Radioactivity in water and possible remedial measures
1. Radon in water
Underground water always contains a certain radon amount, while the radon concentration in surface water is negligible. Radon enters into water from rocks that contain uranium and radium, and radon enters together with water into houses. Radon releases to the atmosphere if you use water in houses (during showering and washing about 50 percent, and during cooking and washing nearly 100 percent); and short-lived radon daughters are also generated. Their inhalation contributes to the exposure to the population. Nevertheless, from the standpoint of exposure, drinking water is less significant.
How to measure radon in water?
The measurement of the radon concentration in water is carried out in a laboratory. The samples of water with a volume of about few tenths litres are taken into the special containers that are sealed to prevent radon release, and the measurement should be performed within four days after sampling. The measurement of the radon concentration in water is classified as the most significant performance from the standpoint of radiation protection, and hence, the measurements need SÚJB permission. About 40 companies have received this permission, and their list can be found on SÚJB web page www.sujb.cz
The mean value of the radon concentration in drinking water from underground water sources in the Czech Republic is about 15 Bq/l (according to the results in 1999), and the maximum values found have reached the order of about thousands of Bq/l, (for interest's sake, water used for treatment in Jáchymov Spa has a value of about 10,000 Bq/l). The radon concentration in water is linked with the content of natural radionuclides in geological subsoil (see the geological radon risk map). The frequent occurrence of higher values may be found, for example, in the following districts: Jindřichův Hradec, Písek, Prachatice, Strakonice, Plzeň - South, Sokolov and Tachov. The estimate of the average exposure to radon from drinking water (again in 1999) is 0.05 mSv per year (i.e., about a hundred times less compared with radon entering buildings directly from soil).
Duties of water suppliers
Pursuant to the Atomic Law and the Regulation no. 307/2002 Coll., all water suppliers to the public water mains are obliged to secure the systematic measurements and evaluation of radon concentration in water at least once a year. If the radon concentration is higher than 300 Bq/l, water must not be supplied, and it is necessary to reduce radon concentration in water by a suitable remedial measure or to replace this water source. If radon concentration is higher than the guidance level of 50 Bq/l, it is necessary to assess a possible elimination of radon in water (in such a case to compare the cost and benefit of the remedial measures). In 1999, it was found that 9 percent of the public water mains had exceeded a level of 50 Bq/l, and 0.6 percent of the public water mains had exceeded a level of 300 Bq/l.
How to remove radon from water?
The aerating equipment is only used to remove radon from underground water in the Czech Republic, that is, radon is removed off water by aerating. There are hundreds of this type of equipment now operating in Czech water treatment plants. Its efficiency is high, normally more than 90 percent. This means that the radon concentration in water is reduced more than ten times; purchase and operating costs of the equipment are about several hundred thousand CZK per a unit, and hence, the equipment is not usually used in small water sources.
Our regulations do not require measuring radon in drinking water used for individual purposes, and hence, no limit has been specified. Only the guidance levels have been specified, and the remedial provisions are recommended in case the following levels are exceeded: up to 200 Bq/l - no measures required; from 200 to 1,000 Bq/l - ventilation of all rooms with a high water consumption (i.e., bathrooms); above 1,000 Bq/l - radon removal from water or a replacement of water sources. Even if the measurement for an individual water supply is not compulsory, it is recommended that the measurement should be done at least in the areas with high radon risk from geological subsoil (see the map). In these areas, there is a high radon concentration probability in water up to thousands of Bq/l.
2. Other natural radionuclides in water
In addition to radon, the other natural radionuclides are present in water; however, in lower concentrations. These are mainly radium (Ra-226) and uranium isotopes (U-234 and U-238). They enter water in the same way as radon, and drinking water that contains such nuclides will also cause a certain exposure to the population.
Determination of natural nuclides in water
The determination of individual natural radionuclides (about some tens of radionuclides) in water is time-consuming and expensive work. Hence, two group indicators were specified, i.e., gross alpha counting and gross beta counting that characterise the content of natural radionuclides (other than radon) in water. The guidance level of 0.2 Bq/l for the gross alpha counting and the guidance level of 0.5 Bq/l for gross beta counting were determined for water that is supplied to the public water mains. If any of these values are exceeded, it is useful to determine the concentration of individual radionuclides in water (and our legal regulations require such measurements).
The gross alpha/beta counting and the measurement of the concentrations of the individual natural radionuclides in water are done in a laboratory. The samples of water with a volume of some litres are taken into plastic containers, and immediately after sampling, nitric acid is added. The measurement of natural radionuclide concentrations is classified as the most significant performance from the standpoint of radiation protection, and hence SÚJB permission is needed. About 20 companies have received the permission, and their list can be found on SÚJB web page www.sujb.cz
The results of gross alpha/beta counting in water that was supplied to the public water mains in 1999 have the mean value for alpha of 0.046 Bq/l and for beta of 0.087 Bq/l. Exceeding of the guidance levels was found in 5 percent of the total number of the public water mains. Higher values were found in the following districts: Písek, Plzeň - South, Litoměřice, Louny and Teplice. The estimate of the average exposure to population from natural radionuclides (other than radon) in drinking water (again according to the results from 1999) is 0.006 mSv/year, i.e., about ten times less compared to the estimate of the exposure to radon in water.
Duties of water supplies
As well as for radon, and pursuant to our regulations, the suppliers of water to the public water mains are obliged to count the gross alpha/beta in water supplied at least one a year. The more detailed analyses that determine the individual radionuclides in water are required only in case the guidance levels are exceeded. If the result exceeds the values that are specified in the regulation, water must not be supplied to the public water mains.
Removal of natural radionuclides from water
The removal of radon and uranium off water is a time consuming and expensive matter, and the problems are also with the existing radioactive waste disposal (there is only one water treatment plant for uranium removal in the Czech Republic). The most suitable solution is to replace this water source.
As for radon, our regulations do not require counting the gross alpha/beta in drinking water for individual water supplies, and no limit is specified either for the gross alpha/beta counting. There are only the guidance levels, i.e., 2 Bq/l for gross alpha and 5 Bq/l for gross beta. If the guidance levels are exceeded, it is recommended that water be used only as service water.