According to a breakthrough study published on April 29 by Environmental Science and Technology Air, specialized rubber soles of rock climbing shoes are releasing potentially harmful chemicals into indoor climbing facilities that can be comparable to busy roads in major cities.
Researchers from the University of Vienna and EPFL Lausanne found that with climbers’ scale walls, their shoes left rubber particles containing various chemical additives that could turn into air and be sucked in by recreational climbers and facility staff.
“The soles of rock climbing shoes are high-performance products,” explained study first author Anya Sherman.
The team analyzed 30 different climbing shoe models, as well as air samples and dust from nine indoor climbing facilities in Austria, Switzerland, France and Spain. They identified 15 rubber-derived compounds (RDCs) in shoe samples, including chemicals such as 6ppd – a rubber stabilizer whose conversion products were associated with salmon deaths in the river.
The most surprising thing is the concentration of these chemicals in the air. “We measure the highest level in the world ever, the highest ever, in the world,” said Thilo Hofmann, professor of environmental geosciences at the University of Vienna.
Rubber particles come from intentional wear of the soles during climbing. This rubber dust can accumulate on climbing and mats, and when the climber’s brush holds or falls on the mat, it can be disturbed, causing the particles to become airborne. Analysis shows that the concentration of these chemicals in some facilities exceeds exposure levels from other known sources.
For the average climber, especially those who spend hours on these facilities, the daily intake of certain compounds is estimated to be as high as 29 nanometers per kilogram per day – significantly higher than the exposure levels measured in previous studies by people working near industrial sites or busy roads.
Although the direct health implications are unclear, researchers are concerned about potential long-term effects. “These substances do not belong to the air we breathe. It makes sense to act until we know all the details about the risk, especially in sensitive groups like children.”
The study highlights previously unknown ways of human exposure to these chemicals that could affect millions of people participating in indoor rock climbing around the world. In the United States alone, an estimated 4.4% of the population visited indoor climbing facilities in 2018, and about 20% were regular visitors who spent several hours multiple times a week in these environments.
The researchers noted that climbing facility operators are collaborative and are interested in improving air quality. Potential solutions include better ventilation systems, more thorough cleaning practices, and designing climbing shoes with less harmful additives.
“Switch to the only material of the only harmful substance,” Hoffman said, adding that manufacturers are not fully aware of the problem at this time. The rubber sole they bought contains “cocktails with bad chemicals.”
Despite findings, Sherman remains positive about the sport: “I will continue to climb and I believe our research will help climb the better conditions in the gym.”
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