Radioactivity in Bottled Water

Objectives

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.

Risk Analysis

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.

Conclusion

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.

Water Dispenser Sanitisation - How to Make it Cost Effective

Definition

It is important to understand the definition of “sanitisation” as used in Europe.  Sanitisation combines cleaning and disinfection in a single step.  “Disinfection”, on the other hand, is a single process which follows an initial cleaning step.

Techniques

The techniques used in dispenser sanitisation can be listed as follows:

·         Replacement of water contact parts by pre-sanitised or disposable components – reservoirs, reservoirs + tubing, taps

·         Manual cleaning and disinfection of components still in place

·         Auto-disinfection

Chemicals, Methods and Utensils

Chemicals include cleaners/acids and disinfectants.  Other methods include ozonation, steam treatment and hot water treatment.  Usual utensils are brushes, paper cloths and scouring pads.

Descalers

Acids are used for descaling reservoirs/piping and hot tanks.  Phosphoric acid is preferred and various concentrations are available from suppliers from 20-75%.  Increased concentration means more rapid descaling.  Some descalers contain detergents, which sometimes cause excessive foaming with heavy scaling.  Some descaling acids contain a disinfectant component, which enables descaling and disinfection.

Direct chill/spiral chill dispensers require a venturi doser to apply the descaler.  Push-fit fittings should be disconnected at the filter and the venturi doser connected.  Add 25-30ml acid, depending on the concentration, and draw into the dispenser with the chill tap.  Remember to rinse the push-fit fittings afterwards.

Disinfectants

Typical disinfectants are listed as follows:

·         Hydrogen peroxide

·         Hydrogen peroxide + silver ions

·         Peracetic acid

·         Ozone

·         Chlorinated materials

Hydrogen peroxide is highly effective against biofilm, leaves no taint and has harmless break-down products.  Peracetic acid is highly effective against biofilm, a small dosage is needed but residual product needs to be rinsed out thoroughly.  Chlorinated materials can create a taint issue if not rinsed out thoroughly and biofilm can resist.  An exception is chlorine dioxide, which leaves no taint and is very effective against biofilm.  The disadvantage of chlorine dioxide is that it has to be generated in situ because of stability issues.  However tablets are available, which generate the disinfectant on addition to water, although these are expensive.  Ozone can be generated with a portable kit and is effective against biofilm.  However it does create an ozone smell in the environment around the dispenser.  Steam provides effective sterilisation in 4 minutes with some units on the market.  However, care is needed in operation.

New Technologies – Auto Disinfection

Auto disinfection is possible with the following materials:

·         Ozone

·         UV

·         Hot Water

·         Silver and Copper

Ozone may be used by ozonating the water in the reservoir on a timed basis overnight.  Another technique ozonates the last section of the supply circuit prior to the tap outlet.  UV may be used to irradiate the reservoir contents or the water line just prior to the tap outlet.  A further technique irradiates the total tap outlet area.  Hot water disinfection uses hot water generated by the hot tank.  A microprocessor releases water into the rest of the dispenser and continues to heat until near boiling. 

Silver may be incorporated into plastic components.  This provides more of a bacteriostatic effect than germ-kill.  The treated plastic works well at low temperatures (5^oC), but is unable to cope at ambient temperature.  Copper is used in pipework.  It has a bacteriostatic action, but oxidation and subsequent passivation of the copper surfaces can reduce this effect.  Copper-silver alloys, unlike copper alone, can generate an electrolytic effect which provides better germ-kill.

Cooler Maintenance

Despite all the new technologies, a sanitary maintenance visit is still required to clean and disinfect the dispenser head, taps exterior and drip tray, otherwise poor in-house maintenance and difficult environments will always pose a problem for hygienic dispensing of water.  High-use dispensers are particularly vulnerable to tap contamination, including colonisation with Pseudomonas aeruginosa.  Sani-cloths may solve the problem for flat surfaces, but a disinfectant spray is necessary for tap areas.  A hydrogen peroxide spray provides a good germ-kill effect in the tap area, but the effect is not long-lasting.  New sprays are now available on the market which provide a long-lasting effect and these are to be recommended.