The sources and fate of 210 Po in the urban air: A review Magdalena Długosz-Lisiecka Technical University of Lodz, Institute of Applied Radiation Chemistry, Wróblewskiego 15, 90–924 Łódź., Poland abstract article info Article history: Received 17 March 2016 Received in revised form 2 June 2016 Accepted 3 June 2016 Available online xxxx The origin of 210 Po activity and its fluctuations in the air are discussed in this paper. In the case of atmospheric aerosol samples, a comparison of the 210 Po/ 210 Pb and 210 Bi/ 210 Pb activity ratios makes it possible not only to de- termine aerosol residence times but also to appraise the contribution of the unsupported 210 Po coming from other sources than 222 Rn decay, such as human industrial activities, especially coal combustion. A simple math- ematical method makes it possible to observe the seasonal fluctuations of the anthropogenic excess of 210 Po in the urban air. The average doses of 210 Po intake with food (including drinking water) and inhalation of urban aerosols are usually lower than those from 210 Po intake by cigarette smokers and negligible in comparison to total natural radiation exposure. © 2016 Elsevier Ltd. All rights reserved. Keywords: Polonium radiotoxicity Radiological hazard Aerosol residence time Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 2. 210 Po/ 210 Pb activity ratio and its limited application in determining aerosol residence time. . . . . . . . . . . . . . . . . . . . . . . . . . . 327 2.1. Aerosol residence time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 2.2. Calculation of excess 210 Po in the air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 3. Mosses and lichens as 210 Po biomarkers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 1. Introduction The murder of Alexander Litvinenko, committed by his former KGB colleagues in November 2006 using green tea laced with 210 Po, raised serious scientific interest expressed in several papers (Harrison et al., 2007, Jefferson et al., 2009) and a few review papers concerning the nat- ural occurrence (Persson and Holm, 2011) and human health effects of low-level exposure to this radionuclide (Seiler and Wiemels, 2012; Hölgye et al. 2015). 210 Po occurs naturally in the environment as one of the decay products of the uranium series, but its concentration is very low (about 0.1 ppb in uranium ores). The 210 Po content in the lithosphere is related to the concentration of 238 U in the earth's crust. However, the presence of 210 Po in the atmo- sphere is mainly caused by the emanation and transport of one of the uranium daughters - gaseous radon - from surface soil. Since the only source of atmospheric radon is soil, the concentrations of outdoor radon are subject to both seasonal and diurnal changes as well as to me- teorological conditions. Therefore, there is a wide range of long-term average outdoor concentrations of radon, from approximately 1 Bq/m 3 to more than 100 Bq/m 3 . However, its average yearly concentrations in surface atmosphere are relatively constant with typical levels of the order of 10 Bq/m 3 (UNSCEAR, 2000). Similar levels of 222 Rn have been observed in the Central Poland area (Bem, 2005). After consecutive decays, the radionuclides of 210 Pb, 210 Bi and 210 Po are formed from atmospheric radon: 222 86 Rn α 3825 days 218 84 Po α 3:10 m 214 82 Pb β 26:8m 214 83 Bi β 19:9m 214 84 Po α 0:2 ms 210 82 Pb β 22:3 years 210 83 Bi β 5:013 days 210 84 Po α 138:376 days 206 82 Pb ð1Þ The total annual entries of 222 Rn and longer lasting 210 Pb (a precur- sor of 210 Po – Eq. (1)) into the atmosphere are estimated at 48 EBq and 23 PBq, respectively (Persson, 2014). In the atmosphere, 210 Pb, 210 Bi and Environment International 94 (2016) 325–330 E-mail address: mdlugosz@mitr.p.lodz.pl. http://dx.doi.org/10.1016/j.envint.2016.06.002 0160-4120/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Environment International journal homepage: www.elsevier.com/locate/envint