Guest Column | March 18, 2014

Occupational Safety And Utility Compliance: Radioactive Iodine In Wastewater Treatment Plants

Sheldon Primus

By Sheldon Primus

Radioactive material in the environment often causes public concern or even panic. However, it is very common for wastewater treatment plants to have some radioactive material passing through the system. Radioactive material may occur naturally or through nuclear fission. Iodine-127 and Iodine-131 are the most common Iodine isotopes found in municipal biosolids, because it has a tendency to re-concentrate in the waste stream. This article will further explain the basic background of radioactive Iodine, its use, health risks, and its presence in the wastewater treatment plant.

My Story

The images of radioactive sludge in the mind can make you think of glowing green discharge leaving a plant, leaving a trail of mayhem for environmentalist and regulatory agencies. Well, indeed I felt the pangs of fear when I got a call “Hey Sheldon, the solid waste company is rejecting our sludge because the Geiger counter went off!”

Well, you don’t say! I bet I’ll have to go back into work this fine Saturday afternoon to deal with this new issue.   So, as you can imagine on my ride in to the plant my mind was racing as to how this can be possible. My Industrial Pretreatment Officer side kicked in and I thought of all the possible sources of radioactive waste. Industrial Pretreatment programs are so important to wastewater plants, because in situations like this the program officers can refer to all of the facility walk-throughs or permits that they have administered.

I then recalled the local college that has a medical research lab that has a “hot room” with radionuclides in drums waiting for the proper half-life to discharge to the facility. Yup, you read that right: There is a “proper” or “allowable” half-life for regulated facilities to discharge radionuclides to the treatment works. Well, I didn’t want my operators to look like this so, I need to find out more information.  

What Is Iodine?

Iodine is a blue/purple-black nonmetallic crystalline solid element; its chemical symbol is “I”, atomic weight: 127, and its atomic number: 53. Iodine can be found in both radioactive and non-radioactive isotopes. The Iodine-129 and Iodine-131 are valuable isotopes in the environment. Iodine-123 and Iodine-124 are generally not a problem in the environment because of the short half-lives. Iodine quickly reacts with other chemicals when present to form compounds. It is also slightly soluble in water and alcohol. It can go directly from a solid to a gas without first becoming a liquid (sublimation) at room temperature. It melts at 236 degrees Fahrenheit. 

Where Does It Come From?

Iodine-127 is present in seaweeds, sponges and other material naturally, while other isotopes are created by nuclear fission of uranium or plutonium atoms during operation of a nuclear reactor. Each isotope has specific half-lives associated with their decay rate. The half-life for the two most common isotopes are:

I-129- Half-life 15.7 million years
I-131-Half-life 8 days

How Is It Used?

The medical field uses iodine for several applications including, medical diagnostic, imaging test, treating thyroid problems, nuclear medicine, cancer treatment, and immunotherapy. Iodine can also be used for lasers (silver iodine) and photography, dyes, and as a nutrient added to table salt.

What’s In The Environment?

The ratio of Iodine-127 (stable, natural Iodine) to Iodine-129 (radioactive) in the environment is 10 million to 1 million. Iodine-129 is present in soil around the planet from the fallout of nuclear weapons testing. It can also move into the groundwater from percolation water.

What Happens To Iodine In The Body?

Iodine is an essential part of the human diet. The human body contains 10 to 20 milligrams of Iodine. It can be taken in the body through eating solid food, drinking water, or breathing air. Lack of iodine in a human’s body can produce goiters. The thyroid gland absorbs more than 90 percent of the body’s Iodine intake. Any excess iodine in the body is passed through the body through urine. 

Body Organs

Biological Half-Life/days





Kidney, Spleen, and Reproductive Organs


What Are The Primary Health Effects?

Radioactive iodine can cause thyroid problems even though they are used to diagnose and treat thyroid issues. Long-term exposure can cause nodules on the thyroid (thyroid cancer). Ironically, high doses of Iodine-131 are used to treat overactive thyroids.

What Is The Risk Of Exposure?

Thyroid cancer is the main risk from chronic exposure of radioactive iodine, though Argonne National Laboratory’s data for Iodine-131 have not shown to be carcinogenic (cancer causing) in the human thyroid. Regular low doses of radioactive iodine will reduce the activity and lowers hormone production of the thyroid gland. Epidemiological studies show that adults are less susceptible to cancer from thyroid irradiation than children.  

Radioactive Material And EPA/NRC

There are a variety of regulations for the release of radionuclide to the environment from the Department of Environmental Protection Agency (EPA) and The US Nuclear Regulatory Commission (NRC). Airborne and liquid release from nuclear reactors, governmental, and industrial facilities are regulated through these agencies. There are established Maximum Contaminant Levels (MCL) from EPA for radioactive iodine and other radionuclides for drinking water plants. NRC has a licensing system for industries that utilize radionuclides.  

NRC regulation 10 CFR 20.2003

§ 20.2003 Disposal by release into sanitary sewerage.

(a) A licensee may discharge licensed material into sanitary sewerage if each of the following conditions is satisfied:

(1) The material is readily soluble (or is readily dispersible biological material) in water; and

(2) The quantity of licensed or other radioactive material that the licensee releases into the sewer in 1 month divided by the average monthly volume of water released into the sewer by the licensee does not exceed the concentration listed in table 3 of appendix B to part 20; and

(3) If more than one radionuclide is released, the following conditions must also be satisfied:

(i) The licensee shall determine the fraction of the limit in table 3 of appendix B to part 20 represented by discharges into sanitary sewerage by dividing the actual monthly average concentration of each radionuclide released by the licensee into the sewer by the concentration of that radionuclide listed in table 3 of appendix B to part 20; and

(ii) The sum of the fractions for each radionuclide required by paragraph (a)(3)(i) of this section does not exceed unity; and

(4) The total quantity of licensed and other radioactive material that the licensee releases into the sanitary sewerage system in a year does not exceed 5 curies (185 GBq) of hydrogen-3, 1 curie (37 GBq) of carbon-14, and 1 curie (37 GBq) of all other radioactive materials combined.

(b) Excreta from individuals undergoing medical diagnosis or therapy with radioactive material are not subject to the limitations contained in paragraph (a) of this section.

[56 FR 23403, May 21, 1991, as amended at 60 FR 20185, Apr. 25, 1995]


So what does this all mean? Are your hands tied to have to accept whatever is sent to you? The answer is no. EPA acknowledges that the local and specific standards should be considered when radionuclides are concerned. The wastewater treatment plant, through its local limits, determines what wastes the plant can accept. Nothing must be allowed to interfere with the process, pass through the system, or inhibit the treatment works. 

Well, I later found out that the problem with my sludge was due to Iodine-127 and Iodine-131, which are used in the medical institutions for diagnostic imaging test, treating thyroid problems, nuclear medicine, cancer treatment, and immunotherapy. Since my plant didn’t have digesters and just a 1.5 day sludge retention time, the waste didn’t have time to decay enough to be undetectable to the solid waste agency. We didn’t have a violation with the treatment works or a process disruption by receiving this waste, so all we needed to do was hold the sludge on plant site a little longer.

So, the moral of the story is to have a great Industrial Pretreatment program and staff. They will protect your plant, give valuable information when troubleshooting plant problems, and police local industries that discharge to the facility.