Radon Levels In Homes Research Articles

Neurotoxic effects of home radon exposure on oscillatory dynamics serving attentional orienting in children and adolescents

Radon is a naturally occurring gas that contributes significantly to radiation in the environment and is the second leading cause of lung cancer globally. Previous studies have shown that other environmental toxins have deleterious effects on brain development, though radon has not been studied as thoroughly in this context. This study examined the impact of home radon exposure on the neural oscillatory activity serving attention reorientation in youths. Fifty-six participants (ages 6–14 years) completed a classic Posner cuing task during magnetoencephalography (MEG), and home radon levels were measured for each participant. Time-frequency spectrograms indicated stronger theta (3–7 Hz, 300–800 ms), alpha (9–13 Hz, 400–900 ms), and beta responses (14–24 Hz, 400–900 ms) during the task relative to baseline. Source reconstruction of each significant oscillatory response was performed, and validity maps were computed by subtracting the task conditions (invalidly cued – validly cued). These validity maps were examined for associations with radon exposure, age, and their interaction in a linear regression design. Children with greater radon exposure showed aberrant oscillatory activity across distributed regions critical for attentional processing and attention reorientation (e.g., dorsolateral prefrontal cortex, and anterior cingulate cortex). Generally, youths with greater radon exposure exhibited a reverse neural validity effect in almost all regions and showed greater overall power relative to peers with lesser radon exposure. We also detected an interactive effect between radon exposure and age where youths with greater radon exposure exhibited divergent developmental trajectories in neural substrates implicated in attentional processing (e.g., bilateral prefrontal cortices, superior temporal gyri, and inferior parietal lobules). These data suggest aberrant, but potentially compensatory neural processing as a function of increasing home radon exposure in areas critical for attention and higher order cognition.

A psycho-social-environmental lens on radon air pollutant: authorities', mitigation contractors', and residents' perceptions of barriers and facilitators to domestic radon mitigation.

Radon is a major indoor air pollutant that poses a significant risk of lung cancer to those exposed in their homes. While mitigation of high radon levels in homes has been shown to be effective, home mitigation rates remain low. This study examines the barriers and facilitators to radon mitigation in homes from the perspectives of authorities responsible for radon risk management, the mitigation industry (contractors), and residents in four European countries (Belgium, Ireland, Slovenia, and the UK) with high radon risks and low mitigation rates. A multi-method approach was used to gather data from various stakeholders, including online surveys, content analysis of legal documents, group interviews, workshops, and focus groups. Authorities, contractors, and residents identified various facilitators to radon mitigation, including legal requirements for mitigation, awareness campaigns, low mitigation costs, availability of financial support, accreditation of mitigation contractors, and a perception of radon as a health threat. However, barriers to mitigation were also identified, such as a lack of awareness, fragmented mitigation processes, and inadequate communication between stakeholders. The study highlights the complexity of the radon mitigation process and suggests that interventions aimed at increasing mitigation rates should target stakeholders beyond just residents, such as constructors, health professionals, and policy makers. An integrated approach to radon mitigation, from policy to provision, is necessary to effectively lower levels of this indoor air pollutant.

Bayesian model selection for multilevel models using integrated likelihoods.

Multilevel linear models allow flexible statistical modelling of complex data with different levels of stratification. Identifying the most appropriate model from the large set of possible candidates is a challenging problem. In the Bayesian setting, the standard approach is a comparison of models using the model evidence or the Bayes factor. Explicit expressions for these quantities are available for the simplest linear models with unrealistic priors, but in most cases, direct computation is impossible. In practice, Markov Chain Monte Carlo approaches are widely used, such as sequential Monte Carlo, but it is not always clear how well such techniques perform. We present a method for estimation of the log model evidence, by an intermediate marginalisation over non-variance parameters. This reduces the dimensionality of any Monte Carlo sampling algorithm, which in turn yields more consistent estimates. The aim of this paper is to show how this framework fits together and works in practice, particularly on data with hierarchical structure. We illustrate this method on simulated multilevel data and on a popular dataset containing levels of radon in homes in the US state of Minnesota.

