Disinfection of therapeutic water – balancing risks against benefits: case study of Hungarian therapeutic baths on the effects of technological steps and disinfection on therapeutic waters

Thermal therapeutic pools in most countries are operated in a manner similar to swimming pools: with water circulation, filtration and disinfection. However, in some countries, including Hungary, therapeutic pools are traditionally not treated this way, in order to preserve the therapeutic qualities of the water. However, dilution and frequent water replacement applied in these pools are often insufficient to ensure adequate microbial water quality, posing a risk of infection to the bathers. In the present case study, the impact of water treatment (including chemical disinfection by hypochlorite or hydrogen peroxide) was investigated on the therapeutic components of the water in seven Hungarian spas of various water composition. Microbial quality was improved by both disinfectants, but hypochlorite reduced the concentration of the therapeutic components sulfide, bromide, and iodide ions by 40–99%, and high levels of disinfection by-products were observed. Hydrogen peroxide only affected sulfide ion (91% reduction). Other technological steps (e.g., transport or cooling by dilution) were found to have significant impact on composition, often outweighing the effect of disinfection. The current case study demonstrated that thermal waters may be treated and disinfected with minimal loss of the therapeutic compounds, if an adequate treatment procedure is selected based on the water composition.

Site preferences and ion dynamics in lithium chalcohalide solid solutions with argyrodite structure: II. Multinuclear solid state NMR of the systems Li6PS5−x Se x Cl and Li6PS5−x Se x Br

A comprehensive multinuclear (7Li, 31P, 35Cl, 77Se, 79Br) nuclear magnetic resonance (NMR) study has been conducted to characterize local structural configurations and atomic distributions in the crystallographically disordered solid solutions of composition Li6PS5−x Se x X (0 ≤ x ≤ 1, X = Cl, Br) with the Argyrodite structure. In contrast to the situation with the corresponding iodide homologs, there is no structural ordering between the 4a and 4c sites, with the halide ions occupying both of them with close to statistical probabilities. Nevertheless, throughout the composition range, the 16e Wyckoff sites of the Argyrodite structure are exclusively occupied by the chalcogen atoms, forming PY4 3− (Y = S, Se) tetrahedra, indicating the absence of P-halogen bonds. 31P magic-angle spinning (MAS)-NMR can serve to differentiate between the various possible PS4−n Se n 3− tetrahedral units in a quantitative fashion. Compared to the case of the anion-ordered Li6PS5−x Se x I solid solutions, the preference of P–S over P–Se bonding is significantly stronger, but it is weaker than in the halide free solid solutions Li7PS6−x Se x . Each individual PS4−n Se n 3− tetrahedron is represented by a peak cluster of up to five resonances, representing the five different configurations in which the PY4 3− ions are surrounded by the four closest chalcogenide and halide anions occupying the 4c sites; this distribution is close to statistical and can be used to deduce deviations of sample compositions from ideal stoichiometry. Non-linear 7Li chemical shift trends as a function of x are interpreted to indicate that the Coulombic traps created by sulfur-rich PS4−n Se n 3− ions (n ≤ 2) within the energy landscape of the lithium ions are deeper than those of the other anionic species present (i.e., selenium-richer PY4 3− tetrahedra, isolated chalcogenide or iodide ions), causing the Li+ ions to spend on average more time near them. Temperature dependent static 7Li NMR linewidths indicate higher mobility in the present systems than in the previously studied Li6PS5−x Se x I solid solutions. Unlike the situation in Li6PS5−x Se x I no rate distinction between intra-cage and inter-cage ionic motion is evident. Lithium ionic mobility increases with increasing selenium content. This effect can be attributed to the influences of higher anionic polarizability and a widening of the lithium ion migration pathways caused by lattice expansion. The results offer interesting new insights into the structure/ionic mobility correlations in this new class of compounds.

Site preferences and ion dynamics in lithium chalcohalide solid solutions with argyrodite structure: I. A multinuclear solid state NMR study of the system Li6PS5-xSexI and of Li6AsS5I

A comprehensive multinuclear (7Li, 31P, 75As, 77Se, 127I) NMR study has been conducted to characterize local structural configurations and atomic distributions in the crystallographically ordered solid solutions of composition Li6PS5-x Se x I (0 ≤ x ≤ 1) and in Li6AsS5I. Throughout the composition range, structural ordering between the atoms on the Wyckoff sites 4a and 4c is maintained, with the I− ions exclusively occupying the 4a sites. 31P magic-angle spinning nuclear magnetic resonance (MAS NMR) can serve to differentiate between the various possible PS4-n Se n 3− tetrahedral units in a quantitative fashion, indicating a preference of P-S relative to P-Se bonding. Each individual PS4-n Se n 3− tetrahedron is represented by a peak cluster containing up to five resonances, representing the five different configurations in which the PCh4 3− units are surrounded by the four closest chalcogenide anions occupying the 4c sites; the distribution of S2− and Se2− over these sites is close to statistical. Non-linear 7Li chemical shift trends as a function of x are interpreted to indicate that the Coulombic traps created by sulfur-rich PS4-n Se n 3− ions (n ≥ 2) within the energy landscape of the lithium ions are deeper than those of the other anionic species present (i.e. selenium-richer PCh4 3− tetrahedra, isolated chalcogenide or iodide ions), causing the Li+ ions to spend on average more time near them. Temperature dependent static 7Li NMR linewidths measured on Li6PS5I and Li6AsS5I indicate a two-step motional narrowing process characterized by a clear dynamic distinction between a more rapid localized intra-cage process and a slower, long-range inter-cage process. In the solid solutions this differentiation gradually disappears, leading to an overall increase of lithium ionic mobility with increasing selenium content, which can be attributed to the influences of higher anionic polarizability and a widening of the lithium migration pathways caused by lattice expansion. Furthermore, the low-temperature phase transition in Li6PS5I, which tends to immobilize the lithium ions below 170 K, is suppressed in the solid solutions. The results offer interesting new insights into the -structure/ionic mobility correlations in this new class of compounds.

Unidirectional ion transport mechanism of a light-driven chloride pump revealed using X-ray free electron lasers

Light-driven chloride-pumping rhodopsins actively transport anions, including various halide ions, across cell membranes. Recent studies using time-resolved serial femtosecond crystallography (TR-SFX) have uncovered the structural changes and ion transfer mechanisms in light-driven cation-pumping rhodopsins. However, the mechanism by which the conformational changes pump an anion to achieve unidirectional ion transport, from the extracellular side to the cytoplasmic side, in anion-pumping rhodopsins remains enigmatic. We have collected TR-SFX data of Nonlabens marinus rhodopsin-3 (NM-R3), derived from a marine flavobacterium, at 10 µs and 1 ms time-points after photoexcitation. Our structural analysis reveals the conformational alterations during ion transfer and after ion release. Movements of the retinal chromophore initially displace a conserved tryptophan to the cytoplasmic side of NM-R3, accompanied with a slight shift of the halide ion bound to the retinal. After ion release, the inward movements of helix C and helix G and the lateral displacements of the retinal block access to the extracellular side of NM-R3. Anomalous signal data have also been obtained from NM-R3 crystals containing iodide ions. The anomalous density maps provide insight into the halide binding site for ion transfer in NM-R3.