Which material is prohibited from disposal in the sewage system according to NRC regulations?

Unused I-123 sodium iodide capsules are prohibited from disposal in the sewage system according to NRC regulations primarily due to the potential risk they pose as radioactive materials. The capsules contain a radioactive isotope that remains hazardous to human health and the environment until it decays to safe levels. Proper disposal methods are essential to ensure that such radioactive waste does not enter the water supply, where it could lead to contamination and pose health risks to nearby populations.

In contrast, other materials listed have specific disposal protocols outlined by NRC regulations. For example, feces from a patient who received I-131 therapy can typically be disposed of in the sewage system after a specified period, since the radioactivity decreases significantly over time in those bodily waste products. Saliva or spit from procedures involving 99mTc may also be permitted for disposal in the sewage under controlled circumstances, as the radiation exposure from such small amounts is often considered negligible. Similarly, urine from a renal test is usually managed based on its low levels of radioactivity and potential for natural dilution in sewage systems. Each of these other materials has guidelines that effectively mitigate any associated risks, allowing them to be treated differently from unused radioactive pharmaceuticals.