As radionuclides decay, they are transformed into one or more nuclides. During the decay process, nuclides emit protons and neutrons (alpha emissions).
The State of California regulates radionuclide concentrations in drinking water supplies due to the potential health hazards associated with exposure to various radionuclides that contribute to the gross alpha emissions.
Measurement of the gross alpha emissions is used to establish the potential for high concentrations of certain radionuclides in a given water supply. A gross alpha analysis yields an estimate of the total alpha emissions from all decaying radionuclides in a sample, but does not speciate radiological constituents.
Gross alpha test results are used to determine the need to further analyze a sample to identify the radiological constituents. Radioactive substances regulated by the State are given in the following table.
Where to Begin
In order to comply with the most stringent of the MCLs (combined Radium-226 and -228), a gross alpha analysis may be used as long as it meets the MDA for Radium-226 and -228 (1 pCi/L).
The Next Step
If your Gross Alpha result exceeds 5 pCi/L, additional testing is required. Speciation tests would determine compliance or non-compliance with the standards.
The first such speciation test is usually uranium rather than radium, because uranium can be speciated easier and is the most probable radionuclide source of the gross alpha count. Once the portion of the total gross alpha attributable to uranium is known, the remaining portion is potentially attributable to radium.
|Type of Radioactivity||Required MDA*||MCL**|
|Combined Radium-226 and Radium 228||1 pCi/L||5 pCi/L|
|Gross Alpha particle activity (including Radium-226 but excluding Radon & Uranium||3 pCi/L||15 pCi/L|
|Total Uranium||1 pCi/L***||20 pCi/L|
|Gross Beta||4 pCi/L||50 pCi/L|
|Tritium||1,000 pCi/L||20,000 pCi/L|
|Strontium 90||2 pCi/L||8 pCi/L|
*MDA= Minimum Detectable Activity
**MCL= Maximum Contaminant Level
***SRLB DLR; U.S. EPA does not regulate Uranium
|Constituent||EPA Method||Standard Method|
|Water||Gross Alpha||900.0||7110 B|
|Gross Alpha||7110 C|
|Gross Alpha & Beta||900.0||7110 B|
|Gross Beta||900.0||7110 B|
|Radon in Water||Draft Method 913.0|
|Total Radium||903.0||7500 RAB|
|Gross Alpha & Beta||7110|
|Gross Alpha & Beta||9310||7110|
*Not recommended for Drinking Water
Which Method to Use
Gross Alpha activity can be obtained by either of two methods: EPA 900.0 or by co-precipitation, SM7110 C. If a sample has high solids, 900.0 cannot be utilized due to the hampering effect of the solids on the alpha emissions. Also, an adequate sample volume cannot be utilized to meet an MDA of 1 pCi/L. In those cases, method SM7110 C should be utilized.
Certifications and/or Accreditations
|California Department of Public Health (CDPH)
Drinking water, wastewater, and hazardous waste