Deposition of particle-attached radon progeny in the respiratory tract - an experimental study of children and adults in home environments

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Summary, in English

A method to study total deposition of aerosol attached radon progeny in children and adults have been validated and used in home environments. Two persons, one child and one adult are tested simultaneously, thus inhaling from the same aerosol and allowing for a direct comparison. The aim of the study was to increase the knowledge of the lung deposition and thereby the knowledge of the radiation dose from indoor radon. In the study 13 children (ages 4-13 years) and 11 adults were tested in their home environments (five dwellings with elevated radon levels 200 - 600 Bq/m3). Two different aerosols were used: the background aerosol particles when no strong indoor sources were present and the relatively small particles from normal candle burning (activity median diameters (AMD) roughly 200 and 50 nm respectively).

An enhanced deposition was found for the children compared to the adults for the smaller particles (mean deposition 38 and 31%), while for the larger background particles no difference was found (31% deposition for both groups). Differences between the deposition of the different short lived radon daughters was found. This was infered to be explained as an ageing effect. In one of the dwellings measurements were performed to estimate hygroscopic growth of the particles upon inhalation. Growth factors between 1 and 4.5 was found.

When comparing the results with a stochastic lung deposition model (hygroscopic growth taken into account) reasonable good agreement was found for the smaller particles (experiments 31% and model 26%), while for the larger background particles a roughly doubled deposition was found (experiments 31% and model 15%).

A comparison of the deposition when breathing through mouth and nose has also been conducted. This part of the study with adults only was performed in a radon exposure chamber. Relatively large (AMD =500 nm) hydrophobic particles from flickering candle burning (black smoke) were used. Mean depositions of 11 and 17% were found when breathing through mouth and nose respectively. Good agreement was found when comparing with the stochastic model.

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