RESUMEN
Radon measurements over a short-term period of a few days have proven a popular choice with the general public, despite the issue that the radon concentration can vary significantly over time and longer periods of integration are recommended. Performing short-term radon measurements using a Poly Allyl Diglycol Carbonate (PADC) detector would see a larger contribution from the statistical error associated with the measurements than for longer term measurements. This motivated the investigation to improve the uncertainty on short-term measurements by utilising a new formulation of high-sensitivity PADC and also by investigating the effect of increasing the scan area and extending the measurement time by just a few days.
Asunto(s)
Contaminantes Radiactivos del Aire/análisis , Glicoles/química , Monitoreo de Radiación/instrumentación , Radón/análisis , Humanos , Monitoreo de Radiación/métodos , IncertidumbreRESUMEN
PURPOSE: To study geographical variations in the level of naturally occurring 210Pb-supported 210Po in permanent teeth of juveniles in the UK. MATERIALS AND METHODS: Permanent teeth extracted from 278 juveniles for orthodontic purposes were obtained from 48 counties in the UK. 210Po activity concentration was measured on the outer enamel surface using TASTRAK alpha-particle-sensitive plastic track detectors. RESULTS: Geometric mean +/- SE activity concentrations in teeth from urban, suburban and rural areas, excluding the high radon area of Devon, were 8.41 + 0.25/-0.24, 7.76 + 0.37/-0.35 and 7.20 +0.49/-0.46 Bq kg(-1), respectively. Overall, there was no significant association between alpha-activity on the outer enamel surface of permanent teeth and proximity to the major UK motorways. However, when the data were considered with respect to the prevailing south-westerly wind on the western side of the UK, a statistically significant association with respect to donors living downwind (on the easterly side) of the motorways was found. This effect was greater for sections of the M5 and M6 motorways that traverse urban areas. 210Po levels in teeth were also associated with domestic radon concentration. This effect was comparable with that from traffic and urban pollution. CONCLUSIONS: Higher levels of 210Pb-supported 210Po are seen in permanent teeth of juveniles near sources of increased exposure in the UK. Inhalation uptake is an important pathway of exposure, especially with respect to domestic radon exposure. The results might be important in assessing integrated exposure to 210Po in the skeleton and consequent high linear energy transfer dose to bone marrow.
Asunto(s)
Dentición Permanente , Exposición por Inhalación , Radioisótopos de Plomo/análisis , Polonio/análisis , Adolescente , Niño , Exposición a Riesgos Ambientales , Humanos , Efectos de la Radiación , Radón/análisis , Población Rural , Población Suburbana , Reino Unido , Población UrbanaRESUMEN
PURPOSE: To examine the microdistribution of natural alpha-radioactivity in deciduous teeth of children and the permanent teeth of juveniles extracted for orthodontic purpose from across the UK. MATERIALS AND METHODS: The microdistribution of 210Pb-supported 210Po and 226Ra in 708 deciduous and permanent teeth and 32 foetal teeth was measured on 1442 TASTRAK alpha-particle track detectors. RESULTS: Of the various findings, a number are of special interest. Around half of the 210Pb activity in the outer enamel of deciduous teeth appears to have been acquired in utero as a result of transplacental transfer. In deciduous and permanent teeth, 226Ra is concentrated mainly in the circumpulpal region, while the highest levels of 210Po are on the highly calcified outer enamel surface. Furthermore, activity concentrations recorded on this surface were In-normally distributed. CONCLUSIONS: 210Pb-supported 210Po activity on the outer enamel surface of permanent teeth constitutes an assay of cumulative environmental exposure with which to assess exposure in bone, both in utero and in childhood. Such assessment can be used to study geographical variations in the alpha-activity in teeth. More work is also required to determine the concentrations of both 210Po and 210Pb in the foetal skeleton.
Asunto(s)
Dentición Permanente , Exposición a Riesgos Ambientales , Diente Primario/efectos de la radiación , Adolescente , Adulto , Niño , Preescolar , Femenino , Humanos , Radioisótopos de Plomo/análisis , Masculino , Polonio/análisis , Efectos de la Radiación , Radio (Elemento)/análisis , Reino UnidoRESUMEN
PURPOSE: To assess increased exposure to airborne pollutants near power lines by investigating theoretically and experimentally the behaviour of 222Rn decay product marker aerosols in the 50 Hz electric field under power lines. MATERIALS AND METHODS: The behaviour of aerosols in outdoor air including those carrying 222Rn decay products was modelled theoretically in the presence of an AC field. TASTRAK alpha-particle spectroscopy was used to characterize 218Po and 214Po aerosols outdoors. Sampling points were chosen along a line at right angles up to 200 m from a number of high voltage power (transmission) lines. Each sampling point comprised an arrangement of mutually orthogonal TASTRAK detectors. Exposures were carried out at different power line locations in various weather conditions. RESULTS: The model predicts a two- to three-fold increase in deposition of aerosols on spherical surfaces mimicking the human head under high voltage power lines. Experimental measurements using detectors mounted on grounded metal spheres showed an enhanced deposition of both 218Po and 214Po aerosols. Enhanced 218Po deposition on 400 kV lines ranged from 1.96+/-0.15 to 2.86+/-0.32. Enhanced 214Po deposition on 275 kV and 132 kV lines were 1.43+/-0.07 and 1.11+/-0.21, respectively, where the latter value was not significant. CONCLUSIONS: The observations demonstrate a mode of increased exposure to pollutant aerosols under high voltage power lines by increased deposition on the body. The total (indoor + outdoor) 218Po and 214Po dose to the basal layer of facial skin is estimated to be increased by between 1.2 and 2.0 for 10% of time spent outdoors under high voltage power lines.
