RADON AND THORON PROGENY IN DUTCH DWELLINGS.

Radon and thoron progenies in Dutch dwellings cause ~400 cases of lung cancer per year. Some 30% of the risk is due to thoron progeny, which demonstrates that the influence of thoron progeny is much larger than previously anticipated. This was concluded from a national survey in 2500 Dutch dwellings, built since 1930. Radon concentrations (15.6 ± 0.3 Bq m-3 on average) are correlated to type of dwelling, year of construction, ventilation system, location (soil type) and smoking behaviour of inhabitants. The survey data support the establishment of a comparatively low national reference level for radon in dwellings in the Netherlands of 100 Bq m-3, in line with recommendations by WHO and ICRP. Some 24 thousand of the 6.2 million dwellings in the Netherlands (built since 1930) are expected to exceed this level. Around 80% of these are located in the relatively small group of naturally ventilated single-family houses in two designated geographical areas. Radon concentrations above 200 Bq m-3 are rare in the Netherlands and simple and inexpensive measures will be sufficient to reduce enhanced radon concentrations to values below the national reference level. Thoron progeny concentrations (0.64 Bq m-3, on average) show correlations with year of construction and smoking behaviour. In 75 additional dwellings, a pilot study was conducted to determine the relationship between the exhalation of thoron from walls and the concentration of thoron progeny in the room. Thoron exhalation values exceeding the median value of 2.2 × 10-2 Bq m-2 s-1 by a factor 10 or more were found frequently, but enhanced concentrations of thoron progeny were measured only occasionally. Under very unfavourable conditions, however, for instance if phosphogypsum is applied as finishing material on all walls and ceilings in the house, strongly elevated thoron progeny concentrations may occur. This survey yielded a maximum recording of 13.3 Bq m-3. There is no reason to expect that such levels are specific to the Netherlands, indicating that in other regions with low radon levels, thoron may be a more important contributor to the population dose as well.

Thoron exposure in Dutch dwellings - An overview.

In the Netherlands considerable attention has been given to the exposure from thoron progeny in dwellings. For this purpose a nationwide survey on the thoron exhalation and thoron progeny concentration has been completed in 2015. Furthermore, extensive laboratory studies have been performed to measure activity concentrations and thoron exhalation rates from regular Dutch building materials. The purpose of this study is to demonstrate if the findings from both field experiments and laboratory results are consistent. For this reason measured properties of building materials and surface barriers, in-situ measurements on air ventilation and thoron(progeny) in dwellings as well as advanced computational modelling on indoor air and aerosol behaviour have been used. The results demonstrate that median and mean thoron progeny concentrations of 0.53 and 0.64 Bq·m-3 found in the survey are comparable with the mean concentration of 0.57 Bq·m-3 obtained from laboratory testing and calculation. Furthermore, upper thoron progeny concentrations from the survey and the calculations are with respectively 13 and 14 Bq·m-3 also in good agreement. Such elevated concentrations lead to an effective doses of around 4 mSv per year. The study also includes worst-case scenarios on the application of surface materials high on 232Th, and the expected reduction in thoron progeny when using mainstream mitigation measures.

Ingredients for a Dutch radon action plan, based on a national survey in more than 2500 dwellings.

