Germanium is considered to be a non-essential element; however, little is still known about its significance for living organisms. It exerts prophylactic and therapeutic effects in the treatment of serious diseases such as cancer, HIV infection, and others. Germanium does not exhibit acute toxicity, but, as it tends to accumulate in various organs and tissues, undesirable and even dangerous side effects have been reported after prolonged and/or high dosage application. In general, inorganic compounds of germanium are more toxic than its organic compounds. Further studies should be performed to elucidate the exact molecular mechanism of germanium action, to determine the safe and effective dose of germanium via curative/mineral waters, and to understand the applications and benefits of using germanium-enriched waters in balneotherapy. The geochemistry of curative (cold CO2-rich, thermal) waters from spas in the Sudetes (Poland) was clarified in terms of components and mineral phases which might govern germanium. Germanium and silicon in thermal (above 20 °C) waters presumably result from the solubility of silicates in crystalline (granites, gneisses) aquifer rocks and might be controlled by neo-formed quartz. The cold CO2-rich waters revealed a significant diversity of aqueous chemistry and relationships of germanium with iron, silicon, or arsenic. Locally, both in sedimentary (sandstones) and metamorphic (gneisses) aquifer rocks, primary (silicates) and/or secondary (oxides) iron-containing minerals likely release germanium into solution. In the CO2-rich waters of the western part of the Kłodzko Region, germanium distinctly correlates with arsenic. It is hypothesized that both elements are co-sourced from crystalline basement and/or migration of substances of post-magmatic origin along deep-seated dislocations related to the seismically active Poříčí-Hronov fault zone. This area was proposed as the most prospective one for finding waters rich in germanium in the Sudetes.Electronic supplementary materialThe online version of this article (10.1007/s10653-017-0061-0) contains supplementary material, which is available to authorized users.

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A wide set of aqueous chemistry data (574 water analyses) from natural environments has been used to testify and validate of the solubility of synthetic hydroxyaluminosilicate (HAS B ) , Al 2 Si 2 O 5 (OH) 4 . The ground and surface waters represent regolith and/or fissure aquifers in various (magmatic, sedimentary and metamorphic) bedrocks in the Sudetes Mts. (SW Poland). The solubility of HAS B in natural waters was calculated using the method proposed by Schneider et al. (Polyhedron 23:3185-3191, 2004). Results confirm usefulness and validity of this method. The HAS B solubility obtained from the field data (logK sp = -44.7 ± 0.58) is lower than it was estimated (logK sp = -40.6 ± 0.15) experimentally (Schneider et al. Polyhedron 23:3185-3191, 2004). In the waters studied the equilibrium with HAS B is maintained at pH above 6.7 and at [Al 3+ ] £ 10 -10 . Silicon activity (log[H 4 SiO 4 ]) ranges between -4.2 and -3.4. Due to the calculation method used, the K sp mentioned above cannot be considered as a classical solubility constant. However, it can be used in the interpretation of aluminium solubility in natural waters. The HAS B has solubility lower than amorphous Al(OH) 3 , and higher than proto-imogolite. From water samples that are in equilibrium with respect to HAS B , the solubility product described by the reaction, Al 2 Si 2 O 5 (OH) 4 + 6H þ $ 2Al 3þ + 2H 4 SiO 4 + H 2 O is calculated to be logK sp = 14.0 (±0.7) at 7°C.

In some countries (e.g. Poland, Czechia, Slovakia, Russia, Germany), oxidation-reduction potential (ORP) measurements are required to document the quality of groundwater which are planned to be used as therapeutic waters. ORP is still rarely studied and not fully availed in therapeutic water research. Studies of ORP in various types of therapeutic, mineral and thermal waters in sites of Poland integrated with geochemical equilibrium approach were employed to characterize two redox-sensitive and bioactive elements, i.e. iron and sulphur. Studied waters present reducing conditions (E H between − 406 and − 41 mV) at outflow or extraction sites; however, they significantly differ in terms of total dissolved solids, temperature, and iron, sulphur(II) and sulphate concentrations. These result in recognizable differences, e.g. in terms of saturation state with respect to aquifer rock minerals and the dominating forms of occurrence of elements studied disclosed on the stability field diagrams. Considering the methodological determinants, ORP orchestrated with geochemical modelling tools might be successfully applied for studying natural linkages between various groundwater in natural systems, protecting the therapeutic water resource, and identifying the changes of water quality both at exploitation sites (springs, wells) and treatment places.

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