Environmental radon studies in Mexico

Radon has been determined in soil, groundwater, and air in Mexico, both indoors and outdoors, as part of geophysical studies and to estimate effective doses as a result of radon exposure. Detection of radon has mainly been performed with solid-state nuclear track detectors (SSNTD) and, occasionally, with active detection devices based on silicon detectors or ionization chambers. The liquid scintillation technique, also, has been used for determination of radon in groundwater. The adjusted geometric mean indoor radon concentration (74 Bq m⁻³) in urban developments, for example Mexico City, is higher than the worldwide median concentration of radon in dwellings. In some regions, particularly hilly regions of Mexico where air pollution is high, radon concentrations are higher than action levels and the effective dose for the general population has increased. Higher soil radon levels have been found in the uranium mining areas in the northern part of the country. Groundwater radon levels are, in general, low. Soil-air radon contributing to indoor atmospheres and air pollution is the main source of increased exposure of the population.     

Enhancement of radon exposure in smoking areas

Radium-226 is a significant source of radon-222 which enters buildings through soil, construction materials or water supply. When cigarette smoke is present, the radon daughters attach to smoke particles. Thus, the alpha radiation to a smoker’s lungs from the natural radon daughters is increased because of smoking. To investigate whether the cigarette tobacco itself is a potential source of indoor radon, the α potential energy exposure level contents of radon (²²²Rn, 3.82d) and Thoron (²²⁰Rn, 55.60s) were measured in 10 different cigarette tobacco samples using CR-39 solid-state nuclear track detectors (SSNTDs). The results showed that the ^{222, 220}Rn concentrations in these samples ranged from 128 to 266 and 49 to 148 Bqm⁻³, respectively. The radon concentrations emerged from all investigated samples were significantly higher than the background level. Also, the annual equivalent doses from the samples were determined. The mean values of the equivalent dose were 3.51 (0.89) and 1.44 (0.08) mSvy⁻¹, respectively. Measurement of the average indoor radon concentrations in 20 café rooms was, significantly, higher than 20 smoking-free residential houses. The result refers to the dual (chemical and radioactive) effect of smoking as a risk factor for lung cancer.     

Residential radon concentration in the Abruzzo region (Italy): a different perspective for identifying radon prone areas

Indoor radon is an important risk factor for human health. Indeed radon inhalation is considered the second cause of lung cancer after smoking. During the last decades, in many countries huge efforts have been made in order to measuring, mapping and predicting radon levels in dwellings. Various researches have been devoted to identify those areas within the country where high radon concentrations are more likely to be found. Data collected through indoor radon surveys have been analysed adopting various statistical approaches, among which hierarchical Bayesian models and geostatistical tools are worth noting. The essential goal of this paper regards the identification of high radon concentration areas (the so-called radon prone areas) in the Abruzzo Region (Italy). In order to accurately pinpoint zones deserving attention for mitigation purpose, we adopt spatial cluster detection techniques, traditionally employed in epidemiology. As a first step, we assume that indoor radon measurements do not arise from a continuous spatial process; thus the geographic locations of dwellings where the radon measurements have been taken can be viewed as a realization of a spatial point process. Following this perspective, we adopt and compare recent cluster detection techniques: the simulated annealing scan statistic, the case event approach based on distance regression on the selection order and the elliptic spatial scan statistic. The analysis includes data collected during surveys carried out by the Regional Agency for the Environment Protection of Abruzzo (ARTA) in 1,861 random sampled dwellings across 277 municipalities of the Abruzzo region. The radon prone areas detected by the selected approaches are provided along with the summary statistics of the methods. Finally, the methodologies considered in this paper are tested on simulated data in order to evaluate their power and the precision of cluster location detection.     

Fracking and indoor radon: Spurious correlation or cause for concern?

Unconventional gas development (fracking) is controversial in large part because of environmental and health concerns. We consider the concern that fracking leads to more carcinogenic radon gas in nearby buildings. Our empirical approach estimates treatment effects where treatment is continuous (number of wells) and varies in intensity (distance to the wells) and in duration of exposure (the time since wells were drilled). The approach allows any potential effect of fracking to vary non-linearly with the distance between the well and test site and, holding distance constant, the time between drilling and testing. Our main model gives a precisely estimated zero effect of wells on radon concentrations in nearby buildings. It also reveals that energy firms drilled wells in places with higher pre-existing radon levels, which, if ignored, makes it appear that wells within 2 km increase indoor radon but wells 3 km away do not. This explains the finding of a prior study showing a link between drilling and indoor radon.     

