Thermal-UV synergy accelerates HBCD emissions from back-coated textiles via volatile and nanoscale particle pathways

Hexabromocyclododecane (HBCD), a brominated flame retardant in legacy back-coated textiles, persists despite restrictions. This study quantifies HBCD emissions from back-coated fabrics subjected to thermal aging (25-90 °C), ultraviolet irradiation (UVA-340, 1.25 W m^-2), and mechanical abrasion (25,000 cycles), emphasizing synergistic thermal-UV interactions. Emissions were characterized using first-order kinetic, dynamic headspace sampling, and size-resolved particulate analysis. Thermal aging at 90 °C yielded 0.167 ± 0.01% volatilization, while UV exposure alone generated 0.162 ± 0.02%. Combined thermal-UV stress accelerated kinetics, yielding a synergy factor S = 1.92 ± 0.25 (p = 0.014) and a 0.233 ± 0.03% cumulative release. The rate constant increased from 0.018 d^-1 (thermal) to 0.129 d^-1 (combined). Mechanical abrasion released particulate-associated HBCD at 6.53 µg m^-2cycle^-1. UV pre-aging shifted particle emissions toward nanoscale fractions (30-260 nm), increasing particle chemical content from 12.5% to 29.2%. Airborne particle concentrations were ≈ 250 µg m^-3 (unaged) and 0.8 -60 µg m^-3 (UV-aged). While cumulative volatile release was low (≤0.233%), matrix depletion reached 48.4%, suggesting polymer-embedded transformation dominate HBCD fate. These findings show multi-stressor environmental conditions significantly alter emission pathways, affecting exposure assessments for legacy materials.