Jan A. J. Stolwijk

Residential radon and risk of lung cancer : A combined analysis of 7 north american case-control studies

Background: Underground miners exposed to high levels of radon have an excess risk of lung cancer. Residential exposure to radon is at much lower levels, and the risk of lung cancer with residential exposure is less clear. We conducted a systematic analysis of pooled data from all North American residential radon studies. Methods: The pooling project included original data from 7 North American case–control studies, all of which used long-term α-track detectors to assess residential radon concentrations. A total of 3662 cases and 4966 controls were retained for the analysis. We used conditional likelihood regression to estimate the excess risk of lung cancer. Results: Odds ratios (ORs) for lung cancer increased with residential radon concentration. The estimated OR after exposure to radon at a concentration of 100 Bq/m3 in the exposure time window 5 to 30 years before the index date was 1.11 (95% confidence interval = 1.00–1.28). This estimate is compatible with the estimate of 1.12 (1.02–1.25) predicted by downward extrapolation of the miner data. There was no evidence of heterogeneity of radon effects across studies. There was no apparent heterogeneity in the association by sex, educational level, type of respondent (proxy or self), or cigarette smoking, although there was some evidence of a decreasing radon-associated lung cancer risk with age. Analyses restricted to subsets of the data with presumed more accurate radon dosimetry resulted in increased estimates of risk. Conclusions: These results provide direct evidence of an association between residential radon and lung cancer risk, a finding predicted using miner data and consistent with results from animal and in vitro studies.

Temperature regulation in man — A theoretical study

SummaryFor purposes of theoretical analysis of experimental results and evaluation of hypothetical concepts a mathematical model of thermoregulation in man is presented. The human body is represented by three cylinders: the head, the trunk, and the extremities. Each cylinder is divided into two or more concentric layers to represent anatomical and functional differences in so far as they are of primary importance in thermoregulation. Heat flow between adjacent layers is by conduction, and all layers exchange heat by convection with a central blood compartment. All three skin layers exchange heat with the environment by conduction, convection, radiation, and evaporation. Signals which are proportional to temperature deviations in the brain and to deviations in average skin temperature are supplied to the regulator portion of the model. The regulator then causes evaporative heat loss, heat production by shivering or changes in the peripheral blood flow to occur in the appropriate locations in the body. If a proposed mechanism of thermoregulation is expressed in quantitative form it describes the relationships between the input signals and the resulting thermoregulatory response; the model can be used to compare the quantitative response resulting from a proposed mechanism with the responses obtained by measurement. A number of experimental results are compared with predictions furnished by the mathematical model using a regulator with an output which is proportional to the product of the input signals. It is emphasized that models of this type should be used in close connection with an experimental program to attain their full usefulness.

A Combined Analysis of North American Case-Control Studies of Residential Radon and Lung Cancer

Cohort studies have consistently shown underground miners exposed to high levels of radon to be at excess risk of lung cancer, and extrapolations based on those results indicate that residential radon may be responsible for nearly 10–15% of all lung cancer deaths per year in the United States. However, case-control studies of residential radon and lung cancer have provided ambiguous evidence of radon lung cancer risks. Regardless, alpha-particle emissions from the short-lived radioactive radon decay products can damage cellular DNA. The possibility that a demonstrated lung carcinogen may be present in large numbers of homes raises a serious public health concern. Thus, a systematic analysis of pooled data from all North American residential radon studies was undertaken to provide a more direct characterization of the public health risk posed by prolonged radon exposure. To evaluate the risk associated with prolonged residential radon exposure, a combined analysis of the primary data from seven large scale case-control studies of residential radon and lung cancer risk was conducted. The combined data set included a total of 4081 cases and 5281 controls, representing the largest aggregation of data on residential radon and lung cancer conducted to date. Residential radon concentrations were determined primarily by α-track detectors placed in the living areas of homes of the study subjects in order to obtain an integrated 1-yr average radon concentration in indoor air. Conditional likelihood regression was used to estimate the excess risk of lung cancer due to residential radon exposure, with adjustment for attained age, sex, study, smoking factors, residential mobility, and completeness of radon measurements. Although the main analyses were based on the combined data set as a whole, we also considered subsets of the data considered to have more accurate radon dosimetry. This included a subset of the data involving 3662 cases and 4966 controls with α-track radon measurements within the exposure time window (ETW) 5–30 yr prior to the index date considered previously by Krewski et al. (2005). Additional restrictions focused on subjects for which a greater proportion of the ETW was covered by measured rather than imputed radon concentrations, and on subjects who occupied at most two residences. The estimated odds ratio (OR) of lung cancer generally increased with radon concentration. The OR trend was consistent with linearity (p = .10), and the excess OR (EOR) was 0.10 per Bq/m3 with 95% confidence limits (−0.01, 0.26). For the subset of the data considered previously by Krewski et al. (2005), the EOR was 0.11 (0.00, 0.28). Further limiting subjects based on our criteria (residential stability and completeness of radon monitoring) expected to improve radon dosimetry led to increased estimates of the EOR. For example, for subjects who had resided in only one or two houses in the 5–30 ETW and who had α-track radon measurements for at least 20 yr of this 25-yr period, the EOR was 0.18 (0.02, 0.43) per 100 Bq/m3. Both estimates are compatible with the EOR of 0.12 (0.02, 0.25) per 100 Bq/m3 predicted by downward extrapolation of the miner data. Collectively, these results provide direct evidence of an association between residential radon and lung cancer risk, a finding predicted by extrapolation of results from occupational studies of radon-exposed underground miners. E. G. Létourneau and J. B. Schoenberg have retired; J. A. Stolwijk holds an emeritus position. We acknowledge the helpful input of the following individuals who served on the International Steering Committee for the North American combined analysis: Ken Chadwick (CEC Radiation Protection Program), Susan Conrath (U.S. Environmental Protection Agency), Sarah Darby (Oxford University), Evan Douple (U.S. National Academy of Sciences), Colin Muirhead (UK National Radiation Protection Board), and Susan Rose (U.S. Department of Energy). Salary support for Drs. Field, Lynch, and Steck was provided in part by grant numbers R01 ES05653 and P30 ES05605 from the National Institute of Environmental Health Sciences, NIH and grant number R01 CA85942 from the National Cancer Institute, NIH. This research was supported by grants from the Canadian Institutes of Health Research (formerly the Medical Research Council of Canada) and the Natural Sciences and Engineering Research Council of Canada to D. Krewski, who currently holds the NSERC/SSHRC/McLaughlin Chair in Population Health Risk Assessment at the University of Ottawa. Financial support for the meetings of the Analysis Team and the Steering Committee was also provided by Health Canada and the U.S. Department of Energy. We are grateful to Dr. Huixia Jiang for assistance with the combined analysis, and to Jackie Monaghan for technical assistance in preparing this report.

