Redox potential research in the field of balneochemistry: case study on equilibrium approach to bioactive elements in therapeutic waters

Abstract

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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“…A recent research report showed that the ORP value of groundwater ranged from −165 to −59 mV. [16] The study suggested that the ORP value was highly influenced by geochemical modeling.…”

Fluoride ions in groundwater of the Turkana County, Kenya, East Africa

“…The redox conditions play an important role in the formation of the chemical composition of groundwater (Appelo and Postma 2005;Dobrzyński et al 2018;Wątor et al 2020). Thus, due to the lack of information about redox potential value (E H ), the nitrogen species were used to determine the redox conditions by the calculation of electron activity (pe) using the N(V)/N(III) redox couple.…”

Methodological aspects concerning sampling and determination of total selenium and selenium species in geothermal waters

“…Unstable parameters such as redox potential, temperature, pH, and electrical conductivity were also measured. If the measurements did not differ by 0.2°C for temperature, 0.1 unit for pH and 5% in the case of electrical conductivity (γ 25 ), the stability criterion is fulfilled (Witczak et al 2013;Korzec et al 2016;Kmiecik et al 2019;Wątor et al 2020). Two samples were collected from each intake -raw and filtered.…”