What is the National Primary Drinking Water Regulations Maximum Contaminant Level (MCL) for Beta particles and photon emitters?

What is the National Primary Drinking Water Regulations Maximum Contaminant Level (MCL) for Beta particles and photon emitters?

• A. 4 mrem/yr
• B. 5 mrem/yr
• C. 15 mrem/yr
• D. 30 mrem/yr

Answer: (A)

The key idea is that some drinking-water contaminant limits are based on radiation dose rather than a simple concentration. For beta particle and photon emitters, the standard sets a maximum allowable dose to the whole body of the public per year, not a specific weight or activity of radionuclide. That dose limit is 4 mrem per year. Using a dose-based limit ensures consistent protection across different beta and gamma emitters, since different radionuclides vary in energy and how they affect the body. The value was chosen to represent an acceptable level of cancer risk from drinking water over time.

The key idea is that some drinking-water contaminant limits are based on radiation dose rather than a simple concentration. For beta particle and photon emitters, the standard sets a maximum allowable dose to the whole body of the public per year, not a specific weight or activity of radionuclide. That dose limit is 4 mrem per year. Using a dose-based limit ensures consistent protection across different beta and gamma emitters, since different radionuclides vary in energy and how they affect the body. The value was chosen to represent an acceptable level of cancer risk from drinking water over time.