[1] Analytica AB, S-977 75 Luleå, Sweden
[2] Division of Applied Geology, Luleå University of Technology, S-971 87 Luleå, Sweden
[3] Finnish Environment Institute, P. O. Box 140, F-00251 Helsinki, Finland
[4] Pirkanmaa Reg. Environment Centre, P. O. Box 297, F-33101 Tampere, Finland