RADNET's stations are sparsely distributed, following a geographical layout based on the principle of ensuring a good coverage of the border with Spain and of the major population centres in mainland Portugal and the Autonomous Regions of Madeira and the Azores.
Radiological control of the environment
The "Radiological control of the environment" fact sheet monitors the concentrations of artificial and natural radionuclides in environmental compartments (atmospheric, aquatic and terrestrial) deemed as direct routes of contamination for Man, in order to ensure the monitoring of the actual exposure of the Portuguese population to radioactivity.
Description:
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). Nowadays, after the discovery of radioactivity and its subsequent use in various areas of activity, the radionuclides found in the environment can have either a natural or an anthropogenic origin. They basically 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 210Pb descendent of a long term disintegration of 222Rn;
- Formation of cosmogenic radionuclides such as 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, which are fission and activation products resulting from anthropogenic activities (nuclear tests, generation of electricity in nuclear power plants, radioisotope production, accidents, etc.).
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.
The radiological surveillance of the environment in Portugal, outlined according to the country's specific characteristics, is the responsibility of the Portuguese Environmental Agency (APA) and is carried out through monitoring programmes consisting of determining the presence of artificial and natural radionuclides in environmental compartments (atmospheric, aquatic and terrestrial), which represent direct contamination pathways for Man.
Radiation exposure can affect human health, namely through genetic modifications and the emergence of various types of neoplasms (leukaemia, lung cancer, skin cancer, stomach cancer, etc.). 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.
Portugal has a Continuous Environmental Radiation Surveillance Network (RADNET), which is fully operational and able to detect events of abnormal increase of environmental radiation. Currently, RADNET has 14 fixed stations for measuring the dose rate of gamma radiation in the air, two fixed stations for measuring the dose rate of gamma radiation in the water (at Fratel Dam in Tagus river and at Pocinho Dam in Douro river), a mobile station (car mounted), a mobile spectroscopic station for use in terrestrial, aerial and aquatic vehicles and two portable stations. An expansion project is underway in which seven more stations with gamma spectrometry of the latest generation were acquired and are undergoing testing and installation phases. The network is continuously measuring the gamma radiation present in the environment, triggering an alarm when the measured radiation levels exceed a pre-set threshold, which corresponds to three times the average value measured in normal conditions. In these cases, the alarm received by the central unit triggers the automatic audible and visual systems installed at the Portuguese Environmental Agency, responsible for managing the RADNET.
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. This monitoring is carried out by Instituto Superior Técnico (IST).
This fact sheet concerns mainland Portugal and the Autonomous Regions of Madeira and the Azores and shall be updated whenever new data is made available.
Objectives and targets:
- Ensure that the RADNET is operational, enabling an immediate notification in the event of the detection of abnormal values and proceed with a prompt and well-coordinated response at the national level;
- Ensure the routine monitoring of environmental radiation and the identification of deviations in values with radiological relevance.
Progress analysis:
Location of the RADNET 2019 stations
Source: APA, 2019
Annual average values of the ambient gamma radiation dose rate in Portugal, between 2010 and 2018
Source: APA, 2019
With regard to the annual average values of the ambient gamma radiation dose rate, the data collected between 2010 and 2018 corresponds to values of the natural radioactive background of the site where the measurement was made. This natural radioactive background varies according to local geology and altitude, justifying the fact that the annual average values obtained in the various stations are considerably different.
It is also possible to observe that the annual averages for each station have remained constant over the mentioned years, allowing us to conclude that there were no significant changes in the levels of ambient gamma radiation, since the conditions have remained normal from the radiological point of view.
From January to December 2018, the RADNET has been operating continuously, with an average time availability of 99% and with no alarms related to abnormal increases in environmental radiation.
The activity present in the atmosphere has been controlled through the continuous sampling of aerosols, at the IST campus in Bobadela, where the Portuguese Research Reactor (RPI) is located, which is currently inactive, awaiting the start of the dismantling process.
Evolution of activity concentration in Beryllium-7 and Lead-210 (mBq m-3) and in the concentration of suspended particles (μg m-3) in aerosols collected at the Technological and Nuclear Campus in Bobadela between 2010 and 2017
Source: IST, 2019
According to 2017 measurements, the monthly average concentration of total suspended particles (TSP) ranged from 15 μg m-3, in February, to 51 μg m-3, in October.
The monthly average activity concentration in 7Be ranged from 1.06±0.10 mBq m-3 to 6.25±0.63 mBq m-3, showing an annual average value of 4.0±1.7 mBq m-3.