Indoor Radon Levels in Homes and Schools in the Western Cape, South Africa-Results from a Schools Science Outreach Initiative and Corresponding Model Predictions.

We describe a school science outreach initiative that introduced learners to applied nuclear physics research by means of a two-day workshop that involved learners and teachers from 5 schools in the Western Cape province of South Africa. During this workshop, the participants were introduced to the naturally occurring, inert, colorless, and tasteless radioactive gas radon (222Rn). During the first day of the workshop, the participants were informed about the detrimental health impacts of inhaling radon and its daughter radionuclides and were shown how indoor radon activity concentrations can be measured using the electret ion chamber (EIC) technology. The learners were then each supplied with a short-term electret (E-PERM, Radelec, Frederick, MD, USA) and associated ion chamber to enable them to make radon measurements in their homes. The teachers in turn were supplied with EICs to enable them make radon measurements in their schools. The participants returned the EICs on the second day of the workshop, one week later. Here, the drop in the potential difference across each electret was measured in order to calculate the average indoor radon activity concentration. A total of 49 indoor radon concentrations were measured. The average indoor radon concentrations were 36 ± 26 Bqm-3 in homes and 41 ± 36 Bqm-3 in schools, while the highest concentration was found to be 144 Bqm-3. These levels were compared to predictions from a model that uses input information about the uranium content associated with the surface geology at each measurement location. The predictions compared well with the measured values.

Review and comparison of measures of explained variation and model selection in linear mixed-effects models

In linear mixed-effects models, several frequentist and Bayesian measures have been proposed to evaluate model adequacy or/and to perform model selection. First, a large set of these measures are selected, presented with comparable notations, discussed in their strengths, weaknesses, and applicability range, and finally commented upon regarding their limitations. Then, these measures are illustrated on the home radon levels data (Gelman & Pardoe, Technometrics, 241-251, 48, 2006). Next, an extensive simulation study is carried out, to evaluate their sensitivity in selecting the correct model from a series of simpler models containing fewer parameters. Finally, recommendations on the use of these different measures are provided.11Additional results are available in the Supplementary Material.

Evaluation of occupational radon exposure and comparison with residential radon exposure in Canada—a population-level assessment

Radon is a naturally occurring radioactive gas and presents everywhere on the Earth at varying concentration in workplaces and at homes. With Canadian labour statistics, time statistics and more than 7600 long-term radon measurements in workplaces, occupational radon exposure is evaluated for all 20 job categories based on North American Industry Classification System. Results are compared with residential radon exposure based on more than 22 000 long-term radon tests conducted in Canadian homes. The average annual effective dose due to radon exposure in workplaces is 0.21 mSv, which is lower than the average annual effective dose of 1.8 mSv from radon exposure at home by a factor of eight. Due to relatively higher radon concentration in residential homes and longer time spent indoors at home, exposure at home contributes to 90% of workers’ total radon exposure (on average 1692 h in workplaces and 5852 h at homes). The analysis presented here is based on province-wide average radon exposures in various indoor and outdoor environments. Since the risk of developing lung cancer increases proportionally with increasing radon exposure, this evaluation indicates that on average reduction of radon levels in homes is very important and an effective way to reduce radon-induced lung cancers in Canada.

КОМУНІКАЦІЙНІ СТРАТЕГІЇ ІНФОРМУВАННЯ ПРО РАДОНОВІ РИЗИКИ

The article analyzes and determines the most effective directions of communication strategies and specific approaches to the choice of ways to inform the population about radon risks. Communicating with the public about radon risks is an integral part of the national radon action plan, and radon risk communication is a specific requirement of the IAEA's Basic Safety Standards. An effective risk communication strategy provides for a multi-stakeholder information flow involving stakeholders (all stakeholders) - representatives of communities living at risk, regulators, experts, radiation safety inspectors, and should focus on informing different audiences and recommending appropriate protective measures. It is also very important to take into account both the demographic and socio-economic context of the population and the use of quantitative and qualitative approaches to information. National and regional departments, local health authorities and non-profit organizations should work together to share knowledge, experience, resources and ideas that will stimulate radon measurements and protective actions. An effective component of a radon risk communication campaign is to identify target audiences that need to be informed and persuaded to take the necessary protection measures, and raising public awareness of the need to reduce radon levels in homes should be a key communication strategy. In the process of risk communication, an important aspect is the approach to the choice of ways of informing and developing the content of information messages. The effectiveness of communications will increase significantly if you join existing other information campaigns, such as energy efficiency, smoking control, labor protection and the like. Communication should be an ongoing process and should be carried out at all stages of the implementation of the radon action plan.

