Radon-222 and Leukemia.

ABSTRACT: Leukemia was the first medically observed human cancer related to ionizing radiation in the 1945 follow-up study of atomic bomb survivors. The bone exposure and dose calculated here are based on the measured solubility of the noble gas 222 Rn in blood. A fraction of the 222 Rn gas in blood distributes as dissolved gas to all organs, with the fraction depending upon the blood flow rate to the organ. The exposure and dose calculated are for men and women based on measurements made for the blood flow rate to the femur, the largest bone in the human skeleton. The annual exposure and dose estimated for continuous 222 Rn inhalation of 100 Bq m -3 are very low and unlikely to cause leukemia. Other neurological issues, from lifetime exposure to low activity concentrations of 222 Rn alpha particle exposure in bone, are unknown.

Radon-222 Brain Dosimetry.

ABSTRACT: The human brain dose from radon-222 (222Rn) exposure is calculated here using 222Rn tissue solubility data. A fraction of 222Rn inhaled dissolves in blood and cellular fluids and circulates to brain and all organs. Radon-222 has a relatively high solubility in blood and body fluids based on human inhalation experiments. The brain dose uses calculated concentrations of 222Rn in blood and cellular fluids from exhaled breath measurements following human exposure in a 222Rn chamber. The annual brain dose from continuous inhalation of a concentration of 100 Bq m-3 is about 450 times less than the dose to bronchial epithelium from inhalation of the same 222Rn concentration. Based on the 222Rn dosimetry here, it is highly unlikely that brain cancer is related to even high 222Rn exposures. Any functional or neurodegenerative issues from exposure to very small doses of 222Rn alpha particles are, at present, unknown.

A Review of Radon Equilibrium Factors in Underground Mines, Caves, and Thermal Spas.

Radon equilibrium factor Feq is an important factor in radon progeny dose assessment. A review of published measurements of Feq shows a range of values from 0.1 to 1.0 reported in studies from more than 26 countries measured in 173 underground mines, and 136 show caves, tourist mines, and thermal spas. The average values of Feq are 0.38 in underground mines and 0.39 for show caves, tourist mines, and thermal spas. The wide range of Feq in those special workplaces suggests that location-, environment-, and operation-specific values are more appropriate than a recommended average value in the calculation of lung bronchial dose. This is especially important in mines or other typically high radon exposure locations because Feq can be used for recording an individual's occupational radon exposure or dose.

Radon carcinogenesis: risk data and cellular hits.

Abundant epidemiological data are now available (2008) on the human lung cancer response for lifetime radon gas exposure to residential concentrations of 100 Bq m(-3), equal to 22 working level months over 40 y. We combined published pooled epidemiological data and dosimetric calculations of alpha particle hits to target basal or mucous cell nuclei in bronchial epithelium. This yields an estimate that about 10,000 basal nuclei (target) cell hits per cm2 per person over a lifetime are involved in radon-related lung cancer. The DNA target cell area (cross section) for a hit is about 2 bp. The present epidemiology indicates that 1000 persons need to be exposed to this hit rate for observable cancers to be detected. The mechanism proposed is that the extensive prior DNA damage in smokers, followed by alpha particle damage to a critical site in checkpoint genes, accounts for the greater lung cancer response in smokers.

Effect of Residential Radon Decay Product Dose Factor Variability on Reporting of Dose.

Guidelines for occupational exposure to radiation are based on annual absorbed or effective dose. Guidelines for Rn exposure are currently based on air concentrations of Rn or decay products. Models of bronchial dose from decay product exposure are based on calculations that have five major parameters with parameter variabilities ranging from 20 to 50%. Many countries currently use the ICRP dose conversion convention, which is a ratio of lifetime Rn lung cancer risk to lifetime atomic bomb dose risk. The results of ongoing epidemiology changed both lifetime risk values, and the dose conversion convention has increased by a factor of 2. Therefore, the current dose conversion convention risk ratio is to be replaced by biokinetic dosimetric models. The main effect of variability in the value of Rn dose factors on industry is that the workplace atmosphere must be characterized accurately, and at present, this is not possible. A history of the dose factor models is central to factor development. The values of the dose model parameters are described illustrating the difficulty in calculation of a dose factor with universal applicability. The objective is to show the range of each parameter and the effect of the dose factor used when reporting occupational or residential bronchial dose.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part I: 222Rn.

Radon exposure limits are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, the equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 20 countries, measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of equilibrium factors suggests that location-specific values are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

A Review of Indoor and Outdoor Radon Equilibrium Factors-part II: 220Rn.