Soil uranium,basement radon and lung cancer in Illinois,USA

Using counties as the sampling unit, a significant association between the chemical form of uranium occurring in soils with basement radon levels was found (Spearman r, 0.266; p > |r|, 0.007). Uranium atoms dispersed throughout the soil matrix are efficient emanators of Rn to soil gas, whereas Rn that is trapped diffuses very slowly from the several U-bearing minerals in Illinois soils and does not contribute significantly to explaining basement Rn. Basement Rn level is correlated with annual incidence of male and female lung cancers. Dispersed U is correlated with annual incidence of lung cancer in females with a Spearman correlation coefficient of 0.162 (p > |r|, 0.104) and males of 0.177 (p > |r|, 0.075).     

Redistribution of uranium by physical processes during weathering and implications for radon production

Erosion of the Edale shales of Derbyshire during the Tertiary and Quaternary has resulted in sediment deposits in and on the underlying karstified limestones. Sorting during sedimentation has generated clay-rich sediments which are uranium enriched due to a clay association of uranium in the shales. Radon production in these sediments is at or close to equilibrium with their uranium content, and their fine grain-size ensures efficient radon release. Such sediments are therefore potent local sources of environmental radon.     

Bivariate geostatistical modelling: a review and an application to spatial variation in radon concentrations

We present a comprehensive review of multivariate geostatistical models, focusing on the bivariate case. We compare in detail three approaches, the linear model of coregionalisation, the common component model and the kernel convolution approach, and discuss similarities between them. We demonstrate the merits of the common component class of models as a flexible means for modelling bivariate geostatistical data of the type that frequently arises in environmental applications. In particular, we show how kernel convolution can be used to approximate the common component model, and demonstrate the method using a data-set of calcium and magnesium concentrations in soil samples. We then apply the model to a study of domestic radon concentrations in the city of Winnipeg, Canada, in which exposure was measured at two sites (bedroom and basement) in each residential location. Our analysis demonstrates that in this study the correlation between the two sites within each house dominates the short-range spatial correlation typical of the distribution of radon.     

Assessment of soil and soil-gas radon activity using active and passive detecting methods in Korea

Radon ((222)Rn) is a carcinogenic gas produced by the radioactive decay of radium ((226)Ra). It has been reported that soil and soil-gas are primary factors that could cause indoor radon problems. Six sites were selected for this study--Sanbook, Gangcheon, Jikyeong, Choojung, Geumsung and Homyoung--each was classified according to bedrock type. In order to investigate soil-gas radon activities and radon emanating power, innovated active and passive detecting methods were developed and applied under both field and laboratory conditions. Statistical analysis of results confirmed that the radon activity values measured using either active or passive methods under field or laboratory conditions could be interchangeable with each other.     

Geological and geochemical factors affecting the radon concentration in homes in Cornwall and Devon,UK

Recently collected data for radon levels in houses in Devon and Cornwall are compared with geological and geochemical information. The region is underlain by granites intruded into folded sedimentary rocks. The highest incidence of affected houses is on granites. The granites are characterised by moderate uranium concentrations, a deep weathering profile and uranium in mineral phase which is easily weathered. However, while the uranium may be removed, radium, the immediate precursor of radon, can remain in situ. Radon is emanated easily from the host rock, and high values of radon in ground and surface waters and soil gases have been detected. The granite areas are also characterised by high values of uranium in stream sediments and waters. In contrast, other zones of high uranium in stream sediment samples do not necessarily exhibit high house radon concentrations, especially when underlain by relatively impermeable rocks. Permeable ground can give rise to high incidences, of affected houses despite having uranium levels close to the crustal abundance. It is concluded that the most efficient method of identifying zones of high radon potential is the soil gas radon survey.     

