The objectives of this short paper are to provide an easy understanding of the sources of radioactivity in bottled water, the regulated limits of the components causing radioactivity, types of analyses required, risks to human health and remedial actions where necessary.
Putting Risks in Perspective
Drinking-water may contain radioactive substances (radionuclides) that could present a risk to human health. These risks are normally small compared with risks from microorganisms and chemicals that may be present in drinking-water. Except in extreme circumstances, the radiation dose resulting from ingestion of radionuclides in drinking-water is much lower than that received from other sources of environmental radiation. The United Nations Scientific Committee on the Effects of Atomic Radiation has estimated that the global average dose per person from all sources of radiation in the environment is approximately 3.0 mSv/year (the unit mSv is adopted as the measure of the effect of radiation on humans and is called “the Indicative Dose”). Of this, 80% (2.4 mSv) is due to naturally occurring sources of radiation. The maximum indicative dose set for drinking-water is just 0.1 mSv.
Indicative Dose for Drinking-water
The annual dose of 0.1 mSv for drinking-water is calculated from the alpha and beta particle levels in a sample of water taken at the point of filling and analysed at an accredited laboratory. Alpha particles are positively charged and emitted by an atomic nucleus undergoing radioactive decay. Beta particles are high speed electrons or positrons also emitted from an atomic nucleus undergoing radioactive decay. They give a total measure of radioactivity from a sample of water measured in units called Becquerels (Bq/l). The latest Directive (Council Directive 2013/51/EURATOM) sets out a procedure for demonstrating that doses from water supplies do not exceed 0.1 mSv per year (assuming a consumption rate of 730 litres per person per year). This calculation is based on maximum alpha and beta particle concentrations of 0.1 Bq/l and 1.0 Bq/l respectively.
However, the WHO is at odds with these maximum concentrations and indicates that the maximum limit should be 0.5 Bq/l and 1.0 Bq/l respectively. However, the EURATOM Directive will be put into the UK Regulations in November 2015, so we must comply with the lower figure for alpha particles.
Annual Water Analysis
Those companies producing between 100 and 1000 cubic metres of water daily must have an annual water analysis which includes alpha and beta particle concentrations. If the values are less than 0.1 Bq/l and 1.0 Bq/l respectively, the indicative dose will calculate out at less than 0.1 mSv and no further action is necessary. However if these values are exceeded, further analyses are required to determine repeatability and, if repeatable, analysis for other radionuclides must be done to determine the cause. Many radioactive isotopes are naturally occurring, such as uranium and radium, which can contribute to high alpha particle readings. Once identified, these materials can be eliminated by appropriate water treatment processes.
The additional risk to health from exposure to an annual dose of 0.1 mSv associated with intake of radionuclides from drinking-water is considered to be low. Individual doses from natural activity in the environment vary widely. The average is about 2.4 mSv/year, but in some parts of the world, average doses can be up to 10 times higher without any observed increase in health risks, as noted in long-term population studies. An indicative dose of 0.1 mSv/year therefore represents a small addition to natural levels.
The nominal risk coefficient for radiation-induced cancer is 5.5 x 10-2/Sv. Multiplying this with an indicative dose of 0.1 mSv/year from drinking-water gives an estimated annual cancer risk of approximately 5.5 x 10-6.
It should be clearly explained that guidance levels should not be interpreted as mandatory limits and that exceeding a guidance level may be taken as a trigger for further investigation, but it is not necessarily an indication that drinking-water is unsafe.
Recommendations and Going Forward
In the event that that alpha/beta particle results are consistently high, identification of the radionuclides causing this is necessary to enable remedial action. For common radio nuclides which occur naturally, water treatment processes are available to remove them. For example, uranium and radium can be removed by precipitation softening, ion exchange or reverse osmosis. It may be possible to treat only part of water source and then blend it with untreated water to bring down levels to an acceptable level.
The new Directive will come into force in English Law in November 2015. This will require an indicative dose of 0.1 mSv from 1 year’s consumption of drinking-water. Initial screening has to be undertaken for alpha and beta activity on a yearly basis. If below the levels of 0.1 Bq/l and 1.0 Bq/l, respectively, no further action to be taken. If either of the screening levels is exceeded, the concentration of individual radionuclides has to be determined. The outcome of this further evaluation will determine what further measures will be needed to reduce the dose, such as further water treatment processes.
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