This project sought to address the very common situation in which contaminated sediments in an aquatic ecosystem do not "respond" well to efforts to clean them up as measured by improved health of the organisms living in that environment. This, of course, translates to increased risks for humans and other predators (e.g., birds) that capture food from those sites.
Given the need for tools to guide site assessments and to make informed remedial designs for contaminated sediment sites, the team pursued the following coordinated modeling and passive sampling measurement objectives seeking:
To improve the abilities to address such sites, the team explored a coordinated use of both measurement and modeling "tools" that could be applied to achieve better results. These tools included:
Passive Sampling and Mass Balance Modeling Approaches - Utilizing passive sampling enabled the team to estimate the spatially varying diffusive fluxes from bed to water column. Integrating these fluxes over the entire LDW bottom yielded a total source strength for PCBs entering the water column from the bed. Using this spatially varying source strength for the 20 congeners the team specifically measured as inputs to the EFDC that had been tuned to match tidal amplitudes, the team could solve for the resulting distributions of each PCB in the LDW water column. It is important to note that passive sampling of the riverine influx of PCBs to the LDW was also performed to account for that PCB input source too. Combining these, the team could not explain the presence of most of the PCB load in the LDW water column.
Inverse Modeling - To perform this "inverse modeling", the team ran the EFDC with singular sources to generate a concentration profile that was unique to each putative source location. Then combining these concentration profiles using a least root mean error fitting approach such that the total PCB distributions in the water column could be be explained by only a few sources, we located a series of likely places in the estuary where PCBs were probably being introduced. The weightings of these inputs clearly indicated the relative importance for each of the PCB congeners that were fit.
Food Web Modeling - Operation of this model yielded biota concentrations that were consistent with past measures of PCBs in those organisms. Having established this linkage with the passive sampler measures and the EFDC modeling, the team showed that the food web model could be exercised for change PCB concentration conditions that might result from various remediation efforts. This effort clearly revealed the degree of biota response to particular changes in PCB exposures due to investments in clean up.
Combining all these results enable us to estimate the spatially varying diffusive fluxes from bed to water column. Integrating these fluxes over the entire LDW bottom yielded a total source strength for PCBs entering the water column from the bed.
Successful development of this integrated modeling-measurement system will allow DoD RPMs to: (i) identify their data needs, (ii) synthesize the data in terms of time- and space-varying exposures, (iii) estimate how those exposures translate into different food web responses for scenarios ranging from monitored natural recovery to targeted site clean-up, and (iv) evaluate potential improvements in FWMs seeking to predict organism concentrations given a more refined exposure field.
Apell, J. N. and P. M. Gschwend. 2016. In situ Passive Sampling of Sediments in the Lower Duwamish Waterway Superfund Site: Replicability, Comparison with Ex situ Measurements, and Use of Data. Environmental Pollution, 218:95-101.
Apell, J.N. and P.M. Gschwend. 2017. The atmosphere as a source/sink of polychlorinated biphenyls to/from the Lower Duwamish Waterway Superfund site. Environmental Pollution, 227:263-270.
Apell, J.N., D.H. Shull, A.M. Hoyt, and P.M. Gschwend. 2018. Investigating the Effect of Bioirrigation on In Situ Porewater Concentrations and Fluxes of Polychlorinated Biphenyls Using Passive Samplers. Environmental Science Technology, 52(8):4565-4573.
Jonker, M.T.O., S.A. van der Heijden, D. Adelman, J.N. Apell, R.M. Burgess, Y. Choi, L.A. Fernandez, G.M. Flavetta, U. Ghosh, P.M. Gschwend, S.E. Hale, M. Jalalizadeh, M. Khairy, M.A. Lampi, W. Lao, R. Lohmann, M.J. Lydy, K.A. Maruya, S.A. Nutile, A.M.P. Oen, M.I. Rakowska, D. Reible, T.P. Rusina, R. Smedes, and Y. Wu. 2018. Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison. Environmental Science Technology, 52(6):3574-3582.