ONE-in-four homes tested in a single county for the cancer-causing radon gas have readings above "safe" levels, it was disclosed yesterday.
Researchers who checked over 1,000 properties in Co Sligo found that 24pc of them had dangerous levels of the gas, which has been linked to 200 lung-cancer deaths each year.
And yesterday, the Radiological Protection Institute of Ireland (RPII) said just 5pc of all Irish homes believed to have high levels of the gas have been identified.
Radon is a naturally occurring radioactive gas produced when uranium decays in rocks and soils. It seeps up though the foundations of older homes and has no smell, colour or taste.
Houses built since July 1998 must have a radon sump in place, which allows the gas to be 'sucked out' of the building if high readings are recorded.
In high-radon areas, including Sligo, Waterford, Galway, Carlow, Wicklow, Mayo and Wexford, a radon barrier must also be in place.
The large number of Sligo properties with high levels of radon was because more properties in that county were tested than any other.
The RPII says that even if a sump or barrier is in a house, homeowners living in high-radon areas should still have levels checked to ensure the gas is not present.
Yesterday, it said just under 5,000 properties across the country have been tested and found to be above safe levels, but up to 91,000 homes and businesses could be affected.
The RPII said that counties in the west, south-east and south are returning the highest rates of homes with high-radon levels.
There is no county without a home with a high level, it said, and in Sligo almost one-in-four homes tested last year were above acceptable levels.
The readings come after homeowners sent radon detectors back to the RPII, which analysed the results and found the high readings.
In Waterford, Galway, Carlow, Wicklow, Mayo and Wexford, the rate is greater than 15pc.
Ten of the 15 highest individual measurements have been found in Kerry, around Tralee and Castleisland, and the county has an overall rate of 14pc of tested homes that are above the acceptable level.
"Many people are unknowingly living with dangerous levels of radiation," RPII chief executive Dr Ann McGarry said. "Homeowners, especially those in high-radon areas, need to take this matter seriously and measure radon levels in their homes to ensure that they and their families are not at risk."
Since beginning a measurement programme in the early 1990s, the RPII has tested almost 38,000 homes.
By the end of last year, just over 5pc (4,922) of around 91,000 homes above the national 'safe' level had been identified.
Measuring for radon and, in the event of a high reading, reducing the levels, are both relatively inexpensive.
To test for radon, a radon detector is placed in a bedroom and a second in a living room for a three-month period. The detectors are small and can be sent and returned by post for analysis. The RPII and a number of private companies provide a radon-measurement service. The cost of a measurement is between €40 and €80.
The RPII said that its website (www.rpii.ie) allows people to search their address on an interactive radon map to see if their home or workplace is in an area where high radon levels have been found. Information can also be obtained on freefone 1800 300 600.