At a glance
| Chemical family | Naturally-occurring radioactive alkaline-earth metal, in the same group as calcium — which is why the body handles it like calcium and deposits it in bone. The regulated form in water is combined radium-226 (uranium series) plus radium-228 (thorium series). |
| CAS number | 7440-14-4 (elemental radium) |
| Classification | Radium-226 and radium-228 (and their decay products) are IARC Group 1 — carcinogenic to humans. The drinking-water hazard is radiological: a cumulative, long-term bone-cancer and leukemia risk. EPA MCL for combined radium 5 pCi/L. |
| Where you encounter it | Naturally in groundwater — private wells and some public systems in radium-bearing geology (parts of the upper Midwest, the Piedmont, the Southwest). It is a decay product of uranium and thorium in rock. Mining, oil-and-gas produced water, and phosphate processing can add to it locally. |
| Sleep micro environment relevance | Indirect — an ingestion exposure via drinking water, on the Atlas as part of the tap-water picture and the private-well testing story the water hub anchors. |
| Activated carbon capture | Not removed by standard carbon. Removal uses ion exchange (a softener's cation resin), reverse osmosis, or radium-selective media. Inferred from standard radium water-treatment engineering; radium behaves as a divalent cation like calcium |
Regulatory & certification status
Radium is regulated as a radionuclide, with a limit set on the added lifetime cancer risk from drinking the water for many years. The rows below give the standards and the natural-occurrence context.
| United States | EPA set an enforceable Maximum Contaminant Level of 5 pCi/L for combined radium-226 and radium-228 in the 2000 Radionuclides Rule (compliance from 2003); the same rule caps gross alpha activity at 15 pCi/L. The limit dates conceptually to the original 1976 interim radionuclide standard. Regulatory — US EPA |
| Cancer classification | The International Agency for Research on Cancer classifies radium-226 and radium-228, and their decay products, as Group 1 — carcinogenic to humans, on the strength of the bone-cancer evidence in radium-exposed populations. Regulatory — IARC |
| World Health Organization | WHO addresses radium within its guidance on radionuclides in drinking water, using a screening approach based on total indicative dose rather than a single radium number, with follow-up testing when gross alpha/beta screening levels are exceeded. Regulatory — WHO |
| The 72-hour test window | Not applicable. Radium is a waterborne ingestion exposure measured by a specialized radiological water-lab test (combined radium, gross alpha), unrelated to the VOC-emission chamber tests used for mattresses and foam. Inferred — from the ingestion-via-water route versus the material/VOC focus of product emissions testing |
What it is
Radium is a naturally-occurring radioactive metal — an alkaline-earth element sitting directly below calcium, barium, and strontium in the periodic table. That chemical kinship is the whole story of why radium is dangerous inside the body: cells that handle calcium cannot fully tell radium apart, so ingested radium is routed to bone and its mineral surfaces, where it lodges and slowly irradiates the surrounding bone marrow and tissue.
The two isotopes that matter in water are radium-226, a member of the uranium-238 decay series (half-life about 1,600 years), and radium-228, from the thorium-232 series (half-life about 5.75 years). Both are alpha- and beta-active through their decay chains, and both are regulated together as "combined radium." Radium-226 also decays to radon-222, tying water radium to indoor-air radon in the same geologies.
The hazard from radium in water is radiological and cumulative: it is not an acute poison, and drinking slightly-elevated water for a day is not an emergency. The concern is decades of ingestion delivering a small internal radiation dose to bone, which raises the lifetime risk of bone cancer (osteosarcoma) and leukemia. That long, quiet timescale is exactly why a number and a test matter — the harm doesn't announce itself.
Where you encounter it
From radium-bearing geology
The dominant source. Radium dissolves into groundwater as it moves through rock containing its uranium and thorium parents — certain deep sandstone and carbonate aquifers, and granite regions. Naturally elevated radium is well documented in parts of the upper Midwest (notably deep sandstone aquifers), the Piedmont, the Central Plains, and the Southwest. Wells drawing from these formations can exceed 5 pCi/L on geology alone.
From uranium's decay chain
Because radium is a decay product of uranium and thorium, it travels with them: water high in uranium or radon is a reason to check radium as well, and vice versa. The three are best thought of as one natural-radionuclide cluster in a given aquifer.
From industrial additions (secondary)
Mining and milling, oil-and-gas "produced water" (which can be radium-rich), and phosphate processing can raise radium in local water and generate radium-bearing wastes (TENORM). These are secondary to natural geology for most affected wells but matter near those activities.
What the research says
The bone-cancer evidence
Radium's carcinogenicity is not theoretical — it is among the most directly documented in occupational medicine. The radium-dial painters of the 1910s–1920s, who ingested radium by tipping their brushes with their lips, developed characteristic bone sarcomas and jaw necrosis; the long-running US radium studies that followed established the dose–response for radium-induced bone cancer. Regulatory This human evidence is the basis for the IARC Group 1 classification.
