Thoron

Understanding thoron

What is Thoron?

Thoron is a naturally occurring radioactive gas, that comes from thorium found in rocks and building materials like concrete, brick, and granite. This means that thoron can be found in your home. It’s invisible, has no smell or taste, and can be harmful to your health, similar to radon.

Where Does Thoron Come From?

Because thoron decays (breaks down) quickly, the gas cannot travel through the foundations of the home, like radon can. The main source of thoron is from the materials used to build your home. The amount of thoron released from these building materials is typically very low.

Health Impact

When thoron decays, it releases particles that can damage your lungs and potentially cause lung cancer. The population of Ireland is exposed to about 0.35 millisieverts (mSv) of radiation from thoron each year. That is about 8.4% of the total radiation dose the average person receives annually. This estimate is based on a thoron survey conducted between 2007 and 2009. This data is available in the 2024 Ionising Radiation National Dose Report, which was published by the EPA and HIQA.

The National Thoron Survey

Why are we conducting a national thoron survey?

The EPA is currently running a survey to measure thoron levels in homes across Ireland. The goal is to:

Raise awareness about thoron.
Understand how much thoron is in Irish homes.
Identify homes that might be at higher risk.
Update the estimated exposure from thoron based on today’s population and types of homes.

We have completed the measurement phase of the survey in 250 homes. The detectors are now being analysed and participants will receive their results in summer 2026. The estimated national average exposure arising from thoron will be published in 2027.

If you'd like to contact us, please email us at: thoron@epa.ie.

FAQs on National Thoron Survey

I took part in the survey, when will the results be available?

Participants will receive their results in summer 2026.
What level of thoron in a house should give cause for concern?

There are currently no reference levels available in Ireland or internationally. The purpose of this survey is to gather data to help inform policy makers on any future guidelines or reference levels that might be set.
Should I worry if my levels are high?

Not unless the EPA contacts you directly and recommends action.
How can I reduce thoron?

Improve ventilation. Unlike radon, thoron comes from walls, so radon sumps or barriers won’t reduce the levels of thoron.