Elevated Indoor Levels of Plastic- and Rubber-Derived Contaminants in Gym Environments

Gyms are widely regarded as health-promoting microenvironments with intense human activity and abundant synthetic materials, yet the burden of emerging contaminants in these spaces remains poorly understood. Here, we report high concentrations of microplastics (MPs) and associated polymer additives in the indoor air of typical gyms, including plasticizers (phthalate esters, PAEs), antioxidants ( p -phenylenediamines, PPDs), and their quinone derivatives (PPD-Qs). Median concentrations of PPDs/PPD-Qs (503 pg/m 3 ), MPs (2069 ng/m 3 ), and particle-phase PAEs (2163 ng/m 3 ) in gym PM 2.5 were one to two orders of magnitude higher than outdoor levels, while PAEs showed pronounced accumulation in the gas phase, indicating that both particle-bound and gaseous fractions should be considered. Gym aerosols exhibited a distinct chemical fingerprint enriched in parent PPDs, suggesting possible contributions from rubber-associated additives in indoor synthetic materials. Exposure assessment further revealed that younger groups showed higher body-weight-normalized intake under the modeled exposure scenarios, with MPs contributing the largest intake among the target contaminant classes. These findings identify gyms as underrecognized exercise-related indoor microenvironments for potential co-exposure to plastic- and rubber-derived contaminants, supporting future monitoring, exposure assessment, and low-emission material design in sports environments.