Study of baseline radon levels in the context of a shale gas development

This study reports the results from continuous measurement of indoor and outdoor radon concentrations in the area surrounding an unconventional shale gas exploration site in North Yorkshire, England, prior to the commencement of hydraulic fracturing. Public Health England has monitored the baseline radon levels in homes and in outdoor air in the Vale of Pickering since 2015. The statistical analysis presented here includes three full years (November 2015‐ –December 2018) of indoor and four and half years (October 2015 – April 2019) of outdoor radon measurements.Stratified sampling was used to select 171 dwellings in four areas, with two different radon potential. Statistical analysis confirms that homes in Kirby Misperton and Little Barugh and those in Yedingham are situated in areas with low radon potential, as was predicted by the UK radon potential map. On the other hand, both Pickering and Malton are confirmed as radon Affected Areas.Radon was measured continuously in the outdoor air using a newly developed outdoor kit containing passive radon detectors. The monitoring points were set up at 36 locations in the same local areas as those selected for the indoor monitoring. The results from statistical analysis show that outdoor radon had a different seasonality pattern to indoor radon. The monitoring of outdoor radon levels over the four and half years indicates a year-to-year variation in outdoor radon concentrations with levels fluctuating between 3 and 9 Bq m−3.There was a very good agreement between long-term average radon concentrations measured using passive detectors and using an active AlphaGUARD monitor.

Financial resources and decisions to avoid information about environmental perils

AbstractEnvironmental perils pose threats that require mitigation. Mitigation requires knowledge of the threat. Ironically, people may opt to avoid information about an environmental peril, especially if they lack resources to respond and the mitigation burden is high or costly. Three experiments (N = 845) examined how available resources and the resource burden of responding to an environmental peril affect the perceived of burden of taking action, and how perceiving burden, in turn, affects avoidance of information about the threat. Experiments 1a and 1b revealed that lower perceived likelihood of taking action and low income predicted a greater tendency to avoid hurricane risk information among Florida residents. Experiment 2 examined receptivity to information about home radon levels and manipulated the burden required to make repairs ($200 vs. $2,000). Having low income and learning repairs were costly corresponded with greater perceived burden of taking action, which predicted a lower likelihood to repair and greater information avoidance. These findings demonstrate that facing a high mitigation burden and lacking resources can lead to remaining uninformed about risks posed by environmental perils. Remaining uninformed is problematic because it may increase people's vulnerability to damage from these threats. However, these findings also identify a potential pathway for intervention. Reminding people of resources they may be unaware of will likely increase their likelihood of preparation and decrease information avoidance.

Geological data and outreach methods for designing targeted home radon testing programs

Indoor radon exposure is the second leading cause of lung cancer in the United States, yet radon risk reduction programs often struggle to increase home radon testing rates. This study compared two outreach methods to improve home radon testing and examined the association between home radon levels and geologic data in Central Appalachian communities in Tazewell County, Virginia, and Mercer County, West Virginia. We recruited 327 residents via phone and 211 residents via in-person workshops in 2016 and 2017. In total, 538 radon test kits were distributed to residents for deployment in their homes and subsequent shipment to a certified laboratory for analysis. We received 225 valid test results, which were subsequently linked to geologic units derived from the United States Geological Survey based on geocoded addresses. Results indicate that participants recruited by phone were more likely to complete the home radon test than those recruited in-person from workshops. Of seven geologic formation categories in the study area, dolomite formations from the Cambrian–Ordovician period were associated with the highest median radon value, 4.25 pCi/L (0.38–124.45 pCi/L). Our results suggest that effectiveness of radon risk reduction programs may be improved by phone education and test kit distribution campaigns, targeting homes on geological formations previously associated with heightened radon levels.