Asunto(s)
Contaminantes Radiactivos del Aire/química , Campos Electromagnéticos , Exposición a Riesgos Ambientales , Aerosoles , Contaminantes Radiactivos del Aire/efectos adversos , Atmósfera , Calibración , Niño , Campos Electromagnéticos/efectos adversos , Cabeza , Humanos , Leucemia Inducida por Radiación/etiología , Cómputos Matemáticos , Modelos Químicos , Polonio/química , Dosis de Radiación , Monitoreo de Radiación , Radón/química , Hijas del Radón/química , Análisis Espectral/métodosRESUMEN
PURPOSE: To investigate corona ions emitted from high-voltage powerlines and assess their effects on exposure to environmental pollutant aerosols. MATERIALS AND METHODS: The charge density of ions in air required to produce a given change in the observed DC field at ground level was calculated. A DC field mill meter was used to map the DC fields near 132, 275 and 400 kV powerlines. RESULTS: The Earth's natural DC field of around approximately 100 Vm(-1) was significantly modified near powerlines in 8 out of 14 cases. Typically, downwind of the powerlines the field direction was reversed giving values to -340 V m(-1). In one case, the effect extended more than 500 m from a 275 kV line. DISCUSSION: These results can be analysed in terms of the charge density present. This analysis suggests that typically 2000 excess negative charges per cm3 are required to match the measured DC fields. Such space charge will result in unipolar aerosol charging in excess of the normal bipolar steady state charge distribution of pollutant aerosols. This may lead to increased lung deposition on inhalation.
Asunto(s)
Contaminantes Atmosféricos/efectos adversos , Contaminantes Atmosféricos/química , Campos Electromagnéticos/efectos adversos , Exposición a Riesgos Ambientales , Aerosoles , Atmósfera , Planeta Tierra , Humanos , Exposición por Inhalación , Iones , Pulmón/metabolismo , Emisiones de Vehículos , VientoRESUMEN
We report the attraction of radon daughter nuclei in normal domestic room air to everyday sources of power frequency electromagnetic fields. TASTRAK plastic track detectors were used to measure alpha-emission from the radon (222Rn) daughters 218Po and 214Po close to 50-Hz mains frequency power cables and domestic appliance leads. We observed that wires carrying mains frequency potential attract radon daughter nuclei in a manner visually similar to the attraction of iron filings to a magnet. Increased deposition of up to a factor of 18 was observed. Further experiments designed to simulate the effect of overhead power lines at ground level showed large scale variations in local plateout and airborne concentration of radon daughters. The effects appear to be due to interactions of the electric component of the EM-field with both the ultrafine and attached fraction of radon daughter aerosols. Three mechanisms have been examined. First, aerosols instantaneously polarize in sympathy with the electric component of an applied mains frequency EM-field and as a result may migrate up strong E-field gradients. This effect is however quite weak and may only affect larger aerosols in strong field gradients. Second, charged aerosols oscillate in a 50-Hz field and in the case of the ultrafine fraction this may lead to significantly increased plateout. Third, there is the possibility that oscillation of charged aerosols induces fluctuations in the magnitude of the instantaneous charges carried and this results in a diffusive-like motion along the field lines. The effect on dose to body organs is considered. Enhanced plateout on the skin is likely, increasing the dose to the basal layer. The dose to internal organs is governed initially by inhalation and lung deposition of radon daughters. Therefore increased local concentration in room air could lead to increased dose by inhalation. E-fields are heavily attenuated by the human body and body values in tissue of no more than 10(-4) of the external field strength have been suggested. Nevertheless calculations suggest that under exposure to strong external fields this may still be sufficient to alter the deposition pattern of the charged component of the ultrafine fraction in the bronchial region. In contrast it is unlikely that internal electric fields could significantly affect the attached radon daughters. In this context the lack of measurements of residual E-fields in the cavities of the mouth, pharyngeal and bronchial regions is of considerable importance and should be addressed. We believe that the observations may have implications for the apparent enigma that there is no persuasive biological evidence to show that power frequency electromagnetic fields can influence any of the accepted stages in carcinogenesis. On the contrary, the observations show that EM-fields can concentrate in their vicinity a cocktail of radon daughter nuclei, a known carcinogen, and presumably other potentially harmful agents.
