In compliance with the new European Directive (98/83 CE), Tritium monitoring and Annual Total Indicative Dose assessment is now mandatory in all water intended for human consumption distributed by private or public networks or used in the food processing industry.
3 frequently asked questions:
What is radioactivity?
Radioactivity is the spontaneous transformation of unstable atoms. The process releases radiation (known as ionizing radiation).
Radioactivity is naturally present in our environment. It stems from the different nuclides (species of atoms) found in our natural environment or in human activities.
How radioactivity works:
- An atom is made up of a nucleus surrounded by orbiting electrons.
- The nucleus is made up of protons (positive charge) and neutrons (neutral), while the orbiting electrons are negatively charged.
- Depending on the proton-neutron balance in the nucleus, nuclides may be stable or unstable.
- Unstable nuclides disintegrate (spontaneously lose their mass) by emitting particles or electromagnetic radiation (photons).
99% of human exposure to radiation stems from natural sources, and more precisely from:
- Radionuclides, present in the earth's crust, rocks, soil, etc. with a lifetime comparable to that of the earth itself,
- Materials resulting from the natural disintegration of Uranium and Thorium
- Cosmic radiation (Tritium, Carbon-14, Beryllium-10, …)
In France, the average annual dose is 2.4mSv per adult, but much depends on the region and lifestyles (Altitude over sea level, amount and type of radionuclides in the soil, air composition, food and drinking water, etc.).
The radioactivity that is potentially present in drinking water can be due to natural concentrations of nuclides, technical processes involving the use of natural nuclides, or on the contrary, to the presence of artificial nuclides in the water supply chain resulting from medical or industrial misuse.
What should we know about radioactivity?
Units of measurement:
Becquerel (Bq): Unit of measurement for nuclear activity, expressed as the activity of a quantity of radioactive nuclides in which one atomic nucleus decays per second
Gray (Gy): Unit of measurement of the dose of radiation absorbed by a (living being) when subjected to ionizing radiation
Sievert (Sv): Unit of measurement equivalent to the dose of ionizing radiation.
Ionizing radiation
Ionizing radiation is radiation which, when passing through a given material, possesses the energy required to extract an electron from an atom or molecule.
3 type of radiation:
Alpha emission:
A nuclide spontaneously emits 2 protons and 2 neutrons (1 alpha particle). This alpha particle corresponds to the complete ionization of the Helium atom (He).
It does not penetrate very far through the air. A single sheet of paper is sufficient to stop the Helium nuclei.
Beta emission:
A nuclide spontaneously emits one positron (+) and one electron (-). The interaction of the electrons when penetrating the material is similar to or weaker than that of the alpha particles, essentially because of the lower collision mass.
Its air penetration is weak and it can only go a few meters. A simple aluminum sheet a few millimeters thick can stop the electrons.
Gamma radiation:
Gamma radiation is an electromagnetic wave like visible light or X rays only with greater energy. This radiation often follows an alpha or beta disintegration.
After the alpha or beta particle has been emitted, the nucleus is excited again as its protons and neutrons have not yet found their balance. They get rid of some of their excess energy through gamma radiation emission.
Depending on the radiation energy, it can penetrate the air over a significant distance: several hundred meters. Only thick concrete or lead can afford protection
Annual dose:
Nuclear activity measurement alone is no indicator as to the effect on human beings. Its effect actually depends on the type of radiation, which includes the type of radiation emitted and on the sensitivity of the tissues in the receiving organ.
Annual dose calculation takes into account all these factors and can be used to assess the risk potential.
Total indicative dose:
The total indicative dose (TID) corresponds to the annual dose received from all the natural and artificial radionuclides detected in a water distribution source, excluding radon and its short-life daughter elements.
Determining radioactivity levels in water
The new radiological analysis provisions spelled out in European directive 98/83/EC on the basis of the WHO report (www.who.int) set the maximum TID at 0.1mSv per year (except for tritium, Potassium 40, radon and its daughter elements). Similarly, tritium exposure of less than 100Bq/l is considered acceptable.
TID is determined on the basis of a daily consumption of 2 liters of water per adult. TID measurement is complex and is only required when total alpha and beta activity measurements exceed the following thresholds:
- 0.1Bq/l for total alpha activity
- 1Bq/l for total residual beta activity
Threshold compliance requires a TID of less than 0.1mSv / year.
If one of these thresholds is exceeded, the contribution of each of the radionuclides in the TID must be determined.
For example, Figure 1 introduces an overview of the criteria indicated in the French Regulation of May 12 2004.
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