102,990 research outputs found
Dynamik der Radonfolgeprodukt-Aktivität imSpeichel nach therapeutischer Radon-Exposition
No full textRadon decay product activity was measured in saliva of 10 male patients 20-30 min after a 1-hour radon exposure in the gallery of the Gasteiner Heilstollen (radon activity 36.2 kBq/m(3), radon progeny activity 20.3 kBq/m(3)), in 1 patient showing relatively high activity (75th percentile) measurements were continued until 65 min after exposure. Patients were asked to collect about 2 mi of saliva in the mouth and produce it on a filter. After drying the filter at 300 degrees C, radon progeny activity was measured. Activity (median) at 20-30 min after leaving the treatment area was 4.5 Bq (25th percentile 1 Bq; 75th percentile 21 Bq). In the patient who underwent additional measurements the activity showed a further increase up to 29 Bq (35 min after radon exposure) before it continuously decreased to a very low activity (1-3 Bq) at 65 min after exposure. The results show that a significantly increased radon decay product activity is found in saliva after speleotherapeutic radon exposure. Maximum values were observed 35 min after radon exposure. Radon decay product activity almost disappeared after about 1 h
An energy efficient approach for radon management in a HVAC environment: executive summary
No full textRadioactive radon gas, after being released from rocks, soils and building structures, can pose a significant health threat to the building occupants. This is of particular concern in tight HVAC (Heating, Ventilating and Air-Conditioning) serviced buildings where there is re-circulating air with limited fresh air intake. A thorough survey was initiated at the Hong Kong University of Science and Technology (HKUST) in 1996 and results indicate a radon average concentration of 107 Bq/m3, which is approximately 50% of the World Health Organisation's (WHO) recommended standard (200 Bq/m3). About 10% of the measurements were in excess of this WHO limit, while 46% of the samples also showed average peak radon concentrations (264 Bq/m3) in excess of this WHO limit.
To overcome these elevated indoor radon concentrations, their characteristics at HKUST was studied. Radon level was found to increase linearly as a function of the length of the HVAC shut off period, and decrease exponentially upon system resumption. Radon level predictive models were developed after a series of room chamber experiments with modification factors defined to account for the indoor sinks in an effort to enhance the accuracy and applicability of the models.
Following a campus-wide energy audit, two energy efficient radon management approaches were derived from the predictive models and were subsequently integrated into the existing HKUST operations. The first was defined as an Active Radon Control Approach (ARCA), where HVAC operation schedules were modified to yield an energy saving potential of around HK$2.7 Million a year. ARCA is optimised to reduce the radon dose to the HKUST occupants following the radiation protection principle of "As Low as Reasonably Achievable (ALARA)", and with considerations of economical and operational constraints.
The other was a Passive Radon Control Approach (PRCA) using Polyurethane-based (P-u) paint to cover building material surfaces to reduce the radon emission
The geographical differences and similarities of radon affected areas in England
No full textThe geographical distribution of radon gas is very uneven. The gas occurs naturally in all buildings at concentrations which can vary from below the United Kingdom national average of 20 Bq m(^-3) to more than 2,000 Bq m(^-3). Five counties have been identified by the NRPB as 'Affected Areas' where more than 1% of homes have radon levels in excess of the current Action Level of 200 Bq m(^-3) (Miles et al., 1992). These counties are Cornwall, Devon, Somerset, Derbyshire and Northamptonshire. The level of radon gas in buildings is largely dependent on the underlying geology but geology does not always provide a full answer as to why spatial variations in radon occur. The implication of land capability on indoor radon levels in the five Affected Areas has been assessed using ARC/INFO and in Northamptonshire die influence of social factors (population density, social class and the proportion of households consisting only of pensioners) has been analysed. There are some similarities in the results for the Affected Areas (especially between the counties located in the south-west of die country) as well as some striking differences (for example, the relationship between urban areas and radon levels differs in all the Affected Areas). Results in Somerset and Northamptonshire are strongly influenced by one or more dominant radon category or land capability grade. In general, higher radon levels are associated with poor quality agricultural land and, in Northamptonshire, with high population density at ward level. The areas of Northamptonshire which have above average proportions in social classes I and II (1991 Census) are more likely to be associated with low radon levels (at district level), whereas areas with high proportions of households consisting only of pensioners tend to be associated with areas where more than 10% of homes are above the Action Level (at ward level)
Measurement Error in Exposure Assessment: An Error Model and its Impact on Studies on Lung Cancer and Residential Radon Exposure in Germany
No full textCase-control studies on lung cancer and residential radon exposure had been conducted in Germany. Relative risk estimates from primary analysis were now subject to accounting for uncertainties in radon exposure and in the most potent confounder smoking. The regression calibration method and an approximate maximum likelihood method were applied. The differentiation between classical error (from assessing radon exposure or packyears) or Berkson error (from using radon exposure instead of alpha dose, from using packyears instead of inhaled dose of smoking carcinogens) was of major importance in this analysis.