Measurement of indoor radon concentration and assessment of doses in different districts of Alexandria city, Egypt

The main objective of this study is to assess the health hazard due to the indoor radon. Measurement studies have been carried out in 56 dwellings belonging to 14 residential areas in Alexandria city, Egypt. Results are obtained using the LR-115 (Type II) alpha track detector in “closed-can” geometry. The dosimeters were installed in bedroom, living room, and the kitchens of each house. For intercomparison purpose, dosimeters are installed in basements, ground floor, and first floor. Measured indoor radon concentrations were found to vary from 15 to 132 Bq m^?3. The average radon concentrations in living room, bedrooms, and kitchen in basements were found to vary from to be 39 ± 10, 63 ± 15 and 81 ± 25 Bq m^?3, respectively. In living room, bedrooms, and kitchen, on ground floor, the average radon concentrations were found to be 35 ± 9, 44 ± 6 and 56 ± 10 Bq m^?3, whereas on first floor, the average values are 29 ± 8, 34 ± 7 and 45 ± 8 Bq m^?3, respectively. The overall mean radon concentration in all surveyed districts has been found to be 44 ± 16 Bq m^?3. The mean annual estimated effective dose received by the residents of the studied area is estimated to be 0.75 mSv. The obtained results are compared with the indoor radon levels prescribed by the International Commission on Radiation Protection and are found to be less than the action level recommended.     

A methodology for assessing the maximum expected radon flux from soils in northern Latium (central Italy)

Northern Latium (Italy) is an area where the Rn risk rate is potentially high because of the extensive outcropping of Neogene U-rich volcanics and the presence of major active tectonic lineaments. The lack of data on Rn risk rates in that area, which is undergoing major urban and industrial development, has prompted this study. It proposes a methodology to evaluate the maximum potential diffusive Rn flux from soils based on the measurement of ²²⁶Ra, ²³²Th and ⁴⁰K activities by γ-ray spectrometry, and the measurement of main soil parameters influencing the Rn emanation. This methodology provides a simple, reliable and low-cost tool for drawing up radon flux maps useful to both public planners and private individuals, who want to operate safely in the study area. The proposed methodology may also be applied to other geographic areas outside the prescribed study area.     

Investigation of fault position and sources of radon by measurement of 238U decay series radionuclide activity in soil samples

North Derbyshire is designated a Radon Affected Area by the National Radiological Protection Board of Great Britain since more than 1% of the housing stock is estimated to have radon levels in excess of the 200 Bq m-3 Action Level. Enhanced radon emissions associated with geological faults make knowledge of their position important in relation to any potential residential or industrial development. A general survey of radionuclides present in the soils of north Derbyshire and their relationship to the underlying geology highlighted the difficulty of identifying the position of geological faults in the field. Using gamma-ray spectroscopy of soil samples the activity of three 238U decay series radionuclides (226Ra, 214Pb and 214Bi), which were taken as evidence of the presence of 222Rn which occurs in the same decay series, was measured to indicate the position of a fault by enhanced activity. The results also provided some evidence of the source of radon emitted at the fault. A comparison of this methodology with the more conventional soil gas analysis method is made.     

Seasonal and spatial variations in Rn-222 and Rn-220 in soil gas,and implications for indoor radon levels

Rn-222 enters dwellings as a component of soil gas drawn from the soil by mass flow driven by the pressure difference between the house and soil beneath. In a site on Northampton Sand Ironstone (Aalenian), a preferred path of emanation (hotspot) was found. A difference of 63 Bq L^–1 Rn-222 was recorded in July between this point and another 3 m away. Rn-222 in this hotspot shows 12% less variation annually than the surrounding rock. During winter, Rn-222 values within 1.6 m of the house were 44% lower than those at more than 4 m away. Rn-222 showed a 99.5% negative correlation with wind run, showing that on this soil wind pressure can significantly reduce radon in the soil at 500 mm depth. Rn-220 in soil gas correlated positively at the 99.5% level with grass and air temperatures. Rn-220 was not associated with the hotspot.     

