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<p>Geothermal systems are typically characterized by high-temperature and high-fluoride properties, increasing attention is focused on their environment impacts, yet understanding of fluoride enrichment mechanisms in the Qiabuqia geothermal system (Gonghe Basin, Qinghai, China) remains limited. This study collected 39 geothermal water samples from the Qiabuqia Geothermal Field. Hydrogeochemical and isotopic analyses were conducted to investigate these mechanisms, providing fundamental insights into the geochemical processes governing fluorine distribution patterns. Shallow geothermal waters (GWQ) exhibited a Cl–SO<sub>4</sub>·Na hydrochemical type, with a mean fluoride concentration of 0.9&#xa0;mg/L and an exceedance rate of 25.7%. In contrast, deep geothermal waters (GWN) were predominantly characterized by a Cl–HCO<sub>3</sub>·Na hydrochemical type, showing significantly elevated fluoride levels (average 4.2&#xa0;mg/L) with a 100% exceedance rate against the WHO drinking water standard (1.5&#xa0;mg/L). Hydrogen (δD) and oxygen (δ<sup>18</sup>O) isotopic compositions of GWQ cluster along the Global Meteoric Water Line (GMWL), indicating their predominant recharge sources originate from surface water and atmospheric precipitation. The GWN exhibited significant hydrogen–oxygen isotope anomalies characterized by δ<sup>18</sup>O enrichment, indicating their recharge sources originate from both vertical leakage of adjacent aquifers and long-distance groundwater migration through regional deep-seated fault systems that serve as dominant conduits for deep hydrothermal circulation. Fluoride enrichment is governed by a combination of thermal controls, mineral dissolution–precipitation equilibria, cation exchange processes, and competitive adsorption mechanisms, reflecting the coupled physicochemical interactions within the hydrothermal system. Quantitative assessment leveraging the Random Forest (RF) algorithm revealed the relative contributions to enrichment: mineral dissolution–precipitation (38%), cation exchange processes (29%), thermal regime (25%), and competitive adsorption (7%), based on feature importance analysis of the hydrogeochemical dataset. The hazard quotient (HQ) assessment for geothermal water exposure revealed distinct risk gradients across population groups: infants exhibited the highest potential health risk at 47%, followed by children (36%), adult males (32%), and adult females (24%), based on the USEPA exposure model accounting for body weight differentials and ingestion rates. Findings not only advance our understanding of this field, but also provide a scientific basis for the rational exploitation of geothermal energy and environmental protection.</p> Graphical Abstract <p></p>

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Formation mechanism and health risk assessment of high fluoride geothermal water in Gonghe Basin, Northwest China

  • 期刊论文

  • 发表日期：

    2025年11月15日

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  • Jianqiang Chen,
  • Zhen Wang,
  • Yongge Li,
  • Haiyan Liu,
  • Yu Yang,
  • Narsimha Adimalla,
  • Chuanshun Zhi,
  • Bo Wang

摘要

Geothermal systems are typically characterized by high-temperature and high-fluoride properties, increasing attention is focused on their environment impacts, yet understanding of fluoride enrichment mechanisms in the Qiabuqia geothermal system (Gonghe Basin, Qinghai, China) remains limited. This study collected 39 geothermal water samples from the Qiabuqia Geothermal Field. Hydrogeochemical and isotopic analyses were conducted to investigate these mechanisms, providing fundamental insights into the geochemical processes governing fluorine distribution patterns. Shallow geothermal waters (GWQ) exhibited a Cl–SO4·Na hydrochemical type, with a mean fluoride concentration of 0.9 mg/L and an exceedance rate of 25.7%. In contrast, deep geothermal waters (GWN) were predominantly characterized by a Cl–HCO3·Na hydrochemical type, showing significantly elevated fluoride levels (average 4.2 mg/L) with a 100% exceedance rate against the WHO drinking water standard (1.5 mg/L). Hydrogen (δD) and oxygen (δ18O) isotopic compositions of GWQ cluster along the Global Meteoric Water Line (GMWL), indicating their predominant recharge sources originate from surface water and atmospheric precipitation. The GWN exhibited significant hydrogen–oxygen isotope anomalies characterized by δ18O enrichment, indicating their recharge sources originate from both vertical leakage of adjacent aquifers and long-distance groundwater migration through regional deep-seated fault systems that serve as dominant conduits for deep hydrothermal circulation. Fluoride enrichment is governed by a combination of thermal controls, mineral dissolution–precipitation equilibria, cation exchange processes, and competitive adsorption mechanisms, reflecting the coupled physicochemical interactions within the hydrothermal system. Quantitative assessment leveraging the Random Forest (RF) algorithm revealed the relative contributions to enrichment: mineral dissolution–precipitation (38%), cation exchange processes (29%), thermal regime (25%), and competitive adsorption (7%), based on feature importance analysis of the hydrogeochemical dataset. The hazard quotient (HQ) assessment for geothermal water exposure revealed distinct risk gradients across population groups: infants exhibited the highest potential health risk at 47%, followed by children (36%), adult males (32%), and adult females (24%), based on the USEPA exposure model accounting for body weight differentials and ingestion rates. Findings not only advance our understanding of this field, but also provide a scientific basis for the rational exploitation of geothermal energy and environmental protection.

Graphical Abstract