Thorium uptake by wheat at different stages of plant growth I. Shtangeeva a, * , S. Ayrault b , J. Jain c a St. Petersburg University, Universitetskaya nab. 7/9, St. Petersburg 199034, Russia b Laboratory Pierre Su ¨e, CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France c Department of Civil Engineering & Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA Accepted 5 January 2005 Abstract Data on biogeochemistry of thorium are rather limited. So far little is known about toxic effects of small amounts of the radionuclide on higher plants. In this study the uptake of thorium by wheat seedlings was measured by greenhouse experiments. Germination of wheat seeds for 6 days in the presence of thorium resulted in accumulation of the metal in all parts of the seedlings. When the Th-rich seedlings were transferred to normal soil and were grown there further for 7 days, Th concentrations in roots and leaves decreased significantly (in leaves the Th content decreased up to the level of Th in the control plants). In seeds, however, Th content remained unchanged. An increase of Th content in roots and seeds was also observed as a result of addition of thorium to soil but in this case the concentration of Th in leaves did not change. The accumulation of Th in plants affected the uptake of other elements including essential macro-nutrients. The most strongly affected part of the plants was leaf. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Thorium; Wheat seedlings; Toxic effects; Macro-nutrients; Trace elements * Corresponding author. E-mail address: irina.shtangeeva@IS1179.spb.edu (I. Shtangeeva). 0265-931X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2004.01.041 Journal of Environmental Radioactivity 81 (2005) 283e293 www.elsevier.com/locate/jenvrad