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

There is growing concern about rubber-derived compounds (RDCs), predominantly originating from tire and road wear particles. Other consumer products, including sports equipment, also contain RDCs and human exposure to these compounds is of particular interest due to demonstrated toxicity to animal species. In this study, we investigated RDCs intentionally incorporated into climbing shoes for enhanced performance. We found high concentrations of 15 rubber derived-compounds (RDCs) in shoe sole samples (Σ15 RDCs: 25 – 3405 µg/g), aerosol particulate matter (Σ15 RDCs: 2.6 - 37 µg/g), and settled dust (Σ15 RDCs: 1.5 - 55 µg/g) in indoor climbing halls. The estimated daily intake via inhalation/ingestion of Σ15 RDCs for climbers and employees in some of these facilities ranged from 1.7 to 48 ng/kg/day, exceeding known intake levels of RDCs from other sources. Abrasion powder resulting from friction between climbing shoes and footholds is the likeliest source of high concentrations of RDCs observed in aerosol particulate matter and settled dust, since other emission sources could be excluded. These findings reveal a previously unknown human exposure route of RDCs.