Food web bioaccumulation models are relied upon heavily in decision making at Department of Defense (DoD) and other contaminated sediment sites. For polychlorinated biphenyl (PCB)-contaminated sites, sediment remediation is conducted to decrease human health risk from consumption of PCBs in fish, not exposure to PCBs in sediments, making the food web bioaccumulation models that establish the relationship between contaminants in fish and sediments incredibly important. Output from these models can be the basis or justification for selection of particular remedial approaches; however, the models have substantial uncertainty. They are often applied over expansive areas but assume a single sediment contaminant concentration for the entire area, working under the presumption that fish will be exposed equally among all locations. It is understood that this is a poor assumption: fish movements are not random, surface sediment contaminant concentrations can be extremely heterogeneous, and fish tissue concentrations reflect the concentration of the area of exposure. However, there is often no basis for assigning spatially explicit exposure patterns. As a result, the relationship between assumed exposures and actual contaminant uptake is tenuous.
The overall objective of this project was to develop and use innovative technologies and approaches that eliminate fundamental uncertainties in food web modeling by unambiguously documenting contaminant exposure (location, water/sediment contaminant concentration, fish diet, and temperature), chemical uptake, and growth over time in individual fish. The technologies studied in this effort sought to collect highly-specific fish contaminant and exposure data to verify and improve food web bioaccumulation modeling structures and application at sites.
Acoustic implants are widely used to track fish movement in high resolution, including three dimensions. However, they have not been adapted to immobilize fish and permit fish recovery. The overall approach was to release fish with known initial concentrations, track the fish over a well-characterized area (sediment/water concentrations), and recover the fish at specific time points. Recovered fish and information from implanted tracking devices would provide high resolution location information, fish contaminant uptake, diet, and other parameters that are highly uncertain in current food web model applications.
An initial prototype was developed to initiate testing and to assess if the device requirements of tracking and surface recovery of implanted fish were met. The prototype achieved a size and weight that could be carried by fish without adverse impact. Iterative testing, modification, and improvement proceeded through four prototype versions to improve component performance, reliability, and overall form factor. Iterations of testing and improvement primarily addressed inconsistent performance of the flotation mechanism and early leakage of tag components that caused early mortality. Tag volume and weight also were reduced.
The final design possessed sufficient power, tracking capabilities, timed activation, and coupled flotation/euthanization agent release mechanisms. However, the euthanization efficacy was not tested due to insufficient progress with the prototype development. Analyses identified why tags leaked and the flaw was isolated and fixed, but the flotation mechanism is not yet consistently reliable. The cause of the inconsistent inflation was isolated and solutions have been identified. Substantial progress was made toward developing a reliable and functioning tag design capable of achieving design requirements, but the flotation mechanism requires modification and the coupled flotation/euthanization mechanism needs to be verified in further prototype development and testing.
An improved understanding in the food-web modeling will expedite sediment cleanup and completion of liabilities by the DoD and other federal agencies by clearly establishing the relationship between sediment and fish tissue contaminant concentrations. Better establishing that linkage will lead to more technically sound site risk assessments and ultimately will expedite sediment cleanup and completion of liabilities by DoD and other federal agencies.