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08 February 2012

Answer to Question #8596 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Therapeutic Nuclear Medicine

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

My son is going to receive 150 mCi of radioactive iodine-131 and is being treated as an outpatient. He will be staying at our house, and we are on a septic system. Will the radiation affect the flora of the septic system? Will it have any effect on how our septic system functions?

There is not enough radioactivity in 150 millicuries of iodine-131 to kill the bacteria in your septic tank. The Environmental Protection Agency website lists the doses to kill bacteria for food irradiation. They range from 1 to 30 kilogray (1 kilogray is 100,000 rad). That is an exceedingly high radiation dose. A colleague of mine did a calculation and came up with a potential dose of 15 rad to the contents from the excreted iodine-131. Compared to 100,000 rad, 15 rad is tiny.

I think that you can feel safe that your septic tank will not be affected. Additionally, the iodine-131 decays with a half-life of eight days so it decays to essentially nothing in two months.

Marcia Hartman, MS

Answer posted on 19 October 2009. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.