The hydrogeologist of the Estonian Geological Institute Joonas Pärn explained that when we talk about groundwater, one can look at the chemical and quantitative status separately. The chemical status is the quality of the water, the quantitative status is the groundwater level.
“Given the climatic zone in which Estonia is located, the groundwater here is in very good condition in terms of quantity, the chemical condition is generally assessed as good,” Pärn said.
According to Siiri Salupere, a radiation protection researcher at the University of Tartu, Estonia has a special aquifer: we drink Cambrian-Bendian groundwater, which contains many naturally occurring dissolved radium isotopes. These are natural radioactive elements, due to which groundwater becomes radioactive. Such water is mainly used in northern Estonia, especially in coastal areas.
It is difficult to study how natural radioactivity in drinking water affects humans, says Salupere. All are exposed to ionizing radiation to some degree. “However, it is widely believed in the scientific community today that even low doses increase the risk of cancer,” he said.
Looking for an answer, it is pointless to go back in history: our ancestors did not come into contact with radioactive drinking water to the extent that we do, because they could not open such a deep well. The Cambrian-Bendia groundwater wells in northern Estonia are generally at least 80 meters deep, but can be up to 300 meters.
To monitor the situation, the World Health Organization and the European Commission have decided to set the maximum permissible level of radioactivity in drinking water. If the radiation dose is greater than 0.1 millisievert per year, ways to reduce groundwater radioactivity should be sought. By comparison, about the same dose can be taken by having a breast cancer screening twice.
At a dose of less than 0.1 millisievert per year, the risk is considered low and it is not necessary to extract radionuclides from the water. Irradiation doses from the use of Cambrian-Bendian groundwater are often between 0.3 and 0.5 millisieverts per year.
Salupere explained that over the course of a year, the average person receives a dose of three millisieverts of ionizing radiation. But this is mainly due to the radon we breathe indoors.
The level of radioactivity can be increased
However, the level of natural groundwater radioactivity may increase over time. Salupere spoke of a study in which scientists have been studying wells on the Viimsi Peninsula for five years. It turned out that the more water came from the Cambrian-Bendia layer, the higher the level of radioactivity. At the same time, the chloride content increased, ie the water became more mineralized.
Geologists were able to determine that both chloride and radium entered the water through cracks in the crystalline rock. If you constantly use the water at the top of the crystal rock, then the water that accumulates in the cracks, rich in radioactive elements, can also begin to penetrate the aquifer. “Perhaps in the future we should pay more attention to issues such as the purification of drinking water from radionuclides and chlorides,” said Salupere.
Banning deep drilling will not solve this problem, because then people will have to get water from somewhere else. However, there are not many options on the north coast. “However, it is better to use the water we have,” says Salupere.
A total of 31 groundwater systems have been set up to assess the groundwater situation in Estonia. According to Joonas Pärn, according to data collected in 2020, eight of them are in poor condition. There are several reasons for this. In Ida-Virumaa, for example, groundwater bodies near oil shale mines are in poor condition. In order for quarries and mines to operate, some aquifers must remain dry. Mining activities also affect groundwater quality.
In and around Pandivere Upland, groundwater is subject to diffuse pollution from agricultural activities, ie nutrient residues and pesticides sometimes degrade groundwater chemistry. “Many aspects converged in this area at the same time. On the one hand, there are fertile soils and active agricultural activity. At the same time, the geological structure contributes to the leakage of water to the earth’s surface,” Pärn said.
Impact of climate change
According to Pärn, it is interesting that groundwater is sometimes in poor condition in terms of chemical composition in places where there is no strong impact of human activity. There, change in water quality can be linked to climate change.
The scientist believes that if there is no sharp increase in water intake from deep underground reservoirs, then in the near future the level of natural radioactivity will not increase much. However, if water intake increases and the level of radioactivity rises, then we will probably need to shut down some of our water intakes and use more groundwater closer to the earth’s surface. “As far as I know, this is already happening in Ida-Virumaa. There are problems not only with natural radioactivity, but also with the high chloride content, which sometimes increases the mineralization of groundwater,” he said.
In summary, it is worth saying that, in general, everything is fine in Europe. Siiri Salupere stressed that there is no reason to panic. However, utilities should consider how they manage Cambrian-Bendia groundwater and whether the technology can be used to reduce radionuclides.
Apart from Estonia, groundwater with a high content of radioactive elements is found, for example, in France, Portugal and Sweden.
The results of the study are published in the journal Critical Reviews in Environmental Science and Technology.