Background/Objectives: Passive sampling measures freely dissolved concentrations of hydrophobic organic compounds (HOCs) such as polychlorinated biphenyls (PCBs) in sediment porewater as this metric correlates well with uptake into sediment-dwelling organism tissue.
There are a number of passive sampling approaches, with polydimethylsiloxane (PDMS) coated solid phase microextraction (SPME) fibers and thin sheets of polyethylene (PE) being two of the most widely-used methods.
Approach/Activities: To evaluate the performance of PDMS and PE, a synchronous deployment of samplers (10-μm thick PDMS, 18-μm thick PE) were co-located in surface sediments at ten locations for a two week in situ deployment at a 0.5-acre shipyard site in the Puget Sound, Washington, USA.
Results/Lessons Learned: As has been observed in previous studies, the thinner PDMS layer was found to reach steady state more rapidly than PE. For example, the percentage of steady state attained during the exposure period was 1.4 times higher for pentachlorinated biphenyls in PDMS compared to PE. The difference was greater (a factor of 2.2) for hexachlorinated biphenyls. Advantages in kinetics were offset in terms of detection limits, which were typically lower with measurements using PE compared to PDMS (due to the greater volume of polymer present in the PE approach). Lower detection limits enabled more PCB congeners to be detected via PE methods than PDMS. Di- to hexachlorinated biphenyls were detected with PE passive sampling, whereas tetra- to pentachlorinated biphenyls were detected with PDMS. A consequence of a greater number of congeners detected at lower concentrations was the concentrations of total PCBs in sediment porewater were found to be greater by PE measurements compared to PDMS. With the exception of one outlier station, concentrations of total PCBs in sediment porewater were on average 2 times greater as measured by PE than PDMS methods. These results are in general agreement with previous studies that found a factor of 2 to 3 agreement between PE and either PDMS or POM passive sampling methods. The differences in detection limits can be mitigated by using additional amounts of SPME fiber; however, the logistics of working with and purchasing additional SPME fiber results in a less economical option, as will be discussed during the presentation.