210Po implanted in glass surfaces by long term exposure to indoor radon

Recent epidemiologic investigations of the relationship between residential radon gas exposure and lung cancer relied on contemporary radon gas measurements to estimate past radon gas exposures. Significant uncertainties in these exposure estimates can arise from year-to-year variation of indoor radon concentrations and subject mobility. Surface implanted 210Po has shown potential for improving retrospective radon gas exposure estimates. However, in previous studies, the ability of implanted 210Po activity to reconstruct cumulative radon gas exposure was not tested because glass was not available from homes with known radon-gas concentration histories. In this study, we tested the validity of the retrospective radon gas reconstruction using implanted 210Po surface activity by measuring glass surfaces from homes whose annual-average radon gas concentrations had been measured almost every year during two decades. Regression analysis showed a higher correlation between measured surface activity and cumulative radon gas exposure in these homes (R2>0.8) than was observed in homes where only contemporary radon gas measurements were available. The regression slope (0.57 ky m(-1)) was consistent with our earlier retrospective results. Surface activity measurements were as reliable for retrospective radon gas exposure reconstruction as yearlong gas measurements. Both methods produced estimates that were within 25% of the long-term average radon gas concentrations in a home. Surface measurements can be used for home screening tests because they can provide rapid, reliable estimates of past radon gas concentrations. Implanted 210Po measurements are also useful in retrospective epidemiologic studies that include participants who may have been exposed to highly variable radon concentrations in previously occupied or structurally modified homes.     

Intercomparison of retrospective radon detectors.

We performed both a laboratory and a field intercomparison of two novel glass-based retrospective radon detectors previously used in major radon case-control studies performed in Missouri and Iowa. The new detectors estimate retrospective residential radon exposure from the accumulation of a long-lived radon decay product, (210)Pb, in glass. The detectors use track registration material in direct contact with glass surfaces to measure the alpha-emission of a (210)Pb-decay product, (210)Po. The detector's track density generation rate (tracks per square centimeter per hour) is proportional to the surface alpha-activity. In the absence of other strong sources of alpha-emission in the glass, the implanted surface alpha-activity should be proportional to the accumulated (210)Po, and hence to the cumulative radon gas exposure. The goals of the intercomparison were to a) perform collocated measurements using two different glass-based retrospective radon detectors in a controlled laboratory environment to compare their relative response to implanted polonium in the absence of environmental variation, b) perform collocated measurements using two different retrospective radon progeny detectors in a variety of residential settings to compare their detection of glass-implanted polonium activities, and c) examine the correlation between track density rates and contemporary radon gas concentrations. The laboratory results suggested that the materials and methods used by the studies produced similar track densities in detectors exposed to the same implanted (210)Po activity. The field phase of the intercomparison found excellent agreement between the track density rates for the two types of retrospective detectors. The correlation between the track density rates and direct contemporary radon concentration measurements was relatively high, considering that no adjustments were performed to account for either the residential depositional environment or glass surface type. Preliminary comparisons of the models used to translate track rate densities to average long-term radon concentrations differ between the two studies. Further calibration of the retrospective detectors' models for interpretation of track rate density may allow the pooling of studies that use glass-based retrospective radon detectors to determine historic residential radon exposures.     

Measurement of 210Po atoms content in glass as an indicator of long-term exposure to radon

Measurements of exposure to radon are performed using numerous research methods which register either temporary or periodic radon concentrations. The method presented below allows for the estimation of average radon concentration in the past. This is possible due to indirect measurement of the contents of 210Pb embedded in glass structure. The half-life of 210Pb is about 22 years. A number of exposures of window glass to radon have been carried out in laboratory conditions (radon chamber) and the obtained results were used to calculate the coefficient that renders it possible to define global indoor exposure to radon. The registration was made using a track detector CR-39, which records alpha particles resulting from the disintegration of 210Po, one of 222Rn decay products.     

