Analysis of Measurement Errors in Passive Sampling of Porewater PCB Concentrations under Static and Periodically Vibrated Conditions.

Although the field of passive sampling to measure freely dissolved concentrations in sediment porewater has been sufficiently advanced for organic compounds in the low- to midrange of hydrophobicity, in situ passive sampling of strongly hydrophobic polychlorinated biphenyls (PCBs) is still challenged by slow approach to equilibrium. Periodic vibration of polyethylene (PE) passive samplers during exposure has been previously shown to enhance the mass transfer of polycyclic aromatic hydrocarbons (PAHs) from sediment into PE. Herein, we used a new vibrating platform, developed based on our earlier platform design, to demonstrate the effectiveness of periodic vibration for strongly hydrophobic compounds such as hexa-, hepta-, and octachloro-PCBs. Uptake of PCBs in PE after 7, 14, 28, and 56 days under different vibration modes was compared to that under static and mixed laboratory deployments. All PCBs reached within 95-100% of equilibrium after 56 days of deployment in the system vibrated briefly every 2 min, while none of the congeners achieved more than 50% of equilibrium in static deployment for the same period. Periodic vibration also increased the dissipation rate of four performance reference compounds (PRCs) from passive samplers. Higher fractional loss of PRCs and closer approach to equilibrium in the vibrated deployment resulted in estimation of corrected porewater concentrations that were statistically indistinguishable from the true equilibrium values even after a short 7-day deployment. Porewater concentrations of the strongly hydrophobic PCB congeners were overestimated by up to an order of magnitude in the static passive sampler after the same deployment time.