Radioactive elements found in tap water


Question:

There are increasing concerns about radioactive contamination in drinking water.  What kinds of radioactive elements have been found in tap water?  In what forms do they exist in tap water?  Wouldn’t it be necessary to use different removal methods for different kinds and forms of the elements? (50s, female, Tokyo)

Answer:

According to the report from the Ministry of Health, Labor and Welfare, two kinds of radioactive elements – iodine 131 and cesium 137, were detected in tap water.  A possible route that these radioactive elements took to get into tap water is;  air -> river -> water purification plants -> households’ tap water.  First, the radioactive elements in the air get into rivers.  At water purification plants, most of the radioactive elements will be filtered out of the water, but some can get through the filters and reach households’ taps.  As shown in Figure 1, filtration process can remove iodine and cesium that are attached to dust particles.  However, those in ion forms and organic iodine could be left in the tap water.



Figure 1.  The forms of iodine and cesium in air, water, water purification plants and households’ tap water.



The removal rate would differ by the purification methods at each water purification plant.  Table 1 is a brief summary of percentages of iodine 131 and cesium 137 that would be removed by different purification methods.  It should be noted, that the removal rates could change by physical and chemical conditions of the water, such as the pH and concentration of chlorine that is added during the purification process to destroy disease-causing bacteria.


Table 1.  Percentages of iodine 131 and cesium 137 removed by different water purification methods




The National Institute of Radiological Sciences tested different water purification methods to see if iodine 131 in tap water is removed from tap water that is already purified at a purification plant.  They reported that the reverse osmosis filter is the only methods that removed iodine 131 left in the tap water.

Even though the reverse osmosis method appeared to be effective, the amount of radioactive elements found in tap water has been below the level that can cause negative health outcomes.  Therefore, no recommendation has been made to change the water purification methods at the water purification plants or to encourage people to use reverse osmosis filters at home.


Science communicator: Megumi Murashima
Supervised by Japan Radiological Society




Links

Detection of radioactive materials in tap water - The Ministry of Health, Labour and Welfare
The National Institute of Public Health (Title and article in Japanese)