Radon Gas in Vietnam's Rong Cave
A scientific discovery in a Vietnamese geopark reveals an invisible threat to those who work underground
In the spectacular Dong Van Karst Plateau Geopark of northern Vietnam, Rong Cave serves as both a vital water source for local communities and an emerging destination for adventurous tourists. But beneath its stunning geological formations lies an invisible hazard—radioactive radon gas. Scientific research has revealed that while brief cave visits pose little danger, the very people who depend on the cave for their livelihood face potentially serious health risks from prolonged exposure to this natural radioactive gas 1 .
Radon is a naturally occurring radioactive gas that you can't see, smell, or taste. It forms from the radioactive decay of uranium, which is found in small amounts in most rocks and soils. As uranium breaks down, it transforms into radium, which then decays into radon gas 2 .
When we breathe in radon, the radioactive particles can damage the delicate cells lining our lungs. This damage can eventually lead to lung cancer—in fact, radon is the second leading cause of lung cancer after smoking, responsible for approximately 21,000 lung cancer deaths each year in the United States alone 2 . For non-smokers, radon represents the number one cause of lung cancer 2 .
The World Health Organization estimates that radon causes between 3% and 14% of all lung cancers worldwide, depending on the average radon levels in each country 4 . What makes radon particularly dangerous is that there's no known safe level—even low concentrations can slightly increase cancer risk, though the risk rises significantly with higher exposure levels 4 .
A team of scientists from Vietnam National University and Indiana University recognized that Rong Cave presented a unique opportunity to study radon exposure in a real-world setting. The cave is not just a tourist attraction—its subterranean lake provides essential agricultural and domestic water for neighboring communities, meaning utility workers regularly enter for maintenance and water management 1 .
The researchers designed a comprehensive monitoring study to answer critical questions: How much radon is present in the cave air? Does it vary by season? And most importantly, what are the potential health risks for different groups of people who spend time in the cave?
To conduct their investigation, the scientists used specialized equipment and methods including portable radon monitors, repeated measurements over 10 months, and dose calculation algorithms recommended by UNSCEAR 1 .
The research focused particularly on the back portion of Rong Cave, where clay-rich sediments and possible gas seepage from deeper strata along geologic faults were suspected to create seasonally elevated radon concentrations 1 .
| Equipment/Tool | Primary Function | Application in Rong Cave Study |
|---|---|---|
| Portable Radon Monitor (SARAD® RTM 2200) | Detect and measure radon and thoron gas concentrations | Continuous monitoring of cave air radioactivity |
| Solid-State Nuclear Track Detectors | Passive, long-term radon measurement | Not used in this study but common in similar research |
| Scintillation-Based Systems | Measure radon decay products | Not used in this study but standard in field |
| UNSCEAR Algorithms | Calculate human radiation doses | Estimated annual inhalation doses for different user groups |
| Meteorological Instruments | Track temperature, pressure, humidity | Correlated environmental factors with radon levels |
Table: Essential research equipment for radon studies 1
The findings, published in the Vietnam Journal of Earth Sciences, revealed significant differences in risk depending on how much time people spent in the cave 1 .
| User Group | Estimated Annual Radiation Dose | Comparison to Safety Standard |
|---|---|---|
| Short-term visitors | Minimal | Well below safety threshold |
| Tour guides | ~1.8 millisieverts (mSv) | Exceeds 1 mSv safety standard |
| Cave utility workers | ~25 millisieverts (mSv) | Greatly exceeds 1 mSv safety standard |
Table 1: Annual radiation exposure for different cave user groups 1
| Radon Level | Lung Cancer Risk for 1,000 Never-Smokers | Lung Cancer Risk for 1,000 Smokers |
|---|---|---|
| 0.4 pCi/L (Average outdoor level) | Minimal risk | About 3 people could get lung cancer |
| 1.3 pCi/L (Average indoor level) | About 2 people could get lung cancer | About 20 people could get lung cancer |
| 4 pCi/L (Action level in homes) | About 7 people could get lung cancer | About 62 people could get lung cancer |
| 20 pCi/L (High concentration) | About 36 people could get lung cancer | About 260 people could get lung cancer |
Table 2: Radon risk comparison for different exposure levels. Note: pCi/L = picocuries per liter, a unit of radioactivity. Data from US EPA 2 .
These numbers become more meaningful when compared to established safety standards. The International Atomic Energy Agency (IAEA) recommends an annual safety threshold of 1 millisievert (mSv) for the general public 1 . While we're all exposed to natural background radiation (about 3 mSv per year globally), additional exposures above this level are concerning from a health perspective.
The Rong Cave study contributes to a substantial body of scientific evidence about radon's health effects. Multiple comprehensive studies have confirmed the link between residential radon exposure and lung cancer 2 .
Two major studies—one in North America and one in Europe—combined data from several previous residential studies and provided definitive evidence that breathing low levels of radon in homes does increase lung cancer risk 2 .
This connection was first observed in underground miners, who historically showed higher rates of lung cancer. The BEIR VI report (Biological Effects of Ionizing Radiation) from the National Research Council analyzed data from 60,000 miners worldwide and found their lung cancer rates increased with cumulative radon exposure 4 .
Based on their findings, the research team offered specific recommendations to protect people who work in Rong Cave 1 :
Implement regular radiation monitoring for cave utility workers and tour guides to track exposure levels and identify high-risk periods.
Avoid prolonged human presence in the cave during periods of seasonally elevated radon concentrations to minimize health risks.
Develop awareness programs to educate workers about the potential hazards and proper safety protocols when working in radon-prone environments.
For homeowners concerned about radon, the solutions include testing (with inexpensive home test kits), increasing ventilation, and sealing foundation cracks. The U.S. Environmental Protection Agency recommends fixing homes when radon levels exceed 4 pCi/L 2 .
The Rong Cave study demonstrates how scientific research can identify hidden environmental health risks and provide guidance for protecting vulnerable populations. While the majestic cave continues to provide water for local communities and wonder for visitors, we now understand the invisible challenge it presents.
Thanks to meticulous data collection and analysis, we know that seasonal patterns affect radon concentrations, and that different groups face different levels of risk 1 . This knowledge enables targeted protection strategies that can help ensure the cave remains a resource without becoming a health hazard.
The story of Rong Cave reminds us that our beautiful planet sometimes hides unexpected dangers—and that scientific research provides the tools to find them, understand them, and manage them effectively.