Radon exposure levels are given in terms of radon gas concentration in the air. However, in the calculation of radon dose to the lung, the radon equilibrium equivalent concentration is used. The measured equilibrium factor times the measured radon gas concentration estimates the equilibrium equivalent concentration. Therefore, equilibrium factor is an important factor in radon dose calculations. A review of published measurements of equilibrium factors shows a range of values reported in studies from more than 13 countries and regions measured in indoor residential, indoor public, and outdoor environments. Values for Rn are reported and discussed here as the second of a two-part series, with special attention paid to results from India and China, where measured equilibrium factors are reported for hundreds and thousands of households, respectively. The wide range of measured equilibrium factors suggests that location-specific values measured in the typical breathing zone are more appropriate than a worldwide average value in the calculation of lung bronchial dose.

SEISMIC PREDICTION USING UNATTACHED RADON DECAY PRODUCTS.

Long-term measurements of the 222Rn concentration, 222Rn decay product activity, particle size distribution, and unattached, and attached 222Rn decay products, were made at two locations using the 22 y radon decay product 210Pb as their tracer. The particle size sampler collects both short lived 222Rn decay products that ultimately decay to 210Pb on the filters, and also airborne 210Pb. The measurements were made outdoors, at a suburban home and at Fernald, OH, a former uranium processing facility, on top of one of the two 226Ra storage silos containing 150 TBq 226Ra. The size distributions showed the unattached fractions, i.e. particle diameter 2-4 nm, to be 1.5% at the home and 14% at the silos. The unattached fraction of 218Po can be shown to be an immediate measure of the 222Rn concentration. The data indicates detection of the pressure driven 222Rn flow at the silo and with the enhanced measurement capability of a filtered air source versus the usual 222Rn gas measurement. It is proposed that real time measurements of unattached 218Po may be used to identify rapidly changing 222Rn concentrations associated with pressure driven soil air flow associated with seismic activity.

Laboratory analyses: environmental and biological measurements.

From its inception in 1951 to the present, the measurement of radioactive fallout from nuclear weapons testing and the many associated programs to establish global distribution and human health effects have contributed significantly to the understanding of worldwide dispersal of contamination. The original measurements of regional surface deposition of fallout nuclides were with duplicate gummed film collectors. Later, collectors were established in a worldwide network to measure total deposition and specific radionuclides such as 90Sr and 137Cs, which evolved into the first large-scale, global environmental monitoring network. Programs were set up to determine dietary intake and human and animal tissue distribution of 90Sr and 137Cs. Some of the first measurements of natural background dietary radium and body potassium were a response to identify analog elements. The impact of the environmental measurements made for fallout went far beyond any dosimetric consequences. For example, present day information on bone tissue turnover rates are derived mainly from radiochemical analysis of 90Sr measurements in human bone. The spin off from the enormous expenditure in effort to make these measurements and to determine the health consequences of global fallout laid a rich basic and applied scientific foundation in many disciplines, particularly in exposure pathways from ground deposition to dietary uptake and human organ biokinetics.

Radon water to air transfer measured in a bathroom in an energy-efficient home with a private well.

Monthly measurements of radon in kitchen and bath tap water along with indoor air concentrations were made from 1994 to 1996 in an energy-efficient home with a private well. The well supplies all water to the home. The radon in cold and hot kitchen water averaged 69±2 and 52±2 Bq l(-1), respectively. Radon in cold and hot water from the bath/shower room shower head averaged 60±1 and 38±2 Bq l(-1), respectively, whereas hot water collected in the shower at the tub base averaged 5±1 Bq l(-1) or a 92% radon loss to air. While the calculated transfer factor of 1/10,000, i.e. radon concentration in air to radon in water, conventionally applies to the whole house, measurements for the specific water release during showering in a bathroom exhibit a larger transfer factor of 1/2300, due to smaller room volume.

An intercomparison for NIRS and NYU passive thoron gas detectors at NYU.

