1. Department of Environmental Health, National Public Health Institute, P.O. Box 95, FIN-70701 Kuopio, Finland, Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland, Radiation and Nuclear Safety Authority, P.O. Box 14, FIN-00881 Helsinki, Finland, Finnish Environment Institute, P.O. Box 140, FIN-00251 Helsinki, Finland, and University of Kuopio, Department of Environmental Sciences, Finland