Scientific Highlight February 2011

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Hortense May
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1 Scientific Highlight February 2011 co-ordinated with the Director of the Institute / Research Unit Institute/ Research Unit / Clinical Co-operation Group / Junior Research Group: Institute of Radiation Protection, Research Group Experimental Radioecology PSP-Element: G Person to contact for further enquiries: Dr. Jochen Tschiersch, tschiersch@helmholtz-muenchen.de, 2763 Title of the Highlight: Thoron in indoor air: modelling for a better exposure estimate Keywords: thoron, decay products, radioactivity, mud building, indoor model Central statement of the Highlight in one sentence: A newly developed model for the indoor exposure of thoron and its decay products makes possible to calculate inhalation doses of dwellers and to identify mitigation strategies. Text of the Highlight: The radioactive gas thoron ( 220 Rn) and its decay products have been regarded as a significant health risk in the indoor environment for only a few years. This is because of new findings of increased thoron concentrations in traditional mud dwellings and considerations leading toward reduced action levels for natural airborne radionuclides. Therefore a compartment model which describes the sources and sinks of thoron and its decay products was developed. It comprises an extensive depiction of the influences of indoor conditions on the occurrence of these radionuclides. Thus it helps to assess the indoor exposure. Measurements were performed in a unique thoron experiment room at the Helmholtz Zentrum München and in mud dwellings in China and India. Mud even with an average 232 Th concentration was identified as a significant thoron source. The spatial distribution of the decay products proved to be homogeneous, which is in contrast to thoron gas. The prominent contribution of the unattached and attached decay product Pb to the exposure was elaborated. The theoretically derived impact of air exchange and aerosol concentration on the concentration of the decay products and their unattached 1

2 fraction could be confirmed. Transfer coefficients between the different compartments of the model were determined. The thoron model with these transfer coefficients predicts annual doses of almost 2 msv for dwellers of traditional Chinese and Indian mud buildings, confirming the potential health impact of thoron. Mitigation strategies such as increased ventilation or filtration of the indoor air can be derived from the model results. Publication: Meisenberg O., Tschiersch J.: Thoron in indoor air: modeling for a better exposure estimate. Indoor Air 21, (2011) Taking account of the HMGU mission: How does the Highlight described relate to the HMGU mission? (1-2 sentences) HMGU mission: The developed model is an important step towards the understanding under which environmental conditions high concentrations of indoor thoron occur. This work facilitates the identification of measures for the mitigation of one of the causes of lung cancer. The internal HMGU co-operation partners with whom the Highlight was compiled, if appropriate: 2

3 The indoor thoron model an overview size distribution building material exhalation 220 Rn spatial distribution The indoor thoron model comprises all sources, sinks and transfers of thoron and its decay products. attached Pb 216 Po deposited Pb Pb Red arrows represent transfer rates which were determined in measurements. 208 Pb Transfer rates shown with green arrows were derived by theoretical calculations.

4 Measurements in situ and in a unique lab Measurements were performed in a unique lab: the thoron experimental house at Helmholtz Zentrum München Calculated model results were validated in mudbrick buildings in China and India.

Calculation of inhalation doses Input parameters into the model (one room): Mud buildings are common worldwide. For this Bavarian one, the model predicts: Spec.

5 Calculation of inhalation doses Input parameters into the model (one room): Mud buildings are common worldwide. For this Bavarian one, the model predicts: Spec. activity 232 Th Density of mud Surface (thereof mud) Volume Air exchange rate Aerosol concentration Daily stay 60 Bq/kg 1600 kg/m 3 60 m 2 (20 m 2 ) 30 m h cm h Thoron 216 Po Pb unatt. Pb att. att. total PAEC [nj/m³] Dose [msv/a] ±0.4

Science of the Total Environment

Science of the Total Environment 49 (211) 3613 3619 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Mitigation of radon and