Health risk profiles of heavy metals and radionuclides in geothermal waters and groundwater, Kanchanaburi Province, Thailand: An interannual comparative baseline assessment

Geothermal systems of Kanchanaburi Province in western Thailand constitute important hydrothermal resources yet represent potential reservoirs of geogenic contaminants. Despite increasing utilization, the combined health risks posed by heavy metals and naturally occurring radionuclides under variable hydrogeochemical conditions remain poorly understood. This study presents an integrated, interannual comparative assessment of trace constituents in major geothermal springs and adjacent groundwater, based on datasets collected in November 2023 and November 2024. The analytical results indicate persistent localized contamination, with mercury (Hg) and radium-226 (Ra-226) exceeding Thai regulatory standards and WHO drinking water guidelines at specific thermal sites. Health risk modeling for adult receptors revealed a distinct interannual shift in the risk profile. In 2023, non-carcinogenic risks were unacceptable (Hazard Index >1), primarily driven by Hg toxicity. Conversely, in 2024, while non-carcinogenic risks declined, carcinogenic risks (CR) increased to unacceptable levels (CR > 1 × 10⁻⁴), driven by the elevated presence of arsenic (As). These findings demonstrate that static, single-point assessments may inadequately characterize for managing geochemically complex systems. Consequently, periodic monitoring strategies are essential to safeguard public health against such interannual variations in toxicological threats.