The drinking-water risk
At the far lower concentrations found in drinking water, the risk is a small added lifetime cancer probability rather than the acute bone disease seen at the extreme historical doses. Inferred from the regulatory basis — the 5 pCi/L MCL is a lifetime-risk cap extrapolated from the higher-dose human data The regulatory limit is set to keep that added risk within the range EPA treats as acceptable for a lifetime of exposure — which is why the response to an over-limit well is treatment, not alarm.
What helps
On a well in radium geology, test for it. Combined radium (and gross alpha) can be added to a well-water panel. Households in the upper Midwest sandstone belt, the Piedmont, and other known regions — and anyone who finds elevated uranium or radon — most need the number.
For water over 5 pCi/L, use ion exchange or reverse osmosis. A cation-exchange water softener captures radium along with hardness; point-of-use reverse osmosis handles drinking and cooking water. Radium-selective media exist for higher loads. See water filters compared.
Check the whole radionuclide cluster. Elevated radium is a reason to test uranium and radon (in both water and indoor air), since they share the same geology.
What does NOT help
- Boiling. Radium is a dissolved metal; boiling concentrates it as water evaporates, like other dissolved contaminants.
- Standard carbon pitcher filters. They don't remove radium. Use ion exchange, RO, or media rated for radium.
- Treating it as an acute poison. The radium water risk is cumulative over years; the response is testing and treatment, not panic over a single glass.
- Assuming city water has it. Public systems monitor and treat for combined radium; the concern is overwhelmingly private wells.
Open questions
- The exact shape of the low-dose bone-cancer risk from lifetime water ingestion — extrapolated from much higher historical doses — carries real uncertainty. Speculation re: precise low-dose slope; the high-dose carcinogenicity is established
- How to best account for the combined dose from radium plus co-occurring uranium and radon in the same water is still refined. Speculation
- National mapping of radium in private wells, and testing uptake in high-radium regions, remains incomplete. Inferred from USGS groundwater survey work and well-testing rates
Where you meet Radium across your home
The same compound turns up in more than one place you live. Here's where it shows up in Embr — each links to the full breakdown for that part of your home.
Citations
- US Environmental Protection Agency (2000). Radionuclides Final Rule — combined radium-226/228 MCL 5 pCi/L (compliance 2003). epa.gov Regulatory
- Agency for Toxic Substances and Disease Registry (1990). Toxicological Profile for Radium. atsdr.cdc.gov Regulatory
- International Agency for Research on Cancer. Radium-226/228 and decay products — Group 1, carcinogenic to humans (Monographs Vol. 100D). iarc.who.int Regulatory
- US Geological Survey. Occurrence of radium-226/228 in US groundwater — natural geologic distribution. usgs.gov Regulatory
Frequently asked questions
Is radium in drinking water dangerous?
At elevated levels, yes — but it's a slow, cumulative risk, not an acute one, and it's almost always natural rather than industrial. Radium is a radioactive metal that the body treats like calcium, so ingested radium concentrates in bone, where its radiation raises the long-term risk of bone cancer and leukemia. This is the same biology behind the historical "Radium Girls." It occurs naturally in groundwater in certain geologies, and because private wells are tested only by their owners, elevated radium can go unnoticed. The EPA limit for combined radium-226 and radium-228 is 5 pCi/L.
What is the safe level of radium in water?
The US EPA enforceable Maximum Contaminant Level for combined radium — radium-226 plus radium-228 — is 5 picocuries per liter (5 pCi/L), set in the 2000 Radionuclides Rule. The same rule sets a gross alpha limit of 15 pCi/L. These are radiological limits: they cap the added lifetime cancer risk from drinking the water over many years. Below 5 pCi/L combined radium is considered acceptable; above it, treatment is warranted for long-term drinking water.
How does radium get into drinking water?
Naturally, in nearly all cases. Radium is a decay product of uranium and thorium, which are present in many rocks. As groundwater flows through radium-bearing formations — certain sandstone and carbonate aquifers, and granite regions — radium dissolves into it. Parts of the upper Midwest, the Piedmont, and the Southwest have naturally elevated radium in groundwater. Human activities such as mining, oil-and-gas produced water, and phosphate processing can add to it locally, but for most affected wells the source is the geology itself.
How do I remove radium from water?
Radium is effectively removed by ion exchange (a water softener's cation resin captures radium along with hardness), reverse osmosis, and specialized radium-selective media. A standard activated-carbon filter does not remove it. For a private well over 5 pCi/L, point-of-use reverse osmosis handles drinking and cooking water, while whole-house cation exchange or a properly sized softener reduces it throughout. Because radium concentrates in the treatment media, spent resin and backwash need appropriate handling. Test first to confirm the level.
Related compounds
Embr researches the chemistry of where you live — including the natural radionuclides in well water. See the methodology page for how this Atlas tags claims by evidence strength, the tap-water hub for the other things in your water, and water filters compared for how to remove radium.
Last reviewed 2026-07-12. If you find a factual error, contact us.