Assessing Human Exposure to Contaminants in House Dust

Kaltofen, Marco Paul Johann

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Assessing Human Exposure to Contaminants in House Dust

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Airborne dusts can transport radioactive materials in the form of isolated individual radioactively-hot particles containing high concentrations of radioisotopes. These airborne particles may be inhaled or ingested, becoming a source of internal radiation exposure. After the March 11, 2011, nuclear reactor accidents at Fukushima Daiichi, in northern Japan; eighty-five Japanese environmental samples and 234 US and Canadian samples were collected and analyzed by gamma spectrometry, autoradiography, scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS), and total alpha and beta counts. Social media and volunteer organizations were an important part of the sample collection effort. The combination of autoradiography and SEM/EDS allowed individual radioactively-hot particles to be isolated and analyzed. Detectable levels of 134Cs and 137Cs were found in 62 of 85 Japanese particulate matter samples. The median dust specific activity for Japanese samples was 2.5 Bq g-1 +/- 1.6 Bq g-1, while the mean dust specific activity was 71 Bq g-1 (RSD = 335 %). The mean was skewed high due to five dust samples with sharply higher specific activities. These five samples had specific activities ranging from 167 kBq g-1 to 5.2 PBq kg-1. Only four of 234 US and Canadian environmental samples had detectable levels of both 134Cs and 137Cs. Gross gamma spectroscopy of Japanese samples also detected 131I and 60Co. US and Canadian dust samples showed primarily naturally-occurring nuclides. More than 300 individual hot particles were identified in Japanese samples. The Japanese particles analyzed by SEM/EDS were found to contain cesium, americium, radium, polonium, tellurium, rubidium and other necessarily or potentially radioactive elements. No cesium-containing hot particles were found in the US, however some dust particles were found that contained uranium, thorium and plutonium. These US particles were all related to identified uranium mines or nuclear materials storage and processing sites. Some of the hot particles detected in this study could cause significant radiation exposures to individuals if inhaled. Where hot particles are present in the environment, radiation dose models must include this exposure component to remain accurate. 

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