An experimental analysis of the contribution of 210Po and of 210Po produced by 210Pb decay to the gross alpha-particle activity of water samples

The contribution of 210Po and of 210Po produced by 210Pb decay to the gross alpha-particle activity of water samples by U.S. Environmental Protection Agency Method 900.0 is investigated as a function of residue mass and geometry and time between sample collection and analysis. It is shown that these factors can cause the contribution to gross alpha-particle activity of 210Po to be up to 2.0 and 1.1 times the initial 210Po activity for grab and quarterly composite samples, respectively, and can cause the contribution to gross alpha-particle activity of 210Po from 210Pb decay to be up to 1.1 times and 1.5 times the 210Pb activity for grab and quarterly composite samples, respectively. It is also shown qualitatively that at least for some residues, there is a loss of polonium due to volatilization when the sample is heated over a flame.     

Concentrations of radionuclides of size fractionated fly-ash emissions from a thermal power plant using Taiwan coal.

Coal, fly ash and bottom ash samples were taken from a 300-MWe coal-fired power plant with a daily coal consumption of 2400 tons. A high volume sampler coupled with several mesh testing sieves was used to separate fly ash samples into different size fractions. Determination of the concentrations of 40K, 238U, 226Ra, 210Pb, 210Po, 228Th and 228Ra was carried out either by gamma or alpha spectrometry. For elements volatilized during combustion, their radionuclide concentrations decrease with increasing particle size. The enrichment factors for all radionuclides mentioned above were studied. Their values range from 31.0 for 210Po to 2.2 for 228Ra. Of all radionuclides studied, 210Po and 210Pb are the most volatile elements; therefore, an increase in the natural radiation level should first be indicated by an increase in these two nuclides.     

Dietary intake of 210Po and 210Pb in the environment of Goa of south-west Coast of India

This paper deals with the distribution and activity intake of 210Po and 210Pb in food, diet, and potable water samples of the Goa region and the estimated committed effective dose due to ingestion of these radionuclides. The activity concentrations of 210Po and 210Pb were determined in about 30 food and diet samples from different places of Goa in order to know the distribution and intake of these radionuclides. The activity concentration of 210Po in fish and prawn samples were significantly higher than concentrations found in vegetable and rice samples. Higher concentrations of 210Po and 210Pb were observed in leafy vegetables than in non-leafy vegetables. Among the diet samples the activity concentrations of 210Po and 210Pb in non-vegetarian meal samples were relatively higher than in vegetarian meal and breakfast samples. The committed effective dose due to annual intake of 210Po was found to be 94.6 microSv, 49.1 microSv, 10.5 microSv, and 2.2 microSv and that of 210Pb found to be 81.6 microSv, 59.9 microSv, 14.6 microSv, and 2.0 microSv for the ingestion of non-vegetarian meal, vegetarian meal, breakfast, and potable water, respectively.     

The pattern of distribution of polonium-210 in the superficial soil layer in Moscow

The pattern of distribution of 210Po, 226Ra, 232Th, and 40K was studied in the superficial soil layer of Moscow. There was a correlation between the soil levels of the natural uranium decay products 210Po and 226Ra. The ratio of specific 210Po, 226Ra activities was 1.3 +/- 2.6 in the soil samples. There is a close correlation between the soil levels of 210Po and its organic substance. The specific activities of the natural radionuclides in the Moscow soil were as follows: 210Po 30-50 Bk/kg, 226Ra 10-30 Bk/kg, 232Th 10-30 Bk/kg, and 40K 200-400 Bk/kg. These levels are no greater than those of those of natural radionuclides in the Earth's crust.     

Radionuclides in the lichen-caribou-human food chain near uranium mining operations in northern Saskatchewan, Canada.

The richest uranium ore bodies ever discovered (Cigar Lake and McArthur River) are presently under development in northeastern Saskatchewan. This subarctic region is also home to several operating uranium mines and aboriginal communities, partly dependent upon caribou for subsistence. Because of concerns over mining impacts and the efficient transfer of airborne radionuclides through the lichen-caribou-human food chain, radionuclides were analyzed in tissues from 18 barren-ground caribou (Rangifer tarandus groenlandicus). Radionuclides included uranium (U), radium (226Ra), lead (210Pb), and polonium (210Po) from the uranium decay series; the fission product (137Cs) from fallout; and naturally occurring potassium (40K). Natural background radiation doses average 2-4 mSv/year from cosmic rays, external gamma rays, radon inhalation, and ingestion of food items. The ingestion of 210Po and 137Cs when caribou are consumed adds to these background doses. The dose increment was 0.85 mSv/year for adults who consumed 100 g of caribou meat per day and up to 1.7 mSv/year if one liver and 10 kidneys per year were also consumed. We discuss the cancer risk from these doses. Concentration ratios (CRs), relating caribou tissues to lichens or rumen (stomach) contents, were calculated to estimate food chain transfer. The CRs for caribou muscle ranged from 1 to 16% for U, 6 to 25% for 226Ra, 1 to 2% for 210Pb, 6 to 26% for 210Po, 260 to 370% for 137Cs, and 76 to 130% for 40K, with 137Cs biomagnifying by a factor of 3-4. These CRs are useful in predicting caribou meat concentrations from the lichens, measured in monitoring programs, for the future evaluation of uranium mining impacts on this critical food chain.     

