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ENVIRONMENTAL RADON & PROGENY

A Greek version of the reserch scientific activities of this topic can be found in odf.pdf and tex.pdf formats.

OVERVIEW

The environmental exposure to radon is a public health problem. This is considered as the second cause of lung cance incidencer, after smoking. Radon in the human environment is an important research topic worldwide. Parts of regions are affected by residuals/wastes of increased natural radioactivity from the mining industry. In the same time radon issue is still not addressed in this area.

The targets of this research include the: a.spatial and seasonal variations of radon in dwellings and the environment; b.study of the effect of geological, hydrographic, meteorological factors, buildings design, type of building materials and other related factors that affect radon concentration; c.assessment of the radiological risk of the population under various conditions and exposure scenaria. d.modelling of radon and progeny generation and concentration peaks; e.focused measrements of radon and progeny in spas; f.special investigations in areas of concern; g.recommendations for minimisation of the radiological risk; h.generation of databases and maps of radon distribution in geographical zones of interest.

Towards the objectives measurements of radon in soil, surface and tap water, outdoor and indoor air are continiously conducted and the corresponding radiological risk of the exposed population is estimated. Specific measurements related to earthquacke prepatory activity from Geosystems are presented under the next topic of this category.

The main research directions are the following: 1.Selection of representative list of sampling points for field research and laboratory investigation; 2.Analysis of geological, hydrographic and building characteristics of specific regions;3.Study of spatial, temporal and seasonal radon variations; 4.Study of factors that affect radon concentrations; 5.Advanced statistical data analysis; 6.Chaotic and Hurst analysis; 7.Indexing areas of high radon potential; 8.SSNTD investigations; 9.Monte-Carlo modelling; 10.Dynamical modelling; 11..Estimation of radiation doses of population groups; 12.Recommendations for remediation;

 

INTRODUCTION

The study of the environmental radioactivity is an actual problem in environmental science. The main contribution to the public exposure is from natural sources. Natural sources of radiation are divided into two main groups: cosmic rays and the radioactive elements contained in the earth's crust, air, water, building materials, etc. The most widespread NORE in the environment are those of the families of Th-232, U-238 and U-235, as well as, K-40. The total quantity of the main nuclides in the specified families includes 39 nuclides which are alpha-, beta- and gamma-emitters. The natural radioactive gas - radon is represented by 3 isotopes: Rn-222, Rn-220 and Rn-219. The radiologically most important is Rn-222 and its short-lived progeny (Po-218, Pb-214 and Bi-214, Po-214). After their inhalation, the emitted ionizing radiation (most importantly, the alpha-particles) can cause malignant transformations of cells in the human lungs. Radon is everywhere in the environment – in soil, water, including drinking water, outdoor and indoor air – and therefore, research of the characteristics of its distribution in various geographical regions, especially in places of big congestion of people, is a subject of research in many countries.

 

Recent studies of indoor radon and lung cancer in Europe, Northern America and Asia provided strong evidence that radon causes a substantial number of lung cancer deaths among the population. Current estimates of the proportion of lung cancer deaths due to radon exposure range from 3 to 14 % [1]. The analysis indicates that the lung cancer risk increases proportionally with the increase of radon exposure [2]. Radon is the second cause of lung cancer after tobacco smoking and the first cause for never smokers. Most of the radon-induced lung cancer cases occur among smokers due to a strong combined effect of smoking and radon. Therefore, studying of the ecological status, including features of the natural distribution of radon and radon sources in target regions is an actual task.

 

Regarding the physicochemical properties, radon is an inert gas without color and odor, 7.5 times heavier than air; it is well dissolved in water. In the environment, The main radon radioactive isotopes are Rn-222, Rn-220 and Rn-219. All these emmit alpha particles. The half-life of the radiologically most important isotope Rn-222 is 3.8 days, but since it permanently escapes into the atmosphere, radon and its short-lived decay products - Po-218, Pb-214, Bi-214 and Po-214. Of interest is Pb-210 (22.3 year) and Po-210 (137 days) which also make up significant contribution to natural radioactivity.Radon-related exposure contributes about 50% to total dose to the general population due to all sources of radiation.

 

Radon is present in rocks, soil, underground waters, air. It can reach significant concentrations especially indoors. Due to this, radon in indoor air, water and soil gas has attended special concern in radioecology studies.

 

Radon emanates finally into the atmosphere and water. Radon in soil gas varies from <1 kBq.m-3 up to >1 MBq.m-3 and depends on the radioactivity and porosity, air infiltration, structures, textures and state of the soils. The main sources of radon entering into the indoor air of buildings are the following:

  • Rocks. Depending on the radium content of rocks as well as other parameters (e.g. grain size, permeability etc.), radon emanates and enters home interior [1]. There exist rocks (e.g. altes, granites, syenites) that exhibit high emanation of radon, and, thus, high ground radon concentrations (more than 50 – 100 kBq.m-3) and can create sizeable radon sites where indoor radon concentration can rise up to > 1000 Bq.m-3;

  • Building materials can contain high concentration of radium which continuously generates radon;

  • Tap water can contain noticeable quantities of radon, especially if sources of water supply are drilled ground waters (artesian waters); (for example, in water supply system of Helsinki radon concentration is about 1200 Bq.L-1 [2].