Estimates of relative lung cancer risk due to radon exposure were found to be higher after accounting for multiplicative classical error in radon exposure and packyears. Outliers in the data strongly influence risk estimates, but their impact is reduced, if classical error is accounted for. In one study, the influence of one outlier explained the particularly large risk-increasing impact of error correction. But also residual confounding due to adjusting for imprecisely measured packyears deflated the risk estimate in this study. It is interesting that the small correlation between radon exposure and packyears had this notable effect. On the other hand, classical errors in packyears had no large impact in the radon-prone study areas. Further, Berkson error did not induce substantial bias on the radon risk estimates, but possibly decreased the power to detect existing effects and inflated the confidence intervals.
It was concluded that such an analysis was extremely valuable to understand the impact of uncertainties in the risk factor of primary interest on the risk estimate under study and the potential for residual confounding by assessment errors in the smoking variable. Note that assuming some error in the risk factors is more realistic than assuming no error. With regard to study design, study regions with no correlation between the variable of primary interest and potential confounders are preferable.
However, the exact magnitude of the error could not be estimated based on the available data. Further investigations regarding residual confounding due to model mis-specification and latent smoking-related variables are necessary to grasp the full dimension of an important issue in epidemiology, i.e. the role of the outstanding confounder smoking for estimating small risks.In Deutschland waren Fall-Kontroll-Studien zu Lungenkrebs und Radon in Innenräumen durchgeführt worden. In der Schätzung des relativen Lungenkrebsrisikos wurden nun Unsicherheiten in der Radonexposition und im stärksten potentiellen „Confounder" Rauchen berücksichtigt. Hierbei wurden die Methode der Regressionscalibrierung und eine approximative „Maximum Likelihood" Methode angewandt. Die Unterscheidung zwischen klassischem Fehler (durch Erhebung der Radonexposition oder der Packungsjahre) und Berkson-Fehler (durch Verwendung von Radonexposition als Surrogat für Alpha-Dosis oder von Packungsjahren als Surrogat für Lungendosis durch inhalierte Karzinogene im Rauch) war von besonderer Bedeutung in dieser Analyse.
Die Risikoschätzer waren höher, wenn multiplikative klassische Messfehler in der Erhebung der Radonexposition und der Packungsjahre berücksichtigt wurden. Ausreißer in den Daten haben einen starken Einfluß auf Risikoschätzer, welcher jedoch durch Berücksichtigung klassischer Fehler reduziert wird. In einer Studie erklärte der Einfluß eines Ausreißers den besonders starken das Risiko erhöhenden Effekt der Fehlerkorrektur. Aber auch „Residual Confounding" durch Adjustierung für ungenau erhobene Packungsjahre verringerte das beobachtete Risiko in dieser Studie. Es ist interessant, dass sich die kleine Korrelation zwischen Radonexposition und den Packungsjahren so stark auswirkte. In höher mit Radon belasteten Studiengebieten hatten klassische Fehler in den Packungsjahren keinen großen Effekt. Ferner bewirkte der Berkson-Fehler keine nennenswerte Verzerrung der Risikoschätzer, aber schmälerte die „Power", um existierende Effekte zu erkennen.
Diese Analyse war extrem nützlich, um die Auswirkung von Messfehlern im primären Risikofaktor auf das zu untersuchende Risiko und das Potential von „Residual Confounding" durch Fehler in der Rauchvariablen zu verstehen. Man halte sich vor Augen, dass die Annahme irgendeines Fehlers in den Risikofaktoren realistischer ist als die Annahme keines Fehlers. Bezüglich des Studiendesigns, ist eine Studienregion, wo die Primärexposition nicht mit dem potentiellen „Confounder" korreliert ist, vorzuziehen.
