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Thoron

Understanding thoron

The National Thoron Survey

FAQs on the National Survey

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 can’t 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. According to a 2024 report, people in Ireland are exposed to about 0.35 millisieverts (mSv) of radiation from thoron each year. That’s about 8.4% of the total radiation dose the average person receives annually (See diagram below). 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 running a survey to measure thoron levels in homes across Ireland. If you received a leaflet, you’re invited to take part. 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 also invited participants on social media to take part – the leaflet is available below if you’d like to view it. 

Download the National Thoron Survey Leaflet here.

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

FAQs on National Thoron Survey

  • Why was I selected?

    2,000 homes were randomly chosen using public data from the 2022 census from the Central Statistics Office (CSO).

  • If I got a leaflet and sign up, does that mean I’ll get a detector?

    We’ve invited 2,000 people, but only 250 homes will be chosen. Not everyone will accept the invitation, so there’s still a good chance you could be picked. If you're interested, we encourage you to take part! 

  • I signed up on social media, will I get selected?

    We will randomly choose some people from those who signed up online. If you’re not picked this time but said you’re interested in future surveys, you might be included in upcoming thoron and radon studies. 
     

  • When will I know if I have been selected?


    We’ll get in touch with you sometime in July to give you more details about delivering your detector. 

  • How long does the test take?

    For this survey, the test lasts 6 months (September 2025 – February 2026).  

  • What does the detector kit look like?

    The picture below shows the detector kit. It has two gas detectors—one for thoron and one for radon—joined together in a single unit. All you need to do is hang it up on your wall. 

    Detector kit hanging from a picture on a wall

     

  • Where should I place the detector kit?

    In the room you use most, like your bedroom, living room, or kitchen. Hang it on a wall near the building materials, using a hook or fixture. If you don’t have a suitable fixture, the EPA can provide temporary adhesive hooks. These hooks are designed to minimise damage and typically do not remove paint or wallpaper. However, we cannot guarantee this, so please use them at your own risk. 

     

  • How does the detector kit work?

    The detector kit is called ‘passive’ because it doesn’t need any power, like a battery, to work. It contains a special material inside that detect tiny gas particles from thoron and radon. These particles leave tiny marks, which are later measured in a lab to find out the levels in your home. 

  • 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.