Physicochemical and microbial characteristics of medicinal groundwater at Sobranecké Spa, a Slovakian heritage site: Implications for balneotherapy

The Sobranecké Spa (“Salus per Aquam”) is historically known for its therapeutic mineral waters and recognized as a heritage site for its cultural significance. Despite its rich tradition and well-documented therapeutic effects, the spa ceased operations in 2004 and now remains in disrepair. However, renewed interest from the Košice self-governing region has prompted efforts to restore its activity. To support this initiative, a hydrogeological study was commissioned by the Technical University of Košice to provide a comprehensive assessment of the physical, chemical, and microbial properties of the mineral water and evaluate health risks related to dermal exposure. The study integrates hydrochemical classification, microbial assessment, and probabilistic risk analysis using Monte Carlo simulation and Sobol sensitivity analysis to evaluate dermal absorption dose (DAD), dermal hazard quotient (HQ) and hazard index (HI) for both adults and children. Hydrochemical results indicated a Na-Cl-type highly mineralized water, shaped by mineral dissolution and ion exchange processes. The microbial analysis focused on coliforms, Escherichia coli, and heterotrophic bacteria to assess potential biological risks. The results showed individual hazard quotients below 1 for most parameters, but H2S drove cumulative hazard index values to 9.5 for adults and 12.1 for children, with children facing 28 % higher risk and persistent dermal health concerns across all scenarios. However, the findings confirm that the mineral waters meet Slovak and European standards for therapeutic use. Due to the study’s single sampling event, long-term seasonal monitoring is recommended to ensure water quality stability and safety for future spa use.