Hannu Arvela

Fallout from Chernobyl and incidence of childhood leukaemia in Finland, 1976-92.

Abstract Objective: To assess effects of fallout from Chernobyl on incidence of childhood leukaemia in Finland. Design : Nationwide cohort study. External exposure measured for 455 Finnish municipalities with instruments driven 19 000 km throughout the country. Values specific to municipalities corrected for shielding due to houses and fallout from A bomb testing. Internal exposure estimated from whole body measurements on a random sample of 81 children. Mean effective dose for two years after incident calculated from these measurements. Data on childhood leukaemia obtained from Finnish cancer registry and verified through hospitals treating childhood cancers. Setting : Finland, one of the countries most heavily contaminated by the Chernobyl accident; the population was divided into fifths by exposure. Subjects : Children aged 0-14 years in 1976-92. Main outcome measures: Standardised incidence ratio of childhood leukaemia and relative excess risk of childhood leukaemia per mSv. From incidence data of Finnish cancer registry for 1976-85, expected numbers specific to sex and age group (0-4, 5-9, and 10-14 years) were calculated for each municipality for three periods (1976-85, 1986-8, and 1989-92) and pooled as exposure fifths. Dose response was estimated as regression slope of standardised incidence ratios on mean doses for fifths for each period. Results : Population weighted mean effective doses for first two years after the accident were 410 µSv for the whole country and 970 µSv for the population fifth with the highest dose. In all Finland the incidence of childhood leukaemia did not increase 1976-92. The relative excess risk 1989-92 was not significantly different from zero (7% per mSv; 95% confidence interval −27% to 41%). Conclusions: An important increase in childhood leukaemia can be excluded. Any effect is smaller than eight extra cases per million children per year in Finland. The results are consistent with the magnitude of effect expected.

Effect of moisture content on emanation at different grain size fractions - a pilot study on granitic esker sand sample.

It is known that in soils and sediments moisture adsorbed on particle surfaces and in the pore system significantly affects the behaviour of recoiling radon ((222)Rn) atoms after decay of parent (226)Ra, leading to increased (222)Rn emanation. As a first step in an effort to characterize the (222)Rn source term in mineralised sediments in the present study, complementing previous studies in the area, granitic esker sand samples were collected in order to test how moisture content affects (222)Rn emanation at different grain size fractions. Emanation fractions measured for natural samples were compared with theoretical calculations. Six different grain size fractions were studied at 0%, 5% and 10% moisture contents relative to the mass of solids. In a further study necessary complementary information on the chemical and structural distribution of (226)Ra was gained by selective leaching experiments. The results showed that (226)Ra concentration increases from 50 Bq/kg at grain size 1-2 mm to 200 Bq/kg at grain size <0.063 mm. Respectively, the emanation factor increased from 0.12 to 0.30 at 5% moisture content. Both emanation factor and radium concentration increased significantly when grain size was below 0.125-0.250 mm. Above this fraction, the emanation fraction was approximately constant, 0.13 at 5% moisture content. In most of the grain size fractions, emanation reaches its maximum at 5% moisture content, being twice as high as in a dry sample. For the small particles (<0.063 mm) the (226)Ra distribution is rather complex and depends on the mineral composition compared to larger particles wherein emanation from the internal pore system and the adjacent matrix is dominating over the contribution from external surface.

Correlations between radon concentration and indoor gamma dose rate, soil permeability and dwelling substructure and ventilation.

Correlations between radon concentration and indoor gamma dose rate, soil permeability and dwelling substructure and ventilation were studied using data from 84 low rise residential houses collected in an area of enhanced indoor radon concentration. The radon concentrations varied from 30 to > 5000 Bq m(-3). Cross-tabulation, comparisons of means and multiplicative models were used to test the significance of the effects. In this study a quite high percentage of explained variation R2 (68%) was found. It was found that the most important factors were the substructure and the permeability of the soil. Due to the rather small sample size and moderate variation in the uranium content of the bedrock of the area, the effect of the indoor gamma dose rate was not so prominent. The effects of ventilation habits and sleeping with open windows were not detected in this study.

