Handbook of Radon.
35. Radon in water: health risks in perspective.
Radon is soluble in water, and in some areas ground water contains very high concentrations. In Devon over one million Bq/m3 was measured in the 1960s, and a couple of central treatment plants are operative.
When water is used for domestic purposes a fraction of the radon in the water will be released into the indoor air. A rule of thumb in the USA is that if water containing 10,000 pCi/l of radon is used in a house it will add 1 pCi/l (37 Bq/m3) to indoor levels. Water used for drinking is thought to pose little risk.
The issue of radon in water, and how it has been addressed in the USA, illustrates what may happen when legislation drafted to deal with one set of problems is applied elsewhere.
The USA has a Safe Drinking Water Act the aim of which is to limit the concentration of any contaminant in drinking water down to a very low risk level. What was in mind here was chemical contamination of drinking water from toxic waste dumps and industrial plants.
Often the level of risk above which action is taken is of the order of 10-4 to 10-5, expressed on a lifetime basis. These are very small risks, but use of the same criteria for radon leads to an action level for radon in water of 200 pCi/l. If water containing 200 pCi/l (7500 Bq/m3) is used in a house it will add only about 0.75 Bq/m3 to the radon level in the indoor air. This is 10% or less of the level present in the outdoor air in many parts of the USA.
In comparison, the US action level for radon in air from ground sources is 150 Bq/m3, close to the UK figure of 200 Bq/m3, although the long term goal set by Congress in the USA is that indoor radon levels should be no higher than those outdoors (which is another story).
What has happened here is that whereas a technology standard has been set for radon in air derived from ground sources, a previously existing health standard has been used for radon in air derived from radon in water. There is something of an apparent paradox, especially for homeowners who draw their water from small private systems and where the cost of meeting a 200 pCi/l level could be quite high on a per-house basis and where money might be better spent in preventing radon entering directly from the ground.
The straightforward logic is that if you can remove a small risk for a small cost, or a moderate risk for a moderate cost, using central funds and a central treatment works, then it may be logical to take action. But for an individual householder, (or a small group of householders) faced with costs of remediation the 300 pCi/l standard recently promulgated in the USA appears ridiculous, despite that it is likely to be limited to wells serving 25 or more people. There has been some debate between the sections of the EPA responsible for setting standards for radon in air and in water.
Care should be taken to classify issues correctly, or there is a danger of mis-allocation of resources to address problems that have been taken out of perspective. In the simplest of terms, the Safe Drinking Water Act in the USA limits chemical pollutants to such a low level that by comparison, radon in fresh air is calculated to be quite dangerous.
There are very few known problems with radon in water in the UK. In one or two areas of Devon, water is held in storage tanks, or subjected to aeration or other treatment, to ensure removal of dissolved radon before supply to consumers. Radon in water need never become an issue for widespread concern in the UK.
Many risk factors are calculated: it may be that there is no risk at all from many pollutants at low levels. Scientists do not know, and some will even admit to their uncertainty. This seems not to prevent inordinate expenditure on some small problems.
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