Radiological control of the environment

Radioactivity is neither a recent phenomenon, nor exclusively the result of anthropogenic actions. In fact, the Earth has always been subject to cosmic radiation and its constitution has always included a series of radionuclides (unstable form of a nuclide that releases energy in the form of ionising radiation to become stable). NNowadays, after the discovery of radioactivity and its subsequent use in several areas of activity, the radionuclides found in the environment can have either a natural or an anthropogenic origin. Essentially, they result from four different sources: 

• Radon (Rn) exhalation into the atmosphere, ²²²Rn and ²²⁰Rn, produced by the radioactive disintegration of radium (Ra), ²²⁶Ra and ²²⁴Ra (natural constituents of soils and rocks) belonging to the natural radioactive series of ²³⁸U and ²³²Th, respectively. A good example of which is the occurrence of lead (²¹⁰Pb) descendent of a long term disintegration of ²²²Rn;
• Formation of cosmogenic radionuclides such as beryllium (⁷Be), through  the interaction of cosmic radiation with atmospheric gases containing carbon, nitrogen and oxygen;
• Technologically enhanced natural radiation, resulting from the industrial use of raw materials containing natural radionuclides;
• Artificial radionuclides, fission and activation products, due to anthropogenic activities (nuclear tests, electricity production in nuclear power plants, radioisotope production, accidents, among others).

Regardless of their origin, radionuclides can be present in the atmosphere in the gaseous or particulate form (associated with atmospheric aerosol). Usually, the particulate form is the one that poses the most significant radiological risk, since these particles interact with the biosphere through atmospheric transport and deposition processes.

Radiation exposure can affect human health, namely through genetic modifications and the development of different types of cancer (leukaemia, lung cancer, skin cancer, stomach cancer, others.). Exposure can be direct (namely via human exposure to the source) or indirect, via the environment (air, water, soil, food) due to the accidental introduction of those substances into the environment.

The radiological environmental surveillance in Portugal, is responsibility of Portuguese Environmental Agency (APA) and carried out through monitoring programmes designed to assess the presence of artificial and natural radionuclides in environmental compartments (atmospheric, aquatic and terrestrial), which represent direct contamination pathways for Man.

Portugal has been operating, since 1989, an Alert Radiological Monitoring Network (RADNET) capable of detecting situations of abnormal increase in radioactivity in the environment. In recent years, all older RADNET stations have been replaced by newer versions able to, in addition to measuring gamma radiation dose rates (in the quantity of H*(10)), also identifying the radionuclides present in the environment, allowing better identification of the potential source of any unexpected increase in radioactivity and increasing the sensitivity of the network.

This network, continuously measuring gamma radiation in the air and in the main international rivers (Tejo, Douro and Guadiana), includes several measuring stations spread across the mainland and autonomous regions, with the aim of ensuring good coverage of the border area with Spain, of large population centres in Portugal and of places relevant to the transit of radioactive materials. Currently has 17 fixed stations for measuring radiation in the environment and three fixed stations for measuring gamma radiation in water.
If necessary, this network can be completed with a station installed in a vehicle and two portable stations, which can be temporarily installed anywhere in the territory, all of them capable of measuring gamma radiation dose rates (in the quantity of H *(10)).

The network continuously measures gamma radiation in the environment and in water, triggering alarms when measured radiation levels exceed pre-defined thresholds. In these cases, the alarm received at the central unit will trigger the automatic, audible and visual systems installed at APA, which is responsible for managing RADNET.

New radioactivity monitoring stations are currently being tested, one for monitoring radioactivity in the air (with the ability to identify the radionuclides present in the environment and  to measuring gamma radiation dose rates, in the quantity of H*(10)) to be installed in the north of the district of Viana do Castelo, and three stations for monitoring aerosols and radioactive iodine installed in Vila Real, Abrantes and Évora, allowing the expansion and diversification of this network. As soon as the testing phase is completed, the values of these new stations will be made available to the public as is already the case for the other stations.

In addition to the RADNET, there is radiological monitoring of the environment based on samples of aerosols, surface waters, food chain components and complete meals. Currently, this monitoring is carried out by Laboratório de Proteção e Segurança Radiológica (LPSR) of Técnico Lisboa.

This fact sheet concerns mainland Portugal and the Autonomous Regions of Madeira and the Azores and will be updated whenever new data becomes available.