Food and household water Food and household water

Food and household water

Food and household water

Household water

Harmaa tietolaatikko Food and Household water

Household water refers to water that is intended for human consumption and for preparing food. The Decree of the Ministry of Social Affairs and Health Relating to the Quality and Monitoring of Water Intended for Human Consumption (1352/2015) sets limits for radiation exposure caused by radioactive substances. Decree 1352/2015 (Finlex.fi)

Radioactivity in drinking water

Radioactive materials, released from soil and bedrock, occur naturally in household water. In a radiation hazard situation, surface and ground water may be contaminated by the fallout.

Radioactive substance concentrations may be different in different water sources. The highest activity concentration of radioactive substances occurs in ground water in the bedrock, whereas the activity concentration in surface water is typically the lowest. Artificial radioactive materials may end up in the surface and ground water through wastewater or as a result of a radiation accident.  

Natural radioactivity

Naturally occurring radioactive materials in drinking water originate from radioactive materials that occur naturally in the soil and bedrock, which are released into water systems from the minerals on the Earth’s crust. The radionuclide concentrations in ground water are significantly higher than those of surface water, since ground water is in contact with the soil and bedrock for a longer period than surface water. The most significant naturally occurring radioactive materials in terms of drinking water belong to the uranium series. Alpha radiation-emitting radon (Rn-222) is the main radiation exposing substance in Finland. Other important uranium series radionuclides are long-lived U-238, U-234, Ra-226 and Po-210 as well as beta radiation-emitting Pb-210. The most significant thorium series radionuclide is Ra-228 that emits beta radiation.

Natural radioactivity in water may also be a result of human actions. Usually, these kinds of increases are minor. In water supply plants, aeration increases the radon concentration in indoor air in the aeration and alkalisation premises, even if the radon concentration in raw water is not high.

In addition to radioactive decay, the amount of radionuclides in water is controlled by different geochemical and physical processes.  For these reasons, the activity concentrations of different isotopes of a different element or the same element in the surface and ground water differ from each other.

Artificial radioactivity

In a radiation hazard situation, surface and ground water may be contaminated by the deposition when radioactive materials fall to the water from air and, later, end up to the ground water. Deposition refers to radioactive materials that have fallen to the ground or water from air. Deposition may come with rain as wet deposition or as dry deposition with particles and gas travelling in the air.

Small amounts of radionuclides resulting from nuclear weapon testing performed in the atmosphere in the 1960s and the Chernobyl nuclear accident may occur in drinking water.

In terms of human radiation protection, the most important radionuclides in the fallout resulting from a nuclear power plant accident are iodine isotopes I-131, I-132, cesium isotopes Cs-137, Cs-134 and strontium isotopes Sr-89, Sr-90. Tritium (H-3) is also important, since it is part of the hydrological cycle as a component of water and migrates to ground water. Furthermore, the deposition may contain several other radioactive substances. Radionuclide I-131 is the most significant short-lived radionuclide, since its proportion in the deposition is significant and it accumulates in the thyroid gland. After an initial phase, the activity concentrations of longer-lived Cs-137, Cs-134 and Sr-90 will fall, having half-lives of several years.

STUK monitors the artificial radioactivity of drinking water nationally in its environmental radiation monitoring programme. Additional information and measurement results

Radioactive material deposition contaminates mainly surface water. The situation caused by the deposition is worst when the deposition occurs during the open-water season. During the winter, ice covers the surface water and slows down the migration of radioactive materials to the water. Furthermore, short-lived radioactive materials disappear before they end up in water.

The risk posed to ground water by radioactive deposition is small when compared to surface water, since ground water is mainly protected by a thick layer of soil. Ground water forms slowly, which means that it will not be contaminated as quickly as surface water. Radioactive materials move from surface water to ground water when surface water is absorbed through the soil. The soil absorbs part of the radioactive materials. A soil’s ability to absorb radioactive materials depends on the thickness and permeability of the soil layer. Cesium binds to the sediment in water and the sediment is absorbed when the water is filtered through the soil layer. Strontium stays dissolved in water for a longer period and will not be eliminated as efficiently as cesium. Furthermore, the concentrations of radioactive materials are also diluted especially in large ground water areas. In general, the migration of radioactive materials from surface water to ground water is minimal.  

The averages of radioactive materials in drinking water (Bq/l or µg/l) in population groups using different sources of water.