A Pilot Study to Examine Exposure to Residential Radon in Under-Sampled Census Tracts of DeKalb County, Georgia, in 2015.

While DeKalb County, Georgia, offers free radon screening for all eligible residents, portions of the county remain relatively under-sampled. This pilot study focused on 10% of the census tracts in the county with the lowest proportion of radon testing; most were in southern DeKalb County. In total, 217 households were recruited and homes were tested for indoor radon concentrations on the lowest livable floor over an eight-week period from March–May 2015. Tract-level characteristics were examined to understand the differences in socio-demographic and economic factors between the pilot study area and the rest of the county. The pilot study tracts had a higher proportion of African Americans compared to the rest of DeKalb County (82% versus 47%). Radon was detected above 11.1 Bq/m3 (0.3 pCi/L) in 73% of the indoor samples and 4% of samples were above 148 Bq/m3 (4 pCi/L). Having a basement was the strongest predictive factor for detectable and hazardous levels of radon. Radon screening can identify problems and spur homeowners to remediate but more research should be done to identify why screening rates vary across the county and how that varies with radon levels in homes to reduce radon exposure.

Variation with socioeconomic status of indoor radon levels in Great Britain: The less affluent have less radon

We demonstrate a strong correlation between domestic radon levels and socio-economic status (SES) in Great Britain, so that radon levels in homes of people with lower SES are, on average, only about two thirds of those of the more affluent. This trend is apparent using small area measures of SES and also using individual social classes. The reasons for these differences are not known with certainty, but may be connected with greater underpressure in warmer and better-sealed dwellings. There is also a variation of indoor radon levels with the design of the house (detached, terraced, etc.). In part this is probably an effect of SES, but it appears to have other causes as well. Data from other countries are also reviewed, and broadly similar effects seen in the United States for SES, and in other European countries for detached vs other types of housing. Because of correlations with smoking, this tendency for the lower SES groups to experience lower radon levels may underlie the negative association between radon levels and lung cancer rates in a well-known ecological study based on US Counties. Those conducting epidemiological studies of radon should be alert for this effect and control adequately for SES.

Geochemical and γ ray characterization of Pennsylvanian black shales: Implications for elevated home radon levels in Vanderburgh County, Indiana

Radon (222Rn) is a radioactive gas that results from the decay of uranium (238U) in the Earth's crust. This study characterizes the presence and relative quantity of radon precursors in the Pennsylvanian black shales of southwest Indiana. Cores were drilled on the campus of the University of Southern Indiana to a depth of 237.7 m (780 ft) during exploration for coal-bed methane. Gamma ray logs were taken to measure radioactive activity as a function of depth in the bore hole. Activity readings of 270, 467, 555, and 388 GAPI (American Petroleum Institute γ ray units) were measured at depths of 124.3 m (408 ft), 154.0 m (505 ft), 187.1 m (614 ft) and 214.0 m (702 ft) in four separate shale layers of the Pennsylvanian stratigraphic column. GAPI units are used in the petroleum industry when drilling to represent the relative intensities of γ radiation from 40K, 232Th, and 238U in bore holes (Belknap et al., 1959). For purposes of this study, the high activity readings on the gamma ray logs were used only to identify at which depths further gamma ray spectroscopy of the cores would be completed in the laboratory. Gamma ray spectroscopic studies of these cores were conducted with a large volume NaI crystal detector to observe γ rays of specific energies. Characteristic γ rays from various isotopes were identified confirming the presence and relative quantity of radon precursors in core samples. Geochemical analysis of cores was also conducted to measure presence and quantity of trace metals and radon precursors.Of 744 homes tested in Vanderburgh County from 2007 to 2013, 169 homes (22.7 percent) had elevated radon levels greater than 148 mBq L−1 (4.0 pCi L−1). Additionally, 246 homes (33.1 percent) had measured radon levels of 74–145 mBq L−1 (2.0–3.9 pCi L−1). About 80 percent of elevated radon levels greater than 148 mBq L−1 (4.0 pCi L−1) are located in proximity to depositional contacts between the Dugger and Shelburn formations, or the Shelburn and Patoka formations. These formational contacts are stratigraphically associated with Pennsylvanian black shales, which are interpreted to be the ultimate source of radon in Vanderburgh County, Indiana. Moreover, high radon levels also occurred in homes built on alluvium, terrace deposits, and outwash adjacent to the Ohio River. These elevated levels are probably due to transmission of radon through soil gas in highly permeable sands and gravels sourced from buried bedrock exposures of Pennsylvanian black shales.

