Answer to Question #12415 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Rocks, Minerals, and Mines

The following question was answered by an expert in the appropriate field:

Q

My family lives along a highway in northern Arizona that is proposed as a route for hauling uranium ore from the Canyon Mine near the South Rim of Grand Canyon National Park to a processing mill in Blanding, Utah. The regional newspaper has repeatedly cited experts from Northern Arizona University who state there is little risk of contamination from the ore dust blowing as the trucks, covered only with tarps, roll through our communities. It is estimated that eight trucks per day will carry more than 22,000 kilograms (kg) of ore over a period of three to five years until the mine is exhausted.

The experts state that the concentration of uranium in the mine's ore is only about 1%, or less than 100 parts per million (ppm), and while there is no safe limit of exposure to radiation, the risk is low. I would agree with these experts that one-time exposure to the ore in these trucks presents minimal risk. However, the many thousands of people who work, reside, and enjoy recreational activities along the proposed hauling route will be routinely subjected to far more than a single exposure. With dust blowing from eight trucks every day in this high-wind area, I am concerned about the risks of dust accumulation and dissemination due to multiple daily exposures over several years.

I have not seen this aspect of the situation addressed by any experts in our regional media. Hauling may begin this year. Your assessment of the risks in this worrisome situation of continuous exposure is most appreciated.

A

Your question—a very common one over the years from people who live in historical uranium mining areas of the southwestern United States—is whether there are any environmental impact or health-related concerns from potentially large numbers of uranium ore trucks moving along roads near where we live. The simple answer is that there should not be a basis for concern, due to several factors, which I explain below and which hopefully will make sense to you.

We live in a naturally radioactive environment. Naturally occurring radioactive materials are present in the rocks and soil of the earth, in the houses we live in, and in the buildings where we work, as well as in the food and drink we consume. There are radioactive aerosols and gases in the air we breathe, and even our own bodies contain naturally occurring radioactive elements. The level of this inescapable natural "background" radiation exposure varies greatly from place to place. For example, according to the US National Council on Radiation Protection and Measurements (NCRP 1987), background soil in the United States contains a mean of 3.1  ppm of uranium (and 6.5 ppm of thorium), although much higher concentrations, especially in areas of mineralization, are not uncommon (NCRP 2009, UNSCEAR 2000). About 2.5 square kilometers (km2) of the earth's surface, 0.3 meter (m) deep, just about anywhere in the temperate zones, contains over 1,000 kg of uranium, and much higher concentrations are found in mineralized (e.g., uranium mining) areas.

In areas where uranium is or has historically been mined (southwestern United States, e.g., Arizona, New Mexico, and Colorado), it would not be unusual for the natural levels of uranium in the soil and rocks to be higher than in other parts of the country. So, in your neighborhood, there might already be higher levels of uranium naturally, due to greater mineralization in the rocks and soils.

As you accurately point out, the concentrations of uranium in the ore being carried by the trucks is quite low, about 1%. And under current practices, the trucks will be covered with tarps to reduce the chance of any dust escaping from the trucks (after all, the operators don't want to lose their valuable ore). But even assuming that some material does spill in small amounts or slight dusting occurs from time to time, the material will not go very far before it settles out onto the ground (adding a very small amount of uranium to what is already in the soil and rocks). The ore in the trucks has not yet been crushed or otherwise processed in any way—it's still just primarily rocks—so the smaller particles that might leave the truck would be relatively large and heavy (at least compared to aerosols, which are very fine material like talcum powder, that could travel some distance in the wind). So any loss from the trucks would be on or very near to the road. And the operator will almost certainly be required by mining permits issued by the appropriate state agency to monitor its activities, conduct radiological surveys from time to time, and ensure there is minimum environmental impact from its activities, including transportation of the ore.

So in conclusion, there should not be any cause for concern because:

  1. The fact that uranium mining has or is occurring in your area suggests that the naturally occurring levels of uranium in the soil and rocks are probably higher than in most areas of the United States.
  2. The trucks will be covered and any small amount of spillage from the trucks will add very little additional uranium to what already exists naturally in the soils and rocks.
  3. It is very unlikely that any spilled material can travel beyond a relatively short distance from the road.
  4. The operators will almost certainly have some regulatory and other legal requirements to minimize any loss of ore to ensure minimum adverse environmental or impact to people living nearby.

Steven H. Brown, CHP

References
National Council on Radiation Protection and Measurements. Exposure of the population in the United States and Canada from natural background radiation. Bethesda, MD: National Council on Radiation Protection and Measurements; NCRP Report No. 94; 1987.

National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. Bethesda, MD: National Council of Radiation Protection and Measurements; NCRP Report No.160; 2009.

United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation. Volume 1: Sources. New York: United Nations; 2000.

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