Estimating the Degree of Equilibrium between Passive Samplers and Pore Water for PCBs: Case Study and Comparison of Methods

摘要

Background. Passive samplers present many advantages over conventional alternatives for measuring hydrophobic organic compound (HOC) concentrations in sediment pore water and surface water based on both cost and data usability. Equilibrium based passive samplers, such as polydiemthylsiloxane (PDMS) coated glass rods (i.e., solid phase micro-extraction (SPME) samplers) enable collection of representative, depth discrete data without needing to collect large volume aqueous samples. The mathematical relationship to calculate pore water or surface water concentrations from sorbed mass in the samplers assumes equilibrium of HOCs such as polychlorinated biphenyls (PCBs) or polyaromatic hydrocarbons (PAH) between the sampler and the surrounding water, where equilibrium means no further changes in the concentrations in the sampler over time. Concentrations in the sampler will approach equilibrium with sufficiently long deployment times but the degree of equilibrium can be measured and corrected for in the pore water concentration calculations. Measuring the degree of equilibrium achieved and then adjusting calculated pore water concentrations provides a higher level of accuracy in the concentration data.