Answer to Question #12844 Submitted to "Ask the Experts"

A few years ago, I got interested in hydroponic gardening and ordered the required materials, including a growing medium called Hydroton, which consisted of natural clay balls that had been baked and dried. When the box arrived, the Hydroton had been badly pulverized in shipping and the bag partially spilled as I opened the box. Because the Hydroton material was baked and dried, the dust from the pulverized clay balls went airborne very easily.

After cleaning it up, I decided to test it with a Geiger counter since I knew that natural clay likely contains natural radioactivity. Holding the Geiger counter right next to the bag, it registered numbers significantly higher than background levels. Usually, background levels in my apartment were around 30 counts per minute (cpm). However, the bag of Hydroton showed radiation levels that were at least in the very high 70s and possibly higher (I don't remember precisely what the highest number reached was).

Unsure what to do with the pulverized and radioactive Hydroton, I put the bag in front of my car in my building's garage. Due to circumstances that arose a few weeks later, I decided to place the bag inside a couple of trash bags, tie them shut, and throw them away, thinking that the bag would just sit in a landfill and, if it eventually broke down and released its contents, it wouldn't do any harm since it was just natural clay anyway. However, after throwing this stuff out, I later discovered that when sanitation workers collect trash, they deliberately tear up the bags and grind up the trash with their machinery so that dangerous gases don't build up in the bags.

This raises for me the question of what kind of risk this pulverized Hydroton dust might have posed to the workers who processed it. Have I caused them to be at increased risk for cancer? I don't know precisely what radionuclides were in this material, though I know natural clay often contains things like thorium, uranium, and radium, and I believe that such elements are alpha emitters that are extremely dangerous if they get into the body. Do you think throwing out this material caused any increased health risk to the sanitation workers? I am worried about whether someone might get lung cancer, leukemia, or bone cancer as a consequence. Could alerting the company at this point make any difference to the health of the workers? (This occurred five or six years ago.)

Your concern is understood and very much appreciated given that you believe you detected elevated levels of radioactivity in the clay. All rocks, soils, and minerals of the Earth contain varying amounts of naturally occurring radioactivity. This radioactivity is primarily what we refer to as the "primordial radionuclides" that is, the naturally occurring radioactive elements that have been with us since the Earth was created 4.5 billion years ago. And you are absolutely correct in that these primordial radionuclides include elements such as uranium, thorium, radium, and also a radioactive form of potassium known as potassium-40 (⁴⁰K). That being said, your concern for the health of workers who may have been exposed to the clay is very commendable, but you have nothing to be worried about as I will show you below.

Table 1 below provides some examples of the wide range of these radioactive elements contained in rocks, soils, and minerals. The amount of radioactivity is expressed in becquerels per kilogram of mass (Bq kg^-1). The becquerel is the standard international unit of radioactivity and is equal to one atom decaying in a second. Radioactive decay occurs because some atoms because have too much energy and to get rid of some of that excess energy the radioactive atom changes into a different radioactive or stable atom by emitting energy as particles (like alpha or beta particles) or photons (like gamma or x rays).

Your Geiger counter reading of the bag of Hydroton pebbles exhibited a count rate more than twice that of background makes perfect sense since the Hydroton as a mineral substance, would be expected to have more naturally occurring radioactivity than air or wood, etc.

As shown in Table 1, different rock and mineral types can have a wide range of these naturally occurring primordial radionuclides. Concentrations can vary by a factor of 10 or more, depending on the mineral, its chemical composition, and where it came from.

Table 1: Natural Radioactivity in Rocks and Minerals (Bq kg^-1)

So again, your concern for the health of workers who may have been exposed to the clay is very commendable, but you have nothing to be worried about. Many materials we use in our daily lives contain as much or a lot more naturally occurring radioactive materials than the Hydroton pebbles. So keep in mind:

• We live in a radioactive environment.
• We are continuously bombarded with radiation energy from space and from the Earth's surface.
• We take in radioactive materials with the air we breathe, the water we drink, and the food we eat.
• Our bodies contain radioactive materials.
• Minerals we use every day in construction and other consumer products contain radioactive materials.
• It has always been that way!

We hope that we have been helpful.

Steve Brown, CHP

References

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

International Atomic Energy Agency. Assessing the need for radiation protection measures in work involving minerals and raw materials. Vienna: IAEA; SRS 49; 2006.

Riekstina D, Berzins J, Krasta T, Svinka R, Skrypnik O. Natural radioactivity in clay and building materials used in Latvia. Latvian Journal of Physics and Technical Sciences. DOI: 10.1515/LPTS-2015-0018. 2015.Turhan S. Radiological impacts of the usability of clay and kaolin as raw material in manufacturing of structural building materials in Turkey. J Radiol Prot. 29(1):75–83; 2009.