In the case of 210Pb, the monthly average activity concentration ranged from 0.120±0.013 mBq m-3 to 1.10±0.12 mBq m-3, with an annual average value of 0.48±0.34 mBq m-3.
The variation in the monthly and annual average concentration for radionuclides detected in aerosols and for total suspended particles (TSP) in the last few years is within the expected limits.
This data does not show any abnormal values or risks for the population and the environment and indicates that the RPI has not been contributing toward any deterioration in air quality at the monitoring site.
Radioactivity in surface waters can be caused by radionuclides dissolved in the aqueous phase and/or by radionuclides adsorbed on suspended particles, which may occasionally be incorporated in sediments and living organisms. In addition to radionuclides of natural origin, such as 238U, 232Th, 226Ra, 228Ra, 222Rn and descendants, it may also be possible to detect 3H and the radionuclides 137Cs and 90Sr (of anthropogenic origin). These radionuclides are activation and fission products resulting from the operation of nuclear power plants. The radionuclide 3H can be released into the environment under normal conditions and/or after a nuclear accident but 137Cs and 90Sr are only present in the environment due to nuclear or radiological accidents and nuclear tests or explosions.
Values of activity concentration in Cesium-137 and Strontium-90 (Bq L-1) in surface water collected in the river Tagus (Vila Velha de Ródão) between 2010 and 2017
Notas: The values represented without the uncertainty bar correspond to the value of the minimum detectable activity for both radionuclides.
Source: IST, 2019
The surveillance of radioactivity caused by radionuclides with an anthropogenic origin, cesium-137 (137Cs), strontium-90 (90Sr) and tritium (3H), in surface waters has also been ensured in the rivers Tagus, Zêzere, Douro, Mondego and Guadiana by the LPSR.
In the river Tagus, the surface water sampling is carried out on a monthly basis in Vila Velha de Ródão, and samples of sediments, fishes and aquatic plants are also collected.
The activities in cesium-137 (137Cs) and strontium-90 (90Sr) in surface waters, in Vila Velha de Ródão, have remained relatively constant, without any major variations from one year to the next. It should noted that, in some 137Cs and 90Sr determinations, the values obtained are lower than the detection limits of the technique that is being used reason for which the presented values have no uncertainty.
Values of activity concentration in Tritium (Bq L-1) in surface waters collected in the river Tagus (Vila Velha de Ródão) between 2010 and 2017
Source: IST, 2019
The activity in 3H, also in Vila Velha de Ródão, has varied throughout the months and the years. In 2015, the variation throughout the year was quite pronounced, having reached the highest value in September/October. In 2017, the values were similar to those of 2016, also showing a smaller variation compared to previous years. This variation may be related to the normal operation of the Spanish Nuclear Plants, whose effluents are discharged into the river Tagus and to the dam discharge system installed along the river Tagus. The analysis of the chart indicates activities below the limit values for the population and the environment.
Simultaneously, the evaluation of the level of radioactivity in the mixed diet provides an indication as to the potential radioactive contamination of Man via the food chain. This evaluation is made through the analysis of individual food products or complete meals, considering that the latter is more representative of the mixed diet.
According to the data from the IST Programme for the routine Radiological Monitoring of the Environment, the results of the programme for the radiological control of the food products deemed as the main constituents of the Portuguese diet (mixed diet) show a relatively low level of artificial radioactivity.
From the broad range of results obtained from 2010 to 2017, for the different types of samples, we conclude that the radioactivity levels fall within the range of the values obtained in previous years. The activity concentrations of radionuclides of natural origin, namely from the uranium, thorium and potassium-40 (40K) families, are values typical of the natural radioactive background, i.e., not changed by human activity. The activity concentrations of radionuclides of artificial origin, namely 137Cs, 90Sr and 3H, are very low and, frequently, below the values of minimum detectable activity.
We conclude that the nationwide results of the radiological monitoring of the environment obtained for different types of samples (aerosols, rainwater, surface waters, waters for human consumption, food products, milk, sediments, soils, etc.), between 2010 and 2017, are low and fall within the range of values obtained in previous years.
Last update:
Wednesday, 24 April, 2019
More information at:
Portuguese Environment Agency – www.apambiente.pt
National Environmental Information System (SINAmb): Monitoring Indicators – sniamb.apambiente.pt/Home/Default.htm
Environmental Radioactivity Alert Network - radnet.apambiente.pt/
EURDEP Platform - eurdep.jrc.ec.europa.eu/Basic/Pages/Public/Home/Default.aspx
Laboratory of Radiological Protection and Safety - www.itn.pt/sec/psr/