Radon exhalation from sub-slab aggregate used in home construction in Canada

Exposure to elevated levels of radon in homes has been shown to result in an increased risk of developing lung cancer. The two largest contributors to indoor radon are radon in soil gas, formed from the rocks and soil surrounding the home, and building materials such as aggregate. This study measured the surface radon exhalation rates for 35 aggregate samples collected from producers across Canada. The radon exhalation rates ranged from 2.3 to 479.9 Bq m(-2) d(-1), with a mean of 80.7±112 Bq m(-2) d(-1). Using a simple, conservative analysis, the aggregate contribution to radon concentrations in an unfinished basement was determined. The maximum estimated radon concentration was 32.5±2.7 Bq m(-3), or ~16 % of the Canadian Radon Guideline. It can be concluded that under normal conditions radon exhalation from aggregate contributes very little to the total radon concentration in indoor air.

Associations of Indoor Home Radon Levels with Marcellus Shale Development

Associations of Indoor Home Radon Levels with Marcellus Shale DevelopmentAbstract Number:2487 Joan A. Casey*, Joseph DeWalle, Paul A. Locke, and Brian S. Schwartz Joan A. Casey* Johns Hopkins Bloomberg School of Public Health, United States, E-mail Address: [email protected] Search for more papers by this author , Joseph DeWalle Geisinger Health System Search for more papers by this author , Paul A. Locke Johns Hopkins Bloomberg School of Public Health, E-mail Address: [email protected] Search for more papers by this author , and Brian S. Schwartz Johns Hopkins Bloomberg School of Public Health and Geisinger Health System, E-mail Address: [email protected] Search for more papers by this author AbstractBackground: Radon causes around 21,000 lung cancer deaths annually in the United States. Most exposure occurs in the home when radon gas infiltrates from rocks and soils through openings. Recent drilling and hydraulic fracturing activity in Pennsylvania may have created new pathways allowing entrainment of radon into homes in a state where many homes already exceed the Environmental Protection Agency (EPA) action level of 4piC/L. Aims: To evaluate associations of proximity to Marcellus shale wells, by stage of development, with home radon levels.Methods: We located Marcellus shale wells and homes with indoor radon level readings using Pennsylvania Department of Environmental Protection data from 2006-2013. We used multilevel linear regression with a random intercept for home to assess associations of proximity to Marcellus shale in various stages of drilling with home radon levels while accounting for potential confounders (season of year, home type [e.g. duplex, apartment], area of home tested [e.g. basement, first floor], and geologic types).Results: There were 399,163 radon tests in 232,726 homes from 2006-2013. The median radon level was 3.3piC/L (interquartile range, 1.5 to 7.4) and 47% of homes had at least one radon reading over the EPA action level. On average, each home had 1.7 readings. There were 6973 Marcellus wells drilled in 39 of the state’s 67 counties over the study period, with 97% drilled after 2008. We will estimate exposure by the proximity of the closest drilled and stimulated well at the time of radon measurement and by an inverse- squared gravity model that will take into account all drilled and stimulated wells in the study area. Multilevel models will be used to estimate associations between the timing of Marcellus shale drilling and fracturing and concurrent indoor home radon level measurements.Conclusions: This research will inform upon potential radiation exposures due to hydraulic fracturing.

