What comes up from below, and the small thing to do about it.
ActSmall · Ground is a free, map-first portal for the radiation and contaminants that come up out of the soil under your home. Click any country to see indoor-radon readings where national surveys exist, adult smoking prevalence (because the two multiply), drinking-water access gaps, and arsenic-affected aquifers where the WHO has documented them. The headline action is usually a $20 home test kit. No accounts. No tracking. Nothing for sale.
Information only.
This site is not radiological, medical, remediation, or treatment advice. For active radon mitigation, suspected well-water contamination, or any acute radiation incident, contact a qualified radon professional, your national radiation protection agency, your water utility, or a medical professional. Read more about scope →
What the map shows
Indoor radon, where surveyed
National arithmetic-mean indoor radon concentrations from named radiation protection agencies (UKHSA, EPA, BfS, SURO, SSM, IRSN, STUK, Health Canada, ARPANSA, and equivalent bodies), classified into elevated, moderate, low, or unsurveyed. Where no comprehensive national survey exists, we display no current reading rather than guessing.
Adult smoking prevalence (World Bank)
Adult current tobacco use prevalence as a share of the population (SH.PRV.SMOK, World Bank Open Data, sourced from WHO Global Health Observatory). Smoking and radon interact multiplicatively in the lung-cancer literature, so the map computes a joint indicator from the two.
Joint radon and smoking risk
A simple computed product of the radon classification and the smoking prevalence. The countries that light up here are the ones where the international cancer agencies have repeatedly identified the highest preventable household-radiation risk - and where a $20 test paired with a cessation conversation is the highest-leverage individual action available.
Safely-managed drinking water gap
Percentage of population without safely-managed drinking water (computed from SH.H2O.SMDW.ZS, World Bank, sourced from WHO/UNICEF Joint Monitoring Programme). Private and small-municipal well users are the population most exposed to naturally-occurring groundwater contaminants like arsenic, radium, and uranium.
Arsenic-affected aquifers, where documented
Country-level flags for the WHO-documented arsenic-affected aquifers - the Bengal basin (Bangladesh, parts of India, Nepal), the Mekong delta (Vietnam, Cambodia), the Chaco-Pampean plain (Argentina), the Hetao basin (Inner Mongolia), and the recognised US, Mexican, and Chilean aquifers. The action for affected basins is targeted well testing.
One next step per country
Every click surfaces one concrete next step that fits the local picture: test your home for radon (the dominant story in most temperate countries with surveyed geology); test your private well (where arsenic basins or aquifer chemistry warrants it); support WHO/UNICEF rural-water work where the access gap is the headline; or just read the primer first.
Why radon, why now
Indoor radon is the second-leading cause of lung cancer after smoking. The World Health Organization, the International Agency for Research on Cancer, and the US Surgeon General all publish converging estimates: residential radon is responsible for somewhere between 3 and 14 percent of all lung-cancer deaths depending on country, with the upper end of that range falling on countries with elevated indoor radon and high smoking prevalence at the same time. The two risks multiply - a smoker in a radon-elevated home faces something like an order of magnitude higher excess lung-cancer risk than a non-smoker in the same home, because the damage pathways compound.
None of that is new. It has been the WHO position since 2009 and the EPA position since the 1980s. What is missing is awareness in the joint-risk population - the people for whom the science is clearest and the action is cheapest. The map exists to surface those places.
From recognition to action, in one click
Click into any country and the map picks one concrete next step that fits it, based on the live data:
Test your home for radon
If the country has documented elevated indoor radon, the headline action is a short-term home radon test. A $15-30 kit goes on the lowest lived-in level for 2 to 7 days, then back in the post to a certified lab; you get a value in Bq/m3 or pCi/L. The WHO recommends action above 100 Bq/m3.
Pair with cessation support
If radon and smoking are both elevated, the same kit is paired with a single phone call or web-form sign-up at a named national quitline. Both decisions on the same day. The lung-cancer math says this pairing has the highest expected outcome of any household-radiation action.
