The use of polychlorinated biphenyls and mercury as environmental tracers of energy and nutrient dynamics in an aquatic system
Polychlorinated biphenyls (PCBs) are ubiquitous. They are one of the most widely studied classes of chemical contaminants with decades of research going into investigating their uptake and elimination pathways, as well as factors regulating their bioaccumulation. More recently, studies have moved away from studying PCBs for toxicokinetic purposes and moved into using them as environmental tracers. The persistence of PCBs and bioaccumulative nature made them useful industrially and subsequently caused the UN to ban their usage, but also makes them the ideal tracer to examine a wide range of ecological questions from trophic ecology and niches, to energy and nutrient dynamics in aquatic systems. PCBs are hydrophobic with uptake and elimination mechanisms dominated by fugacity based processes. Mercury (Hg), on the other hand, has a different mechanism of accumulation because it binds to proteins. Hence Hg has the potential to give different insights as an environmental tracer. Here we use a modified non-steady state PCB bioaccumulation model contrasted to a Hg bioaccumulation model to examine the plausibility of using Hg as an environmental tracer.
Preliminary results demonstrate the importance of assimilation efficiencies on PCB bioaccumulation dynamics. In particular, they highlight the need for a lipid-based assimilation efficiency sub-model instead of a KOW driven model. In addition, they demonstrate the enhanced bioaccumulative potential of Hg as seen by its low elimination rate yet high assimilation efficiency, especially when compared to PCB congeners. Mercury is already being used in some studies as a predictor of organism trophic position due to both its bioaccumulative nature and its affinity for proteins. Our findings suggest that it also has the potential to predict ecological properties of organisms, such as food acquisition and foraging efficiencies. In fact, due to the lower cost and shorter time requirements for analysis, Hg may perform better as an environmental tracer than PCBs. In particular, since it shows a similar potential as PCBs as a metric of nutrient and energy flow in aquatic systems.