Lung Cancer Risk from Occupational and Environmental Radon and Role of Smoking in Two Czech Nested Case-Control Studies

The aim of the present study was to evaluate the risk of lung cancer from combined exposure to radon and smoking. Methodologically, it is based on case-control studies nested within two Czech cohort studies of nearly 11,000 miners followed-up for mortality in 1952–2010 and nearly 12,000 inhabitants exposed to high levels of radon in homes, with mortality follow-up in 1960–2010. In addition to recorded radon exposure, these studies use information on smoking collected from the subjects or their relatives. A total of 1,029 and 370 cases with smoking information have been observed in the occupational and environmental (residential) studies, respectively. Three or four control subjects have been individually matched to cases according to sex, year of birth, and age. The combined effect from radon and smoking is analyzed in terms of geometric mixture models of which the additive and multiplicative models are special cases. The resulting models are relatively close to the additive interaction (mixing parameter 0.2 and 0.3 in the occupational and residential studies, respectively). The impact of the resulting model in the residential radon study is illustrated by estimates of lifetime risk in hypothetical populations of smokers and non-smokers. In comparison to the multiplicative risk model, the lifetime risk from the best geometric mixture model is considerably higher, particularly in the non-smoking population.

Response to EPA Position on Cancer Risk from Low Level Radiation

The paper by J.S. Puskin (2009) on “Perspective on use of Linear-No Threshold Theory (LNT) for radiation protection and risk assessment by the U.S. EPA” begins its scientific section with the statement “Results from laboratory studies of irradiated animals and epidemiological studies of irradiated human cohorts are generally consistent with a linear, no-threshold dose-response, down to the lowest doses”. With regard to animal studies, perhaps the clearest statistically indisputable violations of that statement are in the work at Argonne National Lab on injecting radioactive materials into mice (Finkel and Biskis 1962, 1968, 1969) and at Oak Ridge on gamma ray exposure of mice (Ullrich and Storer 1979). Another is tumor induction by irradiation of mouse skin throughout life (Tanooka 2001) where weekly irradiation with 1.5 Gy, 2.2 Gy, and 3 Gy resulted in tumors to 0%, 35%, and 100% of the mice respectively—hardly a linear no threshold response. With regard to human studies, a clear and statistically indisputable demonstration of LNT failure was of bone cancers among dial painters and others occupationally exposed to ingested radium (Evans 1974) where there were no tumors in the several categories exposed to less than 10 Gy, but for dose ranges around 18 Gy, 35 Gy, 75 Gy, and 200 Gy 25% to 38% in each category developed tumors. Another case of LNT failure is the observation that lung cancer mortality in U.S. counties decreases dramatically with increasing mean radon levels in homes, with or without corrections for smoking prevalence and with full consideration of over 500 potential confounding factors (Cohen 1995, 2006). The Puskin paper then presents a highly over-simplified theoretical basis for supporting LNT down to the lowest doses—the DNA damage is proportional to the number of radiation hits and hence to the dose. This ignores the many microarray studies (e.g. Yin et al 2005) which show that the genes affected by low level radiation are very different from those affected by the cancer-causing high levels from which risk estimates are derived (Tubiana and Aurengo 2005). But more importantly, Puskin’s theoretical discussion deals almost exclusively with cancer initiating events, giving very little attention to processes induced by low level radiation that prevent such events from developing into a fatal cancer. He does list three low dose effects that could break down the linear response—bystander effect, genomic instability, and adaptive response—but concludes that the risk could be either increased or decreased by them. This conclusion may or may not be true for the first two items on his list, but it is definitely not true for adaptive response (UNSCEAR 1994), stimulated production of DNA repair enzymes. This protects against cancers induced by other causes (Azzam et al 1996, Ghiassi-Nejad et al 2002, Zaichkina et al 2003). Other clearly protective processes are ignored by Puskin. Perhaps the most important is stimulation of the immune system by low level radiation (Liu 1992, Makinodan and James 1990, Sakamoto et al 1997, Liu 2003, Ina and Sakai 2005). This is being successfully used as a treatment for cancer (Sakamoto et al 1997). Other such processes include scavenging cancer-inducing corrosive chemicals out of cells (Yamaoka 1991, Yukawa et al 2005), apoptosis of damaged cells, and altered cell-cycle timing which gives more time for DNA damage repair. Puskin ignores the fact that the latent period between exposure and tumor development is increased as exposure decreases (Dougherty and Mays 1969, Raabe 1994) such that tumors induced by low level radiation often would not develop before death from other causes. This alone, independently of all the above discussion, causes an effective threshold for radiation induced cancer. More details on the arguments made above, and many more supporting examples are included in a recent paper (Cohen 2007).