Risk and Benefit Perceptions, Acceptability Judgments, and Self-Reported Actions toward Nuclear Power

Summary Three-hundred and sixty-seven respondents selected from five widely differing groups in two U.S. communities were administered a questionnaire tapping personal action for or against nuclear power, as well as a variety of attitudinal, cognitive, and sociodemographic variables. Respondents included members of environmental groups, college students, blue-collar workers, business people, and nuclear engineers and other technologists. The results indicated that degree of self-reported action was systematically correlated with the rated “acceptability,” risks, benefits, and qualitative characteristics of nuclear power. The results also pointed to other major correlates of personal action, including confidence in various risk-management institutions and organizations. Emphasis is placed upon general methodological issues involved in the study of risk perceptions, acceptability judgments, and actions.

An Overview of the North American Residential Radon and Lung Cancer Case-Control Studies

Lung cancer has held the distinction as the most common cancer type worldwide since 1985 (Parkin et al., 1993). Recent estimates suggest that lung cancer accounted for 1.2 million deaths worldwide in 2002, which represents 17.6% of the global cancer deaths (Parkin et al., 2005). During 2002, the highest lung cancer rates for men worldwide reportedly occurred in North America and Eastern Europe, whereas the highest rates in females occurred in North America and Northern Europe (Parkin et al., 2005). While tobacco smoking is the leading risk factor for lung cancer, because of the magnitude of lung cancer mortality, even secondary causes of lung cancer present a major public health concern (Field, 2001). Extrapolations from epidemiologic studies of radon-exposed miners project that approximately 18,600 lung cancer deaths per year (range 3000 to 41,000) in the United States alone are attributable to residential radon progeny exposure (National Research Council, 1999). Because of differences between the mines and the home environment, as well as differences (such as breathing rates) between miners and the general public, there was a need to directly evaluate effects of radon in homes. Seven major residential case-control radon studies have been conducted in North America to directly examine the association between prolonged radon progeny (radon) exposure and lung cancer. Six of the studies were performed in the United States including studies in New Jersey, Missouri (two studies), Iowa, and the combined states study (Connecticut, Utah, and southern Idaho). The seventh study was performed in Winnipeg, Manitoba, Canada. The residential case-control studies performed in the United States were previously reviewed elsewhere (Field, 2001). The goal of this review is to provide additional details regarding the methodologies and findings for the individual studies. Radon concentration units presented in this review adhere to the types (pCi/L or Bq/m3) presented in the individual studies. One picocurie per liter is equivalent to 37 Bq/m3. Because the Iowa study calculated actual measures of exposure (concentration × time), its exposures estimates are presented in the form WLM5–19 (Field et al., 2000a). WLM5–19 represents the working level months for exposures that occurred 5–19 yr prior to diagnosis for cases or time of interview for control. Eleven WLM5–19 is approximately equivalent to an average residential radon exposure of 4 pCi/L for 15 yr, assuming a 70% home occupancy. Ernest G. Létourneau and Janet B. Schoenberg are retired; Jan A. Stolwijk has emeritus status. Salary support for Drs. Steck and Field was provided in part by grant numbers R01 ES05653 and P30 ES05605 from the National Institute of Environmental Health Sciences, NIH and grant number R01 CA85942 from the National Cancer Institute, NIH.