Estimation of radon exposures to workers at the Fernald Feed Materials Production Center 1952-1988

The Feed Materials Production Center (FMPC) at Fernald, Ohio produced uranium metal products for use in Department of Energy defense programs. Radium-contaminated waste material was stored on-site in two K-65 silos on the west side of the facility and provided a source of 222Ra. The initial objective of this study was to estimate radon exposures to employees at FMPC working from 1952 to 1988. A modified Gaussian plume model was used to estimate exposures to workers. In an effort to validate these model-based estimates, we used 138 CR-39 film assays from window glass sampled in buildings throughout the site. Results from the CR-39 assays indicated a second substantial source of radon, the smaller Q-11 silos located in the production area. A response-surface regression analysis using a cubic spline model was fit to the CR-39 data to estimate 210Po surface activity levels at geographic coordinates throughout the facility. Knowledge of the age of the glass, the amount of contaminated waste in the Q-11 silos, and 210Po decay rates were used to estimate annual exposures to radon decay products (WLM: working level months). Estimated WLM levels associated with the Q-11 source term indicated that employees working in the vicinity during the period when they were filled with radium-contaminated waste (1952-1958) received substantially higher radon exposures than those from the K-65 source during this period. Results of the two models, corresponding to the K-65 and Q-11 sources, were combined to estimate WLM levels by year for each of the 7143 Fernald workers during the period 1952-1988. Estimated cumulative exposures to individual workers ranged from <0.5 to 751 WLM. Estimated radon exposures from this newly discovered source have important implications for future epidemiologic studies of lung cancer in workers at the Fernald facility.     

Computer simulation and experimental studies of implanted 210Po in glass resulting from radon exposure

Retrospective radon exposure measurements rely on an understanding of how the depth distribution of the implanted activity in glass is influenced by processes such as implantation, diffusion, corrosion, and cleaning. In this study, the implantation depth of 210Po was found by step-wise etching with two different etchants to obtain the depth distribution. The depth profiles are compared with results from simulations using the SRIM computer program. Theoretically estimated distributions showed good agreement with experimental 210Pb (or 210Po) activity depth profiles obtained by sequential etching. The maximum depth of implanted activity was about 100 nm, and activity deeper than about 70 nm is associated with the second alpha decay from 214Po activity previously implanted in the glass matrix. However, there was no depth interval where the activity was solely due to a single decay from the surface. The results also show that measurement of the depth profile for both "old" and controlled 222Rn exposure     

Relationship between the 210Pb content of teeth and exposure to Rn and Rn daughters

Existing data on 210Pb in human teeth are reviewed for various countries. The mean value of 210Pb in the teeth of population groups exposed to "normal" levels of radon-daughter exposure is about 2 mBq/g. A detailed analysis of 48 samples from a "normal" Italian population group revealed that smoking habits and age may have some influence on 210Pb content of teeth, while this is not the case for differences in sex. A group of 45 Austrians exposed to elevated levels of radon and radon daughters is compared with the Italian group. After subtraction of background levels of 210Pb as found for the normal Italian population, the incremental 210Pb tooth content due to excessive radon-daughter exposure has been correlated with the individual cumulative exposure corrected for background radon-daughter exposure. A statistical analysis shows the significance of the linear correlation at the alpha = 0.01 level. For the incremental increase of 210Pb in teeth, a value of 1.2 mBq/g has been used for a lifetime exposure to 1 WLM. This result is compared to corresponding data published in the literature, which are predominantly related to the 210Pb content of bone after short-time exposure at high levels, e.g. in uranium mines. The comparison seems to indicate the influence of the exposure rate and the need for a comprehensive model, which takes into account radon-daughter inhalation, radon dissolved in body fluids and 210Pb metabolism.     

