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About Radiological Contaminants (Radionuclides)
Radiological contaminants (also called radionuclides) are radioactive particles that can be naturally occurring or man-made. Radionuclides have an unstable nucleus and release the excess energy (radiation) through radioactive decay. Erosion and decay of natural and man-made deposits can release radionuclides from rock and soil, entering groundwater supplies. While many radiological contaminants are natural to the environment, several are toxic to humans and can increase cancer risks. 
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Continue reading for the USEPA list of regulated radionuclides and resources for each contaminant.  
​WQRF Contaminant Occurrence Map
Check out the Contaminant Occurrence Map for visual representations of drinking water quality data for public water systems across the US.
Contaminant​
MCL*
Potential Health Effects
Resources
Alpha particles​
15 picocuries per Liter (pCi/L)
Increased risk of cancer​
Contaminant Map 
Chemicals > Gross Alpha Particle Activity
Beta particles and photon emitters​
4 millirems per year
 Increased risk of cancer​
Contaminant Map 
Chemicals > Gross Beta Particle Activity
Radon
Recommended** 300 to 10,000 pCi/L 
Inhalation of radon released from water into air linked to risk increase of lung cancer
PSU: Reducing Radon in Water [Link]
USEPA: Basic Information about Radon in Drinking Water [Link]
Radium 226 and Radium 228 (combined)​
5 pCi/L
 Increased risk of cancer​
WQA Technical Fact Sheet: Radium [Link]
Contaminant Map 
Chemicals > Radium(-226 & -228), combined
Uranium
30 ug/L 
Increased risk of cancer, kidney toxicity
WQA Technical Fact Sheet: Uranium [Link]
​Contaminant Map 
Chemicals > Uranium, combined
*MCL = Maximum Contaminant Level - The highest level of a contaminant that is allowed in drinking water
​**Radon is not currently regulated under The National Primary Drinking Water Regulations (NPDWR)​ 
Resources
  • USEPA: Natural Radionuclides in Public Drinking Water [Link]
  • USEPA: Radionuclides Rule [Link]
  • USGS: Radionuclides [Link]
  • USGS: The quality of our Nation's waters: Water quality in principal aquifers of the United States, 1991-2010 [Link]