1. a Department of Environmental Sciences, University of Kuopio, P.O. Box 1627, FIN-70211, Kuopio, Finland
2. b Kuopio Regional Institute of Occupational Health, P.O. Box 93, FIN-70701, Kuopio, Finland
3. c Division of Environmental Health, National Public Health Institute, P.O. Box 95, FIN-70701, Kuopio, Finland