Silicone wristbands for assessing personal chemical exposures: impacts of movement on chemical uptake rates†

Silicone wristbands are utilized as personal passive sampling devices for exposure assessments of semi-volatile organic compounds (SVOCs). While research demonstrates that accumulation of SVOCs on the wristbands correlates with internal dose for many different chemical classes, the mechanisms of accumulation remain poorly understood. Multiple factors such as movement of the individual lead to variable mass transfer conditions at the sampler interface. The objective of this study was to investigate the effect of air flow velocity across the wristband surface on SVOC uptake rates and to evaluate if enhanced rates vary between compounds with a range physicochemical properties. Experiments were conducted in a residential home where wristbands were either held in static conditions or attached to an end-over-end rotator at different speeds for a four week period. We measured the uptake of 17 different SVOCs that are commonly detected in indoor environments and compared their accumulation rates as a function of the rotating velocity. For wristbands moving at tangential speeds of 0.05, 0.5, and 1.1 m s⁻¹ (relevant for a walking pace), the motion enhanced uptake rates by 1.2 ± 0.2, 3.2 ± 0.6, and 4.3 ± 0.8 times the respective rates for the static controls. This enhancement is consistent with gas phase diffusion-controlled mass transfer theory at the wristband interface. Moreover, the enhancement of uptake positively correlated with octanol–air partition coefficients log K_OA (R = 0.6; p < 0.02) of the chemicals and negatively correlated with diffusivity (R = 0.5; p < 0.05). In a comparison with worn wristband studies, the ratio of uptakes rates for worn relative to rotating wristbands correlated with SVOC properties (R = 0.85 for log K_OA). For SVOCs with log K_OA > 9, uptake rates on worn wristbands greatly exceeded (by a factor of 10 to 10⁴) the respective rates in this rotator experiment. These results suggest that a mass transfer mechanism based solely on gas–solid partitioning under variations in air velocity cannot fully explain uptake on worn wristbands. Instead, the results implicate additional processes such as particle phase deposition, direct contact with certain materials, and excretion from skin as pathways of accumulation on the wristband sampler and personal exposure.