Gross Alpha Particle Activity
α·Affects bones, kidneys
A composite measure of alpha-emitting radioactivity in water, used as the EPA's first-line screen for radionuclide contamination. Excludes radon and uranium, which are tested separately.
α
EPA limit
15 pCi/L (excluding radon and uranium, MCL)
Most at risk
Well-water households, residents of regions with naturally elevated radioactivity in groundwater
Found in
Well water
AquaOx filters
Pair with ROPair with RO (depends on specific isotope)
What it does to you
Health effects
Gross alpha is not a single contaminant but a measurement: the total activity of all alpha-emitting radioisotopes in a water sample, with radon and uranium subtracted. The most common isotopes captured by the test are Ra-226, Po-210, and a mix of thorium and minor radium daughters.
The health concern is the cumulative dose from alpha-particle radiation. Alpha particles cannot penetrate skin from outside the body, but when ingested they irradiate the cells of the digestive tract and any organs where the parent isotope accumulates. Bone-seeking isotopes (radium, thorium) elevate bone-cancer and leukemia risk. Soft-tissue accumulators (polonium) elevate liver and kidney risk.
The EPA Maximum Contaminant Level of 15 pCi/L for gross alpha is a screening threshold. A sample above 15 pCi/L triggers follow-up testing to identify which specific isotopes are responsible, so the appropriate treatment can be selected.
Where it comes from
How it gets into your water
The contributors to gross alpha activity are the same naturally occurring radionuclides that show up individually in radium and uranium testing: decay products of the uranium-238 and thorium-232 series, leached from uranium-bearing or thorium-bearing rock as groundwater moves through it.
Affected regions overlap heavily with the radium and uranium hotspots: the Cambrian-Ordovician sandstone aquifer in the Upper Midwest, the Carolinas Piedmont, parts of the Texas Gulf Coast, the Rocky Mountains, and New England granite country. Legacy uranium mining and phosphate processing add localized industrial contributions in specific basins.
Uranium and thorium bedrock
Decay-chain isotopes leach into groundwater
Sandstone and granite aquifers
Same geology that produces elevated radium
Legacy mining and milling
Localized contributions in mining basins
Phosphate processing
Historical contamination in parts of Florida
Find out for yourself
Is it in your water?
Public utilities are required to test for gross alpha under the EPA Radionuclides Rule. A result above the 15 pCi/L MCL triggers isotope-specific follow-up testing for radium, polonium, and other contributors. Results are summarized in each utility's annual Consumer Confidence Report.
Private well owners in known hotspot regions should request a gross alpha screening through their state environmental health department or a certified lab. The screening test typically costs $50 to $100. If the screening exceeds the action level, the lab will run isotope-specific panels to identify the contributing radionuclides, which is essential because different isotopes require different treatment approaches.
The fix
How AquaOx filters it
Gross alpha is not a single contaminant, so there is no single filtration solution. Effective treatment depends on which specific isotopes are responsible for the activity. The standard AquaOx whole-house carbon and KDF media is not optimized for the most common alpha emitters (radium, polonium, thorium).
For households with elevated gross alpha, we recommend pairing AquaOx with an under-sink reverse osmosis unit at the kitchen tap. RO is the most universal solution because it rejects nearly all dissolved radionuclides at the membrane regardless of isotope. If isotope-specific testing identifies radium as the dominant contributor, a properly maintained water softener will also filter much of it through cation exchange.
Always identify the specific isotopes before selecting equipment. Your state environmental health department is the right starting point for both initial screening and follow-up isotope panels.