Hot or Not: What Causes Certain Locations to Have Higher Natural Radioactivity?

Radiation isn't confined to places like Chernobyl or the areas near nuclear reactors. It naturally occurs across the globe. That said, some regions have much higher natural radiation levels than others.

So, what exactly is natural radiation, and how does it form? 'Radiation is energy emitted by unstable atoms. These atoms were formed at the start of the universe more than 4 billion years ago,' says John A. Shanahan, president of Environmentalists for Nuclear Energy – USA, in an email. 'Over time, many of these unstable atoms have emitted enough energy (radiation) to become stable and stop emitting radiation. Some continue emitting radiation at such a gradual pace that they remain unstable. This ongoing radiation is the 'natural radiation' we detect in the earth, water, and air.'

No matter where you reside, some level of natural radiation is inevitable. The International Atomic Energy Agency (IAEA) estimates that the average radiation exposure from natural sources such as radon and thoron is about 2.4 millisieverts (mSv) annually, though it can vary by hundreds of percent. For context, a single chest X-ray exposes you to 0.2 mSv of radiation. Meanwhile, the International Commission on Radiological Protection recommends that 'radiation workers' (like those at nuclear plants) limit their exposure to no more than 100 mSv over a five-year period.

Naturally occurring radioactive elements come from three main sources: soil, stones, and cosmic rays that travel to Earth from space. Some cities worldwide have developed reputations for having unusually high levels of natural radiation.

For instance, the people of Ramsar, Iran are regularly exposed to radiation emitted from the area's nine hot springs, a popular spot for both locals and tourists who use them as spas. Radium in the mineral water of the hot springs, as well as high thorium content in travertine deposits (a form of limestone found in mineral springs) and uranium in the region, contribute to its elevated radiation levels. In fact, Ramsar's radiation levels can reach up to 200 times normal levels, making it the location with the highest natural radiation globally.

In Southern Australia, the Arkaroola Wilderness Sanctuary is home to hot springs with higher-than-average radiation levels, due to the spring water coming into contact with rocks rich in uranium and radon.

If you're uneasy about radiation exposure, you might want to reconsider stepping onto the beaches of Guarapari, Brazil. This well-known tourist destination is infamous for its beaches rich in radioactivity, with readings reaching as high as 175 mSv. The radioactivity comes from monazite, a mineral ore containing thorium, found in local mountains and eroded over time. The same type of thorium-rich sand also contributes to high radiation in Kerala, India, and Yangjiang, China. Experts from the IAEA note that "the largest source of natural radiation comes from varying amounts of uranium and thorium in the Earth's soil."

Radiation exposure is known to damage tissues and can lead to cancer or even death when the dose is sufficiently high, as seen in those exposed to atomic bombs in Hiroshima and Nagasaki. However, residents in areas with high natural radiation don't seem to experience adverse effects. "These regions have radiation levels higher than those allowed for workers in nuclear power and nuclear medicine, yet the people live healthy lives, often even healthier than those exposed to less radiation," says Shanahan. He adds, "All life has adapted to natural radiation, allowing us to thrive. If it hadn't, humanity would have perished long ago."

Shanahan explains that while sunshine is a form of natural low-energy radiation capable of causing illness and cancer, it's not something we typically try to eliminate. Despite the common use of sunscreen to protect against sun radiation, it doesn't mean we should aim to 'clean up' towns with natural radiation exposure. In fact, Shanahan notes that cases of death from natural radiation are rare, and stopping it is likely impossible. He adds, "Radiation continues until the unstable atom decays and reaches a stable state. It's a completely natural process, much like going to the bathroom or vomiting."