An intercomparison on thoron ((220)Rn) measurement was carried out between National Institute of Radiological Sciences, Japan (NIRS), and New York University School of Medicine, USA (NYU). The measurements of (220)Rn concentration at NIRS and NYU were performed by using the scintillation cell method and the two-filter method, respectively, as the standard measurement method. Three types of alpha track detectors based on passive radon ((222)Rn)-(220)Rn discriminative measurement technique were used: Raduet and Radopot detectors were used at NIRS, and four-leaf detectors were used at NYU. In this study, the authors evaluated (220)Rn concentration variation in terms of run for exposure, measurement method, and exposure chamber. The detectors were exposed to (220)Rn gas with approximately 15 kBq m(-3) during the period from 0.75 to 3 d. As a result, the variation of each measurement method among these exposure runs was comparable to or less than that for the two-filter method. Agreement between the standard measurement methods of NIRS and NYU was observed to be about 10%, as is the case with the passive detectors. The Raduet detector showed a large variation in the detection response between the NIRS and NYU chambers, which could be related to different traceability.

Long term measurements of indoor radon equilibrium factor.

To provide detailed information for bronchial dose estimates, aerosol particle size distributions, and radon gas concentration, measurements were made in six residential homes and three laboratory rooms in different office buildings in the city of Ottawa. In the literature, most particle size distribution measurements are taken with samplers operating for a few days at most. In this study, the particle size samplers collected the samples from 77 to 162 d. The equilibrium factor determined from the long-term measurements ranged from 0.6 to almost 1 with an average of 0.75. Even though radon concentrations were quite different between residential setting and office buildings, the average equilibrium factor was similar in the two different indoor environments. The results suggest that at least in some basements, if they were occupied, the radon dose would be about twice as high as normally estimated from the conventional F(eq) value of 0.4.

Residential radon remediation: performance over 17 years.

An exploratory radon measurement in 1990 identified 190 Bq m(-3) in the basement of a newly built home in Central New Jersey. Subsequently, the owner had a sub-slab remediation system installed in the basement, i.e. PVC duct through the basement floor connecting to an exhaust fan venting to the house roof. Sequential radon measurements began in 1992 using the NYU alpha-track detector. The homeowner wanted to insure the long-term durability of this remedial system. Seventeen years of measurements show the system functioned properly and reduced an established baseline concentration of 370 ± 8, 56 ± 1 and 67 ± 1 Bq m(-3) for the basement, first and second floors, respectively, to an average of 19 ± 4, 13 ± 3 and 10 ± 0.1 Bq m(-3). The last measurement, 2007-2008, with a newer NYU detector measured both (222)Rn (radon) and (220)Rn (thoron). The basement thoron concentration was 1.5 ± 0.9 Bq m(-3) or about 8 % of the (222)Rn value.

Employee exposure to (222)Rn and (220)Rn in three fish culture stations in Pennsylvania.

Employee exposures to Rn and Rn were measured in three Commonwealth fish hatcheries using specially designed personal dosimeters to determine whether remediation might be necessary. Employees utilizing the hatch house would wear the dosimeter and keep track of their time in the hatch house. Area detectors were also deployed full time in each hatch house. Exposure measurements were compared to U.S. Nuclear Regulatory Commission, U.S. Environmental Protection Agency, and Occupational Safety and Health Administration exposure limits. All measured employee exposures to Rn and Rn were very low and well below currently established regulatory limits. However, hatch house radon concentrations are significantly elevated above the U.S. Environmental Protection Agency residential guideline of 148 Bq m.

Radon and leukemia in the Danish study: another source of dose.

An epidemiologic study of childhood leukemia in Denmark (2,400 cases; 6,697 controls) from 1968 to 1994 suggested a weak, but statistically significant, association of residential radon exposure and acute childhood lymphoblastic leukemia (ALL). The Danish study estimated a relative risk (RR) = 1.56 (95% CI, 1.05-2.30) for a cumulative exposure of 1,000 Bq m-3 y. For an exposure duration of 10 y their RR corresponds to a radon concentration of 100 Bq m-3. There are two dose pathways of interest where alpha particles could damage potential stem cells for ALL. One is the alpha dose to bone marrow, and two is the dose to bronchial mucosa where an abundance of circulating lymphocytes is found. Compared with an exposure of about 1 mSv y-1 from natural external background, radon and decay products contribute an additional 10 to 60% to the bone marrow equivalent dose. The other pathway for exposure of T (or B) lymphocytes is within the tracheobronchial epithelium (BE). Inhaled radon decay products deposit on the relatively small area of airway surfaces and deliver a significant dose to the nearby basal or mucous cells implicated in human lung cancer. Lymphocytes are co-located with basal cells and are half as abundant. Using a 10-y exposure to 100 Bq m-3, our dose estimates suggest that the equivalent dose to these lymphocytes could approach 1 Sv. The relatively high dose estimate to lymphocytes circulating through the BE, potential precursor cells for ALL, provides a dose pathway for an association.