Answer to Question #1009 Submitted to "Ask the Experts"

Naturally occurring radioactive materials (NORM) are radioactive materials found in nature, formed by natural processes. Some were formed billions of years ago in supernovae and formed part of the cloud of gas from which the solar system formed, while others are formed continually from cosmic ray interactions in the earth's atmosphere or soil.

Primordial radionuclides are those that were present when the earth first formed. They include uranium, thorium, and radioactive ⁴⁰K, each of which has a half-life of a billion years or more. The uranium and thorium, in turn, decay to stable lead through a series of intermediate radionuclides, including isotopes of radium and radon. In fact, the radon we measure our basements for comes from the decay of ²³⁸U that is found in rocks and soils. Other NORM-bearing materials include bananas, salt substitute, and most soils. And, for that matter, the human body also contains measurable amounts of NORM.

Cosmogenic radionuclides are those formed by cosmic ray interactions. Tritium (radioactive hydrogen), a component of nuclear weapons, is formed naturally in this manner, as is ¹⁴C, the isotope used in carbon dating.

All of these radionuclides have different chemical and radiological properties. In particular, many coals contain uranium, and it is concentrated in flyash when the coal is burned. Natural gas may contain amounts of radon, and radium is often concentrated in the scale and sludge found in natural gas and petroleum pipes. Many minerals and ores also contain slightly elevated levels of NORM. However, for the most part, coal, flyash, natural gas, and other such materials do not pose a risk to humans or the environment as a result of their radioactivity.

There are a number of references that discuss NORM. One of the best is Environmental Radioactivity from Natural, Industrial & Military Sources by Merril Eisenbud and Thomas Gesell, published by Elsevier (at this Web site,  type in the name of the book under "search catalog" and "Keyword"). Other documents that discuss NORM-bearing materials are published by the United States Geological Survey, Environmental Protection Agency, and Department of Energy.

It's important to bear in mind that NORM is natural, and the earth has contained NORM since it first formed. Although it is very easy to measure trace amounts of radioactivity, most NORM-bearing materials are not a health hazard.

Andrew Karam, CHP
University of Rochester