WORK TO SAVE DOSE: CONTRASTING EFFECTIVE DOSE RATES FROM RADON EXPOSURE IN WORKPLACES AND RESIDENCES AGAINST THE BACKDROP OF PUBLIC AND OCCUPATIONAL REGULATORY LIMITS

Office workers are exposed to radon while at work and at home. Though there are a multitude of studies reporting radon concentrations and potential lung and effective doses associated with radon progeny exposure in homes, similar studies in non-mine workplaces are lacking. Additionally, there are few, if any, comparative analyses of radon exposures at more "typical" workplace with residential exposures within the same county. The purposes of this study were to measure radon concentrations in office and residential spaces in the same county and explore the radiation dose implications. Sixty-five track-etch detectors were deployed for 3-mo sampling periods in office spaces and 47 were deployed in residences, all within Los Alamos County, New Mexico. The measured concentrations were used to calculate and compare effective dose rates resulting from exposure while at work and at home. Results showed that full-time office workers receive on average about 8 times greater exposure at home than while in the office (2.3 mSv y-1 vs. 0.3 mSv y-1). The estimated effective dose rate for a more homebound person was about 3 mSv y-1. Estimating effective doses from background radon exposure in the same county as Los Alamos National Laboratory, with thousands of "radiological workers," highlights interesting contrasts in radiation protection standards that span public and occupational settings. For example, the effective dose rate from background radon exposure in unregulated office spaces ranged up to 1.1 mSv y-1, which is similar to the 1 mSv y-1 threshold for regulation of a "radiological worker," as defined in the Department of Energy regulations for occupational exposure. Additionally, the estimated average effective dose total of >3 mSv y-1 from radon background exposure in homes stands in contrast to the 0.1 mSv y-1 air pathway effective public dose limit regulated by the Environmental Protection Agency for radioactive air emissions, and both these are substantially lower than effective doses associated with priority radon levels in homes of "tens of pCi L-1 and greater" (>370 Bq m-3), as suggested by the Health Physics Society.

RADON AWARENESS AND MITIGATION IN VERMONT: A PUBLIC HEALTH SURVEY

Radon exposure is associated with an increased incidence of lung cancer, and elevated levels may be found in as many as 1 out of 15 homes. The U.S. EPA recommends testing homes for radon and mitigating over the advisory level of 4 picocuries per liter (4 pCi L(-1), or 148 Bq m(-3)). A sample population from a list of Vermont residents who had tested their residence for radon through the Vermont Department of Health and who had elevated levels were mailed a survey to assess demographic characteristics, knowledge about radon, mitigation rates, types of mitigation, as well as barriers to mitigation. The response rate was 63%. Forty-three percent of respondents mitigated. Roughly half were not completely knowledgeable of radon based upon the ability to associate radon exposure with lung cancer risk. Reasons not to mitigate radon levels in homes were cost and lack of concern over elevated levels. A multivariate logistic regression analysis revealed factors associated with mitigating: an education level of college or higher (p = 0.02), concern that a high radon level would affect real estate value (p = 0.04), and home age less than 10 y (p = 0.05). In summary, less than half of Vermonters with elevated radon levels participating in the Department of Health program mitigated. We identify factors associated with radon mitigation that may lead to improved radon education and mitigation practice.

Weighted Classical Variogram Estimation for Data With Clustering

The classical variogram estimate is convenient but can be unacceptably variable. Improved estimators are possible, especially when the locations of the available data are highly clustered. Using a simple theoretical example, we demonstrate that weighting can dramatically increase the efficiency of classical variogram estimates from clustered data. We give expressions for the weights that lead to minimal variance estimators and indicate some obstacles to the use of these weights. We then introduce a simple iterative weighting scheme intended to approximate optimal weighting. We apply the new weighting to the example that motivated this research—estimating the variogram of home radon levels—and demonstrate its performance in a simulation study.