Answer to Question #599 Submitted to "Ask the Experts"

Q

Suppose the soil of a region is naturally radioactive—will that pose a threat to the health of the people? If so, beyond what limits (in units)?

A

Actually, all soil is radioactive to some extent—some more than others. To give a more complete answer I'd like to take a slight detour, though, and talk about where the soil comes from. Rocks are formed either from magma that rises to the surface of the earth or from sediments weathered from these igneous rocks. Radioactive elements are concentrated in the sorts of magmas that are most often found on land, so most of the rocks we come across have more radioactivity in them than their counterparts in the oceans. This is important because soil forms from weathering the rocks, so if rocks have elevated radioactivity levels, the local soils will too. The amount of radioactivity in rocks (and, therefore, in soils) varies widely. I have a sample container in my office that contains soil from a city in Iran that has the highest levels of radioactivity of any populated place on earth. But the people in this area seem perfectly healthy and live as long as those in neighboring villages and towns. On the other extreme, people living along the U.S. Gulf Coast have some of the world's lowest levels of radioactivity in their soil. Their overall health (making adjustments for standard of living and access to medical care) seems no better and no worse than those in the Iranian town I mentioned above. In addition, several years ago a study was done that compared lung cancer rates across counties with very different radon levels. This study seemed to show that higher levels of radon did NOT result in higher rates of lung cancer. To me, this suggests a few things. First is that natural radioactivity is something we simply can't escape. But that's okay because our cells have evolved mechanisms to repair radiation damage, and they do so quite nicely. Secondly, this suggests to me that natural background radiation, even in extreme cases, is not likely to be a health risk. We can argue, I guess, about VERY extreme cases of exceptionally high radon levels, but unless these high radon levels are in a room in which you spend most of your time, they are unlikely to have an adverse health effect. For more than a few decades, many scientists have been debating about whether or not there is a "safe" level of radiation exposure. This issue is still far from settled, and we may never know for sure. However, I think it is safe to say that exposure to natural levels of radiation, even in areas where they are higher than normal, is less dangerous than driving or occupational injury. From my standpoint (which is, admittedly, somewhat biased), that's safe enough to not spend a lot of time worrying about it. If you are interested in more information about natural background radiation, I would suggest reading one of the following books:

• Environmental Radioactivity (Merril Eisenbud and Thomas Gesell), Academic Press, 1997.
   
• NCRP Report #94, Exposure of the Population in the United States and Canada from Natural Background Radiation, National Council on Radiation Protection and Measurements, 1987.
   
• "Sources and Effects of Ionizing Radiation," Report to the General Assembly, United Nations Science Committee on the Effects of Atomic Radiation (UNSCEAR), 2000.

Andrew Karam, CHP
University of Rochester