RESEARCH ARTICLE Natural radionuclides in trees grown on a uranium mill tailings waste pile Marko Štrok & Borut Smodiš & Klemen Eler Received: 4 January 2011 /Accepted: 16 March 2011 /Published online: 29 March 2011 # Springer-Verlag 2011 Abstract Objective The purpose of the study was to investigate natural radionuclide uptake and allocation by trees. Materials and methods Samples from six Scots pines (P. sylvestris), six Norway spruces (Picea abies) and one sycamore maple (Acer pseudoplatanus) tree, growing on the Boršt uranium mill tailings waste pile in Slovenia were collected. 238 U, 230 Th, 226 Ra and 210 Pb activity concen- trations in wood, shoots and 1-year-old needles or leaves were determined. Particular radionuclides were separated from the samples by appropriate radiochemical procedures and their activity concentrations measured with an alpha spectrometry system. In addition, concentration ratios for different plant parts were calculated. Results and conclusions Results showed that for all radio- nuclides, the highest activity concentrations were found in foliage, followed by shoots and wood. The activity concentrations in trees were from 0.01 to 5.4 Bq kg -1 for 238 U, 0.03–11.3 Bq kg -1 for 230 Th, 2.7–2,728 Bq kg -1 for 226 Ra and 5.1–321 Bq kg -1 for 210 Pb. All activity concentrations were calculated on dry weight basis. The calculated concentration ratios were from 1.05E-5 to 5.39E- 3 for 238 U, 7.65E-6–2.88E-3 for 230 Th, 3.10E-4–3.16E-1 for 226 Ra and 6.70E-4–4.22E-2 for 210 Pb. Keywords Natural radionuclides . Pinus sylvestris . Picea abies . Acer pseudoplatanus . Uranium mill tailings . Alpha spectrometry 1 Introduction About 0.6 millions of tons of uranium mill tailings (UMT), which were left after the uranium extraction process, were dumped onto the Boršt waste pile, Slovenia, close to the former uranium mine at Žirovski vrh. During the operation of the uranium mine, the waste pond was filled with UMT and the pile covered with a 30–40 cm thick soil cover to reduce radon emanation and prevent erosion and wash-off of wastes containing elevated levels of the radionuclides into the surrounding area. With time, grass and trees spontaneously overgrew the waste pile slopes. Due to the relatively thin soil cover, the roots of trees were in contact with the UMT which contains about 995±80 Bq kg -1 of 238 U, 3,930±580 Bq kg -1 of 230 Th, 8,630±340 Bq kg -1 of 226 Ra (Križman et al. 1995). Because 210 Pb in UMT was not determined before, it was determined in this study. Elevated radionuclide activity concentrations in UMT represent a rare opportunity to study the uptake of selected radionuclides by trees grown on such wastes. In the past, there were several studies related to the natural radionuclide uptake by trees growing on different wastes originating from the processing of uranium ores (Petrova 2006; Madruga et al. 2001; Rodríguez et al. 2010; Thiry et al. 2005 and Hinton et al. 2005). Petrova (2006) investigated 238 U and 226 Ra activity concentrations in trees growing on different rock dumps left from uranium mining in Bulgaria. She reported that 238 U activity concentrations in needles and leaves from different tree species were in the range from 0.8 to 105 Bq kg -1 dry weight and in rock Responsible editor: Elena Maestri M. Štrok : B. Smodiš (*) Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia e-mail: Borut.Smodis@ijs.si K. Eler Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000, Ljubljana, Slovenia Environ Sci Pollut Res (2011) 18:819–826 DOI 10.1007/s11356-011-0499-z