Review of low-energy construction, air tightness, ventilation strategies and indoor radon: results from Finnish houses and apartments

Low-energy and passive house construction practices are characterised by increased insulation, high air tightness of the building shell and controlled mechanical ventilation with heat recovery. As a result of the interaction of mechanical ventilation and high air tightness, the pressure difference in a building can be markedly enhanced. This may lead to elevated indoor radon levels. Minor leakages in the foundation can affect the radon concentration, even in the case where such leaks do not markedly reduce the total air tightness. The potential for high pressures to affect indoor radon concentrations markedly increases when the air tightness ACH50, i.e. the air change per hour induced by a pressure difference of 50 Pa, is <1.0 h(-1). Pressure differences in Finnish low-rise residential houses having mechanical supply and exhaust ventilation with heat recovery (MSEV) are typically 2-3 Pa, clearly lower than the values of 5-9 Pa in houses with only mechanical exhaust ventilation (MEV). In MSEV houses, radon concentrations are typically 30% lower than in MEV houses. In new MSEV houses with an ACH50 of 0.6 h(-1), the limit for passive construction, the analytical estimates predict an increase of 100% in the radon concentration compared with older houses with an ACH50 of 4.0 h(-1). This poses a challenge for efficient radon prevention in new construction. Radon concentrations are typically 30% lower in houses with two storeys compared with only one storey. The introduction of an MSEV ventilation strategy in typically very airtight apartments has markedly reduced pressure differences and radon concentrations.

Radon prevention in new construction in Finland – a nationwide sample survey in 2009

The building code for radon prevention and the associated practical guidelines were revised in Finland in 2003-2004. Thereafter, preventive measures have become more common and effective and indoor radon concentrations have been markedly reduced. In this study, the indoor radon concentration was measured in 1500 new low-rise residential houses. The houses were randomly selected and represented 7 % of the houses that received building permission in 2006. The average radon concentration of all the houses measured, which were completed in 2006-2008, was 95 Bq m(-3), the median being 58 Bq m(-3). The average was 33 % lower than in houses completed in 2000-2005. The decrease was 47 % in provinces with the highest indoor radon concentration and 26 % elsewhere in the country. In houses with a slab-on-ground foundation that had both passive radon piping and sealing measures carried out using a strip of bitumen felt in the joint between the foundation wall and floor slab, the radon concentration was on average reduced by 57 % compared with houses with no preventive measures. Preventive measures were taken nationwide in 54 % of detached houses and in provinces with the highest radon concentration in 92 % of houses.

Radon mapping strategy in Finland

Abstract Since 1986, the Radiation and Nuclear Safety Authority (STUK, Finland) has performed systematic indoor radon mapping with municipal health authorities. STUK has made radon measurement plans and radon risk maps to identify radon-prone areas. In the most radon-prone area, there are about 260,000 low-rise dwellings. In this area, it is expected that in 37,000 homes, the action level of 400 Bq/m3 will be exceeded. We have detected about 4800 of them. In the rest of Finland, the numbers are: 1,000,000 low-rise dwellings, 31,000 expected and 1800 detected cases exceeding the limit, respectively. The most active search for high radon houses should be focused on Southern Finland. The search is easiest in areas of permeable soil types like esker areas and other sand and gravel deposits because they are easy to locate from geological maps. It is cheaper and easier to take preventive measures when building new houses than to take mitigation measures later. Due to high indoor radon concentrations, it is reasonable to build radon-safe dwellings in all esker areas throughout the country and on other building sites in most parts of Finland.

Multidisciplinary analysis of Finnish esker sediment in radon source identification.

In order to define the naturally-occurring radioactive materials that are the source of radon in natural environments, a comprehensive analytical (geochemical, physical and chemical) methodology was employed to study sand samples from the Hollola esker in the city of Hollola (Lahti area, Finland). Techniques such as gamma-spectrometry, emanation measurements, sequential chemical extraction, scanning electron microscopy (SEM), electron probe microanalyses (EPMA) and inductively-coupled plasma mass spectrometry (ICP-MS) were used to determine the potential source of radon. Monazite and xenotime, uranium- and thorium-bearing minerals and potential radon sources, occurred in significant amounts in the samples and were also the main reason for the distribution of uranium and thereby radium in separate grain-size fractions. Following deposition, the esker sand has been exposed to no significant weathering, and radium has not therefore been much separated from uranium. However, considering its non-compatibility with crystal lattices, it was recognized rather in easily leachable species (44% of the total (226)Ra) than uranium (21% of the total (238)U) in our analyses. The smallest grain-size fraction of the esker sand had a higher emanation power (0.24) than the other fractions (around 0.17). Due to the small relative proportion of this fraction, however, it contributed only slightly to the total emanation (4%). The emanation power of the leachable species was about three times higher (ca. 0.20) than that of the species tightly bound to the crystal lattice (ca. 0.07).