Environmental radon daughters reveal pathognomonic changes in the brain proteins and lipids in patients with Alzheimer's disease and Parkinson's disease, and cigarette smokers

This paper presents an investigation of the retention of environmental radon daughters, 210Po (alpha particle emitting radio-nuclide) and 210Bi (beta particle emitting radio-nuclide), in lipid and protein fractions of the cortical grey and subcortical white matter from the frontal and temporal brain lobes of patients who had suffered from Alzheimer's disease or Parkinson's disease, of cigarette smokers, and of control subjects. 210Po and 210Bi radioactivity increased tenfold in the cortical grey and subcortical white protein fraction in patients with Alzheimer's disease and smokers, and tenfold in the cortical grey and subcortical white lipid fraction in patients with Parkinson's disease. Free radicals generated by radon daughters may add to the severity of the radio-chemical injury to the brain astrocytes. The pathognomonic distribution of radon daughters to lipids in patients with Parkinson's disease and to proteins in patients with Alzheimer's disease was attributed to high chlorine affinity of radon daughters. The changes in the membrane protein pores, channels, and gates in patients with Alzheimer's disease and in the lipid bilayer in patients with Parkinson's disease are at the core of what the authors think are two systemic brain diseases.     

Theoretical study of the relation between radon and its long-lived progeny in a room

We present a theoretical study of the complex relation between radon and its long-lived progeny implanted in glass surfaces. The well known (extended) Jacobi room model, which is normally used to describe radon and its progeny in a room, was transformed into a two-parameter model revealing a linear correlation between long term radon exposure and surface activity due to implanted radon decay products. Furthermore, this new approach made integration into a Monte Carlo simulation possible so that the large variation of different room model parameters could be taken into account. This allowed the calculation of a probability distribution for radon exposure from the measurement of the implanted 210Po activity. The availability of a 95% confidence interval for the radon exposure is valuable in the application of retrospective radon assessment in epidemiological studies.     

Study of long term radon transport by measuring the difference of the 210Pb and 226Ra activity in soil as a function of the depth

Long term radon transport has been studied by measuring the activity difference of 210Pb and 226Ra in soil as a function of the depth. The results are from test pits of 1-2 m depth made at a dam of a tailings pond and at the plateau of a waste rock pile. Soil samples of about 1 kg were taken at a successive distances of 5 cm and analyzed by means of gamma-ray spectroscopy using low background germanium n-type detectors. It is shown that by this method nearly model independent information about the radon transport over a period of several decades can be inferred from the data.     

Radionuclides in the terrestrial ecosystem near a Canadian uranium mill--Part I: Distribution and doses

Soils, vegetation, small mammals, and birds were measured for uranium series radionuclides at three sites near the operating Key Lake uranium mill in northern Saskatchewan. Sites, impacted by windblown tailings and mill dust, had significantly higher concentrations of uranium, 226Ra, 210Pb, and 210Po in soils, litter, vegetation, tree needles and twigs, small mammals, and birds, compared to a control site. Samples were collected from both upland jackpine and black spruce bog habitats in triplicate at each site. Both habitats were similar in radionuclide accumulation. Absorbed doses averaged 0.92, 8.4, and 4.9 mGy y(-1) to small mammals and 2.0, 5.8, and 2.8 mGy y(-1) to Lincoln's sparrows at the control, tailings, and mill sites, respectively. These doses do not include doses from short-lived radon progeny. The majority of the dose increment at the tailings and mill sites was due to 226Ra, whereas it was 210Po at the control site. Thus, use of a radiation weighting factor of 20 for alpha radiation raised equivalent doses (in mSv y(-1)) by nearly a factor of 20.     

The importance of acid digestion of urine prior to spontaneous deposition of 210Po

Historically, radiochemical analysis of 210Po in urine has used spontaneous deposition of the nuclide directly from raw urine onto a suitable metal disc. Consequently, the urinary excretion fraction for Po in some current metabolic and dosimetric models is based on studies which inherently assume that metabolized (i.e., filtered out of the blood by the kidneys) 210Po is plated with the same efficiency as tracer 210Po which has been added to urine samples. Urine samples collected after intravenous administration of 210Po citrate to two species of nonhuman primates were divided and simultaneously analyzed via two methods: the historical procedure of plating 210Po from raw urine for one sample and a method which includes the addition of 208Po tracer and sample digestion with concentrated HNO3 prior to 210Po deposition for the other sample. A more significant amount of 210Po was consistently recovered when the urine was wet ashed then when it was not wet ashed. A temporal relationship was found to describe the change in the ratio of the deposition recoveries for the two methods. Possible mechanisms for this phenomenon and its dosimetric implications are discussed.     

