Quantitative measurement of aerosol deposition on skin, hair and clothing for dosimetric assessment
pre- and final report

C.L. Fogh, M.A. Byrne, K.G. Andersson, K.F. Bell, J. Roed, A.J.H. Goddard, D.V.
Vollmair and S.A.M. Hotchkiss

Risø National Laboratory, June 1999,
ISBN 87-550-2447-5, 58 p.

Risø-R-1075(EN) (2,7 Mb)
http://www.risoe.dk/rispubl/NUK/nukpdf/ris-r-1075.pdf

Risø-R-1028(EN) (2,2 Mb)
http://www.risoe.dk/rispubl/NUK/nukpdf/ris-r-1028.pdf

Abstract

In the past, very little thought has been given to the processes and implications of deposition of potentially hazardous aerosol directly onto humans. This state of unpreparedness is unsatisfactory and suitable protocols have been developed and validated for tracer experiments to investigate the deposition and subsequent fate of contaminant aerosol on skin, hair and clothing. The main technique applied involves the release and subsequent deposition on volunteers in test rooms of particles of different sizes labelled with neutron activatable rare earth tracers. Experiments indicate that the deposition velocity to skin increases linearly with the particle size. A wind tunnel experiment simulating outdoor conditions showed a dependence on skin deposition velocity of wind speed, indicating that outdoor deposition velocities may be great. Both in vivo and in vitro experiments were conducted, and the influence of various factors, such as surface type, air flow, heating and electrostatics were examined. The dynamics of particle removal from human skin were studied by fluorescence scanning. This technique was also applied to estimate the fraction of aerosol dust transferred to skin by contact with a contaminated surface. The various parameters determined were applied to establish a model for calculation of radiation doses received from deposition of airborne radioactive aerosol on human body surfaces. It was found that the gamma doses from deposition on skin may be expected to be of the same order of magnitude as the gamma doses received over the first year from contamination on outdoor surfaces. According to the calculations, beta doses from skin deposition to individuals in areas of Russia, where dry deposition of Chernobyl fallout led to very high levels of contamination, may have amounted to several Sievert and may thus be responsible for a significant cancer risk.. In an ongoing project the Contamination Physics Group is quantifying the distribution of radiation doses received by humans through all the various pathways in a contaminated indoor environment.

Deposition and Resuspension of Radioactive Material The Chernobyl accident provided a rare opportunity to study the deposition of different forms of radiopollutants under different weather conditions with or without precipitation. Especially, very little was at the time known about deposition to urban surfaces.

Measurements made by the Contamination Physics Group during the passage of the contaminated plume from Chernobyl showed radiocaesium aerosol (particle size of about 1 micron) dry deposition velocities to be in the range of 10-5 m/s on house surfaces. The deposition velocities for most other radionuclides were found to be 5-10 times higher. One experimental technique, which has been applied with great success by the Risø group, involves the use of Beryllium-7, which is almost exclusively created in the stratosphere by cosmic ray spallation of C-12, N-14 and O-16.

Particles to which this natural tracer attaches have been used to study the deposition processes of aerosol in the 0.8 micron size range. Another process that has been measured and modelled by the Contamination Physics Group is resuspension of deposited radioactive matter under different circumstances.

Resuspension in urban areas is a particularly complex topic as it is influenced by a wide variety of factors such as the surroundings, mechanical impact (traffic), particle size, wind speed, humidity, soluble versus non-soluble particles, the roughness of the structure to which deposition occurs, and various factors influencing the degree of fixation of the deposited material. Early phase urban resuspension factors were found to be in the range of 2 10-8 to 1 10-7. In an ongoing research project the contributions to dose from resuspension in a contaminated indoor environment are examined.