Answer to Question #3238 Submitted to "Ask the Experts"
Category: Pregnancy and Radiation — Radioactivity in food and water
The following question was answered by an expert in the appropriate field:
Q
I read your reply to
Question #484. I too live in Plainfield, Illinois, and the radium in water is now at 9.4 picocuries per liter. I know you stated that the levels of 6.4 were okay for children to drink but about how the level of 9.4 for pregnant women and the fetus?
A
- The 226Ra concentration in drinking water is not a constant but varies throughout the year. If the water source is well water, the variation will be about a factor of 2; if surface water, then the annual variation is usually less than this.
- There are some published data on 226Ra in the fetus, as a function of maternal dietary intake. A large study on 226Ra in bone as a function of age (from fetus to age 30) was done in samples from Buenos Aires in 1972 by Daniel and Ambretta Beninson. Dan Beninson, recently deceased, was a very well-known scientist in the radiation field and was Chairman of the International Commission on Radiation Protection for many years and the Argentine representative to the United Nations’ Scientific Committee on the Effects of Atomic Radiation. The dietary intake of 226Ra in Buenos Aires is similar to that in the average US diet.
Radium in bone is usually measured in terms of the calcium content (pCi 226Ra /gm Ca) because they are somewhat similar elements and are found together in the body mainly in bone. The discrimination (bone uptake) against radium is larger in infants and adults than in the fetus, so that even though the dietary radium increases after birth the 226Ra/Ca ratio in bone remains almost constant throughout life.
- Bone cancer induction from 226Ra has been well documented in studies of the radium dial painters and others exposed to extraordinarily high levels of radium. Bone cancer is the one solid tumor that seems to have a clear threshold and requires at least 1,000 rem in the human studies. The very first radiation standards were based on these radium exposure cases and the permissible body burden was set at a factor of 10 less than the bone concentration known to have caused bone tumors. The permissible burden was set at 0.1 uCi (100,000 pCi). No bone tumors were ever seen at this level.
- Therefore, a 226Ra concentration in water of 10 pCi/L (9.4 pCi/L is rounded), and assuming a maternal intake of at least 1 liter of raw water intake per day throughout fetal life, ends up as very few PCi’s 226Ra in the fetus. This delivers a bone dose that is so small that it can be considered to be of no consequence regarding health effects.
Naomi H. Harley, PhD
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