Single High Exposure Research Articles

Efficacy of single versus multiple exposure by electromagnetic modalities on gram-negative and positive bacterial strains in an in-vitro model.

ObjectivesThe primary purpose of the recent experiment was to scrutinize the dissimilarity between single and multiple exposures by electrotherapeutic modalities to determine the development of Gram-positive and Gram negative bacteria spectrum.Material and methodsBacterial strains employed in this study were Gram-negative bacteria such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumonae and Gram-positive bacteria such as Staphylococcus aureus, Staphylococcus saprophyticus and Streptococcus pyogenes. Fluence for Low level laser therapy (LLLT) (810 nm) was 40 J/cm2 for 80 s, for microwave (MWD) a dosage of 100-Watt with duration of 5 min and for magnetic field therapy (MT) duration of 30 min with 100% intensity was used.ResultsRepeated Measures of analysis of variances (RANOVA) for within-subject effects was used to detect a global significant change within the means at dissimilar time points. The experiments of within-subjects revealed a significant difference within groups, df of (3, 40), F value of 39.38 and a p value less than 0.001, representing a significant variation between the three groups between pre and post exposures. There was a significant variation between single exposure and multiple exposures in the experimental sample’s pre-post between the four groups with df (1, 40) f value of 2943.69 and p value less than 0.001. Scanning and Transmission electron microscopy images were also taken into account to determine the extent of damage caused to the bacterial cells surface topography in Gram negative and Gram positive spectrums.ConclusionThe study demonstrated that single high exposure with the LLLT appears to have the most emphatic effect followed by exposure by MWD and MT.

Low concentrations of permethrin and malathion induce numerical and structural abnormalities in KMT2A and IGH genes in vitro.

Pesticides are commonly used worldwide and almost every human is potentially exposed to these chemicals. Exposure to pesticides such as permethrin and malathion has been associated with hematological malignancies in epidemiological studies. However, biological evidence showing if these chemicals induce genetic aberrations involved in the etiology of leukemia and lymphoma is missing. In our previous work, we have shown that a single high exposure (200μm, 24hours) of permethrin and malathion induce damage in genes associated with hematological malignancies in peripheral blood mononuclear cells analyzed by interphase fluorescence in situ hybridization (FISH). In the present study, we assessed by FISH whether exposure to low concentrations (0.1μm, 72hours) of permethrin and malathion induce aberrations in KMT2A and IGH genes, which are involved in the etiology of leukemia and lymphoma. Peripheral blood mononuclear cells were exposed to the chemicals, and damage in these genes was assessed on interphases and metaphases. We observed that both chemicals at low concentration induced structural aberrations in KMT2A and IGH genes. A higher level of damage was observed in KMT2A gene with malathion treatment and in IGH gene with permethrin exposure. We also observed numerical aberrations induced by these chemicals. The most frequent aberrations detected on interphase FISH were also observed on metaphases. Our results show that permethrin and malathion induce genetic damage in genes associated with hematological cancer, at concentrations biologically relevant. In addition, damage was observed on dividing cells, which suggests that these cells maintain their proliferation capacity in spite of the genetic damage they possess.

Reduced methylation-induced mutagenesis in rat splenocytes in vivo by sub-chronic low dose exposure to N-metyl-N-nitrosourea

Estimates of genotoxic effects of mutagens at low and protracted doses are often based on linear extrapolation of data obtained at relatively high doses. To test the validity of such an approach, a comparison was made between the mutagenicity of N-methyl-N-nitrosourea (MNU) in T-lymphocytes of the rat following two treatment protocols, i.e. sub-chronic exposure to a low dose (15–45 repeated exposures to 1mg/kg of MNU) or acute exposure to a single high dose (15, 30 or 45mg/kg of MNU). Mutation induction appeared dramatically lower following sub-chronic treatment compared to treatment with a single high exposure. Furthermore, DNA sequence analysis of the coding region of the hprt gene in MNU-induced mutants showed that acute high dose treatment causes mainly GC→AT base pair changes, whereas sub-chronic treatment results in a significant contribution of AT base pair changes to mutation induction. We hypothesize that O6-methylguanine-DNA methyltransferase is saturated after acute treatments, while after sub-chronic treatment most O6-methylguanine is efficiently repaired. These data suggest (i) that risk estimations at low and protracted doses of MNU on the basis of linear extrapolation of effects measured at high dose are too high and (ii) that the protective effects of DNA repair processes are relatively strong at low sub-chronic exposure.

Defining and investigating occupational asthma: a consensus approach

Background: At present there is no internationally agreed definition of occupational asthma and there is a lack of guidance regarding the resources that should be readily available to physicians running...

Development of a single-meal fish consumption advisory for methyl mercury.