Die genaue Fehlergröße konnte jedoch nicht aus den zur Verfügung stehenden Daten geschätzt werden. Außerdem sind weitere Untersuchungen hinsichtlich des „Residual Confounding" durch Modell-Fehlspezifikation und latente Rauchvariable notwendig, um das volle Ausmaß eines wichtigen Punktes in der Epidemiologie zu verstehen, nämlich die Rolle des herausragenden „Confounder" Rauchen für die Schätzung kleiner Risiken
Probability of Causation for Lung Cancer After Exposure to Radon Progeny: A Comparison of Models and Data
No full textThe estimates of lung cancer risk due to the exposure to radon decay products are based on different data sets from underground mining and on different mathematical models that are used to fit the data. Diagrams of the excess relative rate per 100 working level months in its dependence on age at exposure and age attained are shown to be a useful tool to elucidate the influence that is due to the choice of the model, and to assess the differences between the data from the major western cohorts and those from the Czech uranium miners. It is seen that the influence of the choice of the model is minor compared to the difference between the data sets. The results are used to derive attributable lifetime risks and probabilities of causation for lung cancer following radon progeny exposures
Ionizing and non-ionizing radiation and the risk of childhood cancer-illustrated with domestic radon and radio frequency electromagnetic field exposure
No full textBackground
Children are exposed to many different environmental factors, including exposure to low-dose ionizing radiation and to non-ionizing radiation.
Low-dose ionizing radiation comprises anthropogenic modified radiation and natural ionizing radiation from cosmic rays from the atmosphere, terrestrial gamma radiation from radionuclides in rocks and soils and radiation from radon.
Non-ionizing radiation comprises optical radiation and radiation from electromagnetic fields. The latter comprises radiation from extremely low-frequency electromagnetic fields (ELF-EMF; high voltage power lines, electrical installations) and radiofrequency electromagnetic fields (RF-EMF; broadcast transmitters, mobile phone base stations, mobile and cordless phones).
Both ionizing and non-ionizing radiation are assumed to be associated with childhood cancer.
Aims
Within this dissertation, we primarily aimed to assess whether there is an association between domestic radon exposure and childhood cancers. We further investigated whether there is an association between low-dose ionizing gamma radiation and childhood cancers. We finally assessed whether there is an association between RF-EMF exposure from broadcast transmitters and childhood cancers.
Methods
We performed prospective census-based cohort designs, considering all children, aged less than 16 years and living in Switzerland at the date of census 2000 (December 5th 2000). Time at risk was set to begin at census and lasted until the date of diagnosis, death, emigration, a child’s 16th birthday or until the end of the year 2008. In terms of non-ionizing radiation from far-field RF-EMF sources from broadcast transmitters, we carried out a further prospective cohort analysis, considering all children, aged less than 16 years and living in Switzerland between 1985 and 2008.
We assessed exposure at baseline (date of census 2000) for each child’s home address. For the analyses on RF-EMF exposure to broadcast transmitters and childhood cancers where a longer follow-up was considered, we considered exposure at the time of diagnosis.
For the analyses on domestic radon exposure and childhood cancers, exposure assessment was based on a nationwide radon prediction model. For the analyses on low-dose ionizing gamma radiation and childhood cancers, exposure assessment was based on modelled and measured dose rates from outdoor gamma radiation. For the analyses on RF-EMF exposure to broadcast transmitters and childhood cancers, exposure assessment was based on modeled field strengths.
Results
We estimated arithmetic mean radon concentrations to be 85.7 Bq/m³ (range: 6.9-337.2 Bq/m³) for childhood cancer cases and 85.9 Bq/m³ (range: 0.7-490.1 Bq/m³) for the rest of the study population. Despite relative high radon levels in Switzerland, we found no evidence for an association between domestic radon exposure and childhood cancers.
We found increased leukaemia risk (including acute lymphoblastic leukaemia) with respect to gamma radiation for children who lived at the same address between 1995 and 2000.
Finally, we found no increased leukaemia risk but increased central nervous system (CNS) tumour risks with respect to RF-EMF exposure from broadcast transmitters.
Conclusions and Outlook
The findings of our analyses, indicating no association between domestic radon exposure and childhood cancers were consistent with past studies that estimated doses of domestic radon concentrations for different body organs (lung, red bone marrow, brain).
