Passive samplers are an alternative to actively sampling sediment porewater using Henry samplers and pumping or centrifugation. Passive samplers consist of hydrophobic polymers (e.g. polyethylene, polydimethylsiloxane), which sorb freely-dissolved organic compounds present in sediment porewater. Henceforth, passive samplers are referred to as polymeric samplers for clarity. Polymeric samplers can be directly inserted into saturated sediment in the laboratory or in the field to yield depth-discreet measures of freely dissolved (Cfree) organic contaminant concentrations present in sediment porewater. Cfree measured by polymeric samplers represents the fraction of contaminants not sorbed to settling solids or associated with suspended colloidal matter and has been linked directly to exposure and risk to sediment-dwelling organisms. This has been demonstrated in research supported by a number of organizations including SERDP and ESTCP. However, lack of standardized methods and commercial availability to support polymeric samplers for environmental monitoring purposes has been a barrier to effective technology transfer and polymeric sampler use. This project demonstrated the use of standardized polymeric sampler procedures developed under ESTCP project ER-201216 for quantifying Cfree in contaminated sediment porewater by multiple participating public- and private-sector analytical laboratories, thereby increasing commercial availability, promoting wider acceptance, and increased use.
Commercial and academic laboratories participated in three separate tasks to test and validate standard methods for polymeric sampling, culminating in the final task of using the standardized polymeric sampling method to measure Cfree polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) in a sediment sample.
Results showed that (1) LDPE and PDMS polymers yielded equivalent Cfree results for PAHs and PCBs, regardless of static or active exposures; (2) polymeric samplers provided better quantitation compared to the manual extraction reference method for high molecular weight PAHs and PCBs, which were present at low concentrations; and (3) active exposures achieved equilibrium following continuous mixing for ~ 30 days, suggesting that if polymeric samplers are used to characterize sediment porewater under active exposure conditions for longer than 30 days in the laboratory, performance reference compounds use may be omitted.
Standardization of polymeric sampling methods – coupled with documented method accuracy and reliability through the phased interlaboratory study – is expected to dramatically improve regulatory acceptance. This demonstration supports ongoing DoD efforts to employ polymeric sampling, and encourage remedial project managers (RPMs) to begin using this technology. (Project Completion - 2020)