Sources of harmful radioactive isotopes in wastewater collection systems include:

• A. Hospitals
• B. Research labs
• C. Tracer studies
• D. All of the above

Answer: (D)

Radionuclides can enter wastewater from any activity that uses or generates radioactive material. Hospitals release radioactive substances through patients who have received diagnostic or therapeutic procedures, so their effluent can carry radionuclides into the sewer system. Research laboratories work with various isotopes in experiments, producing liquid waste that may contain residual radioactivity if not properly contained and treated. Tracer studies intentionally use radioactive tracers to track water flow and mixing, and those tracers end up in wastewater when discharged. Since all three sources can contribute, the best answer is the one that includes all of the above. This understanding helps explain why wastewater systems need monitoring and appropriate treatment for potential radioactive contaminants.