Background radiation and childhood leukemia: A nationwide register-based case-control study.

High doses of ionizing radiation are an established cause of childhood leukemia. However, substantial uncertainty remains about the effect of low doses of radiation, including background radiation and potential differences between genetic subgroups of leukemia have rarely been explored. We investigated the effect of the background gamma radiation on childhood leukemia using a nationwide register‐based case‐control study. For each of the 1,093 cases, three age‐ and gender matched controls were selected (N = 3,279). Conditional logistic regression analyses were adjusted for confounding by Down syndrome, birth weight (large for gestational age), and maternal smoking. Complete residential histories and previously collected survey data of the background gamma radiation in Finland were used to assess the exposure of the study subjects to indoor and outdoor gamma radiation. Overall, background gamma radiation showed a non‐significant association with the OR of childhood leukemia (OR 1.01, 95% CI 0.97, 1.05 for 10 nSv/h increase in average equivalent dose rate to red bone marrow). In subgroup analyses, age group 2–<7 years displayed a larger effect (OR 1.27, 95% CI 1.01, 1.60 for 1 mSv increase in equivalent cumulative dose to red bone marrow). Suggestive difference in OR by genetic subtype was found. Our results provide further support to the notion that low doses of ionizing radiation increase the risk for childhood leukemia, particularly at age 2–<7 years. Our findings suggest a larger effect of radiation on leukemia with high hyperpdiploidy than other subgroups, but this result requires further confirmation.

Experiences in radon-safe building in Finland

A study was made of radon-safe buildings in 300 Finnish low-rise residential buildings using data obtained from a questionnaire study. The study also aims at finding the main defects in design and implementation and how the guidance given on radon-safe buildings in slab-on-grade houses has been followed. According to the guidelines, the prevention of the flow of radon-bearing air from the soil into the house is recommended to be carried out through installation of aluminised bitumen felt and use of elastic sealants. Second, as a precaution perforated piping should be installed in the subsoil of the floor slab. The median indoor radon concentration in the houses was 155 Bq/m3. This is 32% lower than the median of the estimated reference values. The action level of 200 Bq/m3 was still exceeded in 40% of the houses. In most houses with slab-on-grade the prevention was based only on the installation of a sub-slab depressurisation system. Sealing was performed in a low number of houses. In 80% of houses with a sub-slab piping connected to an operating fan, radon concentration was below the action level of 200 Bq/m3. In houses with piping but no fan, the corresponding fraction was only 45%. Sub-slab piping without a fan had no remarkable effect on radon concentration. In houses with crawl-space and edge-thickened slabs, radon concentrations were low. The choice of foundation system thus significantly affects the indoor radon concentration. The importance of complete and careful sealing work should be stressed in advice and guides concerning radon prevention.

Population distribution of doses from natural radiation in Finland

Abstract This study presents a review of population distribution of annual doses from sources of natural radiation in Finland. The results are based on previously made representative surveys of gamma radiation outdoors and indoors as well as on surveys of indoor radon concentrations and natural radioactivity in drinking water. Measurements of gamma radiation outdoors are based on a mobile survey on roads. The indoor gamma radiation measurements were carried out using thermoluminescence detectors (TLD)-dosemeters affixed to radon dosemeters. The long-term measurements of indoor radon concentration were performed using alpha track detectors in 3000 dwellings. The measurements of radionuclides in drinking water have been carried out on more than 1000 waterworks and for about 9000 wells drilled in bedrock and for 5000 wells dug in soil. The percentages of population receiving doses exceeding 1.0 mSv due to indoor radon, drinking water and natural gamma radiation were 64%, 0.4% and 0.3%, respectively. The annual dose of 10 mSv is exceeded in the case of 2% of population (total 5.1 million) in exposures to residential indoor radon concentrations.