Alison HealyRadon gas now accounts for up to 200 deaths a year and is the second-highest cause of lung cancer after smoking, according to the Radiological Protection Institute of Ireland (RPII).
The institute has urged all householders to check their radon levels, particularly households in high-radon areas.
About a third of the State is now classified as a high-radon area, with known "hot spots" in counties including Kerry, Louth, Sligo, Galway, Wicklow, Wexford and Kilkenny.
Radon gas is formed by the radioactive decay of uranium, which is present in rock and soil.
Dr Ann McGarry, RPII's chief executive, said radon was "a serious risk to health" and she urged householders to take immediate steps if they found high radon levels. She was speaking at the national radon forum which was held in Dublin yesterday. It coincided with the launch of the RPII's annual report for 2003.
Two small radon-sensitive detectors can be placed in the house for three months to check levels. New regulations were introduced in July 1998 to ensure that all new buildings had radon preventative measures.
Studies in Tralee and Ennis before and after the introduction of the regulations found that radon concentration fell by about 50 per cent.
Dr McGarry said this was welcome but warned that a radon barrier could be ineffective if installed incorrectly.
Radon gas can enter buildings through holes or imperfections in the radon barrier. It then produces radioactive particles which can be inhaled. They attach themselves to lung tissue and may eventually cause lung cancer.
Dr McGarry referred to a case publicised last year where a house in Castleisland, Co Kerry, was found to have radon concentrations almost 250 times higher than the national reference level for radon in homes.
"This radon concentration is by far the highest level ever measured in Ireland and is one of the highest values ever recorded in Europe," she said.
The householder had been diagnosed with lung cancer and his wife had died at a young age from the disease. Dr McGarry said it was not possible to draw specific conclusions from this, but said there was a 30 to 70 per cent risk of contracting lung cancer if lifetime exposure was at such high levels.
The institute's report highlights last year's survey which found unacceptably high levels of radon in water supplies in Co Wicklow.
Levels were so high in one Wicklow well that the water gave those who drank it eight times the permitted radiation dose for workers at the Sellafield nuclear reprocessing plant.
Information on radon gas and maps of high risk areas can be found on the RPII's website www.rpii.ie