Asunto(s)
Campos Electromagnéticos/efectos adversos , Hijas del Radón/química , Aerosoles , Partículas alfa , Exposición a Riesgos Ambientales , Humanos , Neoplasias Inducidas por Radiación/etiología , Hijas del Radón/economíaRESUMEN
Samples of human rib were collected at autopsy and 20 were selected for marrow fat cell measurement, representing an age range of 16-96 years. The mean diameter of fat cells in red bone marrow of human rib was found to increase from around 48 microns at ages 16-29 years to around 65 microns at ages 82-96 years. There was a greater number of fat cells of smaller size range in younger ages compared with that in older ones. The maximum size of fat cells was found to be 102 microns. Calculated radon-derived doses to haemopoietic tissue ranged from 60 to 162 microSv y-1 at average UK exposures of 20 Bq m-3. It was concluded that the bone marrow fat fraction is the important parameter as far as alpha-radiation dose from radon in fat is concerned. This updates the theoretical estimates of dose carried out by Richardson et al. (1991).
Asunto(s)
Adipocitos/efectos de la radiación , Células de la Médula Ósea , Sistema Hematopoyético/efectos de la radiación , Radón , Adolescente , Adulto , Factores de Edad , Anciano , Anciano de 80 o más Años , Médula Ósea/efectos de la radiación , Femenino , Humanos , Masculino , Persona de Mediana Edad , Dosis de Radiación , Costillas/citologíaRESUMEN
The technique of alpha-particle spectroscopy by CR-39 type TASTRAK plastic has been used to study the depth distribution of natural alpha-particle emitters at the surface of human bone. The predominant component of this alpha-particle activity was 210Po supported by 210Pb, although a smaller activity of 226Ra was also detected. Autopsy samples of human femur and cranium were obtained from subjects age 63 to 86. Both cortical and trabecular surfaces were analyzed. The results indicate that 210Pb-supported 210Po is concentrated at the surfaces of human bone from elderly subjects, in a narrow band 3 microns deep or less, by a factor of about four. As a result, the alpha-particle dose to the nuclei of cells lining bone surfaces is around 1.8 times greater than that calculated for a uniform volume distribution. Polonium-210 activity indicates the distribution of 210Pb, and of stable lead, received by continuous intake throughout life at a very low level. A persistent bone surface concentration of lead and other osteotropic metals may be associated with the hypermineralized layer about 1 micron thick which occurs at the surface of resting bone mineral.
Asunto(s)
Partículas alfa , Huesos/efectos de la radiación , Polonio/análisis , Anciano , Anciano de 80 o más Años , Médula Ósea/efectos de la radiación , Exposición a Riesgos Ambientales , Femenino , Humanos , Masculino , Persona de Mediana Edad , Análisis Espectral/métodosRESUMEN
The techniques for alpha-particle autoradiography based on the plastic nuclear track detector CR-39, previously reported, have been developed considerably. The techniques are applied to alpha-autoradiography of human lung tissue in particular but are applicable to any biological tissue. The most important developments are: (i) Improvements in the manufacture and pre-etching of the plastic. These allow activities as low as approximately 10(-15) Ci g-1 to be determined. (ii) High resolution alpha-particle spectroscopy in CR-39 plastic based on the analysis of the structure of the etched track. This enables the energy of individual alpha-particles to be determined to approximately 35 keV. (iii) Calculation of the effective thickness of tissue sampled by the plastic. This relates the tissue activity to the track density on the plastic. (iv) A deconvolution analysis which takes the distributions of track length and dip angle in the plastic and determines the alpha-particle range spectrum and distribution of tissue activity with height above the plastic surface. This enables both the absolute abundance and the microdistribution of alpha-active nuclides present to be determined. (v) The analysis of radon diffusion in tissue to determine the mean radon diffusion distance in tissue and plastic.
Asunto(s)
Partículas alfa , Pulmón/análisis , Radioisótopos/análisis , Adulto , Autorradiografía/instrumentación , Humanos , Masculino , Persona de Mediana Edad , Polonio/análisis , Radiometría/instrumentación , Radón/análisisRESUMEN
A technique for low-level alpha-particle autoradiography of bronchial epithelium utilising the plastic track detector, CR-39, is described. This plastic is new to the field of nuclear track detection and is very sensitive to alpha-particles. The recording properties of CR-39 for alpha-particles are described in detail and the technique for autoradiography discussed. This technique includes two methods of background reduction enabling activities as low as 2 alpha-particles cm-2 to be detected. The location of the point of emission of an alpha-particle from the tissue surface can be determined to an accuracy of a few micrometers. Determination of the lower limit to the energy of individual alpha-particles is possible from measurements of their range in the plastic. Examples are given of the determination of the microdistribution of alpha-particle active nuclei in bronchial tissue including the observation of two 'hot-spots' in the epithelium sample which are attributed to the presence of small particles of uranium with its daughter products.