Peter Gravesen

Mapping indoor radon-222 in Denmark: design and test of the statistical model used in the second nationwide survey

In Denmark, a new survey of indoor radon-222 has been carried out, 1-year alpha track measurements (CR-39) have been made in 3019 single-family houses. There are from 3 to 23 house measurements in each of the 275 municipalities. Within each municipality, houses have been selected randomly. One important outcome of the survey is the prediction of the fraction of houses in each municipality with an annual average radon concentration above 200 Bq m(-3). To obtain the most accurate estimate and to assess the associated uncertainties, a statistical model has been developed. The purpose of this paper is to describe the design of this model, and to report results of model tests. The model is based on a transformation of the data to normality and on analytical (conditionally) unbiased estimators of the quantities of interest. Bayesian statistics are used to minimize the effect of small sample size. In each municipality, the correction is dependent on the fraction of area where sand and gravel is a dominating surface geology. The uncertainty analysis is done with a Monte-Carlo technique. It is demonstrated that the weighted sum of all municipality model estimates of fractions above 200 Bq m(-3) (3.9% with 95%-confidence interval = [3.4,4.5]) is consistent with the weighted sum of the observations for Denmark taken as a whole (4.6% with 95%-confidence interval = [3.8,5.6]). The total number of single-family houses within each municipality is used as weight. Model estimates are also found to be consistent with observations at the level of individual counties. These typically include a few hundred house measurements. These tests indicate that the model is well suited for its purpose.

Residential Radon and Lung Cancer Incidence in a Danish Cohort

High-level occupational radon exposure is an established risk factor for lung cancer. We assessed the long-term association between residential radon and lung cancer risk using a prospective Danish cohort using 57,053 persons recruited during 1993-1997. We followed each cohort member for cancer occurrence until 27 June 2006, identifying 589 lung cancer cases. We traced residential addresses from 1 January 1971 until 27 June 2006 and calculated radon at each of these addresses using information from central databases regarding geology and house construction. Cox proportional hazards models were used to estimate incidence rate ratios (IRR) and 95% confidence intervals (CI) for lung cancer risk associated with residential radon exposure with and without adjustment for sex, smoking variables, education, socio-economic status, occupation, body mass index, air pollution and consumption of fruit and alcohol. Potential effect modification by sex, traffic-related air pollution and environmental tobacco smoke was assessed. Median estimated radon was 35.8 Bq/m(3). The adjusted IRR for lung cancer was 1.04 (95% CI: 0.69-1.56) in association with a 100 Bq/m(3) higher radon concentration and 1.67 (95% CI: 0.69-4.04) among non-smokers. We found no evidence of effect modification. We find a positive association between radon and lung cancer risk consistent with previous studies but the role of chance cannot be excluded as these associations were not statistically significant. Our results provide valuable information at the low-level radon dose range.

Residential radon and brain tumour incidence in a Danish cohort.

Background Increased brain tumour incidence over recent decades may reflect improved diagnostic methods and clinical practice, but remain unexplained. Although estimated doses are low a relationship between radon and brain tumours may exist. Objective To investigate the long-term effect of exposure to residential radon on the risk of primary brain tumour in a prospective Danish cohort. Methods During 1993–1997 we recruited 57,053 persons. We followed each cohort member for cancer occurrence from enrolment until 31 December 2009, identifying 121 primary brain tumour cases. We traced residential addresses from 1 January 1971 until 31 December 2009 and calculated radon concentrations at each address using information from central databases regarding geology and house construction. Cox proportional hazards models were used to estimate incidence rate-ratios (IRR) and 95% confidence intervals (CI) for the risk of primary brain tumours associated with residential radon exposure with adjustment for age, sex, occupation, fruit and vegetable consumption and traffic-related air pollution. Effect modification by air pollution was assessed. Results Median estimated radon was 40.5 Bq/m3. The adjusted IRR for primary brain tumour associated with each 100 Bq/m3 increment in average residential radon levels was 1.96 (95% CI: 1.07; 3.58) and this was exposure-dependently higher over the four radon exposure quartiles. This association was not modified by air pollution. Conclusions We found significant associations and exposure-response patterns between long-term residential radon exposure radon in a general population and risk of primary brain tumours, adding new knowledge to this field. This finding could be chance and needs to be challenged in future studies.

An assessment of Palaeogene and Neogene clay deposits in Denmark as possible host rocks for final disposal of low- and intermediate-level radioactive waste

Abstract In Denmark, mapping and preliminary investigations of Palaeogene and Early Neogene clay deposits have been performed over the past 5 years. The goal was to locate potential host rocks for the final disposal of low- and intermediate-level radioactive waste from the Danish Research Centre Risø, which has to be decommissioned within the next 5–8 years. Five areas with low-permeability Paleocene and Oligocene clay formations, situated in northern Jylland, NE Fyn and southern Lolland, not far from the Baltic coast at Femern Belt, have been suggested. The clay formations are between 75 and 150 m thick, and have large lateral distribution. They are covered by thin layers of glacial clayey tills and the shallow depth to the clay formations is attractive, partly because they are easy to access and partly because there are no groundwater aquifers situated above or below the clay deposits. The paper gives an overall review of the characteristics of the six different clay formations within four of the areas.

Karst Geology and Regional Hydrogeology in Denmark

Upper Cretaceous chalk and Danian limestone aquifers supply about a third of the drinking water for Denmark. Quaternary sediments cover the carbonate aquifers, and at places with less than 15 m of Quaternary sediments, the aquifers, springs, and adjacent ecotones are especially vulnerable to contamination. The near-surface situated chalk and limestones are related to thin Quaternary sediment cover and karst features (springs, lakes, disappearing streams, caves, dolines). This paper categorizes the various observed karstic features into geological, hydrogeological, and structural settings of the chalk and limestone types that are important for management of this important groundwater resource in Denmark.