1. Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, N-0349 Oslo Norway
2. Centre for Environmental Radioactivity (CERAD), Norwegian University of Life Sciences (NMBU), Post box 5003, N-1432 Ås, Norway
3. Faculty of Environmental Sciences and Natural Resource Management (MINA), Norwegian University of Life Sciences (NMBU), Post box 5003, N-1432 Ås, Norway
4. Faculty of Biosciences, Norwegian University of Life Sciences (NMBU), P.O. Box 5003, N-1432 Ås, Norway