COMARE Statement on Radon in Private Water Supplies

Under contract to the Department of the Environment, Transport and the Regions (DETR), the British Geological Survey (BGS) investigated the concentrations of various naturally-occurring radioactive elements in private drinking water supplies in the Tavistock area. The BGS study involved sampling 128 private water supplies and analysing for radon-222, radium-226, uranium-238 and thorium-232. Three supplies with very high radon concentrations were also analysed for polonium-210, a daughter of radon-222. High concentrations of radon-222 were observed in over 50% of the samples analysed and measurable concentrations of the other radionuclides were also found in many of the samples. BGS examined the possibility of losses of radon-222 during pouring and boiling. Experiments undertaken by BGS suggested that losses of radon-222 during pouring could amount to around 10%, while additional losses from boiling amounted on average to just over 70%.

In view of the magnitude of the estimated doses, DETR has requested advice from Department of Health (DH) and the Committee on Medical Aspects of Radiation in the Environment (COMARE) on the health implications of the measured levels of natural radionuclides in the private drinking water supplies. As a next stage the DH requested from the National Radiological Protection Board (NRPB) an assessment of possible doses and risks from ingestion of the drinking water. In undertaking the assessment, NRPB used the measurement data from the BGS report for the location with the highest radon-222 concentration. The corresponding calculated annual average concentration of radon-222 in tap water was 6500 Becquerels per litre (Bq l^-1). Annual effective doses from ingestion of drinking water, assuming losses during pouring and boiling as reported by BGS, ranged up to around 40 mSv to an infant and about 20 mSv to an adult. Assuming total loss of radon-222 during boiling resulted in lower ingestion doses of around 27 mSv and 14 mSv to an infant and adult, respectively. The additional assessed contribution from the other radionuclides measured in water is small at less than 0.1 mSv per year. However, NRPB also considered possible doses arising from inhalation of radon-222 released from the water to air and estimated that this could give rise to an additional annual dose of around 30 mSv.

NRPB has suggested that the draft recommendations of the EU provide an appropriate basis for radiological limitation, and therefore that consideration is given to reducing doses where radon levels in private supplies exceed 1000 Bq l^-1. NRPB has also suggested that further measurements are taken in order to delineate the scale of the problem and that further investigations are undertaken on losses from radon-222 during boiling as this can have a significant impact on the estimate of doses.

The risk to health from consumption of drinking water containing a radon-222 concentration of 1000 Bq l^-1 is similar to the risk from exposure to radon-222 in air at the Action Level of 200 Bq m-3. Lifetime exposure at this level is estimated to result in a lifetime risk of fatal cancer of around 3 to 5% for the general public (this will vary between a value of 1-15% depending on whether an individual is a smoker or non-smoker).

COMARE was asked whether risks to health are such that householders should be advised to reduce high radon levels in private water supplies and whether the committee concurs with the proposed Action Level of 1000 Bq l^-1 and agrees that it provides an appropriate basis for taking such action.

National Radiological Protection Board (NRPB) Assessment Report on Radon in Private Drinking Water Supplies

COMARE Statement on Radon in Private Water Supplies

The Committee notes that a number of sites have been identified in the DETR-funded research into private water supplies in south-west England with radon in water levels above the proposed action level of 1,000 Bq/l, in some cases significantly above. On the basis of our current understanding, such levels would be expected to pose a significant additional health risk, in the longer term, to those consumers who depend upon the supplies as their primary source of household water. The Committee recommends that the owners and users of these water supplies should be informed of the results obtained with minimal delay, and that they should be advised on what action they can take in order to reduce their radon intake.

COMARE is concerned that members of the public should have adequate information when choices have to be made about the acceptability of their drinking water supply. We welcome the proposal for an action level but stress that it should not be taken to imply that elevated radon levels below the action level are completely safe. While the health risk from radon in drinking water is not massive, it is unnecessary and easily preventable. Those with private water supplies in high radon areas should be encouraged to take steps to eliminate radon between source and tap, as occurs with public supplies.

The logic behind the proposed action level of 1,000 Bq/l for radon in water is that it would broadly correspond to the risk posed to non-smokers by the action level for radon in air (200 Bq/m³). To put the radiation doses in some sort of perspective, we note that the proposed action level of 1,000 Bq/l for radon in water would (according to the NRPB's assessment) result in annual doses of 7 to 11 mSv for adults and 9 to 23 mSv for infants. These doses include a not insignificant contribution from radon that escapes from water into room air and is subsequently inhaled. These doses are, of course, in addition to those doses received from background radiation, which in the UK are, on average, about 2-3 mSv a year from all sources of radiation. For comparison the dose limit for exposure of the general public from regulated practices, (which does not apply to naturally occurring radon) is 1 mSv.

Lifetime exposure to the action level for radon in air has been estimated to entail an additional lung cancer risk of 1-3% for non-smokers and 10-15% for smokers. Exposure to the proposed action level for radon in drinking water as the principal source of water for a lifetime might be expected to lead to an additional cancer risk of between 1% and 3% for smokers and non-smokers alike, depending on the effectiveness with which boiling eliminates radon.

The research results obtained in one local authority area in Southwest England are unlikely to be unique. The Committee recommends that further work be carried out to identify other parts of the country where private water supplies are liable to be affected. Additional sampling and measurement should then be carried out in order to determine the extent to which elevated levels of radon in water are a problem in those parts of the country. In addition, there is a need for further work to determine the most effective way to purge radon from small private water supplies. There is, for example, an obvious inconsistency among reports on the effectiveness of simple boiling.

Whilst the Committee recommends that the further work outlined above should be carried out to determine the extent and significance of the problems associated with radon in water, there should be no diminution of efforts to reduce radon in air levels. Radon in air presents a greater hazard than radon in water, certainly in terms of the number of people exposed to high levels, and probably in terms of the maximum risk. Indeed, it should not be forgotten that high levels of radon in a private water supply would be expected to show at least some association with high levels in domestic air and the latter would pose a health burden independent of and additional to that posed by radon in water.

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