A new Euratom directive demands that Member States establish a national action plan for indoor radon. Important requirements are a national reference level for the radon concentration in dwellings, actions to identify dwellings with radon concentrations that might exceed this reference level and the encouragement of appropriate measures to reduce the radon concentrations in dwellings where these are high. This paper provides ingredients and recommendations for a national action plan for radon in dwellings, applicable to the Netherlands. The approach presented here, which may serve as a model for other countries or regions with a comparatively favourable indoor radon situation, is based on the analysis of radon data from a national survey in more than 2500 Dutch dwellings, built since 1930. The annual average activity concentration of radon in dwellings in the Netherlands equals 15.6 ± 0.3 Bq m-3. The 50th and 95th percentiles were found to be 12.2 and 38.0 Bq m-3, respectively. In 0.4 per cent of the dwellings we found values above 100 Bq m-3. Radon concentrations showed correlations with type of dwelling, year of construction, ventilation system, soil type and smoking behaviour of inhabitants. The survey data suggest that it is feasible for the Netherlands to adopt a national reference level for radon in dwellings of 100 Bq m-3, in line with recommendations by WHO and ICRP. We were able to predict dwellings with a moderate probability for radon concentrations above 100 Bq m-3 by applying a combination of three selection criteria: location, type of dwelling and manner of ventilation. Of the existing 6.2 million dwellings in the Netherlands (built since 1930), approximately 23-24 thousand are suspected to exceed this level. Some 80% of these are found in the group of naturally ventilated single-family dwellings in either the southern part of Limburg (approx. 13 thousand) or the Meuse-Rhine-Waal river delta (approx. six thousand). This selected group of dwellings represents 7% of the housing stock. In contrast to many other countries in Europe and elsewhere, radon concentrations in dwellings above 200 Bq m-3 are very rare in the Netherlands. As a result, relatively simple and inexpensive measures in existing Dutch single-family dwellings will be sufficient to reduce indoor radon concentrations above the proposed national reference level of 100 Bq m-3 to values well below.

Evaluating the risk from depleted uranium after the Boeing 747-258F crash in Amsterdam, 1992.

On 4 October 1992, a large cargo plane crashed into an apartment building in the Bijlmermeer quarter of Amsterdam. In the years following the accident, an increasing number of people started reporting health complaints, which they attributed to exposure to dangerous substances after the crash. Since the aircraft had been carrying depleted uranium as counterbalance weights and about 150 kg uranium had been found missing after clearance of the crash site, exposure to uranium oxide particles was pointed out as the possible cause of their health complaints. Six years after the accident, a risk analysis was therefore carried out to investigate whether the health complaints could be attributed to exposure to uranium oxide set free during the accident. The scientific challenge was to come up with reliable results, knowing that - considering the late date - virtually no data were available to validate any calculated result. The source term of uranium was estimated using both generic and specific data. Various dispersion models were applied in combination with the local setting and the meteorological conditions at the time of the accident to estimate the exposure of bystanders during the fire caused by the crash. Emphasis was given to analysing the input parameters, inter-comparing the various models and comparing model results with the scarce information available. Uranium oxide formed in the fire has a low solubility, making the chemical toxicity to humans less important than the radiotoxicity. Best-estimate results indicated that bystanders may have been exposed to a radiation dose of less than 1 microSv, whereas a worst-case approach indicated an upper limit of less than 1 mSv. This value is considerably less than the radiation dose for which acute effects are to be expected. It is therefore considered to be improbable that the missing uranium had indeed led to the health complaints reported.

An automated gross alpha/beta activity monitor applied to time-resolved quantitative measurements of 222Rn progeny in air.

Automated monitors for the determination of airborne radioactivity are widely in use as early warning systems for nuclear emergencies; however, the data acquired for this purpose are seldom used for analyzing spatial and temporal variations of natural radioactivity (especially radon and short-lived decay products). This paper shows that a specific type of airborne gross alpha/beta activity monitor, applied in several European emergency networks, can be effectively used to study the transport of 222Rn progeny in the outdoor environment. Real-time recordings (10-min sampling time) can, independent of the actual equilibrium ratio, be converted to the equilibrium-equivalent decay-product concentration (EEDC) of 222Rn. Medium volume air sampling and a slow-moving tape air sampler yield a low detection limit of < or = 0.1 Bq m-3. This paper further describes all factors and processes contributing to the uncertainty in the data obtained in this way; the total error in single recordings is estimated at 20-25% (95% confidence interval). Data of 222Rn progeny obtained from the Dutch National Radioactivity Monitoring network agree with results of other radon surveys.