Study first to link geothermal gas to asthma.

May 09, 2012

Carlsen, HK, H Zoëga, U Valdimarsdóttir, T Gíslason and B Hrafnkelsson. 2012. Hydrogen sulfide and particle matter levels associated with increased dispensing of anti-asthma drugs in Iceland's capital.  Environmental Research


Adults exposed to low levels of a toxic gas released by natural and industrial sources may experience wheezing, coughing and asthma attacks that require medication, finds a three-year study in Iceland. This is one of the first studies to find a connection between hydrogen sulfide – best known for its rotten egg smell – and respiratory health effects.

In this study, the hydrogen sulfide originated outside the capital city of Reykjavik where underground steam containing the gas is captured to generate heat and electricity. In other places, industrial sources can emit the gas.



Hydrogen sulfide is a toxic gas released naturally and from industrial sources. Its characteristic rotten egg odor can be smelled at very low concentrations (ATSDR 2006).

Certain bacteria produce hydrogen sulfide as they decompose waste matter. It also occurs in some geologic formations, especially geothermal situations. Hot water, steam and magma from inside the Earth carry heat, minerals and gases – like hydrogen sulfide – to the surface, liberating them in springs, geysers and volcanic lava.

In locations with rich geothermal resources such as Iceland, New Zealand, and Hawaii, the steam heat is harnessed to generate power and warm buildings. These power facilities also release low levels of hydrogen sulfide into the air.

More common industrial sources of hydrogen sulfide include oil drilling and refineries, paper mills, large scale livestock production, waste water treatment and landfills (ATSDR 2006). Like the natural sources, low hydrogen sulfide concentrations are measured in the air in communities near these industries (Wing et al. 2008; Heaney et al. 2011).

Hydrogen sulfide can cause serious neurologic damage – including death – at high levels that typically occur only in industrial settings. Lower levels can trigger eye irritation, fatigue and headaches (ATSDR 2006).

Exposure to hydrogen sulfide is not typically associated with respiratory disease, though one previous study found self-reported difficulty breathing associated with hydrogen sulfide levels near industrial livestock production (Schinasi et al. 2011).

What did they do?

Researchers compared respiratory illness in adults to daily air pollution levels in Reykjavik, Iceland.

They measured respiratory illness by counting the number of adults who filled prescriptions for asthma-related drugs each day between March 2006 to December 2009. The researchers gathered the information from a national health database that was limited to adults living near the capital city, which has a population of about 160,000.

Monitors next to a busy intersection measured levels of air pollutants in Reykjavik, including hydrogen sulfide produced by geothermal facilities outside the city. Several traffic-related pollutants were also measured: ozone, nitrogen dioxide and particulate matter less than 10 micrometers in diameter (PM10). An estimated 70,000 cars pass through the crossroads every day.

Air pollution exposures can have delayed health impacts, so researchers calculated average air pollution exposures for up to two weeks prior to each day prescriptions were counted. Both short-term peaks in air pollution and longer averages were considered.

What did they find?

One-hour peaks in traffic pollutants were most consistently associated with increases in the number of adults filling prescriptions for asthma medications. Interestingly, however, increases in the daily averages for hydrogen sulfide were also associated with the number of adults filling prescriptions.

For both types of pollutants, increases in the number of adults filling prescriptions most commonly occurred 3-5 days after increased exposures. This effect might not be observed immediately because it takes a few days to finish medication on hand before ordering more.

These effects were observed even in a city considered to have good air quality. Daily averages for ozone and nitrogen dioxide rarely surpassed the health limits set by the Icelandic government, and this also occurred infrequently for hydrogen sulfide. Only levels of particulate matter frequently surpassed health limits.

What does it mean?

This is one of the first studies to show that exposure to low levels of hydrogen sulfide is associated with poor respiratory health, as shown by the number of people filling asthma medications in the days that follow. Prior studies with workers receiving higher exposures to the gas have shown mainly neurologic effects.

More research is needed to understand whether these results are due to hydrogen sulfide directly or other unmeasured pollutants released simultaneously from geothermal power facilities.

This study also supports previous findings that traffic-related pollutants are detrimental to respiratory health.

Finally, these results indicate that short peaks in air pollutants may cause more respiratory harm than longer averages. Further study of health effects from air pollution peaks compared with longer averages would help to better understand this difference and inform regulations to protect public health.


Agency for Toxic Substances and Disease Registry (ATSDR). 2006. Toxicological profile for hydrogen sulfide (Update). Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

Heaney CD, S Wing, RL Campbell, D Caldwell, B Hopkins, D Richardson and K Yeatts. 2011. Relation between malodor, ambient hydrogen sulfide, and health in a community bordering a landfill. Environmental Research

Schinasi, L, RA Horton, VT Guidry, S Win, S Marshall and K Moreland. 2011. Air pollution, lung function and physical symptoms in communities near concentrated swine feeding operations. Epidemiology

Wing, S, RA Horton, SW Marshall, K Thu, M Tajik, L Schinasi and SS Schiffman. 2008. Air pollution and odor in communities near industrial wwine operations. Environmental Health Perspectives



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