Answer to Question #979 Submitted to "Ask the Experts"

Q

What are the radiotoxic effects on humans caused by naturally occurring radioactive materials (NORM)?

A

The short answer is "It depends." What it depends on is the amount of NORM and the radionuclide in question. Most NORM isotopes are present in such small quantities that they will have no discernable effect. Examples of this are the ¹⁴C and tritium (³H) that are formed by cosmic ray interactions in the atmosphere. These are incorporated into virtually every living organism with no known ill effects. Similarly, 0.01% of all potassium is radioactive; since potassium is a vital nutrient for life, every living organism on earth is exposed to this radiation, again with no observed effect. In addition, we are all exposed to trace amounts of uranium, thorium, radon, radium, and other NORM through dust inhalation, soil ingestion (for example, from unwashed produce), and other routes. NORM can be concentrated by natural or artificial means, sometimes to the point of creating a potential health risk. In the case of uranium, radiotoxic effects are secondary because uranium is more chemically toxic than it is radiotoxic. It is not usual to find uranium separated from its series of radioactive decay progeny isotopes (including isotopes of radium, radon, and thorium) although radon formed near the earth's surface may migrate into basements or caves. In some cases, NORM may be concentrated to the point of posing a potential health risk, but this happens very rarely in nature. In fact, the city of Ramsar, Iran, contains extraordinarily high levels of radium, brought to the earth's surface by groundwater from deep, geologically active rocks in the area. However, even in Ramsar, which has the highest radiation levels in any populated area on earth, it appears as though cancer rates are no higher than in surrounding areas with normal radiation levels. This is also noted in areas of China with higher-than-normal NORM concentrations. The exposure of residents in these areas includes breathing air with radon, drinking water with radium, and eating food containing radium. This all suggests that the effects of exposure to NORM are very slight, barring artificial concentration by human activities. In fact, in most cases, the greatest risk from exposure to NORM is from breathing the dusts containing the NORM, and this risk is from the effects of the dusts and not the radioactivity they contain. With respect to the health risk posed by radiation exposure, I'd suggest looking up one of the "Ask the Expert" postings on radiation health effects or the linear no-threshold controversy. They can address this topic far better than I can here. Andrew Karam, CHP University of Rochester