Assessment and significance of the skeletal doses due to 210Po in radioactive spa workers.

The high exposure due to radon and daughter products found in many Italian radioactive spas, suggested a research program designed to assess the lung and skeletal doses accumulated by the subjects working in those spas. The assessment of such doses will permit the evaluation of the significance of a follow-up of the exposed subjects with epidemiological studies. In this paper some preliminary results will be discussed, mainly related to the estimation of the²¹⁰Po skeletal doses in a few subjects. The²¹⁰Pb²¹⁰Po skeletal burdens in the subjects have been evaluated on the basis of their²¹⁰Pb²¹⁰Po urinary excretion collected at various intervals during a period of 1 year. The experimental results on the most exposed subjects have shown skeletal doses of the order of 20–40 rem/year and lung exposures higher than 100 WLM (Working Level Month).     

Exposure of red bone marrow to ionising radiation from natural and medical sources in France.

This paper presents a review of available data on the average level of equivalent dose to the red bone marrow in France, due to natural and some medical exposures. The sources of exposure to ionising radiation which were studied are medical examinations involving x-rays (diagnostic radiology), inhalation of radon and thoron, cosmic irradiation, terrestrial irradiation and intakes of natural radionuclides. This review is based, where possible, on specific data for France. The influence of age on exposure levels is studied when data are available. The total equivalent dose to the red bone marrow is estimated at 2.4 mSv year(-1), 2.7 mSv year(-1) and 5.4 mSv year(-1) respectively for adults (> or =18 years old), children (3-17 years old) and infants (0-1 year old). The high level of exposure for infants is explained by the important contribution of 210Po. The average equivalent dose to the red bone marrow for adults is also compared with the average committed effective dose due to the same exposure sources. The importance of medical exposure and natural exposure due to intake of natural radionuclides emphasises the importance of obtaining more information about these sources of exposure.     

Health effects from radon-222 in drinking water in Algiers.

As part of a national programme, 222Rn in public water supply systems, private wells and in natural mineral waters has been measured in some locations of Algiers City. Radon concentration was determined by means of a passive method based on the use of electret ion chambers (EIC). The determination of radon concentration in the water samples consisted of sealing a known volume of water in a jar and measuring the airborne radon using an E-PERM (electret-passive environmental radon monitor) device. The radon concentrations in natural mineral waters were found to be the highest of all other water samples. It is found that the mean radon concentration of water samples was lower than the value of 11000 Bq m(-3) (11 Bq l(-1)) reported by the US Environmental Protection Agency. These investigations enabled a first estimate of the corresponding annual effective dose to the stomach and the lungs. It was observed that the annual effective dose resulting from direct consumption of water is far greater than that due to inhalation of radon emanating from tap water. Moreover, it is also shown that the annual effective dose due to inhalation of radon emanating from tap water and flushing water is negligible compared to the total annual dose for indoor radon in Algiers.     

Evidence for and implications of self-background of radon dosimeters with glass-fiber filters

The first national radon survey in The Netherlands was conducted in 1984 with passive radon dosimeters that contain glass-fiber diffusion filters. During the last few years, measurements of outdoor-radon concentrations and information in the literature suggested to us that these dosimeters may give falsely elevated readings. A systematic contribution would be present due to alpha particles from natural radionuclides in the glass-fiber filter producing tracks on the track-etch foil. In the framework of the quality assurance of our laboratories, the origin of this offset was systematically assessed by means of measurements of alpha and gamma radiation from the glass-fiber filters and by intercomparisons between different types of detectors at low radon concentrations. It was found that alpha particles from the decay of 214Po in the glass-fiber filter are the main cause of the extra tracks (only 12% originates from decay of 212Po), leading, for this type of filter, to an offset in concentration of approximately 8 Bq m(-3). The implications of this offset are discussed.