Wristband Passive Samplers as Tools for Quantifying Chemical Exposure: Elucidating Mechanisms of Uptake and Expanding Target Chemicals

Abstract

Polydimethylsiloxane (silicone) wristbands have gained popularity over the last decade as low-cost tools to assess personal exposure to a wide range of semi-volatile organic compounds (SVOCs). The potential of these wristbands has been indicated by prior research demonstrating that concentrations of SVOCs sorbed to the wristbands correlate with paired biomarker concentrations. Therefore, these devices could offer a more convenient strategy for environmental exposure assessment. However, several unknowns remain which temper the full realization of the wristband’s capability. Specifically, although we know that the wristband concentrations correlate with biomarker concentrations, we do not understand the mechanisms and factors influencing these correlations. Another uncertainty is the wristband’s ability to sample metals such as lead (Pb) which are also ubiquitous in our environment and can cause health effects that overlap with SVOCs. This work reviews the motivation for the use of silicone wristbands as passive samplers in chapter 1 and addresses these uncertainties which are outlined in the following specific chapters:2. Measurement of the effect of movement speed on SVOC uptake to unworn silicone wristbands. 3. Quantification of SVOC uptake from gas and particle-phase sorption to worn silicone wristbands. 4. Modification of the wristbands for improved metal sampling and evaluation of their performance compared to other exposure assessment samples.In chapter 2, we suspended silicone wristbands under static conditions on a ring stand or attached them to centrifuge tube rotators, which were spun at different speeds ranging from 0.05 to 1.1 m/s. The results of this experiment showed that faster moving wristbands had greater uptake rates of SVOCs. The fastest speed (~1.1 m/s), equivalent to a leisurely walking pace, displayed uptake rates for most compounds that were 4 to 5 times higher than the uptake rate of static wristbands. We also observed that the magnitude of increase with speed for a given compound was negatively correlated with its diffusivity in air and positively correlated with its octanol-air partition coefficient (log KOA), potentially indicating particle uptake or sampler side limiting mass transfer. When compared to worn wristbands, unworn wristbands moving at 1.1 m/s exhibited lower uptake rates for most compounds. This disparity became more pronounced as the SVOCs increased in KOA indicating an additional mechanism other than diffusion (e.g. particle adsorption or direct surface contact) may be driving uptake of the compounds.In chapter 3, we explored these mechanisms further by recruiting participants to wear two watchband samplers, each containing a silicone segment that can accumulate SVOCs. One watchband was covered with a 10 micron stainless steel screen to filter out particles and while the other watchband was unscreened. The fraction of each SVOC passing the screen and accumulating on the silicone represents the fraction of exposure from the gas-phase. This data revealed that many compounds experienced noticeable uptake on the silicone sampling surface from both gas-phase and suspended particulates. Additionally, when comparing the concentration on the unscreened silicone in the watchband to the concentration on a paired standard wristband, we witnessed a similar trend as in aim 1 in which high KOA compounds had significantly greater concentrations on standard wristbands. Combined, these results point to direct contact with surfaces and skin as major mechanisms of SVOC uptake by standard wristbands. In chapter 4, having known the evidence of particulate SVOC uptake, we investigated the effectiveness of a modified wristband as an exposure assessment tool for Pb and other metals. The modification consisted of placing a polyurethane foam substrate in the cavity of a fitness style watchband. The polyurethane foam contains higher specific surface area than silicone for improved particle uptake and retention. We recruited participants to wear these modified wristbands for five days and to provide dust wipe, blood, and water samples. In some cases additional vacuumed dust and soil samples were also collected. We found that Pb and other metals (Cu, Fe, Mn, Cd, Ca, Na) on PUF were positively correlated with paired dust wipes samples. However, Pb on wristbands was not strongly correlated with Pb in blood. Additionally, we compared ratios of Pb:Fe, Cu:Fe, Mn:Fe, etc. across sample types, which revealed that the particle composition on the PUF was more similar to that of dust wipes and vacuumed dust than outdoor soil. Overall, these modified wristbands can be paired with silicone wristbands to expand the range of chemicals and provide a more comprehensive assessment of exposure.Combined, these three chapters demonstrate that wristband passive samplers capture valuable exposure information by integrating multiple exposure routes and diverse chemical classes, much like the human body itself. Collectively, these results lay the groundwork for mechanistically linking wristband data to health outcomes and for extending the wristband approach to broader exposome assessment.