Answer to Question #9937 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
How can I measure radium-226 (226Ra) and radon-222 (222Rn) dose to different organs of the body from drinking water that contains radon and radium? For example, if there is 0.124 becquerel per liter (Bq L-1) of radium in water, how can I measure the dose from this radium to the stomach, lungs, kidneys, etc.?
First of all, the internal dose to individual organs from either 226Ra or 222Rn cannot be measured directly. Although some measurements of the amount of these radionuclides in the body may be made with a whole-body counter, detection requires very high concentrations. The best that we can do is to estimate the radiation dose from these radionuclides by theoretical models based on the amount taken into the organ of the body most likely affected. Such models and procedures for estimating internal doses from radium and radon have been developed and refined for over 50 years (y).
Radium—About 85 percent of the radium ingested is excreted in a short time. Some of the radium remaining in the body is carried by the blood to the bones. Since radium behaves like calcium, it can be incorporated into bones and remain there for a person’s lifetime, and this represents the greatest risk from ingestion of radium. Although you mention only 226Ra, there is another isotope, radium-228 (228Ra), which may also be deposited in bones. The table below shows how to estimate effective whole-body radiation dose from these radionuclides by theoretical models based on Federal Guidance Report 11 on the Environmental Protection Agency website.
For 226Ra, the dose factor is 3.58 × 10-7 sieverts (Sv) per Bq ingested.
To use this table, you first have to determine the daily intake of radium. This is calculated by the radium concentration in water times the daily amount consumed. At 0.185 Bq L-1 an adult consuming 2 L of water a day would ingest 0.37 Bq of radium. Using Table 2, if the radium is all 226Ra, for ingestion of water at 0.37 Bq a day by an adult, the corresponding effective dose rate would be (0.37 Bq d-1) × (2.7 × 10-7 Sv Bq-1) × (365 d y-1) = 3.65 × 10-5 Sv y-1 or 0.0365 mSv y-1.
You have asked about the dose from 0.124 Bq L-1. For an adult, this would result in about 0.25 Bq a day or (0.25/0.37) × 0.0365 mSv y-1 = 0.025 mSv y-1. In the United States, this amount would be less than 1 percent of the average normal dose of 3.1 mSv y-1 received by everyone from naturally occurring sources of radiation. Bone cancer from ingestion of radium has only been observed for doses above 10,000 mSv.
Radon—When water containing radon is brought into a house, some of the radon may be released into the air by aeration when the water is used for washing dishes and clothes, showers, or toilets, etc. When radon is released into the air, it can be inhaled and result in radiation dose to the lung. While ingestion of water containing radon may result in stomach cancer, that risk is only about 10 percent of the risk of developing lung cancer from radon in air. The current practice is to assume that 370 Bq L-1 of radon in water will result in 0.037 Bq L-1 of radon in air. Inhalation of air at this level for a year will result in an effective whole-body dose of about 2 mSv. In the United States, the Environmental Protection Agency recommends reduction of indoor radon levels above 0.148 Bq L-1.
Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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