Transfer factors and effective half-lives of 134 Cs and 137 Cs in different environmental sample types obtained from Northern Finland: case Fukushima accident Matias Koivurova 1 , Ari-Pekka Lepp € anen * , Antti Kallio Radiation and Nuclear Safety Authority e STUK, Regional Laboratory in Northern Finland, L€ ahteentie 2, FIN-96400 Rovaniemi, Finland article info Article history: Received 24 September 2014 Received in revised form 9 April 2015 Accepted 10 April 2015 Available online Keywords: Fukushima Northern Finland Aggregated transfer factor Effective half-life 134 Cs 137 Cs abstract The Fukushima NPP accident caused a small but detectable cesium fallout in northern Finland, of the order of 1 Bq/m 2 . This fallout transferred further to soil, water, flora and fauna. By using modern HPGe detector systems traces of 134 Cs from the Fukushima fallout were observed in various samples of biota. In northern Finland different types of environmental samples such as reindeer meat, berries, fish, lichens and wolf were collected during 2011e2013. The observed 134 Cs concentrations varied from 0.1 Bq/kg to a few Bq/kg. By using the known 134 Cs/ 137 Cs ratio observed in Fukushima fallout the increase of the Fukushima accident to the 137 Cs concentrations was found to vary from 0.06 % to 6.9 % depending on the sample type. The aggregated transfer factors (T ag ) and effective half-lives (T eff ) for 134 Cs and 137 Cs were also determined and then compared with known values found from earlier studies which are calculated based on the fallout from the Chernobyl accident. Generally, the T ag and T eff values determined in this study were found to agree with the values found in the earlier studies. The T eff values were sample-type specific and were found to vary from 0.91 to 2.1 years for 134 Cs and the estimates for 137 Cs ranged be- tween 1.6 and 19 years. Interestingly, the ground lichens had the longest T eff whereas the beard lichen had the shortest. In fauna, highest T ag values were determined for wolf meat ranging between 1.0 and 2.2 m 2 /kg. In flora, the highest T ag values were determined for beard lichens, ranging from 1.9 m 2 /kg to 3.5 m 2 /kg. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The Great East Japan Earthquake on March 11, 2011 at magni- tude 9 generated a series of large tsunami waves that struck the east coast of Japan, the highest being 38 m at Aneyoshi, Miyako (EERI, 2011). Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) started on March 12. Despite mitigation efforts, large quantities of radionuclides were emitted into the atmosphere and the sea. The estimates of the released activity vary, and according to the IAEA June 2012 Fukushima Dai-ichi status report, approxi- mately 150 PBq of 131 I and 8.2 PBq of 137 Cs were released into the atmosphere (IAEA, 2012). The radioactive release was transported across the Pacific to North America (Bowyer et al., 2011; Diaz et al., 2011), to Europe (Masson et al., 2011) and to Central Asia (Bolsunovsky and Dementyev, 2011). By day 15 after the initial radioactivity releases, traces of fission products from the FDNPP were detectable all across the Northern hemisphere (Thakur et al., 2013). Among the various radionuclides released in large amounts there were cesium-134 ( 134 Cs; T 1/2 ¼ 2.1 yr) and cesium-137 ( 137 Cs; T 1/2 ¼ 30.2 yr), which were detectable in aerosol samples and in fallout and are of major interest for health impact assessments. In Finland, the levels of 137 Cs and 134 Cs were roughly 3e4 orders of magnitude lower than the activity levels encountered in Finland after the Chernobyl accident in AprileMay 1986 (Mustonen, 2012; Paatero, 2010). It has been estimated that <1% of the total release was deposited in the Arctic region, i.e. above latitude 67  N(Thakur et al., 2013). In Finland there are three airborne and fallout moni- toring stations located above 66  N latitude: Rovaniemi (66.5  N), Sodankyl€ a (67.4  N) and Ivalo (68.6  N). 137 Cs is commonly observed in environmental samples due to atmospheric nuclear weapons tests and the Chernobyl accident. * Corresponding author. Tel.: þ358 9 75988371. E-mail address: ari.leppanen@stuk.fi (A.-P. Lepp€ anen). 1 Present address: University of Eastern Finland, Department of Physics and Mathematics, P.O.Box 111, FI-80101 Joensuu, Finland. Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad http://dx.doi.org/10.1016/j.jenvrad.2015.04.005 0265-931X/© 2015 Elsevier Ltd. All rights reserved. Journal of Environmental Radioactivity 146 (2015) 73e79