The invisible footprint of climbing shoes: high exposure to rubber additives in indoor facilities

There is increasing research focused on rubber additives, predominantly originating from tire and road wear particles. Other consumer products including sports equipment also contain rubber additives and the overall human exposure to these compounds is of concern due to demonstrated toxicity to animal species. Rubber additives are intentionally incorporated into climbing shoes for specific performance. We found high concentrations of rubber additives in shoe sole samples, aerosol particulate matter, and settled dust in indoor climbing halls. The estimated daily intake via inhalation for climbers and employees of these facilities exceeds the intake of rubber additives from all other known sources. Abrasion powder resulting from friction of climbing shoes on the holds is responsible for the high concentrations of rubber additives observed in aerosol particulate matter and settled dust, while other emission sources could be excluded. We also show that atmospheric transformation of rubber additives occurs in indoor environments. These findings identify a previously unknown human exposure route to rubber additives and emphasize the global problem of the toxicity burden of plastic additives.