Indoor Radon and Lung Cancer Risk in Connecticut and Utah

Radon is a well-established cause of lung cancer in miners. Residents of homes with high levels of radon are potentially also at risk. Although most individual studies of indoor radon have failed to demonstrate significant risks, results have generally been consistent with estimates from studies of miners. We studied 1474 incident lung cancer cases aged 40–79 yr in Connecticut, Utah, and southern Idaho. Population controls (n = 1811) were identified by random telephone screening and from lists of Medicare recipients, and were selected to be similar to cases on age, gender, and smoking 10 yr before diagnosis/interview using randomized recruitment. Complete residential histories and information on known lung cancer risk factors were obtained by in-person and telephone interviews. Radon was measured on multiple levels of past and current homes using 12-mo alpha-track etch detectors. Missing data were imputed using mean radon concentrations for informative subgroups of controls. Average radon exposures were lower than anticipated, with median values of 23 Bq/m3 in Connecticut and 45 Bq/m3 in Utah/southern Idaho. Overall, there was little association between time-weighted average radon exposures 5 to 25 yr prior to diagnosis/interview and lung cancer risk. The excess relative risk (ERR) associated with a 100-Bq/m3 increase in radon level was 0.002 (95% CI −0.21, 0.21) in the overall population, 0.134 (95% CI −0.23, 0.50) in Connecticut, and −0.112 (95% CI −0.34, 0.11) in Utah/Idaho. ERRs were higher for some subgroups less prone to misclassification, but there was no group with a statistically significant linear increase in risk. While results were consistent with the estimates from studies of miners, this study provides no evidence of an increased risk for lung cancer at the exposure levels observed. We are grateful to Drs. Stuart Shalat and Keith Schiager, who made early contributions to the design and implementation of this study, and to Patty Blanton for expert data management. Lynne Rothney-Kozlak and Jan A. J. Stolwijk were formerly affiliated with Yale University School of Public Health, New Haven, Connecticut, USA.

Seasonal variations in light scattering in the New York region and their relation to sources

Abstract Light scattering data collected during two periods of intensive sampling in New York City (one during summer months and one during winter months) are discussed and analyzed for diurnal patterns, their relationship to pollutant emission sources, meteorological parameters, and the size distribution and chemical composition of the ambient aerosol. The lack of a diurnal pattern for light scattering in summer in combination with a strong positive association with ozone and wind direction dependency suggests that in summer the transport of an aged aerosol in photochemically rich air masses rather than local emissions of primary pollutants is largely responsible for the observed levels of light scattering in New York City. Winter levels of light scattering observed in New York City, while approx. 50% lower than summer levels, were much less dependant on wind direction and closely related to pollutant emissions from local sources. This suggests that locally generated aerosol dominates light scattering in the winter. Particles 0.1–1.3 μm in diameter were strongly correlated with light scattering in New York City during both summer and winter periods. However, a given volume of aerosol between 0.1 and 1.3 μm scattered more light in summer than in winter, indicating the fresher nature of the winter aerosol. Variance in dry particulate light scattering was found to principally account for light extinction variance (calculated from airport visibility observations) in summer and winter. Sulfate aerosol was strongly correlated with light scattering during both summer and winter periods.

Ambient sulfates, photochemical oxidants, and acute adverse health effects: An epidemiological study

Abstract From July 6 to September 19, 1976, two groups of subjects in the New Haven, Connecticut area made daily reports on the presence of acute symptoms through the use of postcard diaries. One group was drawn from telephone company employees, while the other group of presumably more susceptible people was composed of patients from a university allergy and asthma clinic. Daily symptom rates were related to daily 8- and 24-hr meteorological and ambient air pollutant data. At any given pollutant level, smokers and people with asthma, chronic bronchitis, and/or hay fever reported more symptoms than did nonsmokers and those without such illnesses. For the 274 people studied, statistical analyses showed that 8- and 24-hr photochemical oxidant levels were associated with eye irritation and cough, particularly in heavy smokers and those with predisposing illnesses. Suspended sulfates were not associated significantly with acute adverse health effects. Levels of pH observed in 8-hr particulate samples were positively associated with eye, nose, and throat irritation.

Relationship between Sulfate Aerosol and Visibility

An analysis of studies on sulfate and nitrate mass concentration data in comparison with visibility and meteorological observations at airports in Los Angeles, St. Louis, New York, and New Haven supports the contention that prevailing airport visibility observation in the absence of local pollutant sources, precipitation, or fog is strongly associated with local atmospheric sulfate mass concentration. Airport visibility observations may be used to estimate atmospheric sulfate concentrations in the present and in the past. (HLW)

Thermoregulatory shivering during exercise

Abstract Three subjects with lowered internal body temperatures performed brief bouts of bicycle ergometer exercise at 150 and 200 W. Oxygen uptake during exercise was consistently greater than that required by the working muscles, the increase being the result of the additional cost of shivering. Increases in metabolism during exercise above control levels were inversely proportional to internal temperature (with skin temperature constant) below a given internal temperature threshold. Observations of intense shivering during exercise which is proportional to lowered internal temperature in the same manner as during rest provides further evidence against the concept of a decrease in the thermoregulatory set point during exercise in man.