizing the papers, its accessories, and reproducibility of input power and radiant output are discussed.

Effect of Intermittent Exposure to Simulated High Altitude in Erythropoiesis in the Guinea Pig.

ConclusionsGuinea pigs exposed to simulated altitudes of 23,000 and 30,000 feet 6 hours a day and 6 days per week became fully acclimatized after 200 hours, as shown by maximal increase in the values for red corpuscles, hemoglobin, and hematocrit. Reticulocytosis and enlargement of the spleen were also demonstrated.

Instruction in Photography

THIS work, which for many years has held the premier position among English text-books of photography, is to a peculiar extent the record of the author's own experiments and investigations, and in the iew edition much new matter on the subject of colour photography has been added, the product of the attention which Sir W. de W. Abney has devoted to that branch of photography for some years. In other sections of the book it may be noted that the descriptions of lenses are brought up to date, while the chapter on sensitometry includes a description of Mr. Chapman Jones's plate tester. An entirely new chapter has been added to the book entitled “The Failure of a Photographic Law,” and including the well known experiments made by the author upon the effect of intermittent exposures and upon the failure of the. reciprocity law. Here also will be found an interesting discussion of the effect of temperature upon the sensitiveness of plates, while the last part of the chapter is devoted to an account of the author's researches upon the effect of different monochromatic lights upon a plate. The book has been entirely reset, larger type being employed throughout and the printing generally improved. No alteration has been made in the theoretical views set forth, and the ilver sub-bromide theory of the latent image is adopted in its entirety.

On the Effect of Intermittent Exposure on Bromide of Silver Gelatine

On the Effect of Intermittent Exposure on Bromide of Silver Gelatine