The results of the analyses on gamma radiation and childhood cancers indicate that low dose ionizing gamma radiation might be relevant in terms of childhood leukaemia. These results were also found to be consistent with dose estimations for different body organs (red bone marrow, brain). They indicated that the same gamma radiation dose to the red bone marrow over a longer time period is probably necessary for gamma radiation to lead to childhood leukaemia.
The findings from the analyses on RF-EMF exposure from broadcasting and childhood leukaemia were found to be consistent with results from animal, in-vitro and laboratory studies. On the contrary, the findings indicating increased CNS tumours from RF-EMF exposure to broadcast transmitters contradict results from former studies. Our results are further in contradiction to a previous case-control study on wireless phones. This study could not find an increased risk for CNS tumours from the use of wireless phones that lead to substantially higher exposure to the head.
Although no evidence for an association with childhood cancers was found, domestic radon exposure is of public health relevance with regard to lung cancer in adults.
The findings from the analyses on gamma radiation and childhood cancers indicate that gamma radiation is of public health relevance as well, especially when children are exposed to the same gamma radiation dose over a longer time period.
Statements on possible public health relevance concerning non-ionizing radiation of RF-EMF from broadcasting on the other hand are not yet possible, as the results for CNS tumours need further clarification
Non-linear relationship of cell hit and transformation probabilities in a low dose of inhaled radon progenies
No full textCellular hit probabilities of alpha particles emitted by inhaled radon progenies in sensitive bronchial epithelial cell nuclei were simulated at low exposure levels to obtain useful data for the rejection or support of the linear-non-threshold (LNT) hypothesis. In this study, local distributions of deposited inhaled radon progenies in airway bifurcation models were computed at exposure conditions characteristic of homes and uranium mines. Then, maximum local deposition enhancement factors at bronchial airway bifurcations, expressed as the ratio of local to average deposition densities, were determined to characterise the inhomogeneity of deposition and to elucidate their effect on resulting hit probabilities. The results obtained suggest that in the vicinity of the carinal regions of the central airways the probability of multiple hits can be quite high, even at low average doses. Assuming a uniform distribution of activity there are practically no multiple hits and the hit probability as a function of dose exhibits a linear shape in the low dose range. The results are quite the opposite in the case of hot spots revealed by realistic deposition calculations, where practically all cells receive multiple hits and the hit probability as a function of dose is non-linear in the average dose range of 10–100 mGy
Do multiple peaks in the Radon Transform of westward propagating sea surface height anomalies correspond to higher order Rossby wave Baroclinic modes?
No full textThis study examines the presence of multiple peaks from 2 dimensional Fourier and Radon Transform analysis for the entire South Pacific basin from 10 years of sea level anomalies determined from ERS (European Remote Sensing satellite) and T/P altimeter observations and attempts to determine whether their speeds resemble those of higher order baroclinic Rossby wave modes
A Radon-Nikodym derivative for almost subadditive set functions
No full textIn classical measure theory, the Radon-Nikodym theorem states in a concise condition, namely domination, how a measure can be factorized by another (bounded) measure through a density function. Several approaches have been undertaken to see under which conditions an exact factorization can be obtained with set functions that are not σ-additive (for instance finitely additive set functions or submeasures). We provide a Radon-Nikodym type theorem with respect to a measure for almost subadditive set functions of bounded sum. The necessary and sufficient condition to guarantee a one-sided Radon-Nikodym derivative remains the standard domination condition for measures.
Use of the 3D radon transform to examine the properties of oceanic Rossby waves
No full textOne of the most successful applications of satellite-borne radar altimeter data over the oceans in recent years has been the extraction of information about long-wavelength baroclinic Rossby (or planetary) waves, which play a significant role in ocean circulation and climate dynamics. These waves cross ocean basins from east to west at speeds of few centimetres per second at mid-latitudes. The cross-basin propagation time may therefore be several months or even years and an accurate estimation of the speed of the waves is important. We review the methods for obtaining information on Rossby wave velocity from altimetry data, particularly the two-dimensional Radon transform. Unfortunately the use of longitude-time plots, although it allows the estimation of the zonal phase speeds, does not give any information on the speed vector when the propagation of the waves is not purely zonal (east-west). We show how the two-dimensional Radon Transform can be generalised to three dimensions, enabling not only the true propagation velocity component to be determined, but also the direction of the waves and thus any deviation from the pure-westward case. As examples of the application of this extended technique, we show maps of direction, speed and energy of Rossby waves in the North Atlantic Ocean
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