Test your private well
If the country contains a documented arsenic basin or has a large private-well population, the action shifts to well water testing - usually for arsenic, radium, uranium, nitrates, and bacteriological contaminants. National environmental agencies maintain lab lists.
Read the primer
For any country, the recommender also surfaces one entry from the library: the radon primer, the personal dose budget, or the “what this site does not cover and why” explainer. No slogans - the data, the disputes, and what the WHO actually says.
Help fill the survey gap
Countries without a comprehensive national radon survey are not in the “safe” column - they are in the “unknown” column. The action there is writing to your national health ministry or environmental agency in support of a national survey, or publishing your own home test reading openly.
Ask about your next scan
For any country, the universal-action list includes a primer-backed prompt: before your next non-emergency CT, ask whether MRI or ultrasound could replace it for the same answer, and whether the dose can be lowered. Image Gently and Choosing Wisely both publish patient-facing scripts.
Below the headline action sit two small affordances: 30-day reminder downloads a calendar event so the commitment outlives the moment; Tell two people uses your share sheet so reach multiplies without friction. Nothing is tracked or sent anywhere.
And a small library, alongside
The map answers where and what next. The library answers why and how - for anyone who wants to understand the underlying physics, public-health, and policy before they act on it.
- Primers. The single most-misunderstood thing in public radiation coverage is the proportion of dose that comes from indoor radon (a colourless soil gas with a $20 test kit) versus the cinematic sources people argue about online. Read that first.
- What this site does not cover. 5G, smart meters, microwave ovens, and consumer wireless are not on the map - not from squeamishness, but because the WHO and IARC do not class them as a public-health story at consumer exposures. The primer cites their actual positions.
- Project cards. Single-page printable guides - test your home for radon, test your private well. Things a normal person can do this weekend with no special equipment that produce a real reading.
Plain English, source-cited, published under CC BY-SA 4.0 - copy, translate, adapt, and republish freely; please keep source citations intact.
How the data stays current
A small scheduled job pulls public feeds once a day - World Bank Open Data for adult tobacco use prevalence and the drinking-water access gap, joined against hand-authored country-level indoor-radon baselines from the WHO Handbook on Indoor Radon and named national radiation protection agencies (UKHSA, EPA, BfS, SURO, SSM, STUK, IRSN, Health Canada, ARPANSA, and others). The same job revalidates every external link the recommender might surface, so dead links are caught the next morning rather than by you. Your browser only ever talks to our own server for the data layers. We never scrape; we only consume documented public APIs at their publication cadence.
Read more in methodology.
What this site is not
It is not a radon mitigation manual. We do not tell you how to seal a basement, fit a sub-slab depressurisation system, or operate a heat-recovery ventilator - we point you at the named certified-professional networks that do (AARST in the US, UKHSA's qualified-installer list in the UK, the equivalent national programs elsewhere). Mitigation engineering is a regulated trade in most affected countries for good reason.
It is not a medical or dose-prescription site. We do not tell you whether a given Bq/m3 reading is “safe” or what you should do clinically. We display what the WHO, the IARC, and named national agencies have published, with their citations visible, and let you decide.
It is not a 5G or EMF tracker. The WHO and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) have repeatedly found no established public-health hazard at consumer exposures to radiofrequency electromagnetic fields, and the IARC's 2B (“possibly carcinogenic”) classification covers high-use mobile-phone proximity, not ambient cell-tower or Wi-Fi exposure. We display what those bodies say in their own words on the “what this site does not cover” primer; we do not add a map layer that would imply otherwise.
It is not exhaustive. Background radiation, cosmic dose at altitude, medical imaging dose averages, mining legacy, atmospheric weapons-test fallout, and consumer NORM (granite countertops, alum-shale concrete) are all real subjects in the ionizing-radiation literature. We touch them in the library where the action is clear and skip them in the map where it is not.