Geothermal and Health: Evidence on Indoor Air, Thermal Exposure, and Geoscience-Linked Risks

Geothermal energy refers to heat derived from the Earth’s interior and converted into electricity or direct-use heating (e.g., district heating). From a public-health perspective, geothermal systems are not inherently therapeutic; however, geothermal development can create measurable health benefits and risks through pathways involving air emissions, water quality, land use, and occupational exposure. Understanding these pathways is essential because exposure patterns vary widely by site geology, technology (e.g., dry steam vs. flash steam vs. binary plants), and emission-control design.

Air quality is one of the most important determinants of health during geothermal operation. Geothermal reservoirs can release hydrogen sulfide (H2S), carbon dioxide (CO2), methane (CH4), ammonia, and trace gases such as mercury, boron compounds, or arsenic, depending on regional geology. Hydrogen sulfide is the most health-relevant irritant and toxicant in many geothermal settings. At low concentrations it can cause eye and throat irritation, headache, and nausea; at higher or acute exposures it can inhibit cellular respiration and contribute to neurological injury. Clinically, symptom onset may include respiratory irritation followed by more severe manifestations such as pulmonary edema in significant exposures. Because H2S has a characteristic odor yet does not reliably protect against toxicity (olfactory fatigue can occur), risk is managed through continuous monitoring, dispersion modeling, and engineered controls.

Particulate matter (PM) can also arise from drilling, steam venting, or maintenance activities. Fine particles can exacerbate asthma and other chronic lung diseases by promoting airway inflammation and oxidative stress. In addition, geothermal operations may influence local meteorology and dispersion, altering short-term pollutant concentrations. Epidemiologically, the best evidence often comes from occupational cohorts and community air-monitoring studies with exposure assessment, rather than direct clinical trials.

Water quality and water-contact hazards represent another key pathway. Geothermal brines may contain dissolved constituents such as arsenic, boron, antimony, radium isotopes, and salts. If reinjection and containment are inadequate, these substances can contaminate groundwater or surface waters. Health impacts can occur through ingestion (e.g., chronic arsenic exposure linked to skin lesions and increased risks of certain cancers) or through dermal/contact exposures. For communities, health protection typically depends on hydrogeologic characterization, rigorous well integrity testing, and treatment or containment standards for any produced water that is not fully reinjected.

Surface emissions and handling of brines can increase occupational exposure risk. Workers may face inhalation of H2S and other gases, skin and eye exposure to geothermal fluids, and thermal stress from hot surfaces or steam. Occupational medicine frameworks emphasize hazard identification, exposure measurement (personal sampling), and risk reduction using engineering controls, safe work practices, and appropriate respiratory protection. For H2S exposure, gas detection systems, alarm thresholds, and rescue protocols are standard components of a comprehensive safety management system.

Thermal exposure itself can affect health through heat stress mechanisms. Heat stress leads to impaired thermoregulation, dehydration, and strain on the cardiovascular system, particularly in high ambient temperatures or in work environments near hot steam lines. Clinical risk rises with prolonged shifts, inadequate hydration, and limited acclimatization. Prevention includes administrative controls (work-rest cycles), hydration plans, heat illness training, and personal protective equipment designed for thermal hazards.

Geothermal development may also influence mental health indirectly through perception of risk, odor nuisance, and community engagement dynamics. Odor complaints related to H2S can produce anxiety, sleep disturbance, and stress-related outcomes even when measured concentrations are low or intermittent. Public-health interventions therefore benefit from transparent communication, real-time monitoring dashboards where appropriate, and community-based risk assessment to address both objective exposure and subjective burden. Stress physiology—mediated through sympathetic activation and hypothalamic-pituitary-adrenal (HPA) axis pathways—can contribute to insomnia and worsened cardiometabolic risk in vulnerable populations.

Overall, the health impact of geothermal energy is best conceptualized as a site-specific risk-benefit profile shaped by emissions chemistry, containment performance, and monitoring. Evidence supports that modern geothermal facilities with appropriate engineering controls can reduce hazardous emissions and prevent brine migration, thereby limiting community exposure. Continued research using refined exposure modeling, biomarker approaches, and longitudinal study designs can further clarify chronic low-level effects, if any, and guide best practices.

For risk mitigation, a robust program typically includes baseline environmental health assessments; continuous gas and air quality monitoring (especially H2S); well integrity assurance and reinjection management; water testing for key geochemical hazards; occupational respiratory and thermal safety protocols; and community risk communication. When these elements are implemented, geothermal energy can be managed in a way that protects respiratory health, reduces toxic exposure risk, and addresses mental well-being concerns related to odor and perceived hazards. Source: Department of Energy (Creator: @EpicPlain)