The primary objective of this project is to demonstrate an approach to develop site-specific bioaccumulation models to enable more cost effective risk informed decision-making at Department of Defense (DoD) sites. Bioaccumulation models will be developed using field and laboratory exposures of deposit- and suspension-feeding benthos concurrent with deployment of solid-phase microextraction (SPME) passive samplers. Contaminant concentrations measured in porewater and tissues will be used to derive biota-porewater accumulation factors as well as regression models that can then be applied in probabilistic risk assessments. Further development of site-specific regression models will allow DoD to propose the use of passive samplers in lieu of more expensive tissue analysis of resident infauna and/or bioaccumulation testing for long-term monitoring.

The project will combine multiple lines of evidence building upon methods developed through previous ESTCP and SERDP efforts, including the following technologies:

• Concentrations of dissolved-phase polychlorinated biphenyls (PCBs) and/or polycyclic aromatic hydrocarbons (PAHs) will be measured in situ using SPME fibers with performance reference compounds to calculate equilibrium concentrations. SPME fibers will be deployed into sediments in both field and laboratory concurrent to exposures of benthic organisms.
• Bioaccumulation exposures of deposit and suspension-feeding clams in field and laboratory exposures using chambers developed and deployed recently at Penniman Lake at the Naval Weapons Station in Williamsburg, VA and at the Naval Air Station in Pensacola, FL. 
• Chemical analysis of SPME fibers and tissues using gas chromatography with triple quadripole mass spectrometry that allows for increased sensitivity lower detection and quantitation limits.
• Biota-porewater accumulation factors and regression models generate tissue exposure concentrations; probabilistic risk models to compare risk estimates derived using porewater or bioaccumulation data.
• Project-specific Cfree:tissue relationships will be compared to those developed from similar data sets available in the literature. Studies that include similar species and contaminants included in this study, as well as those conducted with other benthic species and contaminants.

This project will bridge the gap between the established methods of measuring Cfree and the application of this technology for risk assessment and long-term monitoring. Once established, the site-specific models are expected to provide site managers with a viable alternative to measuring bioaccumulation, providing site managers with more reliable and readily deployable methods for predicting tissue concentrations, while reducing site assessment and long-term monitoring costs, and uncertainty in risk-based cleanup levels. (Anticipated Project Completion - 2024)