1. Institute of Hydrochemistry and Chemical Balneology, Technical University Munich, Marchioninistrasse 17, D-81377 Munich, Germany, Institute of Chemistry, Department of Analytical Chemistry, Johannes-Kepler-University Linz, Altenbergerstrasse 69, A-4040 Linz, Austria, and Bavarian Water Management Agency, Kaulbachstrasse 37, D-80539 Munich, Germany