Methyl mercury (meHg) contamination of fish is the leading cause of fish consumption advisories in the United States. These advisories have focused upon repeated or chronic exposure, whereas risks during pregnancy may also exist from a single-meal exposure if the fish tissue concentration is high enough. In this study, acute exposure to meHg from a single fish meal was analyzed by using the one-compartment meHg biokinetic model to predict maternal hair concentrations. These concentrations were evaluated against the mercury hair concentration corresponding to the U.S. Environmental Protection Agency's reference dose (RfD), which is intended to protect against neurodevelopmental effects. The one-compartment model was validated against blood concentrations from three datasets in which human subjects ingested meHg in fish, either as a single meal or multiple meals. Model simulations of the single-meal scenario at different fish meHg concentrations found that concentrations of 2.0 ppm or higher can be associated with maternal hair concentrations elevated above the RfD level for days to weeks during gestation. A single-meal fish concentration cutoff of > or = 2.0 ppm is an important consideration, especially because this single high exposure event might be in addition to a baseline meHg body burden from other types of fish consumption. This type of single-meal advisory requires that fish sampling programs provide data for individual rather than composited fish, and take into account seasonal differences that may exist in fish concentrations.

Health and employment after a diagnosis of occupational asthma: a descriptive study.

The objectives of this study were to describe changes in asthma and employment after diagnoses of occupational asthma reported to the SWORD project. Questionnaires were sent to 312 physicians for all 1,940 cases of occupational asthma reported from 1989-92; 1,769 (91%) were returned but information was available for only 1,317 (68%). Of patients reported by occupational physicians, 45% had recovered from asthma compared to only 14% of those reported by chest physicians (excluding medicolegal cases), presumably because of differences in severity. Proportions with the same employer were 49% and 48% respectively. Patients exposed for a year or more after diagnosis recovered from asthma less frequently but were more often employed than those exposed for less than a year. Among those whose asthma was attributed to high molecular weight agents, smokers had developed asthma earlier after exposure began than others but had the best prognosis. Asthma developed following a single high exposure in 18 cases (2%), of which 13 were to irritants and five to known sensitizers.

Long-term lung sequelae following accidental chlorine gas exposure.

Acute exposure to sublethal doses of chlorine gas resulted in persistent pulmonary symptoms in 3 patients who had no past history of respiratory disease. The patients complained of intermittent dyspnea in association with respiratory irritants and physical exertion for more than 2.5 years postexposure. Four months after the accident bronchoalveolar lavage showed an inflammatory cell reaction, whereas 16 months later the differential cytology proved nearly normal. Moderate to severe nonspecific bronchial hyperresponsiveness was assessed in intervals of 4, 20 and 30 months after the accident. All patients showed the typical features of the reactive airways dysfunction syndrome defined as an asthma-like occupational illness after an acute exposure to highly concentrated respiratory irritants. We conclude that a single high exposure to chlorine gas may lead both to acute respiratory injury and to long-term reactive airway dysfunction with typical symptoms of inflammatory changes of the airways and nonspecific bronchial hyperresponsiveness.

Contamination of the air with Mineral Fibers Following the Explosive Destruction of Buildings and Fire

Mineral fibers, including asbestos, are ubiquitous contaminants of the environment. Asbestos fibers are generally present at levels below 1 fiber/L in air though 10 fibers/L may be found in cities; these levels do not appear to be high enough to present a hazard to health. These fibers come mostly from the use of fibrous materials as thermal and acoustic insulation in buildings, and their use as friction materials. Historically, occupational air levels were often very high and as a result there was a high incidence of fibrosis and also cancer in exposed workers, mostly among those in the industries concerned with the winning or processing of asbestos fiber. Levels high enough to produce disease have also occurred paraoccupationally in the families of asbestos workers. The effect of fire and explosion in a building is to disrupt its structure and vastly increase the level of airborne fiber for a considerable distance (kilometers) around it. Air levels of fiber can remain high for months, and as a result the earliest occupational experiences are likely to be repeated. The greatest danger is from exposure to blue and brown asbestos, and it is known that even a single high exposure can be responsible for the development of a tumor decades later.

Eight Years Application of Computerised Glow Curve Analysis at the Rossendorf Nuclear Research Centre

Abstract Since 1983 computerised glow curve analysis has been carried out at the Rossendorf Nuclear Research Centre. The application fields, the methods developed and the results obtained are: (1) Skin dose determination in beta/gamma fields. The glow curve of a fast, directionally heated thick TL detector is deconvoluted into contributions of standard glow curves for beta and gamma irradiation of known depth dose distribution. Doses in tissue depths from 0.05 mm to 1.6 mm are obtainable. (2) Fading reduction. The evaluation of only the separated main peak yields the fading-independent dose and, additionally, the evaluation of the separated low temperature peak gives an indication of the time elapsed since a single high exposure. (3) High range exposure. For exposures of CaSO4:Dy detectors to doses from 0.1 kGy to 5 kGy the saturation effects can be reduced by deconvolution of the glow curve into up to five Gaussian peaks. The dose is obtained from two or more peak areas as well as from the ratio of peak height and location.

Computerised Glow Curve Analysis of CaSO<sub>4</sub>:Dy Teflon Dosemeters for Routine Environmental Monitoring

A computerised glow curve analysis of CaSO4:Dy Teflon environmental dosemeters was applied for fading independent dose evaluation and for the assessment of time elapsed since a single high exposure. The method is based on unfolding the glow curve into a main peak and a sub-peak using Gaussian functions, the least squares technique and a stripping procedure. If only the main peak area is used for dose evaluation the error due to fading can be reduced from 40% to about 5%. Using the fading of the low temperature peak an estimate of the time elapsed since a single high exposure can be made for known and constant storage temperature, but effects from storage temperature and storage time, which both influence the fading, could not be separated from each other.