Radon is a naturally occurring radioactive gas which comes from uranium and radium. Trace concentrations of these elements are found in soils, rocks and building materials. Radon is naturally present in low concentrations in the air. But it can build up indoors in spaces that are poorly ventilated or underground.

Health effects of radon

If radon gas or its radioactive by-products are inhaled, they can damage lunge tissue, which can lead to the development of lung cancer. The vast majority of lung cancer cases — about 90% — are caused by smoking, but studies have shown that radon is also a factor, playing a part in around 10% of cases.

Smoking plays a role here too as it appears that most radon-related lung cancer cases are in people who also regularly smoke. The combination of smoking and radon magnifies the risk of lung cancer by up to 25 times, compared to that of someone who has never smoked. It’s clear that the best thing you can do to protect yourself from lung cancer is to be smoke free.

Most people in Aotearoa New Zealand would be exposed to relatively low levels of radium. It is difficult to quantify the risk though it appears for every 100 Bq/m3 of radon gas a person is exposed to, their risk of lung cancer is increased by 16% — 100 Bq/m3 would be around 4 times the level of exposure for most New Zealanders, much lower than international guidelines.

How much radon you are exposed to

New Zealand soils only contain traces of uranium and radium (the sources of radon). Most people are only exposed to very small amounts of radon.

People in New Zealand are exposed to around 2 mSv of radon per year. This is about double their natural dose of radiation. The rest comes from:

  • cosmic radiation
  • building materials
  • food
  • water
  • traces of other natural radioactivity in the soil
  • naturally occurring levels in our bodies.

For comparison, someone undergoing a CT scan of their chest receives around 7 mSv from the procedure.

Radon levels in New Zealand

Radon levels in Aotearoa New Zealand are generally low, and similar to most places overseas.

A 1988 national survey measured radon levels in 8 to 10 houses in each electorate in Aotearoa and found the average radon level to be 18 Bq/m3. A more recent study performed in 2016 focussing on radon levels in Auckland, Christchurch, Wellington and Dunedin. This study found that the national median radon concentration is 23 Bq/m3. The radon levels were similar in both surveys and were found to be comparable to those found in most places overseas. They were also well within the World Health Organization’s recommended levels.

Two studies have been conducted on radon in workplaces where radon levels would be expected to be much higher. The 2000 study focused on radon in mines and Hydro dams and found an average radon level of 105 Bq/m3. One mine had an average radon level of 276 Bq/m3 due to poor ventilation. A 2023 pilot study assessed radon levels in ten selected workplaces which were at a higher risk for radon exposure. This study found that workplaces which had underground rooms or caves with poor airflow had average radon levels between 130 Bq/m3 and 580 Bq/m3.

These results demonstrate that on average radon levels in New Zealand are low, except for some enclosed spaces with poor airflow. In these instances, the results have been provided to the workplaces with advice to look at ways to improve ventilation.

Previous radon studies

Safe radon levels

It is recommended that radon levels are kept as low as possible. The World Health Organization recommends that indoor radon reference levels be set between 100 and 300 Bq/m3.

Most places in Aotearoa New Zealand have radon levels which are far below these levels.

The biggest risk from radon exposure comes when it is paired with cigarette smoking. Although there are fewer studies in this area, evidence suggests that vaping also has the potential to increase your risk from radon. The best way to protect yourself from the risk from radon is by not smoking or vaping.

Any workplaces that have radon levels above the recommended level, or would be expected to have higher levels, should take steps, such as increasing ventilation, to reduce their potential radon exposure.

How to know if you have elevated radon levels

Places that are more likely to have elevated radon levels are often underground locations, ground level rooms with poor airflow or rooms storing radium such as old aircraft dials. The only method of determining the radon levels is by performing a test.

Recent changes

In 2010 and 2014 the International Commission on Radiological Protection (ICRP) released two new publications on the risk of lung cancer from radon. In these publications the ICRP doubled the estimated risk of lung cancer from radon based on new research results.

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