1. Research and Development Unit of Environmental Health, Department of Environmental Sciences, Bioteknia 2; University of Kuopio; P.O. Box 1627 FIN-70211 Kuopio Finland
2. North Savo Regional Environment Centre; P.O. Box 1049 FIN-70701 Kuopio Finland
3. Department of Biology; University of Joensuu; P.O. Box 111 FIN-80101 Joensuu Finland