Ph.D. Dissertation Defense: Hilda Fadaei
Measuring and Modeling the Effect of PCB Bioavailability on Accumulation in Aquatic Food Chains
Name of Candidate: Hilda Fadaei
Friday, July 28, 2017: 8 am, TRC 206
The primary goal for remediation of sediments contaminated with polychlorinated biphenyls (PCBs) is the reduction of bioaccumulation in the aquatic food web, particularly in fish that is the source of exposure to top level predators and humans. While empirical results are available in the literature on bioavailability reductions after amendment of PCB-contaminated sediment with a strong sorbent like activated carbon (AC) or biochar, there is a lack of quantitative understanding on how reductions in sediment porewater concentrations and reduced uptake at the base of the food chain impact accumulation in fish. Recent advances have been made to accurately measure freely dissolved concentrations of PCBs in sediment porewater using passive sampling that responds rapidly to an in-situ treatment. However, there is a major gap in the development and utilization of fate and biouptake models that can use passive sampling measurements and quantitatively link those measurements to uptake pathways and predict eventual changes in fish concentrations. In addition, well-calibrated partitioning models based on accurate freely dissolved concentrations are lacking that can predict uptake by pelagic organisms, i.e. algae and zooplankton, that serve as food to fish. With a validated model for bioaccumulation, predictive assessments can be performed of a remedy progress upon engineering intervention. The primary objective of this research was to test the ability of the frequently used bioaccumulation models to predict changes in fish uptake upon amendment of AC sediment and to improve the bioaccumulation model predictions by using passive sampling inputs and filling existing data gaps on accumulation in the aquatic food web and uptake efficiency from ingested sediment.
Results from laboratory exposure studies with pelagic and benthic feeding fish indicate that by incorporating changes in porewater and overlying freely dissolved PCB concentrations in kinetic bioaccumulation models and by taking into account changes in food concentration it is possible to predict effectiveness of sediment remediation in reducing PCB uptake in fish. In order to make these models more suitable for benthivorous fish, assimilation efficiency of PCBs in the sediment were independently measured in a separate study and incorporated into the model. The modified model led to reasonable estimations of PCB uptake in the benthic feeding fish and was capable of predicting the dominant exposure pathways in the benthic and pelagic feeding fish as a result of their different swimming/feeding behaviour. Additionally, passive sampling measurements were linked to PCB accumulation in algae and zooplankton and resulted in refined models that can lead to more precise predictions of uptake in the aquatic food chain. Lastly, several scenarios were simulated to show the potential of the bioaccumulation model to be linked to a fate model and the ability of such combination to capture the effect of different inputs in the presence of natural recovery processes and sediment AC amendment.
This research presents a robust modeling framework that is able to predict uptake in fish after in-situ remediation that alters freely dissolved concentrations and bioavailability of pollutants in sediments. The outcome of this research will have implications for risk assessment and management of PCB-impacted sediment.