The above factors can cause significant fluctuations of radon concentration in soil gas, in water and buildings and depend on geographical and seasonal factors of certain region.

 

 

METHODS

 

The main methods include radon research with a complex character in the following topics:

  • Dwellings
  • Soil gas;

  • Natural and undeground waters (rivers, lakes, sea water, spring water, wells, thermal spas) as well as drinking (tap) water;

  • Outdoor and Indoor air;

  • Radon detectors.

The methods include Monte-Carlo modelling, dynamical modelling and investigation through chaos and self-organisation.

 

The methodological approach includes:

  • simultaneous measurements of radon concentrations in room of apartments under different protocolls;

  • specific research on radon content depending on number of storey of the building (carrying out of measurements of radon concentration on various floors of buildings);

  • measurements of radon concentration in soil gas in areas directly adjoining the building under study for establishment correlation with “indoor” radon concentration;

  • measurements of radon progeny and equilibrium factor indoors;

  • study of diurnal and seasonal variations in radon concentrations;

  • measurements of radon exhalation from soil;

  • additional researches of radon content in soil gas in territory, perspective for the future buildings;

  • gamma - spectrometry of soil samples.

This type of reasearch provides information about the multilateral character of dynamics of radon which depend on various conditions and environmental factors.

 

The main methods followed in radon and progeny measurements are the following:

Active methods.

Active methods are based on detecting of alpha emitters: Rn-222 and its decay products Po-218 and Po-214. In some kind of monitors sedimentation of Po-218 and Po-214 on detector surface is employed and alpha particles created at their decay are detected. The pulses are counted up by the electronic counter; so, the concentration of their parent - Rn-222 is determined by the counting-rate.

 

For the measurements modern equipments are used (AlphaGUARD, EQF3023).

 

Passive methods.

Passive methods are based on the counting of tracks created by alpha-particles in SSNTDs. Their density tracks per cm2) is proportional to integrated radon concentration. This allows measuring the average radon concentration for certain period (usually some months). The method is now traceable (for air and water) to radon standards in leading international laboratories [28, 29]. Note that, the paralel use of active and passive methods allows estimation of short-, as well as long-term dynamics of radon in cases of interest.

 

The radiological risk is evaluated by the following quantities:

  • lung dose equivalent;

  • effective dose;

  • dose equivalent to stomach.

These quantities are estimated using established and widely accepted dose models. As an example, this is illustrated characteristically for a case of measurements of radon in water. For this case the following quantities are of interest:

 

A.Lung dose equivalent (per year) calculated by the formula

                                                        H(lung) = A·C

where

H(lung) is the lung equivalent dose per year in mSv.y-1

A – is the radon concentration in water in Bq per L,

C – is adose conversion conversion factor, equal to 0.011 mSv per Bq

 

B.The effective dose E calculated by the formula

                                                           E = A·C1·Y,

where

E is the effective dose in mSv

A – is the radon concentration in water in Bq per L,

C1 – is a dose conversion factor equal to 0.38E-8 Sv.Bq-1 [30]

Y – is annual consumption of a "standard adult", equal to  730 L under the assumption of consuming 2 L of water per day per year[31,32].

 

C.Dose equivalent in stomach H(stomach) (per year) calculated by the formula:

                                                           H(stomach) = A·C2.Y,

where

H (stomach) is the dose equivalent in stomach in mSv per year

C2 – is a conversion factor, equal to 1x10-7 in Sv per Bq [33]

 

 

Novel Character of the reasearch

This research focuses on the study of the distribution of radon and progeny simultaneously in several environmental structures such as: soil, water (both natural and drinking) and air (outdoor and indoor air). Related measurements are conducted during summer and winter. Statistical data analysis is performed to data on a sceduled basis. In such a way, the research allows to obtain reliable information to estimate the radiological risk related to radon. Such data allow the systematic investigation in the field of radon-related radiological risk for the population. This is significant especially in the the view of radon as an environmental risk hazard in association to policy makers and decision making.

 

 

Multidisciplinary character of the research

The approach employed in this research is multidisciplinary. In particular, it is anticipated to establish interrelations between geographical-geological, building features and natural radiation environment in target regions. A facultative research of radon in soil-gas and radon exhalation from the ground potentially can contribute to: (1) understanding of the mechanism of climatic processes in target regions; (2) study of tectonic processes and seismic activity; (3) geological exploration for oil/gas.

 

 

Relevance and importance of the research

The importance of the radon problem nowadays is well accepted among the International Organisations. For example, for minimization of health hazards due to indoor radon the World Health Organization (WHO) proposes a reference level 100 Bq/m3 . However, if this level cannot be reached under the prevailing specific conditions, the reference level should not exceed 300 Bq/m3 which corresponds to approximately 10 mSv per year, according to the recent calculations by the International Commission on Radiation Protection. For example, the government of Canada lowered its indoor radon guideline from 800 to 200 Bq/m3 [3]. Thus, studying the radon content in various environmental structures that can serve as “sources” of radon in air, soil, water and building materials can assist the quantification of the influennce of the several affecting factors and, most imortantly, the related significant effects on public health.

 

Finally the implementation of the given reserach helps to increase the public awareness to the radon problem and stipulate the employement of preventive actions on reducing the related radiological risk. It promotes also monitoring of territories that are intended to be used for building purposes and assists the development of the necessary regulation by the state and municipal bodies.

 

References

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