The colourful holds in climbing gyms collect rubber abrasion from the soles, which also gets into the air. Photo: Aaron Kintzi/CeMESS
A study led by researchers from EPFL and the University of Vienna shows that concentrations of concerning chemicals as high as those by a busy road can be found in the air of bouldering gyms.
Those who climb indoors are doing something for their health. But climbing shoes contain chemicals of concern that can enter the lungs of climbers through the abrasion of the soles. In a recent study, researchers from EPFL and the University of Vienna have shown for the first time that high concentrations of potentially harmful chemicals from the wear of climbing shoe soles can be found in the air of bouldering gyms, in some cases higher than on a busy street. The shoes contain rubber compounds similar to those used in car tires - including additives suspected of being harmful to humans and the environment. The results have been published in the journal Environmental Science and Technology Air.
From tires to climbing shoes
"The soles of climbing shoes are high performance products, just like car tires", explains Anya Sherman, first author of the study and an environmental scientist at the Centre for Microbiology and Environmental Systems Science (CeMESS) at the University of Vienna. Additives are specific chemicals that make these materials more resilient and durable; they are essential for their function.
Sherman enjoys climbing herself - as a balance to her work in the lab and on the computer. At a conference, she met Thibault Masset, postdoctoral researcher from EPFL's Central Environmental Laboratory (CEL), who researches similar topics and also enjoys climbing. The two researchers and equal first authors of the study came up with the idea of testing the rubber from their own climbing shoes using the same scientific methods they use to analyze car tires. "We wondered whether, like tire particles in outdoor environments, climbing shoes particles could become resuspended in indoor air. To investigate this, we developed an analytical workflow inspired by the methods we previously used to analyze additives in tires", explains Masset.
The researcher collected dust samples from various locations across Switzerland, France, and Spain. Additionally, he analyzed 30 different shoe soles sourced from retailers to compare their chemical composition with the particles found in climbing gyms. "These analyses, along with air sampling performed in Vienna using an impinger - a device that simulates the human respiratory system to measure airborne particles - provided us with a comprehensive overview of the chemicals present in climbing gyms and the potential exposure levels for both climbers and staff," he explains.
Concerning results
"Air pollution in the bouldering gyms was higher than we expected", says Thilo Hofmann, Vice Director of CeMESS and corresponding author of the study. What was striking was that the concentration of rubber additives was particularly high where many people were climbing in a confined space. Hofmann concludes: "The levels we measured are among the highest ever documented worldwide, comparable to multi-lane roads in megacities."
In the 30 pairs of shoes tested by the CEL, the team found some of the same chemicals as in car tires: among the 15 rubber additives found was 6PPD, a rubber stabilizer whose transformation product has been linked to salmon kills in rivers.
What this means for human health is still unclear. But Hofmann stresses: "These substances do not belong in the air we breathe. It makes sense to act before we know all the details about the risks, especially with regards to sensitive groups such as children."
Raising awareness to improve indoor air quality
The team also points out that the operators of all studied bouldering gyms were very cooperative and showed a high level of interest in improving the air quality in their gyms. "This constructive cooperation should lead to the creation of the healthiest possible climbing hall environment, for example through better ventilation, cleaning, and designing climbing shoes with fewer additives," says Sherman
"Our research also aims to increase awareness among rubber manufacturers. Now that we have identified potentially harmful chemicals in indoor climbing gyms, their use in the products themselves should be excluded," adds Masset.
As more research is needed to understand how these substances affect the human body, the EPFL researcher submitted a research proposal to further explore this aspect in collaboration with toxicologists. "In the meantime, I will keep climbing, prioritizing well-ventilated gyms during off-peak hours whenever possible. Climbing gyms are great spaces to exercise and have fun, especially for urban communities that don't have direct access to outdoor climbing. I hope good air quality can be maintained so that both climbers and staff can interact in a safe environment", he concludes.
