Indoor climbers could be putting themselves at risk of cancer and other diseases.

A study has found that the air in popular indoor rock climbing wall facilities is laden with potentially toxic rubber particles.

Scientists sampled the air in two climbing gyms as well as dust samples from those and two other facilities. 

Concentrations of some of the rubber particles found swirling through the air exceeded those in several global megacities. 

The graphic created by the researchers shows the four types of samples analyzed in their study

The researchers sampled climbing shoes, the powder left behind on footholds, air in the climbing halls, and dust that had settled around the facilities

The team of scientists found nine of the 15 rubble particles they tested for in air samples and 12 out of the 15 in dust samples.

The substances are not all carcinogenic – most of them can cause headache, dizziness, irritation in the respiratory system, and skin irritation. 

But one of the chemicals detected, benzothiazole, has been linked to a higher risk of bladder cancer among factory workers.

Rubber is a key component of any good climbing shoe. It gives the shoes optimal friction on climbing holds and provide the wearer with flexibility and the right amount of stiffness to grip where necessary and maintain their shape.

But with every climb and every foothold, particles of the rubber in the shoes – the same kind that makes car tires – are released into the air and on the footholds themselves. 

Many climbers have brushes for the climbing holds, which makes matters worse by constantly stirring up pollutants in the air, which people inhale and subsequently swallow.

Researchers from the University of Vienna sampled the air, soles of climbing shoes, the powder left behind on footholds, and settled dust around the facilities.

The concentrations of particulate matter in the air exceeded World Health Organization guidelines by around 20 times.

The WHO guidelines for indoor particulate matter concentrations are set at 45 micrograms per cubic meter (µg/m3) for a 24-hour period. In the climbing halls the researchers visited, the concentrations of breathable particles ranged from 900 µg/m3 to 1,040 µg/m3.

Indoor wall climbing is a popular recreational activity. Actor Jason Momoa [pictured] has been a rock climber all his life and took part in a climbing contest in Barcelona in 2016 

They said: ‘[Chemical classes] PPDs and PPDqs concentrations in the respirable fraction were higher than those measured in Chinese megacities and similar to roadside sites and city centres in China during air pollution events.

‘Concentrations of [chemicals] DPG, BTZ, and 2OH-BTZ in aerosol [particulate matter] samples were one or two orders of magnitude higher than in 18 megacities worldwide and BTZ and 2OH-BTZ were up to 10-fold above concentrations from industrial areas in Spain.’

Most of the rubber particles detected have been known to cause irritation to the respiratory tract as well as the skin. Some of them are known to be toxic to fish, while benzothiazole (BTZ) is a cancer-causing agent in rodents.

After checking for concentrations of the 15 different chemicals in air samples, where they detected nine, and dust samples, where they detected 12, they investigated climbing shoes and the footholds they cling to.

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They sampled 30 different shoe soles across a variety of brands and found one or more of the chemicals in all of them. One shoe showed evidence of all 15 chemicals.

Overall, concentrations of the chemicals in the shoes averaged 711 micrograms per gram of shoe sole material.

The researchers said: ‘With a global increasing urbanization, we expect to live, work, and recreate in safe indoor environments. Particularly in indoor sports facilities, where respiration increases, air quality standards need to be high and safe.

‘Rubber formulations containing potentially toxic [rubber-derived chemicals] should not be used in climbing shoes, or other consumer products where elevated human exposure is likely to occur.’

The team’s work, published on a pre-print server, has not undergone the peer review process yet, so their findings can be taken with some caution for now.

At the same time, it is well documented that rubber additives used to make tires, some of which are also used in climbing shoes, spillover from the road and seep into the environment.

Tests conducted by Emissions Analytics, an engineering consulting company based in the UK, reported last year that tires produce roughly 2,000 times more particle pollution by mass than tailpipes.