Radioactive substance

Water from a water distribution network

Surface water

Ring wells/
ground water

Bore wells

Natural radioactivity

Radon-222 (Bq/l)

27

<3

50

460

Uranium-234 (Bq/l)

0,02

<0,01

0,02

0,35

Uranium-238 (Bq/l)

0,015

<0,01

0,015

0,26

Uranium-238 (µg/l)

0,23*

0,90**

<1

1,2 – 1,7

21 - 24

Radium-226 (Bq/l)

0,003

0,003

0,016

0,05

Radium-228 (Bq/l)

-

-

-

0,03

Polonium-210 (Bq/l)

0,003

-

0,007

0,048

Lead -210 (Bq/l)

0,003

-

0,013

0,040

Artificial radioactivity

Tritium (Bq/l)***

<2

-

-

-

Strontium-90 (Bq/l)***

0,004

0,004

-

-

Cesium-137 (Bq/l)***

0,005

0,008

-

-

*surface water used as the source of the water from a water distribution network
**ground water used as the source of the water from a water distribution network
***the water from a water distribution network is the average of five large cities (Helsinki, Oulu, Rovaniemi, Tampere and Turku) and the surface water is the average of four rivers (Kemijoki, Oulujoki, Kokemäenjoki and Kymijoki)

Doses and exceedances

The average radiation dose of Finns who drink from bore well water is approximately one tenth of the average dose of Finns, which is approximately six millisieverts annually. The dose of Finns drinking tap water or ground water from a well is even lower.

According to the Radiation and Nuclear Safety Authority’s estimation, approximately 20,000 people drink bore well water in which the radon concentration exceeds 1,000 becquerels per litre. This is 10% of bore well water drinkers. Of all Finns, this is less than 0.5%. Radon concentrations above 10,000 becquerels per litre occur also, but only rarely.

According to the Radiation and Nuclear Safety Authority’s estimation, approximately 26,000 people drink bore well water in which the uranium concentration exceeds 30 microgrammes per litre. This is 13% of bore well water drinkers. Bore well water drinkers’ exposure to uranium has been studied among Southern Finns. Regardless of the long-term exposure to relatively high uranium concentrations, no serious health hazards among bore well water drinkers have been identified in Finland.

Exposure to uranium may weaken the functioning of kidneys, which is shown as greater excretion of phosphate, glucose and calcium in the urine. Uranium exposure has also been associated with increased blood pressure.

The correlation between the uranium exposure of bore well water drinkers and cancer has also been studied in Finland. The study found no correlation between the exposure to bore well uranium and cancer risk.

The activity concentrations of other radioactive substances (Ra-226, Ra-228, Pb-210 and Po-210) in drinking water are usually low when compared to the radon or uranium concentration.    

Health hazard

Radon is the radionuclide in drinking water causing the greatest radiation dose in Finland. When radon is swallowed in water, the digestive system is exposed to a radiation dose. Clearly more significant, however, is radon gas that is released from water into breathing air which exposes the lungs.

If the drinking water contains 1,000 becquerels per litre (Bq/l) of radon, water that has been drunken causes an annual dose of approximately 0.13 millisieverts (mSv). Concentration 1,000 Bq/l increases the radon concentration in inhaled air by on average 40 becquerels per cubic metre (Bq/m³), which causes a dose of approximately 2 mSv. The radon inhaled into the lungs increases the risk of lung cancer.

Long-term exposure to high radon levels considerably increases the risk of lung cancer. Further information about radon and lung cancer

Natural uranium is a weakly radioactive substance (mainly isotope U-238). The chemical toxicity of uranium is regarded as a more significant health risk than the radiation dose caused by it. Uranium is a heavy metal, and toxic in large doses especially to the kidneys and skeletal system. Uranium that has not been excreted from the body will accumulate, for example, in the kidneys, skeletal system and liver. Mild uranium-related adverse effects have been identified in the kidneys and skeletal system of Finnish bore well water drinkers.

Regardless of the considerably great uranium exposure caused by drinking water, no serious health hazards have been detected. Nor has a link been found between bore well water uranium and risk of leukemia, gastric cancer, kidney cancer or bladder cancer.

The activity concentrations of other radioactive substances (Ra-226, Ra-228, Pb-210 and Po-210) in drinking water are usually low when compared to the radon or uranium concentration. The risk of cancer caused by them is also minor.

Occurrence

The radon concentrations of bore well water are usually highest in granite areas in Uusimaa, Southwest Finland, Häme, Kymenlaakso and Southern Karelia (Figure 1). The highest concentrations of uranium are found in Uusimaa, Kymenlaakso, Häme and Southwest Finland. The lowest concentrations of uranium are found in Northern Karelia, Satakunta, Pirkanmaa, Southern Ostrobothnia, Ostrobothnia and Lapland.

Figure 1. Radon concentrations in bore well water.

Figure 2. Uranium concentrations in bore well water.

Map: Averages of radon (upper map) and uranium concentrations (lower map) in bore well water in a grid of 10 x 10 km. The radon material covers approximately 11,300 bore wells and uranium material approximately 5,000 bore wells.

Bore well radon and uranium atlas (Porakaivoveden radon- ja uraanikartasto). Vesterbacka P; Vaaramaa K. (2013) (in Finnish) (Julkari.fi)

Contact

Contact

  • Kaisa Vaaramaa / Head of Laboratory
    Tel. +358975988521