Assessment of radon concentration and heavy metal contamination in groundwater of Udhampur district,Jammu & Kashmir,India

Radon concentration was measured in water samples of 41 different locations from Udhampur district of Jammu & Kashmir, India, by using RAD7 and Smart RnDuo monitor. The variation of radon concentration in water ranged from 1.44 ± 0.31 to 63.64 ± 2.88 Bq L^?1, with a mean value of 28.73 Bq L^?1 using RAD7 and 0.64 ± 0.28 to 52.65 ± 2.50 Bq L^?1, with a mean value of 20.30 Bq L^?1 using Smart RnDuo monitor, respectively. About 17.07% of the studied water samples recorded to display elevated radon concentration above the reference range suggested by United Nation Scientific Committee on the Effects of Atomic Radiations (UNSCEAR). The mean annual effective dose of these samples was determined, and 78.95% samples were found to be within the safe limits set by World Health Organisation (WHO) and European Council (EU). The study revealed good agreement between the values obtained with two methods. Heavy metals (Zn, Cd, Fe, Cu, Ni, As, Hg, Co, Pb and Cr) were determined in water samples by microwave plasma atomic emission spectrometer, and their correlation with radon content was also analysed.     

Measurement of radon,thoron and their daughters in the air of marble factories and resulting alpha-radiation doses to the lung of workers

Concentrations of radon (²²²Rn) and thoron (²²⁰Rn) were measured in the air of different marble factories by using a nuclear track technique. The influence of the marble dust nature and ventilation on radon and thoron concentrations was investigated. It was observed that measured radon and thoron concentration ranged from 310 to 903 Bq m⁻³ and 6 to 48 Bq m⁻³, respectively. In addition, alpha-activities due to the unattached and attached fractions of ²¹⁸Po and ²¹⁴Po radon short-lived progeny were evaluated in the marble factories studied. Committed equivalent doses due to the attached and unattached fractions of ²¹⁸Po and ²¹⁴Po nuclei were evaluated in the lung tissues of marble factory workers. The dependence of the resulting committed equivalent dose on the concentration of the attached and unattached fractions of the ²¹⁸Po and ²¹⁴Po radionuclides and mass of the tissue was investigated. The resulting annual committed effective doses to the lung of marble factory workers due to the attached and unattached fractions of the ²¹⁸Po and ²¹⁴Po radionuclides were calculated. The obtained results show that about 80% of the global committed effective doses received by workers in the studied marble factories are due to the attached fraction of the ²¹⁸Po and ²¹⁴Po radon short-lived daughters from the inhalation of polluted air. Male workers spending 8 h per day (2080 h per year) in a marble factory receive a maximum dose of 34.46 mSv y⁻¹ which is higher than the (3–10 mSv y⁻¹) dose limit interval given by the ICRP. Good agreement was found between data obtained for the average effective dose gotten by using this method and the UNSCEAR and ICRP conversion dose coefficients.

     

DNA damage in oral epithelial cells of individuals chronically exposed to indoor radon (<Superscript>222</Superscript>Rn) in a hydrothermal area

Hydrothermal areas are potentially hazardous to humans as volcanic gases such as radon (²²²Rn) are continuously released from soil diffuse degassing. Exposure to radon is estimated to be the second leading cause of lung cancer, but little is known about radon health-associated risks in hydrothermal regions. This cross-sectional study was designed to evaluate the DNA damage in the buccal epithelial cells of individuals chronically exposed to indoor radon in a volcanic area (Furnas volcano, Azores, Portugal) with a hydrothermal system. Buccal epithelial cells were collected from 33 individuals inhabiting the hydrothermal area (Ribeira Quente village) and from 49 individuals inhabiting a non-hydrothermal area (Ponta Delgada city). Indoor radon was measured with Ramon 2.2 detectors. Chromosome damage was measured by micronucleus cytome assay, and RAPD-PCR was used as a complementary tool to evaluate DNA damage, using three 10-mer primers (D11, F1 and F12). Indoor radon concentration correlated positively with the frequency of micronucleated cells (r _s = 0.325, p = 0.003). Exposure to radon is a risk factor for the occurrence micronucleated cells in the inhabitants of the hydrothermal area (RR = 1.71; 95% CI, 1.2–2.4; p = 0.003). One RAPD-PCR primer (F12) produced differences in the banding pattern, a fact that can indicate its potential for detecting radon-induced specific genomic alterations. The observed association between chronic exposure to indoor radon and the occurrence of chromosome damage in human oral epithelial cells evidences the usefulness of biological surveillance to assess mutations involved in pre-carcinogenesis in hydrothermal areas, reinforcing the need for further studies with human populations living in these areas.